Paint products: Accelerated stability and quality testing

On line article at SpecialChem4coatings.com

Paint products: Accelerated stability and quality testing
Part I: Direct measurement of separation and segregation by multisample analytical centrifugation

Scope

To assure continued consumer satisfaction the following stability issues of paint products have to be minimized or avoided:

• syneresis - separation of the liquid dispersion media
• Pigment segregation - change of colour composition inside a container
• Particle segregation - change of particle size distribution inside a container

These stability issues have to be addressed not only during development of new paint products but also for quality assurance during production on a regular basis. This application note demonstrates that multisample analytical centrifugation can be used as an efficient tool for the accelerated evaluation of separation stability of paint products.
In addition this technique provides for high resolution data of particle size distributions of pigments or emulsions.

In part II the application of multi-sample analytical centrifugation for optimization of deagglomeration of pigment particles will be addressed.

Formula V - Formulation Science and Technology 2007

Formula V 19 - 22 November Potsdam, Germany

' Formulating opens the way for tailoring products for specific applications and combining components with often contradicting properties. Formulation science and technology is a core discipline for industries and applications like home care, cosmetics, plant protection and coatings but also of emerging importance in fields like electronics, composite materials and biomedical technology.'

Poster contributions

Accelerated screening of formulations towards freeze-thaw stability

T. Sobisch, D. Lerche, L.U.M. GmbH, www.lum-gmbh.com

Rudower Chaussee 29, 12489 Berlin, Germany

The formulation of dispersion based products as well as process development/monitoring and quality assurance require efficient and objective analytical tools for shelf life prediction and stability determination. Freeze/thaw stability is often used as measure of long term stability. On the other hand high freeze/thaw stability is often required as a material property. To this end the potential of multisample analytical centrifugation was evaluated as an accelerated test procedure.
A new multisample approach is presented using analytical centrifugation (STEP-Technology), which allows for an accelerated characterization of destabilization processes (creaming, sedimentation, coalescence, phase separation). The kinetics of these destabilizing processes can be traced simultaneously for up-to 12 different samples with temperature control in the range between 4 and 60 °C.
Analytical centrifugation measures in a rapid way the inherent stability of the samples. Therefore, alterations due to accelerated aging by freeze/thaw cycling can be traced far more earlier than by naked eye.

The wide application potential of this approach is demonstrated by examples of measurements on paints, cosmetics and food products.

Thickener performance traced by multisample analytical centrifugation

T. Sobisch, D. Lerche, L.U.M. GmbH, www.lum-gmbh.com

Rudower Chaussee 29, 12489 Berlin, Germany

Polymeric thickeners are important ingredients to adjust flow properties and stability of formulations. The effect of polymeric additives on dispersion properties is rather complex (viscosity of the continuous phase, adsorption and depletion effects, interaction with other ingredients). Therefore optimum formulation requires extensive experimental investigations.

A new multisample approach is presented using analytical centrifugation (STEP-Technology), which allows for an accelerated characterization of separation stability. Even more, comparing measurements at different centrifugal acceleration information on flow properties is also available (Newtonian, shear thinning or thickening behaviour, yield point, compressive yield stress). The kinetics of separation can be traced simultaneously for up-to 12 different samples with temperature control in the range between 4 and 60 °C.
The potential of multisample analytical centrifugation for formulation design was demonstrated investigating the effect of particle (calcium carbonate, silica) and polymer (polyacryl amide) concentration on dispersion properties of different stabilized suspensions.

making palm oil production less polluting - the wastewater issue

besides the issue of rain forest destruction conventional palm oil production generates up-to 4 tonnes highly contaminated wastewater and more then 40 cubic meter methane per tonne of palm oil produced.

To reduce environmental impact German researchers have developed a treatment process using wastewater and plant residues of oil production for co composting.

Concerns Over Bisphenol A

Human exposures are usually as high as those causing profound effects in rodents

"THE SUSPECTED LINK between low levels of human exposure to bisphenol A (BPA), a monomer widely used to make polycarbonate plastic and epoxy resins, and adverse health affects was bolstered last week with the publication of four toxicology studies that investigated the link.

The most significant paper is a consensus statement from 38 scientists released online in Reproductive Toxicology (DOI: 10.1016/j.reprotox.2007.07.005). It concludes that human exposure to BPA, primarily from food containers, is within the range shown to be biologically active in animal studies. In rodents, low BPA exposures in the womb cause increases in the rates of prostate and breast cancer, reproductive abnormalities, lowered sperm counts, early onset of puberty in females, and obesity and insulin-resistant diabetes."

.................
"Despite growing evidence of toxic effects in lab animals, manufacturers of BPA insist that their product is safe. Steven Hentges, executive director of the polycarbonate/BPA group at the American Chemistry Council, an industry group, disputes the new research in Reproductive Toxicology. He says it is not credible, pointing to a European Food Safety Authority report that indicated no adverse effects of BPA"

Risk due to endocrine effect of compounds used in personal care products

COMMENTARY: Do Personal-Care Products Need a Makeover? (By Gary Ginsberg)

E/The Environmental Magazine - Norwalk,CT,USA
'The typical surfactants, emulsifiers, oils and fragrances are
generally safe. However, as with many things, the devil is in the details
and it's the small ...'

problems associated with phtalates, parabens, benzophenons, bisphenol A, triclosan

What´s Toxic, What´s not

Powered by ScribeFire.

Gefährdungen durch Chemikalien in Bekleidungstextilien - Übersicht

BfR- Bundesinstitut für Risikobewertung gibt einführende Übersicht über Gefährdungen durch Chemikalien in Bekleidungstextilien

depleted uranium amunition leads to groundwater contamination - Uranmunition im Boden führt zu radioaktiver Grundwasserkontamination

Langzeitstudie zur Auflösung von Uranmunition im Boden

"In einer bisher einmaligen Langzeitstudie haben Wissenschaftler vom GSF Forschungszentrum für Umwelt und Gesundheit in Kooperation mit dem Forschungszentrum Dresden-Rossendorf (FZD) untersucht, was mit panzerbrechender Uranmunition passiert, die lange im Boden lagert und damit Verwitterungs- und Auswaschungsprozessen ausgesetzt ist. Die Ergebnisse zeigen, dass die Munition schnell zersetzt wird und Uranverbindungen in das Grundwasser gelangen können."

