Laaser Jennifer E, McGovern Michael, Jiang Yaming, Lohmann Elise, Reineke Theresa M, Morse David C, Dorfman Kevin D, Lodge Timothy P
Department of Chemistry and ‡Department of Chemical Engineering & Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States.
J Phys Chem B. 2017 May 4;121(17):4631-4641. doi: 10.1021/acs.jpcb.7b01953. Epub 2017 Apr 25.
The role of charge density and charge annealing in polyelectrolyte complexation was investigated through systematic comparison of two micelle-polyelectrolyte systems. First, poly(dimethylaminoethyl methacrylate)-block-poly(styrene) (PDMAEMA-b-PS) micelles were complexed with poly(styrenesulfonate) (PSS) at pH values above and below the pK of PDMAEMA to investigate the role of charge annealing in the complexation process. Second, complexes of poly(DMAEMA-stat-oligo(ethylene glycol) methyl ether methacrylate)-block-poly(styrene) (P(DMAEMA-stat-OEGMA)-b-PS) micelles with the same PSS at low pH were used to investigate how the complexation process differs when the charged sites are in fixed positions along the polymer chains. Characterization by turbidimetric titration, dynamic light scattering, and cryogenic transmission electron microscopy reveals that whether or not the charge distribution can rearrange during the complexation process significantly affects the structure and stability of the complexes. In complexes of PDMAEMA-b-PS micelles at elevated pH, in which the charge distributions can anneal, the charge sites redistribute along the corona chains upon complexation to favor more fully ion-paired configurations. This promotes rapid rearrangement to single-micelle species when the micelles are in excess but traps complexes formed with PSS in excess. In complexes with static charge distributions introduced by copolymerization of DMAEMA with neutral OEGMA monomers, on the other hand, the opposite is true: in this case, reducing the charge density promotes rearrangement to single-micelle complexes only when the polyanion is in excess. Molecular dynamics simulations show that disruption of the charge density in the corona brush reduces the barrier to rearrangement of individual ion pairs, suggesting that the inability of the brush to rearrange to form fully ion-paired complexes fundamentally alters the kinetics of complex formation and equilibration.
通过对两种胶束 - 聚电解质体系进行系统比较，研究了电荷密度和电荷退火在聚电解质络合中的作用。首先，在高于和低于聚甲基丙烯酸二甲氨基乙酯（PDMAEMA）的pK值的pH条件下，使聚（甲基丙烯酸二甲氨基乙酯） - 嵌段 - 聚（苯乙烯）（PDMAEMA - b - PS）胶束与聚（苯乙烯磺酸盐）（PSS）络合，以研究电荷退火在络合过程中的作用。其次，使用聚（DMAEMA - 无规 - 乙二醇甲醚甲基丙烯酸酯） - 嵌段 - 聚（苯乙烯）（P（DMAEMA - 无规 - OEGMA） - b - PS）胶束与相同的PSS在低pH下形成的络合物，来研究当带电位点沿聚合物链处于固定位置时络合过程有何不同。通过比浊滴定、动态光散射和低温透射电子显微镜表征发现，络合过程中电荷分布是否能够重排会显著影响络合物的结构和稳定性。在较高pH下的PDMAEMA - b - PS胶束络合物中，电荷分布可以退火，络合时电荷位点会沿着冠链重新分布，以形成更完全的离子对构型。当胶束过量时，这会促进快速重排为单胶束物种，但会捕获与过量PSS形成的络合物。另一方面，在由DMAEMA与中性OEGMA单体共聚引入静态电荷分布的络合物中，情况则相反：在这种情况下，只有当聚阴离子过量时，降低电荷密度才会促进重排为单胶束络合物。分子动力学模拟表明，冠层刷中电荷密度的破坏降低了单个离子对重排的势垒，这表明刷无法重排形成完全离子对络合物从根本上改变了络合物形成和平衡的动力学。
