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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.
ABSTRACT
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.
REFERENCES:
Characterization of liquid nanoparticle dispersions by multisample analytical centrifugation
T. Sobisch, D. Lerche
L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489
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
[1] M.D. Rintoul,
[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
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.