Exposure to depleted uranium (DU) particles strongly increases risk of lung cancer

The Alchemist Newsletter: May 8, 2007

'Exposure to depleted uranium (DU) particles is a source of growing concern internationally as it increases the risk of lung cancer, according to John Pierce Wise Sr of the University of Southern Maine. Writing in the journal Chemical Research in Toxicology the researchers explain that DU has a density twice that of lead and so is used in military armor and munitions. However, DU dust produced in combat can lead to frequent and widespread exposure of military personnel and civilians during an after combat. Few studies have been undertaken, bit Wise and his colleagues have now tested the effects of DU on cultures of human lung cells. "This is the first report on the cytotoxicity and clastogenicity [chromosome damaging potential] of particulate and soluble DU in human bronchial cells," the researchers say.'

Fast evaluation of dispersion properties for particle size analysis / Charakterisierung der Dispersionseigenschaften für die Partikelgrößenanalyse

LUMiFuge / LUMiSizer - Application

Evaluation of dispersion properties for particle size analysis

Scope

To obtain reasonable information about the size of particles in powders and suspensions full dispersion of the particles is required prior to particle size measurement. Therefore the question arises how to select dispersion conditions and dispersion media properly. Often not the size distribution of aggregates/agglomerates is of interest but the distribution of the size of primary particles. In this case intense processing and suitable dispersants have to be applied. Multisample analytical centrifugation can be used as an efficient screening tool to assist in sample preparation. Even more it allows for high resolution determination of particle size distributions.

LUMiFuge / LUMiSizer - Anwendungsschrift

Charakterisierung der Dispersionseigenschaften für die Partikelgrößenanalyse

Problemstellung

Sinnvolle Ergebnisse zur Partikelgrößenverteilung von Pulvern und Suspensionen sind nur erhältlich, wenn die Partikel bei der Messung hinreichend gut dispergiert vorliegen. Es ergibt sich die grundsätzliche Frage, wie die experimentellen Dispergierungsbedingungen und das Dispersionsmedium zu wählen sind. In vielen Fällen interessiert nicht die Verteilung der Aggregate sondern die der Primärpartikel. In diesen Fällen müssen die Agglomerate intensiv mechanisch beansprucht und Dispergiermittel eingesetzt werden. Die Analytische Zentrifugation mit Multiprobenrotor läßt sich als effizientes Werkzeug beim Screening der geeigneten Probenvorbereitung einsetzen. Darüber hinaus ermöglicht die Analytische Zentrifugation die Bestimmung der Partikelgrößenverteilungen mit hoher Auflösung.

Poster presented at the 4th World Congress on Emulsions Lyon 2006

Evaluation of long term stability of model emulsions by multisample analytical centrifugation

T. Sobisch, D. Lerche,

L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489 Berlin, Germany,

www.lum-gmbh.com, info@lum-gmbh.de

F. Aguilar, G.G. Badolato, H.P. Schuchmann,

Institute of Engineering in Life Sciences, Department of Food Process Engineering, University of Karlsruhe, Haid-und-Neu-Str. 9, 76131 Karlsruhe, Germany

Abstract

Destabilisation processes in emulsions are very complex. Aging and breaking of emulsions are the result of several processes – creaming or sedimentation, flocculation, coalescence, Ostwald ripening, phase inversion – which can occur separately or simultaneously. This is the main reason why the development of reasonable procedures for shelf life prediction is very difficult and always depends on the product which is subject to evaluation.

Multisample analytical centrifugation with photometric detection (STEP-technology) is a tool for an accelerated characterisation of any demixing processes (creaming, sedimentation, phase separation) as well as for the quantification of time dependent structural alterations (e.g. flocculation, coalescence, Ostwald ripening).
Model emulsions were designed exhibiting creaming, coalescence, flocculation or Ostwald ripening as the dominating mechanism for instability. To answer the question whether multisample analytical centrifugation can be used to predict the long term stability of emulsions results obtained are compared with rheological measurements, particle size analysis by light scattering and common accelerated stability tests like freeze/thaw cycling and storing at 45 °C.

In all cases the creaming (or sedimentation) velocity measured by analytical centrifugation markedly increased during storage induced by increasing salt concentration (flocculation), increasing droplet size (using emulsifier with lower HLB value) or increasing the fraction of clove oil (Ostwald ripening). During a relatively short period of observation only a small part of these alterations could be detected using conventional methods of emulsion characterization.

Method of multisample analytical centrifugation

The multisample analytical centrifuge (LUMiFuge, LUM GmbH, Berlin Germany) used in this study employs the STEP technology, which allows to measure the intensity of the transmitted light as function of time and position over the entire sample length simultaneously (measurement scheme see Figure).

Measurement scheme of the multisample analytical centrifuge with photometric detection. Parallel NIR-light is passed through the sample cells and the distribution of local transmission is recorded at preset time intervals over the entire sample length.

The data are displayed as function of the position within the sample, representing the distance from the centre of rotation. The transmission profiles obtained are representative for the variation of droplet (particle) concentration inside the sample (low transmission means high, high transmission means low droplet concentration).

The progression of the transmission profiles provides information on the kinetics of the separation process and allows particle characterization.

At the same time up to 8 different samples can be analysed simultaneously at constant or variable centrifugal speed up to 2300 g. The separation behaviour of the individual samples can be compared and analysed in detail by tracing the variation in transmission at any part of the sample or by tracing the movement of any phase boundary.

As for a given type of sample cells the position corresponds to a defined sample volume the relationship between the position and the volume can be established by calibration. This allows to directly determine separated phase volumes and to calculate packing densities.

For further details of the application of the method for characterization of emulsions see [1,2,3].

Silicon oil-in-water emulsions with and without induced flocculation

Oil-in-water emulsions φ= 30 %

Sample preparation:

1. 40 % oil / 1% sodium dodecyl sulfate

Process:Microfluidizer® 500 bar

2. Diluted with deionized water or concentrated salt solution to result in 30 % oil and 0, 150 and 300 mM NaCl

Creaming without centrifugation (high salt concentration)

Centrifugation – creaming at 1100 g (low salt concentration)

• During the storage time no significant changes in droplet size and viscosity at 0 and 150 mM NaCl

• Creaming and water separation clearly visible after the addition of salt (c > 500 mM NaCl)

• For small concentration of salt the height of separated water (in a cylinder) not detected or remains constant

• The creaming velocity measured by the analytical centrifuge increases during storage, increasing the salt concentration and increasing the temperature

• All emulsions were very vulnerable to freeze/thaw cycling

Coalescencing vegetable oil-in-water emulsions –

stabilised with emulsifiers having different polarity

Oil-in-water emulsions j = 30 %

Process:Microfluidizer® 500 bar

Non ionic emulsifier Emulsions

η mPa/s x_3,2 µm

Tween 20, HLB 16.7 3.73 0.66

Tween 80, HLB 15 3.11 0.62

Tween 65, HLB 10.5 3.12 1.35

Centrifugation – creaming at 1100 g

Movement of the position of the interface emulsion –water (distance to the centre of rotation) during centrifugation measured just after preparation of the emulsions.

