Polyelectrolyte Excluded Volume Paradox
Polyelectrolyte Excluded Volume Paradox
复制标题
聚电解质排除体积悖论
DOI：
10.1021/ma60065a004
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发表时间：
1978
期刊：
影响因子：
5.5
通讯作者：
J. Skolnick
中科院分区：
文献类型：
--
作者：
M. Fixman;J. Skolnick
将德拜-休克尔屏蔽的库仑相互作用直接应用于聚电解质中的排除体积效应，已知给出了可能太大几个数量级的链段-段排除体积的估计。认为这一应用的主要缺陷在于传统的排除体积理论假设不适用于电荷相互作用，而不是静电势本身。这一假设认为相邻片段对之间的协同作用并不重要，因为这种相互作用很弱。试图通过选择包含许多单体单元的链段来恢复这一假设的适用性。该管段被建模为杆，并且要求长于德拜筛网长度。必须为线电荷密度选择一个数值，而不是为杆的轮廓长度选择一个数值。在电荷密度很低的情况下，本工作再现了排除体积的传统公式，但在实际应用中找到了小得多的值。对聚丙烯酸作了说明性的应用，其电荷密度被选择为扩展构型的结构值的大约两倍，这与以前的工作一致。德拜-休克尔相互作用被发现工作得很好。
Straightforward application of the Debye-Huckel screened Coulomb interaction to the excluded volume effect in polyelectrolytes is known to give estimates of the segment-segment excluded volume that may be too large by several orders of magnitude. It is argued that the major defect in this application lies in a conventional assumption of excluded volume theory that does not apply to charge interactions, rather than in the electrostatic potential itself. This assumption is that the cooperative interaction of neighboring segment pairs is unimportant because the interaction is weak. An attempt is made to restore the applicability of this assumption through the choice of a segment that incorporates many monomer units. The segment is modeled as a rod and is required to be longer than the Debye screening length. A numerical value has to be chosen for the linear charge density but not for the contour length of the rod. The present work reproduces the conventional formula for the excluded volume if the charge density is very low, but much smaller values are found for practical applications. An illustrative application is made to poly(acry1ic acid), for which the charge density is chosen to be about twice the structural value for the extended configuration, in agreement with previous work. The Debye-Huckel interaction is found to work quite well.