Particle Dynamics in Crystallizing Colloidal Suspensions

这项研究将率先使用一种新出现的光 散射技术，扩散波光谱（DWS），以 研究胶体系统中结构形成的动力学。 在应用于胶体悬浮液的DWS中，光从许多 在离开系统之前的胶体颗粒。散射光 用PM管测量。 对于每个特定的光子路径， 粒子在路径中的位移（>ri（t））引起 散射强度的变化。通过测量散射 强度作为时间的函数， 可以获得散射光。假设：（1）网 沿着沿着光子路径的散射的相位变化是高斯的 随机变量，（2）在一个粒子的位移向量 光子路径（>ri（t））和散射矢量qi是不相关的， （3）传播方向在一个 长度L*。 有了这些假设， 的贡献 一个光子路径的相关函数可以写成 的均方位移>r2，l* 和路径长度s。 为了获得长度为s的路径长度对 总散射强度，即光在时间上的能量密度 t和位置r（每单位体积U（t，r）的光子）是第一个 通过求解特定样品的扩散方程获得 几何形状，并且从该函数，加权因子可以是 得到了输运平均自由程是通过校准得到的 在粒子上测量自相关的过程 它们不相互作用，并且均方位移可以是 从理论上估计。该技术将用于探测 离子强度和浓度对短时粒子影响 无序和有序系统中的动力学。

This study will pioneer the use of a newly emerging light scattering technique, diffusive wave spectroscopy (DWS), to the study of the dynamics of structure formation in colloidal systems. In DWS applied to colloidal suspensions, light scatters off of many colloid particles before leaving the system. The scattered light is measured by a PM tube. For each particular photon path, the displacement of the particles in the path (>ri(t)) gives rise to a change in the scattering intensity. By measuring the scattering intensity as a function of time, the autocorrelation g1(t) of the scattered light can be obtained. It is assumed that (1) the net phase change for the scatterings along a photon path is a Gaussian random variable, (2) the displacement vector of a particle in a photon path (>ri(t)) and the scattering vector qi are uncorrelated, and (3) the direction of propogation becomes uncorrelated over a length l*. With these assumptions, the contribution to the correlation function for one photon path can be written in terms of the mean square displacement >r2, l* and the path length s. To obtain the contribution of path lengths of length s to the total scattering intensity, the energy density of the light at time t and position r (the photons per unit volume U(t,r)) is first obtained by solving a diffusion equation for the particular sample geometry, and from this function the weighting factor can be obtained. The transport mean free path is obtained by a calibration procedure in which an autocorrelation is measured on particles which are not interacting and the mean square displacement can be estimated from theory. The technique will be used to probe the influence of ionic stregth and concentration on short time particle dynamics in disordered and ordered systems.