Determan Michael D, Guo Liang, Lo Chieh-Tsung, Thiyagarajan P, Mallapragada Surya K
Department of Chemical and Biological Engineering, Iowa State University and Ames Laboratory, 144 Spedding Hall, Ames, Iowa 50011, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2008 Aug;78(2 Pt 1):021802. doi: 10.1103/PhysRevE.78.021802. Epub 2008 Aug 27.
We investigated the structural features of micelles formed by the self-association of the pentablock copolymer poly[ N,N -(diethyl amino)ethyl methacrylate]-block-poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethyleneoxide)-block-poly[ N,N -(diethylamino)ethyl methacrylate] (PDEAEM-PEO-PPO-PEO-PDEAEM) in aqueous solutions by using small-angle neutron scattering SANS. The pentablock copolymer solutions exhibit micellar and gel phases in response to changes in both the temperature and pH by virtue of (1) the lower critical solution temperature of the PPO blocks and (2) the polyelectrolyte character of the pendant PDEAEM blocks. Two modeling schemes were employed to describe the SANS data of semidilute copolymer solutions at higher temperature as they contain interacting charged micelles at pH<7.5 and interacting neutral micelles at higher pH. We have elucidated the structures of the micelles in terms of size, shape, polydispersity, association number, number density, and surface charge. At low pH the charged spherical micelles are less packed with the copolymers presumably due to the electrostatic repulsion between the charged pendant groups. On the other hand, at higher pH the hydrophobic character of the neutral pendant groups enable them to sequester within the micelle core along with the PPO, thus increasing the number density and the core size of the spherical micelles. At higher copolymer concentration reversible thermoresponsive sol-gel transitions were observed at all pH conditions and the rheological behavior of the gels nicely correlates with different organization of micelles with different shapes.
我们通过小角中子散射（SANS）研究了五嵌段共聚物聚[甲基丙烯酸N，N-（二乙氨基）乙酯]-嵌段-聚环氧乙烷-嵌段-聚环氧丙烷-嵌段-聚环氧乙烷-嵌段-聚[甲基丙烯酸N，N-（二乙氨基）乙酯]（PDEAEM-PEO-PPO-PEO-PDEAEM）在水溶液中自缔合形成的胶束的结构特征。由于（1）PPO嵌段的低临界溶液温度和（2）侧链PDEAEM嵌段的聚电解质特性，五嵌段共聚物溶液在温度和pH值变化时会呈现胶束相和凝胶相。采用两种建模方案来描述高温下半稀释共聚物溶液的SANS数据，因为在pH<7.5时它们含有相互作用的带电胶束，而在较高pH值时含有相互作用的中性胶束。我们从尺寸、形状、多分散性、缔合数、数密度和表面电荷等方面阐明了胶束的结构。在低pH值下，带电的球形胶束与共聚物的堆积较少，这可能是由于带电侧基之间的静电排斥作用。另一方面，在较高pH值下，中性侧基的疏水特性使它们能够与PPO一起隔离在胶束核心内，从而增加了球形胶束的数密度和核心尺寸。在较高的共聚物浓度下，在所有pH条件下都观察到了可逆的热响应溶胶-凝胶转变，并且凝胶的流变行为与不同形状胶束的不同组织密切相关。
