Structure Formation in Suspensions with a Liquid Crystalline Medium: Percolation Phenomena
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- 作者：G. Pulla Reddy ; D. K. Chokappa ; V. M. Naik ; and D. V. Khakhar
- 刊名：Langmuir
- 出版年：1998
- 出版时间：April 28, 1998
- 年：1998
- 卷：14
- 期：9
- 页码：2541 - 2547
- 全文大小：126K
- 年卷期：v.14,no.9(April 28, 1998)
- ISSN：1520-5827
文摘
Measurements of the storage modulus of suspensions of marbleparticles in a surfactant-based lyotropicliquid-crystalline medium (lamellar, smectic B) are reported. Thesuspension is a model system for severalfood and consumer products. The storage modulus is found to remainnearly constant with an increasein the particle volume fraction until a critical value is reached,beyond which a sharp increase in thestorage modulus is obtained. The critical volume fraction is foundto increase with an increase in particlesize. The storage modulus of the suspensions exhibits a power lawdependence on the oscillation frequency,and the power law exponent decreases sharply near the critical volumefraction. The experimental dataindicate a transition from a multidomain lamellar liquid-crystallinestructure to a structure with a rigidsample spanning network. A network model for the suspension isproposed in which a large number ofparallel lamellae bridge randomly placed particles with surfaces closerthan a specified distance, themaximum layer size (sm). The networkformation is essentially a continuum percolation problem,forwhich the dimensionless critical number density is found by numericalsimulations to be 
c =
d5/14/i09/eqn/la970558te10001.gif">Lm
0.87 where Lm is the maximum distance betweenthe centers of bonded particles and 
c is thecriticalnumber density. The modulus (Gc) of thepercolation network is obtained computationally as thestressrequired for a small tensile deformation of the network. Thecomputed modulus is found to be of the formGc 
2/3( -c)2.5, which is in good agreement withexperimental data.
c =0.87 where Lm is the maximum distance betweenthe centers of bonded particles and c is thecriticalnumber density. The modulus (Gc) of thepercolation network is obtained computationally as thestressrequired for a small tensile deformation of the network. Thecomputed modulus is found to be of the formGc 2/3( -c)2.5, which is in good agreement withexperimental data.