Already at this stage distinct differences in stability traced due to bigger droplets (Tween 65) or higher viscosity (Tween 20)

• During storage no significant changes in droplet size and viscosity

• Creaming velocity increase due to bigger droplet sizes with decreasing emulsifier HLB value (more coalescence during production) or lower viscosity

• Increased destabilization at higher temperature
• Only unstable emulsion vulnerable to freeze-thaw cycling
  

Ostwald ripening in water-in-oil emulsions

Water-in-oil emulsions j = 30 %

Process:Microfluidizer® 500 bar

Continuous phase mixture clove/vegetable oil viscosity η

Sample 1 50/50 76 mPa/s

Sample 2 75/25 47 mPa/s

Sample 3 25/75 102 mPa/s

Sample 4 0/100 141 mPa/s

Emulsifier: polyglycerol polyricinoleat PGPR 90 – HLB 1

• Marked Ostwald Ripening only at mass fraction clove oil > 0.5

• Emulsions droplet size and sedimentation velocity increase during storage, however the viscosity remains unchanged

• Instability increases increasing the storage temperature

• Results of droplet size measurements and sedimentation velocity are in good agreement

Conclusion

The investigations revealed that analytical centrifugation is well suited for accelerated stability testing of emulsions of varying composition and for various types of slow destabilizing mechanisms. Whereas measurements of droplet size distributions and viscosity measurements were not able to always detect the beginning of destabilization, centrifugal analysis enabled to detect instabilities faster and more accurately. The multisample technique therefore is ideally suited for screening purposes in emulsion product development.

Acknowledgement

This study was supported by a grant from the Bundesministerium für Wirtschaft und Technologie (grant number KA 0047301AWZ3).

References

[1] T. Sobisch, D. Lerche, Rapid characterization of emulsions for emulsifier selection, quality control and evaluation of stability using multisample analytical centrifugation

SCI/RSC/SCS conference Cosmetics and Colloids, London 15 February 2005

http://www.soci.org/SCI/groups/col/2005/reports/pdf/gs3257_sob.pdf

[2] T. Sobisch, D. Lerche,

Rapid selection of dispersants and evaluation of emulsion stability by analytical centrifugation

La Rivista Italiana delle Sostanze Grasse 6/2005 308 – 316

[3] T. Sobisch, D. Lerche, 2007

Application of multisample analytical centrifugation for fast evaluation of long term stability and freeze/thaw stability of emulsions

http://docs.google.com/Doc?id=dcvcr5vw_1fqx3hp

PERFLUORIERTE VERBINDUNGEN - Hintergrundpapier Umweltbundesamt

Zitat:

Perfluorierte Verbindungen sind verstärkt in die öffentliche Diskussion geraten: „Perfluorierte Verbindungen in aller Munde“, „Gift in Pommes“: Unter diesen und ähnlichen Titeln berichten die Medien über Funde in Trinkwasser und Nahrungsmitteln.

.....

Das ist leider nicht alles: Für Umweltschützer ist es ein Problem, dass Perfluorcarbonsäuren und -sulfonsäuren überall verbreitet sind: Sie lassen sich in Flüssen, in den Weltmeeren, in Robben, Nerzen, Füchsen, Eisvögeln und Fischen aus der kanadischen Arktis und selbst in der Leber von Eisbären auf Grönland nachweisen. Besonders bedenklich sind jedoch die weltweiten Nachweise im menschlichen Blut.

Hintergrundpapier Perfluorierte Verbindungen

Pflanzenschutzmittel in der Umwelt - Übersicht

Pflanzenschutzmittel in der Umwelt

Übersicht des
Bayerischen Landesamtes für Umwelt
Infozentrum UmweltWissen

'Pflanzenschutzmittel bekämpfen Pflanzenkrankheiten. Leider wirken sie aber nicht nur gegen die
Schaderreger, sondern oft auch gegen andere Lebewesen. Mittlerweile kann man Spuren von
Pflanzenschutzmitteln fast überall nachweisen: im Boden, im Wasser, in der Luft, in unseren Lebensmitteln,
aber auch im Fett der arktischen Eisbären und im Eis der Zugspitze. Aus Umweltsicht
ist daher jede Maßnahme wichtig, die die Anwendung von Pflanzenschutzmitteln reduzieren hilft.
In dieser Publikation finden Sie einen einführenden Überblick über dieses weite Themenfeld.'

PARTEC 2007 conference papers

PARTEC 2007
Nuremberg, Germany 27-29.3.2007
International Congress on Particle Technology together with POWTECH 2007 / TechnoPharm 2007

Tandem Lecture

Particle interactions in dispersions of micro and nanoparticles / Sedimentation of Colloidal Particles

T. Sobisch1), D. Lerche1), F. Babick 2), G. Salinas Salas 3)

¹⁾ L.U.M. GmbH, Germany, 2) TU Dresden, Germany, 3) Universidad de Talca, Chile

ABSTRACT

The behaviour of dispersions in liquid media, i.e. dispersion stability, flow, separation and packing behaviour, is determined by interparticle forces. This is of fundamental importance for their application in diverse fields such as nanomaterials, coating, paper making, ceramics, sludge dewatering, to name just a few. The first part of the present work reports on the use of multisample analytical centrifugation for investigation of the sedimentation kinetics and the packing and compression behaviour to characterize the colloidal stability and microstructure in aqueous dispersed systems for two different fields of great practical importance, namely mineral particle suspensions and pigment dispersions. The second part focuses on the effect of non-hydrodynamic interactions on the sedimentation behaviour of colloidal systems in liquid media. In many situations complex dependencies prevent a priori calculation of sedimentation kinetics. An experimental study on the influence of double layer interactions on the sedimentation velocity will be presented.
The new multisample approach uses the STEP-technology. Space and time resolved extinction profiles quantify the alteration of particle concentration and packing behaviour without the need for sample dilution. The latter is a necessary prerequisite for ensuring that the liquid dispersions maintain their original properties. The multisample technique applied implies the potential for more systematic studies for targeted colloidal stability.

Introduction

The behaviour of dispersions in liquid media, i.e. dispersion stability, flow, separation and packing behaviour, is determined by the nature and degree of interparticle forces. This is of fundamental importance for their application in diverse fields but also for solid-liquid separation processes. For the characterisation of dispersions analytical techniques are preferable, which avoid sample dilution, thus leaving the dispersion properties unchanged. To this end analytical centrifugation has proven as an efficient tool [1-5] for the quantification of particle porosity [6], particle interaction and particle aggregation [7-11] from both, sedimentation kinetics and packing behaviour.

