等温滴定量热法
聚电解质
化学
丙烯酸
焓
疏水效应
吸热过程
高分子化学
滴定法
聚丙烯酸钠
化学工程
无机化学
热力学
有机化学
物理化学
吸附
聚合物
单体
物理
工程类
原材料
作者
Cornelia G. Sinn,Rumiana Dimova,Markus Antonietti
出处
期刊:Macromolecules
[American Chemical Society]
日期:2004-04-02
卷期号:37 (9): 3444-3450
被引量:174
摘要
The interaction of poly(sodium acrylate) (NaPAA) and poly(sodium styrenesulfonate) (NaPSS) with water over a broad range of concentrations was followed by isothermal titration calorimetry (ITC) and compared to the corresponding low molecular weight salts, sodium acetate and sodium sulfate. Astonishingly, the backbone of NaPSS, known to be more hydrophobic, remains unseen in the dilution enthalpy, and NaPAA and NaPSS show very similar and close to ideal dilution curves. The NaPSS dilution is even more exothermic than Na2SO4. This is related to the specific structure of water screening the hydrophobic polystyrene backbone. Counterintuitively, binding of Ca2+ ions to PAA, a spontaneous process, shows to be highly endothermic; i.e., the binding is solely driven by entropy. This suggests that not Coulomb interactions, but liberation of water molecules from the hydration shells of the components is the driving energy source for the binding of multivalent ions onto polyelectrolytes. Analysis of binding titrations of Ca2+ to three different industrial scale inhibitors (poly(acrylic acid), poly(aspartic acid), poly(acrylic-co-maleic acid) (Sokolan)) allows to qualify their performance. The experiments underline that the understanding of polyelectrolytes and counterion condensation on the basis of Coulomb descriptions, i.e., ions as point charges and water as a homogeneous dielectric media, is at least misleading, as it disregards the predominant thermodynamic effects, the chemical specificity of the components in response to the structure of water.
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