Modeling the buildup of polyelectrolyte multilayer films having exponential growth
Modeling the buildup of polyelectrolyte multilayer films having exponential growth
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DOI：
10.1021/jp035740j
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发表时间：
2004-01-15
影响因子：
3.3
通讯作者：
Schaaf, P
中科院分区：
文献类型：
--
作者：
Lavalle, P;Picart, C;Schaaf, P
文献中已经报道了两种类型的多层膜。这些是（i）其质量和厚度随着沉积的双层的数量增加而线性增加的膜和（ii）指数生长的膜。我们提出了一个模型，指数增长的电影，允许讨论他们的行为在一个统一的方式。该模型基于构成多层的至少一种聚电解质的部分链在整个膜中的扩散和扩散。简而言之，使膜与能够扩散到膜中的聚电解质溶液接触。在电影内部，这些锁链构成了“自由”的锁链。在随后的冲洗步骤中，它们中的一些从膜向外扩散。剩余的链离开膜，因为它进一步与相反电荷的水溶液接触。当“自由”链到达膜/溶液界面时，它们被相反电荷的聚电解质络合。这些复合物，这是由两种类型的聚电解质，有助于形成额外的质量的多层。该模型依赖于在德拜-休克尔近似的框架内的膜中的静电势的评估，并考虑到唐南效应，这是由于在膜中的非补偿固定电荷。它还包括没有聚电解质在多层内扩散的情况，在这种情况下，膜线性生长。该模型预测存在的自由能垒，防止总扩散的任何“自由”的扩散膜在冲洗步骤中向外，接触后的反渗透溶液。它还预测，通常只有一个的两个聚电解质，包括膜扩散容易进入它。两个聚电解质，包括膜可以扩散“进入”和“出”的多层膜只有当膜内的非补偿固定电荷的浓度是非常小的。几个预测的模型进行了讨论，根据已经发表的实验结果或新的。
Two types of polyelectrolyte multilayer films have been reported in the literature. These are (i) films whose mass and thickness increase linearly as the number of deposited bilayers increases and (ii) films that grow exponentially. We present a model for the buildup of exponentially growing films that allows a discussion of the behavior of them in a unified manner. This model is based on the diffusion both in and out the whole film of part of the chains of at least one of the polyelectrolytes constituting the multilayer. In short, the film is brought into contact with the solution of polyelectrolytes that are able to diffuse into the film. Inside of the film, chains of this polyelectrolyte constitute the "free" chains. At the subsequent rinsing step, some of them diffuse outward from the film. The remaining chains leave the film as it is brought into contact further with the polyelectrolyte solution of opposite charge. As the "free" chains reach the film/solution interface, they are complexed by the polyelectrolytes of opposite charge. These complexes, which are composed of both types of polyelectrolytes, contribute to the formation of the additional mass of the multilayer. The model relies on the evaluation of the electrostatic potential in the film within the framework of the Debye-Huckel approximation and takes into consideration the Donnan effect, which is due to noncompensated fixed charges in the film. It also includes the situation where none of the polyelectrolytes diffuse within the multilayer, in which case the film grows linearly. The model predicts the existence of a free-energy barrier that prevents total diffusion of any "free" polyelectrolyte outward from the film during a rinsing step, following contact with a polyelectrolyte solution. It also predicts that usually only one of the two polyelectrolytes that comprise the film diffuses readily into it. Both polyelectrolytes that comprise the film can diffuse "into" and "out of" the multilayer only when the concentration of noncompensated fixed charges within the film is very small. Several predictions of the model are discussed in the light of experimental results that have already been published or are new.