超分子聚合物刷PVP-Chol表面图案化及其力诱导的可逆结构转变（英文）

Surface Patterning and Force-Induced Reversible Structural Transformation of a PVP-Chol Supramolecular Polymer Brush

傅里叶变换红外(FT-IR)光谱、表面压力-分子面积(π-A)等温线和原子力显微镜(AFM)结果表明,聚乙烯吡咯烷酮(PVP)与胆固醇分子(Chol)在溶液中和气/液界面上可通过氢键作用形成刷状的超分子聚合物PVP-Chol。当表面压力低于2.5 m N?m^(-1)时,界面膜主要由富含胆固醇的微区与PVP-Chol纳米纤维构成的微区共存。在相对较低的表面压力下(<2.5 m N?m^(-1)),PVP-Chol微区形貌随界面膜压缩发生有序的变化:从最初的无规结构逐渐变为月牙形、心形和圆形结构;表面压超过2.5 m N?m^(-1)后,圆形的PVP-Chol微区最终消失并转变为少量的纤维聚集体结构。值得注意的是,在1.0 m N?m^(-1)之前,PVP-Chol纳米纤维高度随AFM成像过程中压电陶瓷外加电压的变化在1.8到4.3 nm之间出现了可逆转变,表明扫描探针针尖与样品之间的作用力可诱导超分子聚合物刷PVP-Chol发生从圆柱状到椭柱状的可逆结构转变。

A supramolecular polymer brush composed of polyvinytpyrrolidone-cholesterol （PVP-Chol） was fabricated based on intermolecular hydrogen bonding between the ketone groups of the PVP moieties and the hydroxyl groups of the cholesterol, both in solution and at the air/water interface. These confirmations were confirmed by Fourier transform infrared （FT-IR） spectroscopy, surface pressure versus molecular area （E-A） isotherms, and atomic force microscopy （AFM）. At surface pressures up to 2.5 mN·m^-1, the interfacial film was composed of cholesterol-enriched regions and PVP-Chol nanofibril domains. Interestingly, oversurface pressures, the structure of the PVP-Chol-enriched domains evolved frominitial irregular shapes, to crescent and heart-shaped zones, and then to circular shapes. This transition indicated the controllability of such domains during compression of a complex monolayer at relatively low surface pressures. Above 2.5 mN·m^-1, the circular PVP-Chol domains disappeared and fibrous aggregates were formed at the air/water interface. The height of the comb-like PVP-Chol nanofibrils could be reversibly varied between approximately 4.3 and 1.8 nm by adjusting the voltage applied to piezoceramics during the AFM scanning process. These results demonstrate that the reversible structural transformation of the PVP-Chol complex from cylindrical to elliptic cylindrical is induced by the applied force of the AFM tip up to a value of 1.0 mN·m^-1. These data provide important and useful information that improves our understanding of the relationship between the structures and performances of supramolecular polymer brushes, and should extend the range of applications of chotesterol-functionalized polymers fabricated via a simple mixing strategy.