Adsorption of branched and dendritic polymers onto flat surfaces: a Monte Carlo study.
Adsorption of branched and dendritic polymers onto flat surfaces: a Monte Carlo study.
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DOI：
10.1063/1.4849176
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发表时间：
2013-12
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影响因子：
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通讯作者：
J. Sommer;J. Kłos;O. Mironova
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文献类型：
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作者：
J. Sommer;J. Kłos;O. Mironova
使用基于键涨落模型的蒙特卡罗模拟，我们研究了具有柔性间隔基的星爆树枝状聚合物在平坦表面上的吸附。在较宽的降低温度 τ 范围内对不同代数 G 和间隔基长度 S 进行计算，作为单体与表面之间相互作用强度的量度。我们的模拟表明了两步吸附场景。在吸附临界点 τc 以下，发现树枝状聚合物处于弱吸附状态。在这里，树枝状聚合物保持其形状，但通过吸附的间隔物粘附到表面。通过将温度降低到间隔基长度相关值 τ*(S) < τc 以下，就会发生向强吸附态的阶梯式转变。在平坦吸附状态下，树枝状聚合物的形状可以通过二维树枝状聚合物的平均场模型很好地描述。我们还对星形聚合物进行了模拟，其显示出与线性链完全相似的简单交叉行为。通过分析吸附转变的有序参数，我们确定了树枝状聚合物的吸附临界点，其位置接近星形聚合物的吸附临界点。虽然吸附的间隔物的有序参数显示出关键的交叉缩放，但结合了关键和不连续过渡效应的整体有序参数并不显示简单的缩放。通过分析树枝状聚合物的形状各向异性，证实了从弱吸附状态到强吸附状态的阶梯式转变。我们提出了一个基于间隔吸附概念的平均场模型，该模型预测由于排除的体积势垒而导致树枝状聚合物的不连续转变。后者是由于平坦吸附状态下树枝状聚合物的密度增加造成的，在该状态达到热力学稳定之前必须克服这一问题。
Using Monte Carlo simulations based on the bond fluctuation model we study the adsorption of starburst dendrimers with flexible spacers onto a flat surface. The calculations are performed for various generation number G and spacer length S in a wide range of the reduced temperature τ as the measure of the interaction strength between the monomers and the surface. Our simulations indicate a two-step adsorption scenario. Below the critical point of adsorption, τc, a weakly adsorbed state of the dendrimer is found. Here, the dendrimer retains its shape but sticks to the surface by adsorbed spacers. By lowering the temperature below a spacer-length dependent value, τ*(S) < τc, a step-like transition into a strongly adsorbed state takes place. In the flatly adsorbed state the shape of the dendrimer is well described by a mean field model of a dendrimer in two dimensions. We also performed simulations of star-polymers which display a simple crossover-behavior in full analogy to linear chains. By analyzing the order parameter of the adsorption transition, we determine the critical point of adsorption of the dendrimers which is located close to the critical point of adsorption for star-polymers. While the order parameter for the adsorbed spacers displays a critical crossover scaling, the overall order parameter, which combines both critical and discontinuous transition effects, does not display simple scaling. The step-like transition from the weak into the strong adsorbed regime is confirmed by analyzing the shape-anisotropy of the dendrimers. We present a mean-field model based on the concept of spacer adsorption which predicts a discontinuous transition of dendrimers due to an excluded volume barrier. The latter results from an increased density of the dendrimer in the flatly adsorbed state which has to be overcome before this state is thermodynamically stable.