水合作用与 pH 调控两性离子聚合物刷的相变行为

Hydration and pH regulating phase transition of zwitterionic polymer brushes

本文基于Flory-Huggins理论,建立理论模型研究水合作用与pH调控两性离子聚合物(ZP)刷的相变行为.理论模型考虑ZP的水合作用,以及ZP刷体系中的静电作用.研究发现,在不同pH条件下,ZP刷的体积分数随着水合作的减弱而的增加.随着pH的变化,ZP刷构象随着水合性转变行为明显改变,这是由于pH调控ZP链单体带有过多的净电荷(正电荷或负电荷),致使ZP链内出现静电排斥导致ZP刷溶胀.另外,当ZP链单体呈现过多的净电荷,会在很大程度上决定ZP刷体系静电势,影响ZP刷的相变行为.通过考察体系自由能,我们还发现,ZP刷体系自由能呈现了极大值,随着pH值的变化,自由能呈现的极大值随之改变,由此表明了体系的不稳定性,进而导致ZP刷体系发生相变.

Based on the Flory-Huggins theory,we built a theoretical model to study the phase transition behavior of zwitterionic polymer(ZP)brushes regulated by hydration and pH.The theoretical model takes into account the hydration of ZP,as well as the electrostatic effect in the ZP brush system.We found that the volume fraction of ZP brushes increases with the weakening hydration under different pH conditions.With the change of pH,the conformation of the ZP brush changes significantly with the hydration transition behavior,which is due to the excessive net charge(positive or negative)of the pH-regulated ZP chain segment,which results in electrostatic repulsion within the ZP chain and ZP brush swells.In addition,when the ZP chain segment presents too much net charge,it will largely determine the electrostatic potential of the ZP brush system and affect the phase transition behavior of the ZP brush.By investigating the free energy of the system,we also found that the free energy of the ZP brush system shows a maximum value.With the change of pH value,the maximum value of the free energy shows a change,indicating the instability of the system.And then,this leads to a phase transition in the ZP brush system.