Lin Wei, Galletto Paolo, Borkovec Michal
Department of Inorganic, Analytical, and Applied Chemistry, University of Geneva, Sciences II, 30 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland.
Langmuir. 2004 Aug 31;20(18):7465-73. doi: 10.1021/la049006i.
Poly(amidoamine) (PAMAM) dendrimers were shown to adsorb strongly on negatively charged latex particles, and their effect on the particle charge and aggregation behavior was investigated by light scattering and electrophoretic mobility measurements. Time-resolved simultaneous static and dynamic light scattering was used to measure absolute aggregation rate constants. With increasing dendrimer dose, the overall charge could be tuned from negative to positive values through the isoelectric point (IEP). The aggregation is fast near the IEP and slows down further away. With decreasing ionic strength, the region of fast aggregation narrows and the dependence of the aggregation rate on the dendrimer dose is more pronounced. Surface charge heterogeneities become important for higher dendrimer generations. They widen the fast aggregation region, reduce the dependence of the aggregation rate on the dendrimer dose, and lead to an acceleration of the rate in the fast aggregation regime near the IEP. The ratio of the dendrimer charge and the particle charge exceeds the stoichiometric ratio of unity substantially and further increases with increasing generation. The tentative interpretation of such superstoichiometric charge neutralization involves coadsorption of anions and the finite thickness of the adsorbed dendrimer layer.
聚（酰胺胺）（PAMAM）树枝状大分子被证明能强烈吸附在带负电荷的乳胶颗粒上，并通过光散射和电泳迁移率测量研究了它们对颗粒电荷和聚集行为的影响。采用时间分辨同时静态和动态光散射来测量绝对聚集速率常数。随着树枝状大分子剂量的增加，总电荷可通过等电点（IEP）从负值调节到正值。在IEP附近聚集很快，而在更远的距离则减慢。随着离子强度的降低，快速聚集区域变窄，聚集速率对树枝状大分子剂量的依赖性更加明显。对于更高代数的树枝状大分子，表面电荷不均匀性变得很重要。它们拓宽了快速聚集区域，降低了聚集速率对树枝状大分子剂量的依赖性，并导致在IEP附近的快速聚集区域速率加快。树枝状大分子电荷与颗粒电荷的比值大大超过了化学计量比的1，并且随着代数增加进一步增大。对这种超化学计量电荷中和的初步解释涉及阴离子的共吸附和吸附树枝状大分子层的有限厚度。
