Anion-specific effects on the behavior of pH-sensitive polybasic brushes.
Anion-specific effects on the behavior of pH-sensitive polybasic brushes.
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DOI：
10.1021/acs.langmuir.5b00116
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发表时间：
2015-03
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影响因子：
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通讯作者：
J. Willott;Timothy J. Murdoch;Ben A. Humphreys;S. Edmondson;E. Wanless;G. Webber
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文献类型：
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作者：
J. Willott;Timothy J. Murdoch;Ben A. Humphreys;S. Edmondson;E. Wanless;G. Webber
用原位椭偏仪和石英晶体微天平(QCM-D)研究了弱碱性聚甲基丙烯酸2-二甲氨基乙酯(Poly(DMA))、聚(2-二乙氨基)甲基丙烯酸乙酯(Poly(DEA))和聚(2-二异丙氨基)甲基丙烯酸乙酯(Poly(DPA))刷子的阴离子特定溶剂化和构象行为，并相应地增加了固有疏水性。在渗透刷区，随着初始低盐浓度的增加，刷子带电时通过吸收溶剂而渗透膨胀，并克服了具有吸引力的疏水链间和链内相互作用。随着离子强度的增加，刷子进入盐化刷子区域，当静电电荷被屏蔽时，它们会脱溶和坍塌。在这里，当刷子坍塌时，它们会转变为更均匀、更坚硬的构象，与离子强度较低的类似溶剂化刷子相比，这种构象消耗的能量更少。值得注意的是，在这些不同的区域，刷子的行为不仅取决于离子强度，而且还受到添加盐的性质的影响，所添加的盐基于其在众所周知的Hofmeister或溶致系列中的位置，研究了醋酸钾、硝酸盐和硫氰酸盐。强烈的共渗性醋酸酯阴离子对疏水聚合物的亲和力很低，而大部分未屏蔽的静电空间斥力使刷子在较高的醋酸盐浓度下保持高度溶剂化。温和的杂化硝酸盐和强烈的杂化硫氰酸盐阴离子对刷子表现出依赖于聚合物疏水性的亲和力。增加硫氰酸盐浓度会导致刷子在比其他两个阴离子更低的离子强度下崩溃。这项对弱多元电刷的研究表明了所有离子、溶剂和聚合物相互作用的重要性。
The anion-specific solvation and conformational behavior of weakly basic poly(2-dimethylamino)ethyl methacrylate (poly(DMA)), poly(2-diethylamino)ethyl methacrylate (poly(DEA)), and poly(2-diisopropylamino)ethyl methacrylate (poly(DPA)) brushes, with correspondingly increasing inherent hydrophobicity, have been investigated using in situ ellipsometric and quartz crystal microbalance with dissipation (QCM-D) measurements. In the osmotic brush regime, as the initial low concentration of salt is increased, the brushes osmotically swell by the uptake of solvent as they become charged and the attractive hydrophobic inter- and intrachain interactions are overcome. With increased ionic strength, the brushes move into the salted brush regime where they desolvate and collapse as their electrostatic charge is screened. Here, as the brushes collapse, they transition to more uniform and rigid conformations, which dissipate less energy, than similarly solvated brushes at lower ionic strength. Significantly, in these distinct regimes brush behavior is not only ionic strength dependent but is also influenced by the nature of the added salt based on its position in the well-known Hofmeister or lyotropic series, with potassium acetate, nitrate, and thiocyanate investigated. The strongly kosmotropic acetate anions display low affinity for the hydrophobic polymers, and largely unscreened electrosteric repulsions allow the brushes to remain highly solvated at higher acetate concentrations. The mildly chaotropic nitrate and strongly chaotropic thiocyanate anions exhibit a polymer hydrophobicity-dependent affinity for the brushes. Increasing thiocyanate concentration causes the brushes to collapse at lower ionic strength than for the other two anions. This study of weak polybasic brushes demonstrates the importance of all ion, solvent, and polymer interactions.