Chen Yong, Koberstein Jeffrey T
Department of Chemical Engineering, Columbia University, 500 West 120th Street, MC4721, New York, NY 10027, USA.
Langmuir. 2008 Sep 16;24(18):10488-93. doi: 10.1021/la801589q. Epub 2008 Aug 12.
We describe a generic method for polymer surface modification and functionalization that is applicable for substrates of arbitrary shape. The method involves the deposition of monolayer and submonolayer films of photoactive block copolymers from supercritical fluids. Poly(styrene-b-tert-butyl acrylate), poly(S-b-tBA), block copolymer monolayers form spontaneously on polystyrene substrates by adsorption from scCO2 when hexane is used as a cosolvent. Atomic force microscopy indicates the films are flat and without pores after modification. Ethylene glycol contact angles increase linearly with deposition pressure until a constant value, equal to that of pure P tBA, is attained at pressures of 18 MPa or greater at 40 degrees C. This trend mimics the change in block copolymer solubility with pressure and indicates that the block copolymer self-assembles and orders at the surface, presenting a P tBA layer at the air interface with the PS block orienting toward the PS substrate. The P tBA layer thickness, determined by angle dependent X-ray photoelectron spectroscopy, reaches a saturated monolayer value of ca. 2 nm for pressures of 18 MPa and higher, consistent with the thickness expected for unperturbed PtBA chains comprising a wet brush. This concept for polymer surface modification initially produces a hydrophobic surface due to surface adsorption of the low surface tension PtBA block, but can also be used to prepare hydrophilic, functional surfaces, either modified or patterned with carboxylic acid groups, by photolytic or acid catalyzed deprotection/hydrolysis of the tert-butyl ester groups.
我们描述了一种适用于任意形状底物的聚合物表面改性和功能化的通用方法。该方法涉及从超临界流体中沉积光活性嵌段共聚物的单层和亚单层膜。当使用己烷作为共溶剂时，聚（苯乙烯 - b - 丙烯酸叔丁酯），聚（S - b - tBA）嵌段共聚物单层通过从scCO₂中吸附在聚苯乙烯底物上自发形成。原子力显微镜表明改性后的薄膜是平整且无孔的。乙二醇接触角随沉积压力线性增加，直到在40℃下18MPa或更高的压力下达到与纯P tBA相同的恒定值。这种趋势模仿了嵌段共聚物溶解度随压力的变化，表明嵌段共聚物在表面自组装并有序排列，在空气界面呈现P tBA层，PS嵌段朝向PS底物。通过角度相关的X射线光电子能谱确定的P tBA层厚度，对于18MPa及更高的压力达到约2nm的饱和单层值，这与构成湿刷的未受干扰的PtBA链预期的厚度一致。这种聚合物表面改性的概念最初由于低表面张力的PtBA嵌段的表面吸附而产生疏水表面，但也可用于通过叔丁酯基团的光解或酸催化脱保护/水解来制备亲水性、功能化表面，这些表面可以用羧酸基团进行改性或图案化。