The first part of the present work reports on the use of multisample analytical centrifugation for investigating the sedimentation kinetics, the packing and compression behaviour with regard to the colloidal stability and microstructure in aqueous dispersed systems.
The sedimentation of stabilised suspensions strongly depends on the particle concentration. Even for dilute systems the decrease in the settling velocity compared to that of isolated particles is quite significant. This is primarily due to hydrodynamic interactions (HI), which are long-range interaction, since disturbances in the flow field decline reciprocally with the distance from the surface. The sedimentation of colloidal particles is additionally affected by the electric double layer surrounding them. The double layer leads to electroviscous effects as well as to electrostatic repulsion between neighbouring particles. Both phenomena can amplify the hydrodynamic hindrance to considerable extent. The second part of our paper presents an experimental study on the influence of double layer thickness on the sedimentation of charged colloidal particles. Investigations were carried out using multisample analytical centrifugation, in which the sedimentation velocity of monosized silica particles was studied at different particle concentration and varying ionic strengths. The results are discussed with regard to the applicability of theoretical models and (semi-)emiprical approximations.

REFERENCES:

[1] R. Buscall, Colloids Surfaces 5 (1982) 269–283.
[2] T. Gilányi, G. Horváth-Szabó, E. Wolfram, J. Colloid Interface Sci. 98 (1984) 72–77.
[3] E. Tombácz, I. Deér, I. Dékány, Colloids Surfaces A 71 (1993) 269-276.
[4] E. Tombácz, B. Horváth, I. Ábrahám, Colloids Surfaces A 71 (1993) 277–285.
[5] S. Tcholakova, N.D. Denkov, I.B. Ivanov, B. Campbell, Langmuir 18 (2002) 8960-8971.
[6] T. Sobisch, D. Lerche, S. Fischer, C. Fanter, Progr. Colloid Polym. Sci. 133 (2006) 169-172. [7] T. Sobisch, D. Lerche, Tenside Surf. Det. 39 (2002) 232-236.
[8] T. Sobisch, D. Lerche, Chemistry Preprint Archive 2002 (2002) 9, 170-184.
[9] T. Sobisch, D. Lerche, In: U. Teipel (Hrsg.): Symposium Produktgestaltung in der Partikeltechnologie Band 2 (2004) 433-448.
[10] T. Sobisch, D. Lerche, Chemistry Preprint Archive 2003 (2003) 7, 198-218.
[11] T. Sobisch, D. Lerche, T. Detloff, M. Beiser, A. Erk, Filtration 6 (2006) 313-321.
[12] D. Lerche, J. Dispersion Sci. Technol. 23 (2002) 699–709.
[13] T. Sobisch, D. Lerche, Colloid and Polymer Science 278 (2000) 369–374.
[14] T. Sobisch, D. Lerche, Filtration 4 (2004) 270 – 274.
[15] G.K. Batchelor, J. Fluid Mech. 52 (1972) 245.
[16] J Happel, H Brenner. Low Reynolds Number hydrodynamics. Nijhoff, The Hague, 1983. [17] DME Thies-Weesie, AP Philipse, G Nägele, B Mandl, R Klein. J. Colloid Interface Sci. 176 (1995) 43-54.
[18] JF Richardson, WN Zaki. Trans. Instn. Chem. Engrs 32 (1954) 35-53
[19] M Smoluchowski, in : Handbuch der Elektrizität und des Magnetismus, Bd.2, Leipzig 1914. [20] Levine S. et al. J. Colloid Interface Sci. 57 (1976) 3, 424-437
[21] Keh & Ding. J. Colloid Interface Sci. 227 (2000) 540-552

paper Ostwald-Kolloquium
27.3. 2007 17.10

Characterization of liquid nanoparticle dispersions by multisample analytical centrifugation

T. Sobisch, D. Lerche

L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489 Berlin, Germany, www.lum-gmbh.com

ABSTRACT

Reducing particle dimensions to nanoscale leads to qualitatively new properties. This holds also for liquid dispersions, which are the most often used form of application of nanoparticles. For characterization of nanoparticle dispersions techniques are preferable, which avoid dilution, thus don’t modify dispersion properties. To this end multisample analytical centrifugation proved as an efficient tool. The new multisample approach uses the STEP-technology. Space and time resolved extinction profiles quantify the alteration of particle concentration but also packing behaviour and phase separation during centrifugation.

Examples are presented for examination of colloidal crystallization and of microgels. The effect of initial volume concentration and sediment pressure on the speed and extend of the crystallization process was studied. Further, the behaviour of microgels was characterized as function of centrifugal acceleration, temperature and concentration.

1 Introduction

Application of nanoparticles in diverse fields is fast developing. For practical applications the colloidal stability of nanoparticle dispersions and the particle size distribution is of paramount importance. This relates to the need for a high through-put tool for the analysis of the dispersion properties during formulation, selection of processing conditions and for quality control of manufactured batches. Analytical control over the dispersion properties at various stages is considered as a key to the successful application of nanoparticles. The phase behaviour of nanoparticle dispersions and the phenomenon of colloidal crystallization is closely related to the nature of particle interactions and particle polydispersity, i.e. colloidal crystallization is favoured by a low degree of particle aggregation and low polydispersity of particle size.
Colloidal crystallization has received considerable attention both from a theoretical and an experimental perspective [1 - 6]. Appearance of crystallization in colloidal suspensions has been deduced so far from visual inspection of Bragg Reflections [3-6]. In case of nanosized materials optical detection with high resolution of the local position offers an alternative approach [7]. Microgel particles are often applied as a physical model for soft deformable particles, for the study of rheological properties and phase transitions. Aqueous microgel suspensions are characterized by a strong dependence of particle size on temperature tuneable by the degree of cross linking. Relating to their specific tuneable properties microgel particles have wide ranging potential applications in the field of sensors, catalysis and controlled drug release. Physicochemical characterization of suspension behaviour and thermal and mechanical properties of these materials is essential for quality control and technical applications.
The paper describes the application of multisample analytical centrifugation for qualitative and quantitative characterization of nanoparticle suspensions and microgel particles as function of concentration, temperature and centrifugal pressure applied. The method allows tracing the distribution of light transmission over the whole sample length during centrifugation. Thereby the kinetics and extent of separation processes can be investigated in-situ.

REFERENCES:

[1] M.D. Rintoul, S. Torquato, Physical Review Letters 77 (1996) 4198.

