Brady Michael A, Limpoco F T, Perry Scott S
Department of Materials Science & Engineering, University of Florida, Gainesville, FL 32611, USA.
Langmuir. 2009 Jul 7;25(13):7443-9. doi: 10.1021/la900371k.
Lateral and normal forces between a surface-bound, brushlike copolymer, poly(ethylenimine)-graft-poly(ethylene glycol) (PEI-g-PEG), and a silica colloidal probe were investigated with atomic force microscopy (AFM) and related to the relative mass of the solvent absorbed within the polymer as measured with the quartz crystal microbalance. PEI-g-PEG was adsorbed onto an oxide-passivated silicon wafer through its exposure to physiologically buffered solutions of the polymer. Frictional forces were measured between the colloidal probe and the substrate by AFM as the polarity of the solvent was systematically varied. Reduced friction forces and greater film thicknesses were encountered under solvents of higher polarity, which are attributed to the extended conformation of the brushlike copolymer under these conditions. Lateral and normal forces detected between the colloidal probe and this surface-bound PEI-g-PEG were found to be similar under certain solvent conditions to those measured for poly(L-lysine)-graft-poly(ethylene glycol), a brushlike copolymer with a different molecular architecture. To this end, friction force studies of both symmetric and asymmetric PEI-g-PEG-coated interfaces served to identify the contributions of conformational and bridging effects in the observed tribological behavior.
利用原子力显微镜（AFM）研究了表面结合的刷状共聚物聚（乙烯亚胺）-接枝-聚（乙二醇）（PEI-g-PEG）与二氧化硅胶体探针之间的横向力和法向力，并将其与用石英晶体微天平测量的聚合物中吸收的溶剂的相对质量相关联。通过将PEI-g-PEG暴露于聚合物的生理缓冲溶液中，使其吸附在氧化物钝化的硅片上。随着溶剂极性的系统变化，用AFM测量胶体探针与基底之间的摩擦力。在极性较高的溶剂下，摩擦力减小，膜厚度增加，这归因于在此条件下刷状共聚物的伸展构象。发现在某些溶剂条件下，胶体探针与这种表面结合的PEI-g-PEG之间检测到的横向力和法向力与具有不同分子结构的刷状共聚物聚（L-赖氨酸）-接枝-聚（乙二醇）测量的力相似。为此，对对称和不对称PEI-g-PEG涂层界面的摩擦力研究有助于确定观察到的摩擦学行为中构象和桥接效应的贡献。
