Virginia Tech, M/C 0211, Department of Chemical Engineering, Blacksburg, VA 24061, USA.
J Colloid Interface Sci. 2012 Jan 1;365(1):72-80. doi: 10.1016/j.jcis.2011.09.015. Epub 2011 Sep 17.
We have measured the force between a weakly charged micron-sized colloidal particle and flat substrate in the presence of highly charged nanoparticles of the same sign under solution conditions such that the nanoparticles physically adsorb to the colloidal particle and substrate. The objective was to investigate the net effect on the force profile between the microparticle and flat substrate arising from both nanoparticle adsorption and nanoparticles in solution. The experiments used colloidal probe atomic force microscopy (CP-AFM) to measure the force profile between a relatively large (5 μm) colloidal probe glass particle and a planar glass substrate in aqueous solutions at varying concentrations of spherical nanoparticles. At very low nanoparticle concentrations, the primary effect was an increase in the electrostatic repulsion between the surfaces due to adsorption of the more highly charged nanoparticles. As the nanoparticle concentration is increased, a depletion attraction formed, followed by longer-range structural forces at the highest nanoparticle concentrations studied. These results suggest that, depending on their concentration, such nanoparticles can either stabilize a dispersion of weakly-charged colloidal particles or induce flocculation. This behavior is qualitatively different from that in nonadsorbing systems, where the initial effect is the development of an attractive depletion force.
我们已经测量了在溶液条件下带相同电荷的高浓度纳米颗粒存在下，弱电荷微米级胶体颗粒与平面基底之间的力，其中纳米颗粒物理吸附到胶体颗粒和基底上。目的是研究来自纳米颗粒吸附和溶液中纳米颗粒的净效应对微粒子和平坦基底之间的力分布的影响。实验使用胶体探针原子力显微镜（CP-AFM）在不同浓度的球形纳米颗粒的水溶液中测量相对较大（5μm）胶体探针玻璃颗粒和平面玻璃基底之间的力分布。在纳米颗粒浓度非常低的情况下，由于更多高电荷纳米颗粒的吸附，表面之间的静电排斥增加是主要影响。随着纳米颗粒浓度的增加，形成了耗尽吸引力，然后在研究的最高纳米颗粒浓度下出现了更长程的结构力。这些结果表明，根据其浓度，此类纳米颗粒可以稳定带弱电荷的胶体颗粒的分散体，也可以诱导絮凝聚集。这种行为与非吸附系统中的行为明显不同，在非吸附系统中，最初的效应是发展出吸引力的耗尽力。
