Department of Physical Chemistry, Faculty of Pharmacy, University of Santiago de Compostela, Santiago de Compostela, Spain.
J Colloid Interface Sci. 2012 Nov 1;385(1):202-10. doi: 10.1016/j.jcis.2012.06.015. Epub 2012 Jun 23.
The behavior of poly(2-hydroxyethyl methacrylate) (PHEMA) polymer monolayer spread on water was studied under various experimental conditions. The influence of subphase pH and temperature, compression speed, elapsed time from the deposit of the monolayer and the recording of the surface pressure-area (π-A) isotherms, as well as the number of polymer molecules deposited at the air/water surface (surface concentration) was studied. The obtained results show that PHEMA exhibits a very stable monolayer given that it is unaffected by modifications in the majority of these variables. Only the elapsed time between the spreading of the monolayer and the beginning of compression causes a small change in the π-A isotherms that consists in an increase in the area occupied by the film. This is attributed to the greater unfolding with time of the polymer's monomers at the air/water interface. The plateau that appears on π-A curves of the PHEMA monolayer is attributed to the reorientation of their hydroxyethyl polar groups through their C-O-C bonds, as well as to the reorientation of the ethylene (CH(2)) groups that link the monomers, which provokes a folding of the polymer's chains causing an accordion configuration. The existence of this structure is confirmed by the presence of numerous noise peaks in the relative thickness versus time curve corresponding to this region. In the same fashion, the images observed from Brewster angle microscopy (BAM) reveal the existence of light-dark "bands" relative to the different regions of this particular structure.
研究了在不同实验条件下，聚（2-羟乙基甲基丙烯酸酯）（PHEMA）聚合物单层在水面上的行为。研究了亚相 pH 值和温度、压缩速度、从单层沉积到记录表面压力-面积（π-A）等温线的时间间隔、以及在空气/水表面沉积的聚合物分子数（表面浓度）的影响。所得结果表明，PHEMA 表现出非常稳定的单层，因为它不受这些变量中大多数的变化的影响。只有在单层展开和开始压缩之间的时间间隔会导致π-A 等温线发生微小变化，这种变化表现为薄膜占据的面积增加。这归因于聚合物单体在空气/水界面上随时间的展开程度更大。PHEMA 单层的 π-A 曲线上出现的平台归因于其羟乙基极性基团通过 C-O-C 键的重新定向，以及连接单体的乙烯（CH(2)）基团的重新定向，这导致聚合物链的折叠，从而产生手风琴状结构。这一结构的存在通过对应于该区域的相对厚度随时间变化曲线中存在大量噪声峰得到证实。同样，从布鲁斯特角显微镜（BAM）观察到的图像显示出相对于该特定结构的不同区域存在明暗“带”。
