Temperature effect on the build-up of exponentially growing polyelectrolyte multilayers. An exponential-to-linear transition point.
Temperature effect on the build-up of exponentially growing polyelectrolyte multilayers. An exponential-to-linear transition point.
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DOI：
10.1039/c6cp00345a
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发表时间：
2016-03
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影响因子：
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通讯作者：
A. Vikulina;Y. Anissimov;Prashant Singh;Vladimir Z. Prokopović;K. Uhlig;M. Jaeger;R. von Klitzing;C. Duschl;D. Volodkin
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文献类型：
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作者：
A. Vikulina;Y. Anissimov;Prashant Singh;Vladimir Z. Prokopović;K. Uhlig;M. Jaeger;R. von Klitzing;C. Duschl;D. Volodkin
在这项研究中，研究了温度对指数生长的聚电解质多层膜的堆积的影响。它的目的是了解多层膜的生长机制，因为它对定制多层膜的制备至关重要。采用浸渍法制备聚L赖氨酸/透明质酸(PLL/HA)模型多层膜，温度范围为25~85℃。由于聚合物在薄膜中的有限扩散，薄膜的生长在转折点从指数区域转变为线性区域。随着堆积温度的升高，两个区域的薄膜生长速率都有所提高；过渡点位置向更多的沉积步骤移动，证实了扩散介导的生长机制。在较高的制备温度下，不仅聚合物扩散到膜中的速度更快，而且膜的孔/透性更强，导致膜的生长速度更快。根据在薄膜生长过程中切换制备温度时的薄膜生长速率的分析，推测后一种机制。有趣的是，在25-45°C的温度范围内，所制备的薄膜是平衡的，并且保持完好(没有膨胀或收缩)。根据Arrhenius图计算出PLL与HA在多层膜中的平均络合活化能对于PLL单体来说约为0.3kJ·mol(-1)。最后，关于多层膜的生长，讨论了下列已知依赖于温度的过程：(I)聚合物扩散，(Ii)聚合物构象变化，和(Iii)聚合物间相互作用。
In this study, the effect of temperature on the build-up of exponentially growing polyelectrolyte multilayer films was investigated. It aims at understanding the multilayer growth mechanism as crucially important for the fabrication of tailor-made multilayer films. Model poly(L-lysine)/hyaluronic acid (PLL/HA) multilayers were assembled in the temperature range of 25-85 °C by layer-by-layer deposition using a dipping method. The film growth switches from the exponential to the linear regime at the transition point as a result of limited polymer diffusion into the film. With the increase of the build-up temperature the film growth rate is enhanced in both regimes; the position of the transition point shifts to a higher number of deposition steps confirming the diffusion-mediated growth mechanism. Not only the faster polymer diffusion into the film but also more porous/permeable film structure are responsible for faster film growth at higher preparation temperature. The latter mechanism is assumed from analysis of the film growth rate upon switching of the preparation temperature during the film growth. Interestingly, the as-prepared films are equilibrated and remain intact (no swelling or shrinking) during temperature variation in the range of 25-45 °C. The average activation energy for complexation between PLL and HA in the multilayers calculated from the Arrhenius plot has been found to be about 0.3 kJ mol(-1) for monomers of PLL. Finally, the following processes known to be dependent on temperature are discussed with respect to the multilayer growth: (i) polymer diffusion, (ii) polymer conformational changes, and (iii) inter-polymer interactions.