[2] http://www.icmm.csic.es/cefe

[3] A. Imhof, J.K.G. Dhont, Physical Review Letters 75 (1995) 1662.

[4] W.K. Kegel, Langmuir 16 (2000) 939.

[5] K. Yoshinaga, M. Chiyoda, H. Ishiki, T. Okubo, Colloids and Surfaces A 204 (2002) 285.

[6] A.P. Philipse, G.H. Koenderink, Adv. Coll. Interface Sci. 100-102 (2002) 613.

[7] T. Sobisch, D. Lerche, Interaction between tailored particle interfaces characterized by analytical centrifugation,

Chemistry Preprint Archive, Volume 2003, Issue 7, July 2003, Pages 198-218

http://www.sciencedirect.com/preprintarchive,

[8] T. Sobisch, D. Lerche, Application of a new separation analyzer for the characterization of dispersions stabilized with clay derivatives, Colloid and Polymer Science 278 (2000) 369–374.

[9] D. Lerche, Dispersion stability and particle characterisation by sedimentation kinetics in a centrifugal field, J. Dispersion Sci. Technol. 23 (2002) 699–709.

[10] T. Sobisch, D. Lerche, Use of analytical centrifugation for evaluation of solid-liquid separation in decanter centrifuges: Application for selection of flocculants for sludge dewatering, Filtration 4 (2004) 270–274.

[11] T. Sobisch, D. Lerche, T. Detloff, M. Beiser, A. Erk, Tracing the centrifugal separation of fine particle slurries by analytical centrifugation, Filtration 6 (2006) 313-321.

posters

Characterization of carbon black dispersions by multisample analytical centrifugation

T. Sobisch, D. Lerche, N. Quintas, T. Detloff
L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489 Berlin, Germany, www.lum-gmbh.com

ABSTRACT

Carbon black dispersions are widely applied in inks and paints. A high dispersity and high degree of dispersion stability is of paramount importance. Analytical centrifugation with photometric detection revealed a surprising phenomenon in several industrial application labs, the so called ‘Backfolding’. After a distinct time of centrifugation a marked reduction in turbidity is observed in the supernatant, separated so far. A close correlation was suspected between the degree of the ‘Backfolding’ and product performance. A detailed investigation of this phenomenon was performed in the centrifugal field as function of preparation conditions of carbon black dispersions, volume fraction, centrifugal acceleration, temperature, viscosity and additives.

Analytical centrifugation can be used for an integral characterization of dispersion quality influenced by viscosity, density difference, particle stabilization and particle size distribution. The new multisample approach uses the STEP-technology. Space and time resolved extinction profiles quantify the alteration of particle concentration and packing behaviour during centrifugation without the need for sample dilution. The latter is a necessary prerequisite for ensuring that the liquid dispersions maintain their original properties. The multisample technique applied implies the potential for systematic studies for targeted colloidal stability.

Separation behaviour and dispersion properties of clay suspensions traced by multisample analytical centrifugation

T. Sobisch, D. Lerche

Clay minerals are used in diverse fields, mostly as rheological additives or for adsorption purposes. The properties of clay suspensions strongly depend on processing and suspension composition. The separation behaviour in the centrifugal field in turn is determined by the dispersion degree obtained and on particle interactions. Therefore analytical centrifugation can be used for optimization of separation/classification after processing and for process development and quality control as well.

Investigations using multisample analytical centrifugation with photometric detection (STEP-technology) are presented.

Depending on dispersion quality a characteristic separation behaviour is observed during centrifugation of clay dispersions. Due to attractive particle interactions usually zone sedimentation is observed. Addition of dispersants might result in polydisperse sedimentation of individual particles (colloidal stable dispersions). Packing behaviour and dewaterability are also directly related to particle interactions and to the degree of delamination. Increasing the degree of delamination the effective volume concentration increases (packing density decreases) Adding efficient dispersants packing density increases due to reduction of attractive particle interactions.

The influence of the duration of dispersion, dispersion intensity and dispersants on degree of delamination, particle interactions, separation behaviour and particle size distributions was exemplified for sepiolites of different origin.

Evaluation of Particle Size Analysis by Novel
Centrifugal Sedimentation Method

T. Detloff1), D. Lerche

1) L.U.M. GmbH, Rudower Chaussee 29, 12489 Berlin, Germany, www.lum-gmbh.com, info@lum-gmbh.de

The particle size distribution of dispersions of fine particles were determined by a multisample analytical photocentrifuge LUMiSizer®, which allows to determine space and time resolved extinction profiles (STEP-Technology) during the centrifugation of up to 12 samples simultaneously. While the variation of the light extinction curves caused by centrifugal segregation allows a qualitative description, a rigorous formulation can give access to detailed quantitative characterization. It will be shown that the particle size distribution may be derived by two procedures: analyzing the variation of the extinction at any point of the sample over centrifugation time or analyzing the extinction variation over the entire sample length at any time of centrifugation. For higher concentrations multiple light scattering and the corresponding flux density function were taken into account.

Furthermore we report on studies regarding the validation of this new approach. In these respect measurements with different “well known” and certified particles where done to proof the accuracy of the PSD of concentrated and diluted dispersions. The sensitivity regarding different monomodal and polymodal particle samples will be demonstrated.

Contact person: Torsten Detloff, L.U.M. GmbH, Rudower Chaussee 29, Germany, phone: +49‑(0)‑30‑67 80 60 30, fax: +49‑(0)‑30‑67 80 60 58, t.detloff@lum-gmbh.de

A Novel Simulation Method for Separation Processes in Gravitational and Centrifugal Field

T. Detloff1), D. Lerche

1) L.U.M. GmbH, Rudower Chaussee 29, 12489 Berlin, Germany, www.lum-gmbh.com, info@lum-gmbh.de

Separation processes and dewatering/deliquoring are of great importance across a variety of industries and have a great number of applications (e.g. waste water treatment mineral processing, geotechnical engineering, industrial sludge or bio-, food and pharma separation). Therefore the sedimentation/flotation behaviour of diluted and concentrated dispersions plays a key role. The Simulation of these processes is more and more important because of the time and cost saving factor. During decades since the pioneering work of Kynch in 1952 [1] different investigations were done to model the separation process of concentrated dispersions driven by gravity or a centrifugal field [2]. Also models for polydisperse dispersions which may be flocculated or forming compressible sediments were developed [3].

Based on these work, the authors will present a software tool to simulate the separation process of mono- and polydisperse dispersions (suspensions and emulsions), including flocculation and sediment compressibility in different container geometries. The simulation results will be compared with conducted experiments using space and time depended concentration detection in gravitational and centrifugal field.

