Entropy and enthalpy of polyelectrolyte complexation: Langevin dynamics simulations
Entropy and enthalpy of polyelectrolyte complexation: Langevin dynamics simulations
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DOI：
10.1063/1.2178803
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发表时间：
2006-04-21
影响因子：
4.4
通讯作者：
Muthukumar, M
中科院分区：
文献类型：
--
作者：
Ou, ZY;Muthukumar, M
我们报告了一个系统的研究Langevin动力学模拟的能量的两个相反电荷的聚电解质之间的络合在稀溶液中的良好的溶剂与抗衡离子和盐离子明确包括相同的电荷密度。通过比较络合前和络合后的库仑能来量化双络合的焓。直接从模拟和比较的平均场晶格模型明确占反吸附的熵的络合物的熵。在弱库仑相互作用强度下，例如，在高介电常数的溶剂或具有弱电荷的聚电解质的溶剂中，由于两个相反电荷的链之间的静电吸引力，络合由负焓驱动，相反释放熵仅起辅助作用。在强相互作用机制中，络合作用由大的反相释放熵驱动，并由正的焓变反对。盐的加入通过在所有库仑相互作用强度下屏蔽静电相互作用来降低双金属络合的焓。在盐的存在下，反相释放熵也降低，但这种降低仅在较高的库仑相互作用强度下才变得显著。更重要的是，在库仑相互作用强度的范围内，适合高电荷的聚合物在水溶液中，络合焓弱依赖于盐浓度和counterweight释放熵表现出很大的变化作为盐浓度的函数。我们的研究定量地证实了高电荷库仑体系中的络合作用是熵的起源。
We report a systematic study by Langevin dynamics simulation on the energetics of complexation between two oppositely charged polyelectrolytes of same charge density in dilute solutions of a good solvent with counterions and salt ions explicitly included. The enthalpy of polyelectrolyte complexation is quantified by comparisons of the Coulomb energy before and after complexation. The entropy of polyelectrolyte complexation is determined directly from simulations and compared with that from a mean-field lattice model explicitly accounting for counterion adsorption. At weak Coulomb interaction strengths, e.g., in solvents of high dielectric constant or with weakly charged polyelectrolytes, complexation is driven by a negative enthalpy due to electrostatic attraction between two oppositely charged chains, with counterion release entropy playing only a subsidiary role. In the strong interaction regime, complexation is driven by a large counterion release entropy and opposed by a positive enthalpy change. The addition of salt reduces the enthalpy of polyelectrolyte complexation by screening electrostatic interaction at all Coulomb interaction strengths. The counterion release entropy also decreases in the presence of salt, but the reduction only becomes significant at higher Coulomb interaction strengths. More significantly, in the range of Coulomb interaction strengths appropriate for highly charged polymers in aqueous solutions, complexation enthalpy depends weakly on salt concentration and counterion release entropy exhibits a large variation as a function of salt concentration. Our study quantitatively establishes that polyelectrolyte complexation in highly charged Coulomb systems is of entropic origin.