Colloidal Depletion and Structural Force Synergism or Antagonism in Solutions of Mutually Repelling Polyelectrolytes and Ionic Surfactants
Colloidal Depletion and Structural Force Synergism or Antagonism in Solutions of Mutually Repelling Polyelectrolytes and Ionic Surfactants
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DOI：
10.1021/acs.langmuir.9b02143
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发表时间：
2019-12-03
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.
在含有聚丙烯酸钠（Na-PAA）阴离子聚电解质和十二烷基硫酸钠（SDS）阴离子表面活性剂的溶液中，使用胶体探针原子力显微镜测量了二氧化硅球和二氧化硅板之间的损耗和结构力，在高pH下，两种物质相互静电排斥，并从二氧化硅表面排斥。对SDS和Na-PAA浓度范围进行测量，以跨越只有一种或两种物质在单组分溶液中存在时会产生可检测的损耗或结构力的条件。在混合溶液中，确定了以下条件：(1)相对于单组分溶液，损耗吸引力协同增强或拮抗减弱；（ii）由于两个物种在不同长度尺度上同时耗竭，耗竭吸引的范围显著扩大，排斥性结构力屏障被消除；（iii）当一个物种是优势消耗物，并且在混合物中的力与优势消耗物的单组分溶液中的力难以区分。力测量的解释，借助于芘增溶试验的SDS胶束和动态光散射研究的组装状态的聚电解质或表面活性剂。胶体力的变化归因于离子强度，但不包括Na-PAA对SDS胶束的体积效应、SDS对Na-PAA链在溶液中聚集的离子强度效应以及离子强度对反离子对聚电解质渗透压的影响。虽然先前的研究表明，当聚合物和表面活性剂形成混合配合物时，耗尽力协同作用会发生，但这项工作表明，它也可能发生在非络合混合物中，并且它表明，在试图预测这种混合物中的力时，应考虑到各种效应。
Depletion and structural forces were measured between a silica sphere and plate in solutions containing sodium polyacrylate (Na-PAA) anionic polyelectrolyte and sodium dodecyl sulfate (SDS) anionic surfactant using colloidal probe atomic force microscopy, at high pH where the two species are electrostatically repelling from each other and from the silica surfaces. Measurements were performed for a range of SDS and Na-PAA concentrations to span conditions where only one of the species or both of the species would exert a detectable depletion or structural force when present in a single-component solution. In mixed solutions, conditions were identified (i) where depletion attraction was synergistically enhanced or antagonistically weakened relative to single component solutions; (ii) where the range of the depletion attraction was significantly extended and the repulsive structural force barrier was eliminated, due to simultaneous depletion of both species over different length scales; and (iii) where one species was the dominant depletant and forces in mixtures were indistinguishable from those in a single component solution of the dominant depletant. Force measurements were interpreted with the aid of pyrene solubilization assays of SDS micellization and dynamic light scattering investigation of the state of assembly of the polyelectrolyte or surfactant. The variety of colloidal force effects were attributed to ionic strength and excluded volume effects of Na-PAA on SDS micellization, ionic strength effects of SDS on Na-PAA chain clustering in solution, and ionic strength effects on the counterion contribution to polyelectrolyte osmotic pressure. While prior studies have shown that depletion force synergism occurs when polymers and surfactants form mixed complexes, this work shows that it can occur in noncomplexing mixtures as well, and it indicates the variety of effects that should be taken into account when attempting to predict forces in such mixtures.