References:

[1] G. J. Kynch, A theory of sedimentation. Trans. Faraday Soc. 48 (1952) 166-176.

[2] G. Anestis, W. Schneider, Application of Theory of Kinematic Waves to Centrifugation of Suspensions, Ingenieur-Archiv 53 (1983) 399-407.

[3] S. Berres, R. Bürger, On gravity and centrifugal settling of polydisperse suspensions forming compressible sediments, Int. J. Solids Structures 40 (2003) 4965-4987.

Filtech 2007 conference papers

Filtech 2007 International conference & exhibitition for filtration and separation technology
February 27 - March 1, 2007
Wiesbaden Germany

paper

Characterization of interparticle forces for solid-liquid separation processes using multisample analytical centrifugation

T. Sobisch, D. Lerche

Dispersion Stability & Particle Analysis, L.U.M. GmbH

Rudower Chaussee 29 (OWZ), 12489 Berlin, Germany

info@lum-gmbh.de, www.lum-gmbh.com

ABSTRACT

The behaviour of dispersions in liquid media, i.e. dispersion stability, flow, separation and packing behaviour, is determined by the nature and degree of interparticle forces. This is of fundamental importance for their application in diverse fields but also for solid-liquid separation processes.

The present work reports on the use of multisample analytical centrifugation for investigation of the kinetics and polydispersity of the sedimentation process as well as of the packing and compression behaviour. The method was applied for two different systems of practical importance, namely, polydisperse fine particle suspensions with varying degree of interparticle attraction and for pigment dispersions modified by milling.

The shape and evolution of these extinction profiles allow conclusions about the nature of the sedimentation process (free sedimentation of individual particles, hindered settling, zone sedimentation). Strong repulsive particle interactions lead to a polydisperse sedimentation behaviour, i.e. particles move with different sedimentation velocities according to their particle size. In case of strong attractive particle interactions all particles are moving with identical velocity. If only weak attractive forces act between the particles a sedimentation front of the main fraction of particles evolves, however, a part of the fine fraction still exhibits polydisperse sedimentation behaviour.

Packing density, obtained after compression, is related to the total interparticle potential energy. The packing behaviour further is directly related to the dewatering (deliquoring) behaviour of the sediment. For colloidal stable dispersions the equilibrium packing density is reached almost instantaneously after applying the centrifugal force and a virtually incompressible sediment is formed. For polydisperse suspensions segregation will occur especially at lower initial volume fractions. Increasing the degree of interparticle forces a pronounced compressional behaviour was experienced, packing density becomes very sensitive to changes in centrifugal pressure. However, for strongly flocculated particle dispersions even at high centrifugal pressures only moderate deliquoring can be achieved.

The sedimentation of pigment dispersions investigated is characterized by zone sedimentation. Packing density increases markedly as deagglomeration proceeds during wet milling. Sedimentation analysis allows for direct measurement of the dispersion degree without dilution.

KEYWORDS

Physicochemical aspects, centrifugation, particle interactions and characterization, solid-liquid separation, clarification, classification, dewatering

Introduction

The behaviour of dispersions in liquid media, i.e. dispersion stability, flow, separation and packing behaviour, is determined by the nature and degree of interparticle forces. This is of fundamental importance for their application in diverse fields but also for solid-liquid separation processes.

For characterization of dispersions techniques are preferable, which avoid dilution, thus don’t modify dispersion properties. To this end analytical centrifugation proved as an efficient tool [1-5]. Both, sedimentation kinetics and packing behaviour cover information on particle porosity [6], particle interaction and particle aggregation [7-11]. Fig. 1 shows a schematic overview of the relations between the nature of particle interactions and the sedimentation/packing behaviour.

Fig.1 Schematic overview of relations between the nature of particle interactions and sedimentation/packing behaviour

If strongly repulsive interparticle forces dominate, in dilute systems particles are fully dispersed and sediment individually (colloidal stable dispersions). As the centrifugal acceleration increases with the distance from the centre of rotation sedimentation speeds up until the final sediment height is reached and dense packing is obtained. In case of weakly attractive interactions particles are weakly flocculated. As long as individual flocs sediment the shape of sedimentation curves is similar to that of colloidal stable dispersions. However after formation of a space filling network sedimentation gradually slows down until the centrifugal pressure cannot compress the dense network further (consolidation). Strongly attractive interactions cause strong flocculation. Large flocs sediment very fast and form loose irregular particle networks, which show high resistance against consolidation. The final sediment height is reached only slowly.

The present work reports on the use of multisample analytical centrifugation for investigation of the kinetics and polydispersity of the sedimentation process as well as of the packing and compression behaviour. The method was applied for two different systems of practical importance, namely, polydisperse fine particle suspensions with varying degree of interparticle attraction and for pigment dispersions modified by milling.

paper

Comparison of particle separation in centrifuges with cylindrical tubes or disc rotors .
Experiments and theoretical models

Dietmar Lerche and Torsten Detloff

Dispersion Stability & Particle Analysis, L.U.M. GmbH

Rudower Chaussee 31, 12489 Berlin, Germany

info@lum-gmbh.de, www.lum-gmbh.com

ABSTRACT

Separation and purification of nano- and microparticles becomes essential for technical applications in manifold industrial fields such as biotechnology, drug development, coating and pigment to name only a few. Despite numerous papers since the pioneering work of Kynch, the separation process of concentrated dispersions driven by gravity or a centrifugal field, are not completely understood yet, especially, if particles interact with each other. In the centrifugal case additional difficulties emerge from the Coriolis coupling between the radial and the azimuthal velocity and the geometry of the "containers". Batch centrifuges operate either with containers of constant cross section (CCS geometry) or with disc/cylindrical rotors, where the cross sectional area changes with the distance from the axis of rotation (CSAC geometry). In this paper we shall focus on the sedimentation in these different cell geometries. Experimentally the separation process of dispersions of monodisperse silica and polydisperse quartz at different volume concentrations was investigated by analytical centrifugation (LUMiSizer®). Space and time resolved extinction profiles (STEP-Technology) during the centrifugation were measured using cells with CCS or CSAC geometries. In general, the sediment height in the CSAC cells is smaller compared to CCS ones, but the alteration of the concentration in the vicinity along the radius is similar for both cell types. Experiments were compared with model calculations based on the kinematic Kynch model advanced by Buerger. It will be shown that from results of tube centrifugation (CCS cells) the sedimentation behavior in a disk or cylinder centrifuge (CSAC cells) may be well predicted. This allows to use analytical tube centrifugation to optimize the separation and purification processes of nano- and microparticles by industrial cylinder.

