Ferretti R, Zhang J, Buffle J
Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, Sciences II, 30 quai Ernest Ansermet, Geneva 4, 1211, Switzerland
J Colloid Interface Sci. 1998 Dec 15;208(2):509-517. doi: 10.1006/jcis.1998.5864.
The structure of hematite aggregates in the presence of fairly monodisperse polyacrylic acid (PAA) with two different molecular weights (Mw = 1.36 x 10(6), Mw/Mn = 1.53; Mw = 3.69 x 10(4), Mw/Mn = 1.60) was studied using static light scattering (SLS). The fractal dimensions were calculated from the scattering exponents, after taking into account the finite size of aggregates, using exponential and Gaussian cutoff functions. Three flocculation regimes, namely, pre-DLA, DLA (diffusion-limited aggregation), and post-DLA, were defined based on the polymer concentration. In the DLA regime, fractal dimension values, Df = 1.84 +/- 0.02 and 1.73 +/- 0.02, were obtained using exponential and Gaussian cutoff functions, respectively. A fractal dimension of approximately 2.0 was found, as expected, in the pre-DLA regime (at PAA concentrations lower than the optimal dosage for a DLA regime) where the flocculation rate was reaction limited. In contrast, in the post-DLA regime, the flocculation was slow but the structure of aggregates was as tenuous as in the DLA regime with a fractal dimension Df approximately 1.8. Moreover, for all three regimes, the Df values were independent of the molecular weights of PAA. The lower fractal dimension in post-DLA was probably due to the increased concentration of polymer chains between adjacent particles in aggregates. The steric hindrance favored tip-to-tip aggregation, leading to a more tenuous structure. Copyright 1998 Academic Press.
利用静态光散射（SLS）研究了在存在两种不同分子量（Mw = 1.36 x 10(6)，Mw/Mn = 1.53；Mw = 3.69 x 10(4)，Mw/Mn = 1.60）的相当单分散的聚丙烯酸（PAA）情况下赤铁矿聚集体的结构。在考虑聚集体的有限尺寸后，使用指数和高斯截止函数从散射指数计算分形维数。基于聚合物浓度定义了三种絮凝状态，即预扩散限制聚集（pre-DLA）、扩散限制聚集（DLA）和后扩散限制聚集（post-DLA）。在DLA状态下，分别使用指数和高斯截止函数获得分形维数值Df = 1.84 +/- 0.02和1.73 +/- 0.02。正如预期的那样，在预DLA状态（PAA浓度低于DLA状态的最佳剂量）下，絮凝速率受反应限制，发现分形维数约为2.0。相比之下，在后DLA状态下，絮凝缓慢，但聚集体的结构与DLA状态一样疏松，分形维数Df约为1.8。此外，对于所有三种状态，Df值均与PAA的分子量无关。后DLA中较低的分形维数可能是由于聚集体中相邻颗粒之间聚合物链浓度的增加。空间位阻有利于尖端对尖端的聚集，导致结构更加疏松。版权所有1998年学术出版社。
