Mohraz Ali, Solomon Michael J
Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109-2136, USA.
J Colloid Interface Sci. 2006 Aug 1;300(1):155-62. doi: 10.1016/j.jcis.2006.03.048. Epub 2006 Mar 27.
The internal dynamics of fractal cluster gels of colloidal boehmite rods with aspect ratios r = 3.9, 8.6, and 30.1, and colloidal polystyrene spheres (r = 1) are reported. Increasing r decreases the minimum colloid volume fraction for gelation. The behavior of the dynamic structure factor of rod gels is consistent with the internal dynamics of a constrained Brownian fractal object. Colloidal boehmite gels display an abrupt transition from floppy to brittle dynamics at phi approximately 10(-4). Moreover, the fractal cluster size of rod gels is not the determinant of the relaxation time of density fluctuations as it is in spherical particle gels. Instead, the relative behavior of the magnitude and time scale of the constrained fluctuations suggests that the fractal rod network is viscously coupled only on local, rather than cluster, scales. We hypothesize that noncentral forces between the anisometric particles are responsible for this anomalous behavior.
本文报道了长径比r = 3.9、8.6和30.1的勃姆石棒状胶体以及聚苯乙烯球状胶体（r = 1）的分形簇凝胶的内部动力学。r增大时，凝胶化所需的最小胶体体积分数降低。棒状凝胶的动态结构因子行为与受约束的布朗分形物体的内部动力学一致。勃姆石胶体凝胶在约10⁻⁴的体积分数下显示出从柔软动力学向脆性动力学的突然转变。此外，棒状凝胶的分形簇尺寸并非密度涨落弛豫时间的决定因素，而在球状颗粒凝胶中情况则不同。相反，受约束涨落的幅度和时间尺度的相对行为表明，分形棒状网络仅在局部而非簇尺度上存在粘性耦合。我们推测，各向异性颗粒之间的非中心力是导致这种异常行为的原因。
