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.