Depletion Forces Induced by Mixed Micelles of Nonionic Block Copolymers and Anionic Surfactants
Depletion Forces Induced by Mixed Micelles of Nonionic Block Copolymers and Anionic Surfactants
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非离子嵌段共聚物和阴离子表面活性剂的混合胶束诱导的耗尽力
DOI：
10.1021/acs.langmuir.0c01574
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发表时间：
2020
期刊：
影响因子：
3.9
通讯作者：
Tilton, Robert D.
中科院分区：
文献类型：
--
作者：
Lele, Bhagyashree J.;Tilton, Robert D.
使用胶体探针原子力显微镜测量含有非离子 Pluronic P123 聚（环氧乙烷-b-环氧丙烷-b-环氧乙烷）三嵌段共聚物和阴离子十二烷基硫酸钠（SDS）表面活性剂的溶液中二氧化硅球和二氧化硅板之间的耗尽力。先前的研究通过形成大型假聚电解质复合物，在含有 SDS 和单聚 Pluronic F108 嵌段共聚物的溶液中建立了协同消耗力增强。目前的工作涉及一个更复杂的系统，其中聚合物高于其临界胶束浓度，并且表面活性剂的结合不仅改变胶束的大小和电荷，而且改变每个胶束的聚合物数量。在浓度高达 64 mM 的 10000 ppm P123（1 wt%，相当于 1.72 mM，基于平均摩尔质量）溶液中测量力分布，并与胶束 P123 溶液和不含 P123 的 SDS 溶液进行比较。尽管不含 SDS 的胶束 P123 溶液中的力分布纯粹是排斥性的，但 P123/SDS 络合对 2 至 32 mM 的 SDS 浓度产生协同消耗力增强。通过比较 P123/SDS 混合物和借助动态光散射、静态光散射和十二烷基硫酸盐离子选择性电极测量获得的各自单组分溶液中消耗剂的流体动力学尺寸、摩尔质量、电荷和浓度，解释了在有限 SDS 浓度范围内发生的协同作用。这些测量表明，络合作用产生的效应与消耗力相互抵消：相对于不含 SDS 的 P123 胶束，降低混合胶束流体动力学直径往往会减弱消耗力，而增加电荷并减少每个胶束聚合物的聚集数量（从而增加胶束消耗剂的数量浓度）往往会增强消耗力。
Depletion forces were measured between a silica sphere and a silica plate in solutions containing nonionic Pluronic P123 poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymers and anionic sodium dodecyl sulfate (SDS) surfactants using colloidal probe atomic force microscopy. Prior research established synergistic depletion force enhancement in solutions containing SDS and unimeric Pluronic F108 block copolymers via formation of large pseudo-polyelectrolyte complexes. The current work addresses a more complex system where the polymer is above its critical micelle concentration, and surfactant binding alters not only the size and charge of the micelles but also the number of polymers per micelle. Force profiles were measured in 10 000 ppm P123 (1 wt %, corresponding to 1.72 mM based on average molar mass) solutions containing SDS at concentrations up to 64 mM and compared to micellar P123 solutions and to P123-free SDS solutions. Whereas force profiles in the SDS-free micellar P123 solutions were purely repulsive, P123/SDS complexation produced synergistic depletion force enhancement for SDS concentrations between 2 and 32 mM. The synergism that occurred within a finite SDS concentration range was explained by comparing the hydrodynamic size, molar mass, charge, and concentration of depletants in P123/SDS mixtures and their respective single-component solutions obtained with the aid of dynamic light scattering, static light scattering, and dodecyl sulfate ion-selective electrode measurements. These measurements showed that complexation produced effects that would be mutually counteracting with respect to depletion forces: decreasing the mixed micelle hydrodynamic diameter relative to SDS-free P123 micelles would tend to weaken depletion forces, while adding charge and decreasing the aggregation number of polymers per micelle (thereby increasing the number concentration of micellar depletants) would tend to strengthen depletion forces.