Faculty of Pharmacy and ‡Department of Chemistry, Université de Montréal , C.P. 6128, succursale Centre-ville, Montréal, Québec, Canada H3C 3J7.
Langmuir. 2017 Apr 18;33(15):3610-3623. doi: 10.1021/acs.langmuir.7b00006. Epub 2017 Apr 4.
Normal and friction forces between immobilized two-dimensional (2D) homogeneous non-close-packed colloidal arrays made of different particles are compared in aqueous media. Soft pH-responsive (microgels) and nonresponsive hard (silica) particles of different sizes were used to create the 2D arrays. The results show that the friction of soft responsive structured layers can be successfully modulated by varying the pH, with a friction coefficient varying by nearly 3 orders of magnitude (10 to 1). This important change in lubricating properties is mainly correlated with the particle swelling behavior, i.e., the friction coefficient decreasing exponentially with an increase in the swelling ratio regardless of the size, surface coverage, and degree of ionization of the particles. In addition, the robustly attached microgel particles were able to sustain high pressure (up to 200 atm) without significant surface damage. The 2D arrays of nonresponsive hard particles also gave rise to a very low friction coefficient (μ ≈ 10) under similar experimental conditions and could sustain a larger pressure without damage (≤600 atm). The low friction dissipation observed between the hard arrays resulted from a rolling mechanism. Even though rolling requires nonimmobilized particles on the substrates, the results show the importance of attaching a certain proportion of particles on the surfaces to reduce friction.
在水介质中比较了固定二维（2D）均匀非密排胶体阵列之间的正常力和摩擦力，该阵列由不同的粒子组成。使用软 pH 响应（微凝胶）和非响应硬（二氧化硅）不同大小的粒子来创建 2D 阵列。结果表明，通过改变 pH 值可以成功调节软响应结构化层的摩擦力，摩擦系数变化近 3 个数量级（10 到 1）。这种润滑性能的重要变化主要与颗粒溶胀行为相关，即摩擦系数随溶胀比的增加呈指数下降，而与颗粒的大小、表面覆盖率和离解度无关。此外，牢固附着的微凝胶颗粒能够在没有明显表面损伤的情况下承受高达 200 大气压的高压。在类似的实验条件下，非响应硬粒子的 2D 阵列也产生了非常低的摩擦系数（μ≈10），并且在没有损坏的情况下可以承受更大的压力（≤600atm）。在硬阵列之间观察到的低摩擦耗散是由于滚动机制造成的。尽管滚动需要在基底上具有非固定的粒子，但结果表明将一定比例的粒子附着在表面上以减少摩擦的重要性。