KEYWORDS: Analytical centrifugation, Separation behaviour, Silica, Quartz, Container Geometry, Kinematic Model

Application of multisample analytical centrifugation for fast evaluation of long term stability and freeze/thaw stability of emulsions

Contribution to the 4th World Congress on Emulsions Lyon 2006

Application of multisample analytical centrifugation for fast evaluation of long term stability and freeze/thaw stability of emulsions

T. Sobisch, D. Lerche

L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489 Berlin, Germany

www.lum-gmbh.com, info@lum-gmbh.de

The development of emulsion based products as well as process development/monitoring and quality assurance require efficient and objective analytical tools for shelf life prediction and stability determination. Freeze/thaw stability is often used as measure of long term stability. On the other hand high freeze/thaw stability is often required as property of the final product. To this end the potential of multisample analytical centrifugation was evaluated as an accelerated test procedure.

A new multisample approach is presented using analytical centrifugation, which allows for an accelerated characterization of destabilization processes (creaming, sedimentation, coalescence, phase separation). The kinetics of these destabilizing processes can be traced simultaneously for up-to 12 different samples with temperature control in the range between 4 and 45 °C. No dilution is necessary, which otherwise could lead to changes of dispersion properties.

Analytical centrifugation measures in a rapid way the inherent stability of the samples. Therefore, alterations due to slow aging may be investigated combining first a shorted common accelerated stability test like freeze/thaw cycling and second a rapid evaluation by analytical centrifugation.

The wide application potential of this approach is demonstrated by examples of measurements on cosmetic creams and on beverages.

1 Introduction

The development of emulsion based products as well as process development/monitoring and quality assurance require efficient and objective analytical tools for shelf life prediction and stability determination. Freeze/thaw stability is often used as measure of long term stability. On the other hand high freeze/thaw stability is often required as property of the final product. To this end the potential of multisample analytical centrifugation was evaluated as an accelerated test procedure.

Multisample analytical centrifugation is efficient in characterization and measurement of the speed of destabilizing processes like creaming, coalescence and phase separation (1-7). It detects very small differences in stability and allows for an accelerated characterization of emulsions without dilution, thus avoiding changes of emulsion properties.

Analytical centrifugation traces the inherent stability, but cannot foresee destabilizing processes that will happen during storage of the sample. But, it will see the results of destabilizing processes far faster than visual observation. Therefore, to this end a combination with suitable stress tests is the method of choice.

As a demonstration the evaluation of aging of cosmetic creams and of beverages is presented, which is important in relation to development of new formulations and in quality control of manufactured products. The stability of samples aged during storage at ambient conditions or by a freeze-thaw cycle (accelerated aging) was compared with the initial stability just after manufacturing.

Full article

Application of multisample analytical centrifugation for fast evaluation of long term stability and freeze/thaw stability of emulsions

http://www.AppliedColloidsSurfactants.info, http://AppliedColloidsSurfactants.blogspot.com, mailto:AppliedColloidsSurfactants@gmail.com

Contribution to the 4th World Congress on Emulsions Lyon 2006

Application of multisample analytical centrifugation for fast evaluation of long term stability and freeze/thaw stability of emulsions

T. Sobisch, D. Lerche

L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489 Berlin, Germany

www.lum-gmbh.com, info@lum-gmbh.de

The development of emulsion based products as well as process development/monitoring and quality assurance require efficient and objective analytical tools for shelf life prediction and stability determination. Freeze/thaw stability is often used as measure of long term stability. On the other hand high freeze/thaw stability is often required as property of the final product. To this end the potential of multisample analytical centrifugation was evaluated as an accelerated test procedure.

A new multisample approach is presented using analytical centrifugation, which allows for an accelerated characterization of destabilization processes (creaming, sedimentation, coalescence, phase separation). The kinetics of these destabilizing processes can be traced simultaneously for up-to 12 different samples with temperature control in the range between 4 and 45 °C. No dilution is necessary, which otherwise could lead to changes of dispersion properties.

Analytical centrifugation measures in a rapid way the inherent stability of the samples. Therefore, alterations due to slow aging may be investigated combining first a shorted common accelerated stability test like freeze/thaw cycling and second a rapid evaluation by analytical centrifugation.

The wide application potential of this approach is demonstrated by examples of measurements on cosmetic creams and on beverages.

1 Introduction

The development of emulsion based products as well as process development/monitoring and quality assurance require efficient and objective analytical tools for shelf life prediction and stability determination. Freeze/thaw stability is often used as measure of long term stability. On the other hand high freeze/thaw stability is often required as property of the final product. To this end the potential of multisample analytical centrifugation was evaluated as an accelerated test procedure.

Multisample analytical centrifugation is efficient in characterization and measurement of the speed of destabilizing processes like creaming, coalescence and phase separation (1-7). It detects very small differences in stability and allows for an accelerated characterization of emulsions without dilution, thus avoiding changes of emulsion properties.

Analytical centrifugation traces the inherent stability, but cannot foresee destabilizing processes that will happen during storage of the sample. But, it will see the results of destabilizing processes far faster than visual observation. Therefore, to this end a combination with suitable stress tests is the method of choice. As a demonstration the evaluation of aging of cosmetic creams and of beverages is presented, which is important in relation to development of new formulations and in quality control of manufactured products. The stability of samples aged during storage at ambient conditions or by a freeze-thaw cycle (accelerated aging) was compared with the initial stability just after manufacturing.

2 Experimental

2.1 Materials and sample preparation
Two different commercial cosmetic o/w creams and two emulsion based beverage samples were used as received close to the date of production, after storage under ambient laboratory conditions over 2 month (cosmetic creams) and after one freeze/thaw cycle (24 h at -10 °C followed by 24 h at 25 °C).

2.2 Method of multisample analytical centrifugation

The multisample analytical centrifuge (LUMiFuge, LUM GmbH, Berlin Germany) used in this study employs the STEP-Technology, which allows to measure the intensity of the transmitted light as function of time and position over the entire sample length simultaneously (Measurement scheme see Fig. 1).

Fig. 1 Measurement scheme of the multisample analytical photocentrifuge. Parallel NIR-light is passed through the sample cells and the distribution of local transmission is recorded at preset time intervals over the entire sample length

The data are displayed as function of the position within the sample, as distance from the centre of rotation (transmission profiles, see Fig. 2). The progression of the transmission profiles contains the information on the kinetics of the separation process and allows particle characterization.

