Hard-surface effects in polymer self-consistent field calculations.
Hard-surface effects in polymer self-consistent field calculations.
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DOI：
10.1063/1.2740633
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发表时间：
2007-06
期刊：
影响因子：
--
通讯作者：
D. Meng;Qiang Wang
中科院分区：
文献类型：
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作者：
D. Meng;Qiang Wang
我们在自洽场计算中研究了由于聚合物熔体被不可穿透（硬）表面限制而产生的几种影响。为了充分表示这种限制，总（归一化）聚合物链段密度（体积分数）通常被限制在一个强加的轮廓上，该轮廓在短距离内从受限制熔体内部的 1 连续减小到表面上的 0。该轮廓的选择强烈影响自洽场计算的数值性能。此外，对于二嵌段共聚物 A-B，硬表面限制同时具有能量和熵效应：一方面，聚合物密度从 1 降低，减少了 A-B 排斥力，有利于表面附近有更多 A-B 界面的形态。另一方面，链末端的富集和表面附近中间链段的耗尽有利于平行形态，其中链主要垂直于表面取向。这两种效应在大小上相当，并且对于不对称二嵌段共聚物，导致中性表面对较短嵌段的熵偏好，如先前提出的[Q. Wang 等人，Macromolecules 34, 3458 (2001)]。硬表面效应在实践中很弱，因此仅在表面接近中性时才显现出来。
We have investigated several effects due to the confinement of polymer melts by impenetrable (hard) surfaces in the self-consistent field calculations. To adequately represent such confinement, the total (normalized) polymer segmental density (volume fraction) is usually constrained to an imposed profile that continuously decreases from 1 in the interior of confined melts to 0 at the surfaces over a short distance. The choice of this profile strongly influences the numerical performance of the self-consistent field calculations. In addition, for diblock copolymers A-B the hard-surface confinement has both energetic and entropic effects: On one hand, the decrease of polymer density from 1 reduces A-B repulsion and favors morphologies with more A-B interfaces near the surfaces. On the other hand, the enrichment of chain ends and depletion of middle segments near the surfaces favor parallel morphologies where chains orient mainly perpendicular to the surfaces. These two effects are comparable in magnitude, and for asymmetric diblock copolymers result in an entropic preference of a neutral surface for the shorter block as proposed previously [Q. Wang et al., Macromolecules 34, 3458 (2001)]. The hard-surface effects are weak in practice and thus manifested only when the surfaces are nearly neutral.