Lipar Irena, Zalar Petra, Pohar Ciril, Vlachy Vojko
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, P.O.B. 537, 1001 Ljubljana, Slovenia.
J Phys Chem B. 2007 Aug 30;111(34):10130-6. doi: 10.1021/jp073641q. Epub 2007 Aug 9.
Experimental and theoretical results for the thermodynamic properties of polyanetholesulfonic acid and its lithium, sodium, and cesium salts in aqueous solution at 298 K are presented. The osmotic pressure was measured using membrane and vapor pressure apparatus in the concentration range c(m) = 0.001-0.30 monomoles/dm(3). The osmotic coefficients obtained from these measurements were low, from 0.2 to 0.45 in this concentration range, indicating a strong interaction between counterions and polyions. The osmotic coefficients of the polyacid and its lithium and sodium salts appeared to be equal within experimental error, but the results for the cesium salt were lower. This indicates a somewhat stronger binding of cesium ions to the polyanion. In addition, enthalpies of dilution, DeltaH(D), from a certain concentration, m(m), to m(m) = 0.0044 monomoles/kg were measured. The measured heats of dilution were exothermic, with the acid producing the strongest and the cesium salt the weakest effect. These results were compared with previously published data for polyelectrolytes of similar structure, namely, polystyrenesulfonic acid and its alkaline salts. The osmotic pressure results indicate that polystyrenesulfonates bind the counterions more strongly than polyanetholesulfonic acid and its salts. Consistent with this finding, the enthalpies of dilution reveal that more heat is released upon dilution of polyanetholesulfonates (stronger exothermic effect) in comparison with the corresponding solutions of polystyrenesulfonic acid in its alkaline salts. These findings can be explained in terms of the structural differences between the two polyions. The experimental results were analyzed in relation to popular electrostatic theories such as the Manning condensation theory and the Poisson-Boltzmann cell model approach, where the polyion is pictured as a uniformly charged line or cylinder. In addition, we performed Monte Carlo simulations for a model polyanetholesulfonic anion having discrete charges. In all of the calculations, the solvent was treated as a continuum with the dielectric constant of pure water under the conditions of measurement. The theoretical considerations mentioned above yield results in semiquantitative agreement with the measured quantities.
本文给出了298K下聚苯乙烯磺酸及其锂盐、钠盐和铯盐在水溶液中的热力学性质的实验和理论结果。在浓度范围c(m)=0.001 - 0.30单摩尔/立方分米内，使用膜渗透压仪和蒸气压装置测量了渗透压。从这些测量中获得的渗透系数较低，在此浓度范围内为0.2至0.45，这表明抗衡离子与聚离子之间存在强相互作用。在实验误差范围内，聚酸及其锂盐和钠盐的渗透系数似乎相等，但铯盐的结果较低。这表明铯离子与聚阴离子的结合稍强一些。此外，还测量了从某一浓度m(m)到m(m)=0.0044单摩尔/千克的稀释焓ΔH(D)。测得的稀释热是放热的，其中酸产生的效应最强，铯盐产生的效应最弱。将这些结果与先前发表的类似结构的聚电解质，即聚苯乙烯磺酸及其碱金属盐的数据进行了比较。渗透压结果表明，聚苯乙烯磺酸盐比聚苯乙烯磺酸及其盐更强烈地结合抗衡离子。与此发现一致，稀释焓表明，与聚苯乙烯磺酸在其碱金属盐中的相应溶液相比，聚苯乙烯磺酸盐稀释时释放出更多的热量（更强的放热效应）。这些发现可以根据两种聚离子之间的结构差异来解释。根据流行的静电理论，如曼宁凝聚理论和泊松 - 玻尔兹曼元胞模型方法，对实验结果进行了分析，其中聚离子被描绘为均匀带电的线或圆柱体。此外，我们对具有离散电荷的聚苯乙烯磺酸根阴离子模型进行了蒙特卡罗模拟。在所有计算中，在测量条件下，将溶剂视为具有纯水介电常数的连续介质。上述理论考虑得出的结果与测量量在半定量上一致。
