Department of Polymer Chemistry, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Langmuir. 2010 Sep 7;26(17):14073-80. doi: 10.1021/la100374j.
The effect of annealing on the structure and the helix orientation in Langmuir-Blodgett (LB) monolayers of diblock copolymers (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) with unidirectional helix orientation deposited on hydrophilic silicon substrates was characterized by means of small-angle X-ray reflectivity, transmission Fourier transform infrared spectroscopy, and atomic force microscopy. Upon annealing at 100 degrees C for 24 h, the alpha-helices became less tilted toward the substrate surface normal. Surface area shrinkage accompanied the change in tilt, indicated by an increase in both film thickness and electron density, resulting in more compact and uniform films. The enhancement of the helix orientation by thermal annealing was greater for the PMLGSLG block and for the diblock copolymers with the shorter block lengths. For these diblock copolymers, annealing resulted in postorientation of the PMLGSLG block helices almost perpendicular to the substrate surface. This effect originates from a considerable increase in intermolecular packing of the PLGA block caused by hydrogen bonds between the carboxylic groups upon annealing, as well as the high mobility of the PMLGSLG block helices for rearrangement favored by the melted side chain mantle at elevated temperatures.
通过小角 X 射线反射、传输傅里叶变换红外光谱和原子力显微镜，研究了具有单向螺旋取向的聚（α-谷氨酸）（PLGA）和聚（γ-甲基-L-谷氨酸-ran-γ-硬脂酰-L-谷氨酸）（PMLGSLG）的嵌段共聚物（PLGA-b-PMLGSLGs）的结构和螺旋取向在 LB 单层膜中的退火效应。在 100°C 下退火 24 小时后，α-螺旋变得不那么倾向于垂直于基底表面。表面面积收缩伴随着倾斜的变化，这表现为膜厚度和电子密度的增加，导致更紧密和均匀的膜。热退火对 PMLGSLG 嵌段和较短嵌段长度的嵌段共聚物的螺旋取向增强更大。对于这些嵌段共聚物，退火导致 PMLGSLG 嵌段的螺旋几乎垂直于基底表面的后取向。这种效应源于退火时羧酸基团之间氢键引起的 PLGA 嵌段的分子间堆积显著增加，以及高温下熔融侧链幔层有利于 PMLGSLG 嵌段螺旋重排的高迁移率。
