Charbonneau Céline, Chassenieux Christophe, Colombani Olivier, Nicolai Taco
LUNAM Université, Université du Maine, IMMM - UMR CNRS 6283, Département Polymères, Colloïdes, et Interfaces, Université du Maine, avenue O. Messiaen, 72085 Le Mans cedex 9, France.
Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Jun;87(6):062302. doi: 10.1103/PhysRevE.87.062302. Epub 2013 Jun 3.
Transient polyelectrolyte hydrogels were formed by self-assembly of triblock copolyelectrolytes with a central hydrophilic block, poly(acrylic acid) (PAA), and two hydrophobic end blocks, poly(n-butyl acrylate(50%)-stat-acrylic acid(50%)) [P(nBA(50%)-stat-AA(50%))]. The relaxation of the concentration fluctuations was investigated by dynamic light scattering as a function of the concentration, the pH, the temperature, and the ionic strength. A relatively fast mode was observed at all polymer concentrations caused by cooperative diffusion of the polymers. Above the critical percolation concentration a second slow relaxation mode was observed caused by a linear displacement of small heterogeneities in the network with constant velocity. The relative amplitude of the slow mode was determined by the strength of the electrostatic repulsion. The velocity of the displacement in the transient network is shown to be directly correlated to the terminal relaxation time of the shear modulus and has the same Arrhenius temperature dependence. Both the velocity of the displacement and the mechanical relaxation strongly slow down with decreasing degree of ionization below 0.7 and increasing ionic strength above 0.5 M. A ballistic relaxation process has been reported earlier for colloidal gels, and the present study shows that it can also occur in polymeric networks.
瞬态聚电解质水凝胶由具有中心亲水嵌段聚丙烯酸（PAA）和两个疏水端嵌段聚（丙烯酸正丁酯（50%）-无规-丙烯酸（50%））[P（nBA（50%）-无规-AA（50%））]的三嵌段共聚物自组装形成。通过动态光散射研究了浓度涨落的弛豫，其作为浓度、pH值、温度和离子强度的函数。在所有聚合物浓度下，由于聚合物的协同扩散，观察到一个相对较快的模式。在临界渗滤浓度以上，观察到第二个缓慢弛豫模式，这是由网络中小不均匀性以恒定速度的线性位移引起的。慢模式的相对振幅由静电排斥力的强度决定。瞬态网络中位移的速度显示与剪切模量的末端弛豫时间直接相关，并且具有相同的阿累尼乌斯温度依赖性。随着电离度降低到0.7以下和离子强度增加到0.5 M以上，位移速度和机械弛豫都强烈减慢。早期报道了胶体凝胶的弹道弛豫过程，本研究表明它也可以发生在聚合物网络中。
