Department of Mechanical Engineering, University of Maryland, College Park, MD-20742, USA.
Soft Matter. 2017 Jun 7;13(22):4159-4166. doi: 10.1039/c7sm00466d.
We employ scaling theory and Molecular Dynamics (MD) simulations to probe the compression of the semi-dilute polymer brush bilayers (BBLs) in the weak interpenetration (IP) regime. Such a regime is characterized by two layers of interacting polymer brushes grafted on opposing planar surfaces having a separation d, such that d < d < 2d, with d being the unperturbed brush height. Currently, scaling theories are known for polymer BBLs with a much larger degree of IP (i.e., d < d) - in such regimes, the brush height can be quantified by the corresponding IP length δ. On the other hand, we show that in the weak IP regime, the brush height is not solely dictated by δ. We develop new scaling theories to show that δ in this weak IP regime is different from that in the strong IP regime. Secondly, we establish that the compressed brush height in this weakly IP regime can be described as d ∼ N with χ < 1 and varying monotonically with d/d. MD simulations are carried out to quantify δ and χ and the results match excellently with our new scaling theory predictions. Finally, we establish that our scaling theory can reasonably predict the experimentally witnessed variation of the interaction energy dictating the compressive force between the interpenetrating brushes in this weakly IP regime.
我们运用标度理论和分子动力学（MD）模拟来研究弱贯穿（IP）区中半浓聚合物刷双层（BBL）的压缩。这种情况的特点是两层相互作用的聚合物刷接枝在具有分离距离 d 的相对平面上，使得 d < d < 2d，其中 d 是未扰刷的高度。目前，标度理论已知适用于具有更大 IP 程度的聚合物 BBL（即，d < d）- 在这种情况下，可以用相应的 IP 长度 δ 来量化刷的高度。另一方面，我们表明在弱 IP 区中，刷的高度不仅仅由 δ 决定。我们开发了新的标度理论来表明，在这个弱 IP 区中，δ 与在强 IP 区中的不同。其次，我们确定在这个弱 IP 区中，压缩刷的高度可以描述为 d ∼ N，其中 χ < 1 并且随 d/d 单调变化。进行 MD 模拟以量化 δ 和 χ，结果与我们的新标度理论预测非常吻合。最后，我们确定我们的标度理论可以合理地预测在弱 IP 区中决定相互贯穿刷之间压缩力的相互作用能的实验观测变化。
