Detailed structure of molecularly thin polyelectrolyte multilayer films on solid substrates as revealed by neutron reflectometry
Detailed structure of molecularly thin polyelectrolyte multilayer films on solid substrates as revealed by neutron reflectometry
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DOI：
10.1021/ma980910p
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发表时间：
1998-12-15
期刊：
影响因子：
5.5
通讯作者：
Kjaer, K
中科院分区：
文献类型：
--
作者：
Lösche, M;Schmitt, J;Kjaer, K
利用中子反射仪，我们对自组装聚电解质多层膜的内部结构进行了高分辨率的解析，并用组成空间精化技术对数据进行了分析，得到了这类体系的详细分子图。我们发现这种表面膜由层状结构组成，在这些层状结构中，每一层的聚阴离子和聚阳离子相互紧密地相互交错。然而，如果在制备过程中保持良好的定义和恒定的环境条件，沉积技术可以产生可预测的结果。对于聚苯乙烯磺酸(PSS)和聚烯丙基胺盐酸盐(PAH)的交替层，吸附在原子平坦的表面上，连续沉积的层的粗化导致连续几代吸附聚合物的吸附位置逐渐增加，从而随着沉积层数的增加而增加层厚度。然而，由于相邻聚电解质物种的相互渗透，这种增加很快就稳定到平衡厚度。在完全水合的薄膜(100%相对湿度)中，水占薄膜内体积的40%以上。与PSS相关的水(以体积计)大约是PAH的两倍。如果有的话，掺入的无机盐只起到很小的作用。沉积层结构的平衡厚度可以通过用于制备的溶液的离子强度I来微调。结果表明，每层厚度d(1p)与i的关系是线性的，其灵敏度为d(1p)/i=16埃×L/摩尔。随着膜层厚度的增加，相邻层之间的界面粗糙度σ增大，其值与0.4xd(1p)相近。与沉积溶液的离子强度相比，制备过程中使用的聚阴离子的聚合度只对决定沉积薄膜的整体结构起到很小的作用。这里报告的结果与最近的一项研究(Tarabia等人)在数量上是一致的。J.Appl.太棒了。1998，83,725-732)，如果假设在两个研究中研究的样品膜中聚电解质分子的水化是相似的。
Using neutron reflectometry we have resolved-to high resolution-the internal structure of self-assembled polyelectrolyte multilayer films and have developed a detailed molecular picture of such systems by analyzing the data with a composition-space refinement technique. We show that such surface films consist of stratified structures in which polyanions and polycations of individual layers interdigitate one another intimately. Nevertheless, the deposition technique leads to results that are predictable, if well-defined and constant environmental conditions are maintained during the preparation. For alternating layers of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), adsorbed onto atomically flat surfaces, a roughening of successively deposited layers leads to a progressively larger number of adsorption sites for consecutive generations of adsorbed polymer, and thus to an increase in layer thicknesses with an increasing number of deposited layers. Because of the interpenetration of adjacent polyelectrolyte species, however, this increase settles quickly into an equilibrium thickness. In fully hydrated films (100% relative humidity), water occupies greater than or equal to 40% of the volume within the films. About twice as much water (by volume) is associated with PSS as with PAH. Incorporated inorganic salt plays a minor role only, if any. The equilibrium thickness of the deposited layer structure may be fine-tuned via the ionic strength, I, of the solutions used for the preparation. We show that the dependence of the thickness d(1p) per layer pair on I is linear, with a sensitivity, Delta d(1p)/Delta I = 16 Angstrom x L/mol. Concurrently with the layer thickness the interface roughness sigma between adjacent layers increases: sigma similar to 0.4 x d(1p). In contrast to the ionic strength of the deposition solutions, the degree of polymerization of the polyanions used in the preparation plays a minor role only in determining the overall structure of the deposited films. The results reported here are quantitatively consistent with those of a recent study (Tarabia et al. J. Appl. Phys. 1998, 83, 725-732), if one assumes that the hydration of the polyelectrolyte molecules in the sample films investigated in the two studies is similar.