Simulation of scattering and phase behavior around the isotropic-nematic transition of discotic particles.
Simulation of scattering and phase behavior around the isotropic-nematic transition of discotic particles.
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DOI：
10.1016/j.jcis.2012.03.046
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发表时间：
2012-07
影响因子：
9.9
通讯作者：
Rui P. S. Fartaria;Nadeem Javid;J. Sefcik;M. Sweatman
中科院分区：
文献类型：
--
作者：
Rui P. S. Fartaria;Nadeem Javid;J. Sefcik;M. Sweatman
本文详细研究了长径比L/D ≥ 0.1的分散颗粒体系中的各向同性-非均相转变，并与化学改性粘土颗粒的广泛的胶体悬浮液有关。采用蒙特卡罗模拟技术，计算了各相的状态方程、径向分布函数、结构因子和归一化散射强度。结果被解释并与先前报道的自由能计算相关[Fartaria和Sweatman，Chem.Phys.Lett. 478（2009）150]，表明对于较低的纵横比，几乎连续的各向同性-均质转变。考虑到这种行为，我们检查了每个相的结构信息，以确定如何使用实验散射数据来区分这两个相。在每个阶段的径向分布函数强烈地依赖于纵横比，并为较大的纵横比的显着增加的局部有序的dissolved颗粒（在这里表示为切球）的观察之前的相变。然而，在r/D=0.1附近的g（r）中看到的这种最近邻排序在受到通常统计误差的实验散射数据中很难辨别。计算了L/D=0.1，0.04和0.01时各向同性相和均质相在各向同性-均质转变处和远离各向同性-均质转变处的结构因子和散射强度。虽然对于较大的纵横比，可以从7 QD周围的第一散射峰的高度和形状检测到各向同性-均质相变，但是随着纵横比的减小，该特征变得不那么具有区分性。相反，低散射矢量振幅（Q→0）下的散射强度可以用于检测低纵横比下的相变。这些结果提供了有用的见解，指导解释的X射线和光散射测量的胶体分散体的薄血小板经历各向同性的相变。
The detailed study of the isotropic–nematic phase transition in a system of discotic particles of aspect ratios L/D⩽0.1 presented here is relevant to a broad range of colloidal suspensions of chemically modified clay particles. Using Monte Carlo simulation techniques the equation of state, radial distribution functions, structure factors and normalized scattering intensities are calculated for each phase. The results are interpreted and related to previously reported free energy calculations [Fartaria and Sweatman, Chem. Phys. Lett. 478 (2009) 150], suggesting a nearly continuous isotropic–nematic transition for lower aspect ratios. Given this behavior we examined the structural information for each phase to determine how experimental scattering data might be used to distinguish the two phases. The radial distribution functions in each phase depend strongly on aspect ratio, and for larger aspect ratios a dramatic increase in the local ordering of discotic particles (represented here as cut-spheres) is observed just before the phase transition. However, this nearest-neighbor ordering seen in g(r) around r/D=0.1 would hardly be discernible in experimental scattering data subject to usual statistical errors. The structure factors and scattering intensities were calculated for L/D=0.1, 0.04 and 0.01 for the isotropic and nematic phases at and away from the isotropic–nematic transition. While the isotropic–nematic phase transition can be detected from the height and shape of the first scattering peak around 7QD for larger aspect ratios, this feature becomes much less discriminatory with decreasing aspect ratio. Instead, scattering intensities at low scattering vector amplitudes (Q→0) can be used for detection of the phase transition at low aspect ratios. These results provide useful insight to guide interpretation of X-ray and light scattering measurements for colloidal dispersions of thin platelets undergoing isotropic–nematic transitions.