At the same time up to 8 different samples can be analysed simultaneously at constant or variable centrifugal speed up to 2300 g. The separation behaviour of the individual samples can be compared and analysed in detail by tracing the variation in transmission at any part of the sample or by tracing the movement of any phase boundary.

As for a given type of sample cells the position corresponds to a defined sample volume the relationship position – volume can be established by calibration.
For further details of the application of the method for characterization of emulsions see (1-7).

3 Results and Discussion

Fig. 2 Centrifugation of a cosmetic cream of the o/w type at 1100 g for 18 hours. Evolution of transmission profiles with time – first recorded profile undermost (red), last profile uppermost (green).

Figure 2 displays the transmission profiles obtained by centrifugation at 1100 g for the least stable cream analysed after just being manufactured.

The sharp drop in transmission at about 88.5 mm marks the filling height of the sample. The lowest transmission belongs to the first profile (lowest transmission). The destabilizing process, separation of an aqueous phase, starts from the bottom of the cell. The boundary water -emulsion is moving upwards (last profile highest transmission in the bottom region). That is, the separation process is characterized by creaming of oil droplets inside the continuous aqueous phase. From this it becomes obvious that the cream is an oil-in-water emulsion. The type of emulsion oil-in-water (o/w) or water-in-oil (w/o) can easily be deduced from the primary process of destabilization traced by the evolution of transmission profiles – creaming of oil droplets or sedimentation of water droplets.

It has to be noted that the cream has a high inherent stability, given the long time and high speed of centrifugation necessary to produce these changes.

The more stable creams exhibited only a small increase of transmission near the cell bottom. For a comparative investigation therefore the change in transmission of the bottom region was chosen as a measure of stability.

Fig. 3 Change of integral transmission (113 – 114 mm) during centrifugation at 1100 x g for 18 hours – effect of 2 month aging at ambient temperature

Figure 3 shows the effect of two month of aging at ambient temperature for the most and for the least stable sample. The just prepared samples show a distinct less pronounced demixing during centrifugation than the samples after 2 month aging at ambient laboratory conditions. The most likely cause is slow flocculation, which lead to a (temporary) stabilization against creaming due to an increase in viscosity. However, further flocculation is expected to cause irreversible destabilization. In contrast other aging processes like coalescence and Ostwald ripening would have led to a direct destabilization.

The effect of accelerated aging by a freeze-thaw cycle (thawing after storage at -10 °C, for 24 hours compared to the samples not subjected to the freeze-thaw cycle) is depicted in Fig. 4. It is readily obvious from this comparison that aging by one freeze-thaw cycle markedly enhances the differences in stability already inherent in the samples before freezing. As seen the separation of the continuous phase at the bottom is initially slow and speeds up only after a prolonged time of centrifugation. This indicates a stabilizing barrier against creaming (probably a flocculated network). The freeze-thaw cycle obviously reduces the stabilizing barrier causing a marked decrease of the induction period time.

In the case investigated the order of stability of the different creams does not change during aging (2 month, or after an additional freeze-thaw cycle), i.e. the inherent stability of the samples as prepared is altered during aging for all samples the same way. To trace slow destabilizing processes a combination with common accelerated aging tests is the method of choice.

Fig. 4 Change of integral transmission (113 – 114 mm) during centrifugation at 1100 x g for 18 hours – effect of a freeze-thaw cycle after 2 month aging at ambient temperature

Evaluation of long term stability is often complicated by slow diffusion based destabilization processes, which cannot be foreseen by analytical centrifugation. However, the result of these processes can be traced far more faster then by naked eye. An example is given in Fig. 5 for emulsion based beverage samples. In this case the stability was measured by the variation of turbidity during centrifugation. As can be seen the fresh samples exhibited a similar behaviour. However, they were markedly destabilized after only one freeze-thaw cycle. After this, sample 1 showed a substantial higher loss of stability. The same trends were observed after 6 week of storage but less pronounced.

Fig. 5 Effect of aging on emulsion based beverages, influence of 1 freeze-thaw cycle on speed of clarification measured as variation in transmission, centrifugation at 1100 g

4 Conclusions

The investigations revealed that analytical centrifugation was well suited for accelerated stability testing of commercial emulsions in case of slow destabilizing mechanisms. In one case analytical centrifugation traced differences in separation stability just after manufacturing, which were enhanced during only one freeze-thaw cycle. In the other case differences in stability were revealed after freeze-cycling only.

The multisample technique is ideally suited for screening purposes.

5 References

(1) T. Sobisch, D. Lerche, Rapid emulsifier selection and evaluation of emulsion stability by multisample analytical centrifugation, this conference - Topic: - 3 Behaviour, characterization and processing, Workshop: 3.1 New techniques of characterization

(2) T. Sobisch, D. Lerche, G.G. Badolato, F. Aguilar, H.P. Schuchmann, Evaluation of long term stability of model emulsions by multisample analytical centrifugation, this conference:

Topic: - 3 Behaviour, characterization and processing, Workshop: 3.1 New techniques’ of characterization

(3) D. Lerche, T. Sobisch, S. Küchler, Shelf life prediction of emulsions by based on multisample analytical centrifugation, this conference - Topic: - 3 Behaviour, characterization and processing, Workshop: 3.1 New techniques of characterization

(4) T. Sobisch, D. Lerche, Rapid characterization of emulsions for emulsifier selection, quality control and evaluation of stability using multisample analytical centrifugation, 2005,

SCI/RSC/SCS conference Cosmetics and Colloids, London 15 February 2005

http://www.soci.org/SCI/groups/col/2005/reports/pdf/gs3257_sob.pdf

(5) T. Sobisch, D. Lerche, Rapid selection of dispersants and evaluation of emulsion stability by analytical centrifugation, La Rivista Italiana delle Sostanze Grasse 82 (2005) 304 – 312

(6) T. Sobisch, D. Lerche, S. Küchler, A. Uhl, Rapid stability assessment for liquid and paste like foods by multisample analytical centrifugation, Paper Proceedings Euro Food Chem XIII, Macromolecules and their degradation products in food – physiological, analytical and technological aspects, Hamburg, Germany, September 19 – 23 2005, Eds. T. Eklund, M. Schwarz, H. Steinhart, H.-P. Their, P. Winterhalter, pp. 672 – 675, Gesellschaft Deutscher Chemiker e.V., 2005, ISBN 3-936028-31-1

(7) D. Lerche, T. Sobisch, S. Küchler, 2002, Stability analyser LUMiFuge 116 for rapid evaluation of emulsion stability and demulsifier selection, Chemistry Preprint Archive, Volume 2002, Issue 6, June 2002, Pages 195-201 http://www.sciencedirect.com/preprintarchive