光学与粒径耦合多分散性的动态光散射研究

THE COUPLING OF OPTICAL AND SIZE POLYDISPERSITIES BY DYNAMIC LIGHT SCATTERING

研究了满足ＲａｙｌｅｉｇｈＧａｎｓＤｅｂｙｅ（ＲＧＤ）近似条件的球形稀溶液的光学和粒径多分散性耦合的动态光散射技术检测问题．在分析中采用了球壳Ｌ和球核Ｒ－Ｌ都连续变化且壳层变化满足Ｌ＝αＲ（其中α＜１和Ｒ是壳球半径）的壳核硬球模型．得出了在溶剂折射率ｎｍ和壳层折射率ｎｓ匹配时，即ｎｍ＝ｎｓ，平均散射强度Ｉ（ｑ）和等效扩散系数Ｄｅ（ｑ）与散射矢ｑ间的关系．给出了用以检测窄分散系统小多分散性程度的等效扩散系数极值点位置与多分散系数间的线性关系，导出了上述溶液模型下的“测量”静态结构因子Ｓｍ（０）．

Abstract We study the detection theory of polydispersities for dilute suspension of optical and size polydisperse spherical particles, for which the Rayleigh Gans Debye (RGD) approximation is valid.To develop the theory a concentric core shell hard sphere model is adopted,in which particles possess a continuous variation in the core size and shell thickness,the latter is directly proportional to the radius of core,thus giving rise to a distribution in the particle refractive indices.We assume the shell thickness to be L=αR ,where α<1 and is a constant. We extend the “measured” dynamic structure factor to the general case where the optical and size polydispersities are combination,and a new “measured” static structure factor S m (K) is derived. We analyse the dependence of the average scattered intensity I(q) and the effective diffusion coefficient D e (q) which is obtained from the first cumulant measured by dynamic light scattering in the case that the refractive index of the solvent and that of the shell are matched,i.e., n m=n s , on the scattering vector q .A linear relation between the extreme point of the effective diffusion coefficient and the polydispersity δ is obtained, which gives a method to detect the small size polydispersities of a disperse system.