Surface and Corrosion Science, Department of Chemistry, Royal Institute of Technology, Drottning Kristinas väg 51, SE-10044 Stockholm, Sweden.
Langmuir. 2011 Jun 21;27(12):7537-48. doi: 10.1021/la200441u. Epub 2011 May 16.
The growth of polysaccharide multilayers consisting of positively charged chitosan (CH) and negatively charged heparin (HEP) was monitored in situ by employing a quartz crystal microbalance (QCM-D) and dual-polarization interferometry (DPI). The main focus was on how the physicochemical properties of the solution affect the growth and structure of the resulting multilayer film. These results showed that when increasing the ionic strength of the polysaccharide solutions at a fixed pH, both the "dry" (optical) (DPI) mass and wet (QCM) mass of the adsorbed multilayer film increased. The same effect was found when increasing the pH while keeping the ionic strength constant. Furthermore, the growth of multilayers showed an exponential-like behavior independent of the solution conditions that were used in this study. It was also established that chitosan was the predominant species present in the chitosan-heparin multilayer film. We discuss the viscoelastic properties of the adsorbed layers and their variation during the multilayer buildup. Interestingly and contrary to common interpretation of the QCM-D results, we found that under one particular solution condition (pH 4.2 and 30 mM NaCl) the increase in the dissipation of oscillation energy from the adsorbed layer was a consequence of layer stiffening rather than indicating a more hydrated and viscous film. On the basis of the widely used Voigt viscoelastic model for an adsorbed layer, we show that it is the film viscosity and shear that define the layer viscoelasticity (structure) of the film and not the absolute value of energy dissipation, which in fact can be very misleading.
采用石英晶体微天平（QCM-D）和双折射干涉测量（DPI）原位监测了由带正电荷壳聚糖（CH）和带负电荷肝素（HEP）组成的多糖多层的生长。主要关注的是溶液的物理化学性质如何影响所得多层膜的生长和结构。这些结果表明，当在固定 pH 值下增加多糖溶液的离子强度时，吸附多层膜的“干燥”（光学）（DPI）质量和湿（QCM）质量都会增加。当保持离子强度不变而增加 pH 值时，也会发现相同的效果。此外，多层的生长表现出与本研究中使用的溶液条件无关的指数样行为。还确定了壳聚糖是壳聚糖-肝素多层膜中主要存在的物质。我们讨论了吸附层的粘弹性及其在多层堆积过程中的变化。有趣的是，与 QCM-D 结果的常见解释相反，我们发现，在一种特定的溶液条件下（pH 4.2 和 30 mM NaCl），从吸附层中振荡能量耗散的增加是由于层变硬而不是表明更水合和粘性的膜。基于广泛使用的吸附层的 Voigt 粘弹性模型，我们表明，正是膜的粘度和剪切定义了膜的粘弹性（结构），而不是能量耗散的绝对值，实际上这可能非常具有误导性。
