Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong.
Langmuir. 2013 Sep 3;29(35):11038-45. doi: 10.1021/la401671m. Epub 2013 Aug 20.
Using total internal reflection microscopy (TIRM), we have systematically measured the interactions between a microsphere and a flat hydrophilic surface in the presence of polyethylene oxide (PEO) polymer solution. Our results reveal that PEO significantly mediates the interaction forces between the two surfaces. At low polymer concentration, the interactions between two surfaces in the presence of PEO are mainly dominated by repulsive forces, originating from diffuse layer overlap. At intermediate polymer concentration, a long-range and weak attraction sets in. This force is likely attributed to the depletion attraction due to the presence of free PEO chains in bulk solution; however, a simple hard-sphere AO model fails to precisely describe the attraction. At high polymer concentration where PEO chains overlap, the attraction disappears, and levitation of the microsphere probe is detected. We argue that at this overlapping region, the correlation length of PEO chains is much smaller than the size of single PEO molecule, leading to weakening and disappearing of the depletion attraction. Finally, at very high concentration, oscillatory structural force is obviously found, indicating the significant structural ordering of the PEO chains under confinement.
我们利用全内反射显微镜（TIRM），系统地测量了在聚氧化乙烯（PEO）聚合物溶液存在的情况下，一个微球与一个亲水平面之间的相互作用。我们的结果表明，PEO 显著调节了两个表面之间的相互作用力。在低聚合物浓度下，PEO 存在时两个表面之间的相互作用主要由扩散层重叠产生的排斥力主导。在中等聚合物浓度下，会出现长程且较弱的吸引力。这种力可能归因于由于在本体溶液中存在游离的 PEO 链而产生的空间排斥力；然而，简单的硬球 AO 模型无法准确描述这种吸引力。在 PEO 链重叠的高聚合物浓度下，吸引力消失，并检测到微球探针的悬浮。我们认为，在这个重叠区域，PEO 链的相关长度比单个 PEO 分子的尺寸小得多，导致空间排斥力的减弱和消失。最后，在非常高的浓度下，明显发现了振荡结构力，表明 PEO 链在受限条件下的显著结构有序性。
