Polyelectrolytes in multivalent salt solutions: Monomolecular versus multimolecular aggregation
Polyelectrolytes in multivalent salt solutions: Monomolecular versus multimolecular aggregation
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DOI：
10.1021/ma010717m
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发表时间：
2002-01-29
期刊：
影响因子：
5.5
通讯作者：
de la Cruz, MO
中科院分区：
文献类型：
--
作者：
Huang, CI;de la Cruz, MO
我们分析了隔离的N个单体的大小在多价盐的存在下，与价Z作为一个函数的浓度在溶液中的单体phi的强电荷链。相反电荷的多价离子沿着单体凝聚并诱导单体吸引，当它们的价态z > 1时，单体吸引导致链和多价离子的致密有限尺寸聚集体（胶束）的形成。我们计算了p = 1，2，3，4，.的聚集体中链的数密度。通过使所有p-聚集链的化学势与聚集体中的自由离子和凝聚离子的化学势相等，在低浓度的多价盐m，我们观察到单分子（p = 1）沉淀链时，phi < phi*，其中phi* 一致的mz。当phi增加到phi* 以上时，链重新溶解在溶液中并采取拉伸构象。当m增加到临界值m** 以上时，具有p > 1链的聚集体的数量密度增加，使得当phi** < phi < phi* 时，具有p* > 1链的聚集体更多。如果我们在分析中只包括表面自由能，我们发现p* =无穷大。然而，如果我们在自由能中包括将p个链限制在区域R（p）=（pN）（1/3）a中的链熵，则p* 可以是有限的并且大于或等于1。这种情况出现时，链被约束到拉伸构象，如在亚稳态的环形和球形线圈中观察到的多价离子的长双链DNA的聚集体。
We analyze the segregation of strongly charged chains of N monomers of size a in the presence of multivalent salts with valence z as a function of the concentration of monomers phi in the solutions. The multivalent ions of opposite charge condense along the monomers and induce monomer attractions that lead to the formation of dense finite size aggregates (micelles) of chains and multivalent ions when their valence z > 1. We compute the number density of chains in aggregates with p = 1, 2, 3, 4, ... chains by equating the chemical potential of all the p-aggregated chains and of the free and condensed ions in the aggregates. At low concentration of multivalent salts m, we observe monomolecular (p = 1) precipitated chains when phi < phi*, where phi* congruent to mz. When phi increases above phi*, the chains redissolve in the solution and adopt stretched conformations. As m increases above a critical value m**, the number density of aggregates with p > 1 chains increases such that there are more aggregates with p* > 1 chains when phi** < phi < phi*. If we only include the surface free energy in the analysis, we find p* = infinity. However, if we include the chain entropy of confining p chains in a region R(p) = (pN)(1/3)a in the free energy, p* can be finite and greater than or equal to one. This situation arises when the chains are constrained to stretched conformations, such as in metastable toroidal and in spherical coil aggregates observed in long double-stranded DNA in multivalent ions.