Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland.
J Phys Chem B. 2010 Feb 4;114(4):1562-7. doi: 10.1021/jp907348e.
We studied the coalescence behavior of a fluorinated elastomer colloid, stabilized by fixed surface charges, with a glass transition temperature of about -20 degrees C, as a function of temperature under diffusion-limited cluster-cluster aggregation (DLCA) conditions. We first measured the aggregation kinetics by in situ dynamic light scattering and then simulated it through the Smoluchowski approach (i.e., population balance equations) using the only unknown parameter, the fractal dimension D(f) of the clusters, as the fit parameter. It was found that the estimated D(f) value increased as the temperature increased, starting from 1.7 at 25 degrees C and reaching the upper limit of 3.0 for T > or = 55 degrees C. These results indicate that the coalescence extent increases as the temperature increases. Such temperature-dependent coalescence behavior cannot be explained by thermodynamic considerations, and it must be related to a certain kinetic resistance. We explain this effect by considering the resistance of the fixed charges to relocation on the particle surface, which decreases as the temperature increases.
我们研究了在扩散限制聚集(DLCA)条件下,作为温度函数的固定表面电荷稳定的具有约-20℃玻璃化转变温度的氟化弹性体胶体的聚结行为。我们首先通过原位动态光散射测量了聚集动力学,然后通过 Smoluchowski 方法(即种群平衡方程)进行了模拟,其中唯一未知参数是聚集体的分形维数 D(f),作为拟合参数。结果发现,估算的 D(f) 值随着温度的升高而增加,从 25℃时的 1.7 增加到 T≥55℃时的上限 3.0。这些结果表明,聚结程度随温度升高而增加。这种依赖于温度的聚结行为不能用热力学考虑来解释,它必须与某种动力学阻力有关。我们通过考虑固定电荷在粒子表面上重新定位的阻力来解释这种效应,该阻力随着温度的升高而降低。
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