Particle Dynamics in Crystallizing Colloidal Suspensions

结晶胶体悬浮液中的粒子动力学

• 批准号: 9303763
• 负责人: Alice Gast
• 金额: $ 5万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1993
• 资助国家: 美国
• 起止时间: 1993-02-15 至 1994-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9303763&HistoricalAwards=false
• 关键词: Particle; Dynamics; Crystallizing; Colloidal; Suspensions

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.

这项研究将率先使用一种新兴的光散射技术，扩散波光谱（DWS），来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，光在离开系统之前会从许多胶体颗粒中散射出去。散射光由PM管测量。对于每个特定的光子路径，路径中粒子的位移（>ri(t)）引起散射强度的变化。通过测量散射强度与时间的关系，可以得到散射光的自相关系数g1(t)。假设(1)沿光子路径散射的净相位变化为高斯随机变量，(2)光子路径中粒子的位移矢量（>ri(t)）与散射矢量qi不相关，(3)传播方向在长度l*上不相关。在这些假设下，一个光子路径对相关函数的贡献可以用均方位移>r2， l*和路径长度s来表示。为了得到长度s的路径长度对总散射强度的贡献，首先通过求解特定样品几何形状的扩散方程得到光在时间t和位置r处的能量密度（单位体积U（t,r）的光子数），由该函数可以得到权重因子。通过测量不相互作用的粒子的自相关和从理论上估计均方位移的校准程序，获得输运平均自由程。该技术将用于探索离子强度和浓度对无序和有序系统中短时间粒子动力学的影响。