Trindade Suelen G, Piculell Lennart, Loh Watson
Institute of Chemistry, University of Campinas (UNICAMP), P.O. Box 6154, Campinas, São Paulo 13083-970, Brazil.
Division of Physical Chemistry, Lund University, P.O. Box 124, Lund S-221 00, Sweden.
Langmuir. 2022 Mar 8;38(9):2906-2918. doi: 10.1021/acs.langmuir.1c03322. Epub 2022 Feb 21.
We used diblock poly(acrylic acid)--poly(2-dimethylamino ethyl methacrylate) (PAA--PDMAEMA) polyampholytes to prepare core-shell complexes with ionic surfactants. The dispersions have been characterized by means of small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (Cryo-TEM), dynamic light-scattering, and zeta potential methods. Using cationic or anionic surfactants it is possible to produce particles with either positively or negatively charged shells, both having an internal liquid-crystalline core structure. For the different systems, different preparation protocols were found to be successful to produce stable and reproducible particles. The particle morphologies depend on the surfactant used. Complexes with the cationic surfactant hexadecyltrimethylammonium (CTA) form oblate particles, while complexes with dodecyl sulfate (DS) form cylindrical rods. In both complexes, the smallest dimension of the core does not exceed twice the block length of the core-forming polymer block. For the particles with CTA, nonelectrostatic attractive interactions among the PDMAEMA chains in the shells seem to be present, affecting the particle shape. In both types of particles, the surfactant in the core forms rod-like aggregates, arranged in a two-dimensional hexagonal structure with the surfactant rods aligned with the axis of rotational symmetry in the particle. With charged polymer chains in the shell, the aggregates present a striking stability over time, displaying no change in particle size over the time scale investigated (10 months). Nevertheless, the aggregates are highly dynamic in nature, and their shapes and structures can be changed dramatically in dispersion, without intermediate precipitation, by changes in the composition of the medium. Specifically, a transition from aggregates with cationic surfactant to aggregates with anionic surfactant can be achieved.
我们使用双嵌段聚（丙烯酸）-聚（甲基丙烯酸2-二甲基氨基乙酯）（PAA-PDMAEMA）聚两性电解质与离子表面活性剂制备核壳复合物。通过小角X射线散射（SAXS）、低温透射电子显微镜（Cryo-TEM）、动态光散射和zeta电位法对分散体进行了表征。使用阳离子或阴离子表面活性剂可以制备具有带正电或带负电外壳的颗粒，两者都具有内部液晶核结构。对于不同的体系，发现不同的制备方案能够成功制备出稳定且可重复的颗粒。颗粒形态取决于所使用的表面活性剂。与阳离子表面活性剂十六烷基三甲基铵（CTA）形成的复合物为扁球形颗粒，而与十二烷基硫酸盐（DS）形成的复合物为圆柱形棒状颗粒。在这两种复合物中，核的最小尺寸不超过形成核的聚合物嵌段的嵌段长度的两倍。对于含有CTA的颗粒，壳层中的PDMAEMA链之间似乎存在非静电吸引相互作用，从而影响颗粒形状。在这两种类型的颗粒中，核中的表面活性剂形成棒状聚集体，以二维六方结构排列，表面活性剂棒与颗粒的旋转对称轴对齐。由于壳层中存在带电荷的聚合物链，这些聚集体在很长时间内都具有显著的稳定性，在所研究的时间尺度（10个月）内颗粒尺寸没有变化。然而，这些聚集体本质上是高度动态的，并且通过改变介质组成，它们的形状和结构可以在分散体系中发生显著变化，而不会发生中间沉淀。具体而言，可以实现从含有阳离子表面活性剂的聚集体到含有阴离子表面活性剂的聚集体的转变。
