Microstructure of equilibrium fluid clusters in colloid-polymer suspensions

被引:15
作者
Gopalakrishnan, V. [1 ]
Zukoski, C. F. [1 ]
机构
[1] Univ Illinois, Dept Chem & Biomol Engn, Urbana, IL 61801 USA
来源
PHYSICAL REVIEW E | 2007年 / 75卷 / 02期
关键词
D O I
10.1103/PhysRevE.75.021406
中图分类号
O35 [流体力学]; O53 [等离子体物理学];
学科分类号
070204 ; 080103 ; 080704 ;
摘要
Several studies on colloidal depletion systems have reported the existence of a fluid phase consisting of clusters of particles above a critical polymer concentration that acts as a precursor regime to the gel phase at low colloid volume fractions (phi <= 0.20). The clusters are found to be stable against further aggregation suggesting that individual particles are localized within a cluster. However the clusters themselves behave as distinct entities in an equilibrium fluid phase. In this study, we probe the internal microstructure of the cluster entities by ultrasmall angle x-ray scattering (USAXS) techniques. These studies reveal that over the accessible length scales, the microstructure of the particle clusters are similar to that observed in dense space-spanning depletion gels. The origin of these clusters is unclear but the scattering patterns as they settle with time reveal that the percolation of the clusters to form space-spanning gels does not influence their internal microstructure. These observations lend support to the hypothesis that the formation of space-spanning depletion gels at a given volume fraction is driven by the percolation of the particle clusters. Settling experiments at phi=0.08 also provide rough estimates of the cluster sizes that appear consistent with the observations from the USAXS experiments.
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页数:9
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