From exponential to linear growth in polyelectrolyte multilayers
From exponential to linear growth in polyelectrolyte multilayers
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DOI：
10.1021/la053218d
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发表时间：
2006-04-25
期刊：
影响因子：
3.9
通讯作者：
Schaaf, P
中科院分区：
文献类型：
--
作者：
Porcel, C;Lavalle, P;Schaaf, P
存在两种类型的多层膜：厚度随沉积步骤的数量线性增加的那些，其结构良好，以及厚度呈指数增加的那些，其类似于水凝胶。这个简单的图片最近略有演变的发现，一些指数增长的薄膜进入线性增长阶段后，一定数量的沉积步骤。在这项研究中，我们研究了透明质酸/聚（L-赖氨酸）（HA/PLL）多层膜的构建过程，构成了最知名的指数增长系统之一。该膜通过使用两种沉积方法来构建：众所周知的浸渍方法和最近的喷涂方法，其中将浸渍溶液交替地喷涂到垂直基底上。这项研究的目的是双重的。首先，我们研究主要参数的影响（即，喷涂速率和喷涂时间）对薄膜生长过程的影响。我们发现，对于浸渍法，薄膜厚度首先与沉积步骤的数量呈指数关系，并在一定数量的沉积步骤后，它遵循线性演化。我们发现，类似的行为与浸渍法观察。第二，因为喷涂方法允许不同参数的集结非常细微的变化，我们使用这种方法来研究指数到线性的过渡。我们发现，无论控制沉积过程的参数的值如何，这种转变总是发生在大约12个沉积步骤之后。我们讨论了我们的结果，根据Hubsch等人提出的模型（Hubsch. E.的; Ball，V.; Senger，B.; Decher，G.; Voegel，J. C.; Schaaf，P. Langmuir 2004，20，1980-1985）以及后来Salomaki等人（Salomaki，M.; Vinokurov，1.一、Kankare，J. Langmuir 2005，21，11232-11240），其中假设指数到线性转变是由于膜重构，其逐渐禁止构成膜的聚电解质之一在膜的一部分上扩散。然后，该“禁止”区域随着沉积步骤的数量而增长，使得仍然与扩散有关的膜的外部区域保持恒定的厚度，并且随着总膜厚度的增加而向上移动。
There exist two types of polyelectrolyte multilayers: those whose thickness increases linearly with the number of deposition steps, which are nicely structured, and those whose thickness increases exponentially, which resembles hydrogels. This simple picture has recently slightly evolved with the finding that some exponentially growing films enter into a linear growth phase after a certain number of deposition steps. In this study, we investigate the buildup process of hyaluronic acid/poly(L-lysine) (HA/PLL) multilayers that constitute one of the best known exponentially growing systems. The films are built by using two deposition methods: the well-known dipping method and the more recent spraying method where the polyelectrolyte solutions are sprayed alternately onto a vertical substrate. The goal of this study is twofold. First, we investigate the influence of the main parameters (i.e., spraying rate and spraying time) of the spraying method on the film growth process. We find that, as for the dipping method, the film thickness first evolves exponentially with the number of deposition steps, and after a given number of deposition steps, it follows a linear evolution. We find that similar behavior is observed with the dipping method. Second, because the spraying method allows the very tine variation of the different parameters of the buildup, we use this method to investigate the exponential-to-linear transition. We find that this transition always takes place after about 12 deposition steps whatever the values of the parameters controlling the deposition process. We discuss our results in light of a model proposed by Hubsch et al. (Hubsch. E.; Ball, V.; Senger, B.; Decher, G.; Voegel, J. C.; Schaaf, P. Langmuir 2004, 20, 1980-1985) and later by Salomaki et al. (Salomaki, M.; Vinokurov, 1. A.; Kankare, J. Langmuir 2005, 21, 11232-11240) in which it is assumed that the exponential-to-linear transition is due to a film restructuring that progressively forbids the diffusion of one of the polyelectrolytes constituting the film over part of the film. This "forbidden" zone then grows with the number of deposition steps so that the outer zone of the film that is still concerned with diffusion keeps a constant thickness and moves upward as the total film thickness increases.