溶液中盐浓度对聚氧化乙烯构象的影响

Effect of Different Salt Solutions on the Conformation of Polyethylene Oxide

采用带有示差、光散射和粘度三检测器联用的凝胶色谱仪(TDA-GPC)和动态光散射(DLS)联用的方法,以聚氧化乙烯标样(PEO-24K)作为研究对象,研究了稀溶液中盐浓度对聚氧化乙烯构象的影响。通过比较在不同浓度的盐溶液中的特性粘数([η])、流体力学半径(Rh)和Mark-Houwink指数(α)等物理参数的大小,得出了PEO的构象变化:在较低盐浓度溶液中,PEO形成典型的无规线团构象;随着盐浓度的增加,溶液中的PEO分子链逐渐发生聚集、收缩、坍塌,线团尺寸减小,并发生由无规线团逐渐向密堆积的坍塌球转变的构象变化,同时溶液黏度增大。这种构象变化主要是由于溶液中的盐分子与PEO竞争溶液中的水分,使得PEO链段的溶剂化程度减少造成的。本文还研究了温度对PEO构象的影响:当温度降低时,PEO分子链发生收缩,由无规线团逐渐收缩为坍塌球。

The influence of salt concentration on the conformation of poly (ethylene oxide) in dilute solution was studied by using gel permeation chromatograph (TDA-GPC) coupled with differential light scattering and viscosity three detector coupled with dynamic light scattering (DLS) and polyoxy-ethylene standard sample (PEO-24K) as the research object. By comparing the physical parameters such as intrinsic viscosity (η), hydrodynamic radius (Rh) and Mark-Houwink exponent (α) in different concentration of salt solution, the conformational changes of PEO were obtained: in lower concentration of salt solution, the typical random conformation of PEO was formed;with the increase of salt concentration, the molecular chain of PEO in solution gradually developed. The size of the coil decreases as the coil aggregates, shrinks and collapses, and the conformational change from random coil to densely packed collapse ball occurs. Meanwhile, the solution viscosity increases. This conformational change is mainly due to the reduction of solvation of PEO chains due to the competition between salt molecules in solution and water in PEO solution. The effect of temperature on the conformation of PEO has also been studied. When the temperature decreases, the molecular chain of PEO shrinks from random coils to collapsed spheres.