Switching the Interpenetration of Confined Asymmetric Polymer Brushes
Switching the Interpenetration of Confined Asymmetric Polymer Brushes
复制标题
切换受限不对称聚合物刷的相互渗透
DOI：
10.1021/acs.macromol.6b00310
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发表时间：
2016
期刊：
影响因子：
5.5
通讯作者：
Abbott S
中科院分区：
文献类型：
--
作者：
Abbott S
研究了两种聚合物电刷在接近平面的表面上的互穿。当压实聚合物刷在每个表面都有一个不对称的电荷，一个是中性的，另一个是弱电荷的，我们发现刷子的穿透性成为一个可以由水溶液的pH控制的参数。利用数值自洽场理论(NSCF)，利用中子反射仪和表面力仪相结合的实验环境，研究了电刷侵彻程度的高低转换。首先，检查一对不带电的聚环氧乙烷(PEO)刷子，其中一个刷子被氢化，以区别于含氢的刷子。我们在nSCF和这些实验中都发现，刷子之间没有明显的重叠，因为两者都压实成聚合物块，几乎没有水化。然而，当弱聚电解质聚(2-(二甲氨基)甲基丙烯酸乙酯)(PDMAEMA)电刷被限制在氢化中性PEO电刷上，并且水化溶液的pH值低于聚阳离子的pKaof 7.5时，PDMAEMA上带电基团的存在允许两个聚合物电刷接触时发生显著的相互渗透。由于施加的围压，一旦聚合物刷子脱水，这种相互渗透仍然存在。将pH值提高到高于pKa的值时，聚电解质电刷中的电荷会被移除，导致两种电刷之间几乎不会相互渗透。因此，当一个刷子是弱聚电解质时，通过简单地调节水化溶液的pH值，可以改变聚合物刷子对之间的相互渗透状态。由于聚合物刷子被广泛研究和使用来减少固体表面之间的摩擦，这种效应可能对摩擦性能可控的聚合物刷子的设计和操作具有重要意义。
The interpenetration of two polymer brushes on approaching flat surfaces has been investigated. When compacting polymer brushes with an asymmetric charge on each surface, one neutral and the other weakly charged, we find that the brush interpenetration becomes a parameter that can be controlled by the pH of the hydrating solution. The switching between high and low degrees of brush interpenetration was investigated with numerical self-consistent field theory (nSCF) and experimentally using a sample environment which combines neutron reflectometry with a surface force type apparatus. Initially, a pair of uncharged poly(ethylene oxide), PEO, brushes are examined, where one of the brushes is deuterated to distinguish it from a hydrogenous counterpart. We find in both nSCF and these experiments that there is no significant overlap between the brushes as both compact into polymer blocks with little hydration. However, when a weak polyelectrolyte poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA, brush is confined against a deuterated neutral PEO brush and the pH of the hydrating solution is below the polycation’s pKaof 7.5, then the presence of charged groups on the PDMAEMA allows significant interpenetration to occur between the two polymer brushes on contact. This interpenetration remains once the polymer brushes dehydrate due to the confining pressure that is applied. Raising the pH to a value above the pKa, removes the charges from the polyelectrolyte brush resulting in little to no interpenetration between the two brushes. Therefore, by simply adjusting the pH of the hydrating solution the interpenetration state between polymer brush pairs can be switched when one brush is a weak polyelectrolyte. Since polymer brushes are widely investigated and used to reduce friction between solid surfaces, this effect may have significant implications in the design and operation of polymer brushes with controllable friction properties.
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