A Monte Carlo study of titrating polyelectrolytes
A Monte Carlo study of titrating polyelectrolytes
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滴定聚电解质的蒙特卡罗研究
DOI：
10.1063/1.471071
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发表时间：
1996
影响因子：
4.4
通讯作者：
C. Peterson
中科院分区：
文献类型：
--
作者：
M. Ullner;B. Jönsson;B. Söderberg;C. Peterson
蒙特卡罗模拟已被用于研究无盐环境中线性滴定聚电解质的三种不同模型：（i）具有刚性键的刚性聚合物（刚性棒）;（ii）具有刚性键的柔性聚合物;以及（iii）具有柔性键的柔性聚合物。使用一个非常有效的枢轴算法，使其能够模拟非常长的链，多达几千滴定组。的结果进行了比较，平均场近似的刚性杆和变分的结果从弗洛里型的方法。结果发现，刚性棒平均场模型给出了定性正确的描述的表观离解常数为所有三个模型。在室温下，能量对表观解离常数的贡献往往超过熵项，这部分解释了这种方法的相对成功。在柔性键的情况下，构象行为和表观解离常数的行为都很好地描述了一个二次项的变分分析，这在很大程度上要归功于键本身的调和性。该方法是不太成功的刚性债券，这变得明显的高电荷链的谐波熵项是不正确的。这可以通过用在强耦合状态下有效的表达式来代替它来补救。还发现了经验缩放表达式，主要用于端到端距离。
Monte Carlo simulations have been used to study three different models for linear, titrating polyelectrolytes in a salt‐free environment: (i) a rigid polymer with rigid bonds (rigid rod); (ii) a flexible polymer with rigid bonds; and (iii) a flexible polymer with flexible bonds. The use of a very efficient pivot algorithm has made it possible to simulate very long chains, with up to several thousand titrating groups. The results have been compared to a mean field approximation for a rigid rod and variational results emanating from a Flory type approach. It is found that the rigid rod mean field model gives a qualitatively correct description for the apparent dissociation constant for all three models. At room temperature, the energy contribution to the apparent dissociation constant often dominates over the entropic term, which partly explains the relative success of this approach. In the case of flexible bonds, both the conformational behavior and the behavior of the apparent dissociation constant are well described by a variational ansatz with a quadratic term, largely thanks to the harmonicity of the bonds themselves. The approach is less successful for rigid bonds, which becomes evident for highly charged chains where a harmonic entropy term is incorrect. This can be remedied by replacing it with an expression valid in the strong coupling regime. Empirical scaling expressions have also been found, primarily for the end‐to‐end distance.