表面吸附与分子间疏水缔合在水润滑体系中的协同效应研究

Lubrication, in which the lubricating liquid is confined within the thin slit between two substrates, has been extensively studied for one and half a century. When locomotion occurs, lubricant could greatly reduce friction and minimize wear of the underlying substrates, which is highly relevant for engineering applications, biological apparatus, consumer industry, etc. Biological lubrication, as one of high effective water lubrication system has been paid lot of attention to. Most researchers owed the lubrication to the hydration of the attached layer, either chemically or physically, which may result in a repulsive force due to different interactions. It should be noted that most of the tribopair studied was molecularly smooth mica, between which only the adsorbed or attached lubricant layer in nano scale remained under physiological pressures. However, the surfaces in vivo are usually not molecularly flat and have asperities of different scales, thus full direct contact could not reach even under extremely high loads. In this case, the complicated rheological behavior of lubricants (synovial fluid, mucus, etc.) trapped in the cavities could not be ignored in boundary region. .In this project, water lubrication is not only decided by surface behavior, but also by the rheological characteristic of bulk lubricant trapped in the confined space between the two friction substrates. Here, the lubricant is the aqueous solution with intermolecular hydrophobic association. Only at the concentration high enough for the formation of intermolecular hydrophobic associations in bulk solution, the polymer aqueous solution could effectively reduce friction, especially for the boundary friction. To explore whether the generally used hydrophobically associative polymer solution could supply the efficient boundary lubrication, several hydrophobic modified watersoluble polymers (neutral polymer, polyelectrolyte and polyamino acid) with various structures (block, branch length or density) will be synthesized. The influence of pH value, ionic strength, temperature and concentration on intermolecular hydrophobic association, rheological behavior (steady or dynamic response, relax characteristic) as well as the hydrophilicity of the copolymer will be investigated. Based on it, the relationship between structure, hydrophobic associate and rheological response should be built. The adsorption behavior of hydrophobic modified polymer aqueous solution on different substrate will be studied. And then, the relationship between surface property and surface adsorption (tight adsorption and loose adsorption) should be determined. Based on examining the frictional behavior of various substrates (stiff, soft and surface modified) with the synthesized hydrophobic modified polymer aqueous solution as lubricant under various conditions, we try to figure out the role of intermolecular hydrophobic associate, surface adsorption in water lubrication system. The synergistic effect of intermolecular hydrophobic associate and surface adsorption will be illustrated and then the mechanism of water lubrication system will be proposed and guide the design of biomimetic water lubricated materials. .Research of the present project has far-reaching academic and practical significance and will improve the relevant theoretical system of polymer solution rheology especially for friction rheology.

以水润滑体系不仅是界面行为，还与被限制在摩擦副间受限空间内的润滑液分子间疏水缔合结构的流变特性有关为指导思想，拟制备具有不同疏水结构（嵌段或接枝型、嵌段或接枝长度、密度等）的水溶性大分子（中性聚合物、聚电解质、聚氨基酸等），获得pH 值、离子强度、温度、浓度等因素对疏水改性聚合物水溶液流变响应（稳态、动态流变行为及缔合结构的松弛特性）的影响规律，建立疏水改性聚合物结构—分子间疏水缔合—流变响应之间的关系；考察不同疏水改性聚合物水溶液在不同性质（疏水、亲水）的基板（硬基板，软基板）上的吸附行为，建立基板表面性质—表面吸附（紧密吸附和松散吸附）之间的关系；考察各种条件下，疏水改性聚合物水溶液为润滑液的摩擦行为，探明表面吸附及分子间疏水缔合在水润滑体系中的作用，明确二者在润滑过程中的协同效应，揭示水润滑机理，为仿生水润滑材料的设计及应用提供理论依据，具有重要的理论意义及实际价值。

通过深入研究疏水缔合聚合物水溶液的流变行为，确定了具有多重相互作用的水溶液体系的特殊弱应力过冲现象。在此基础上，探索了疏水与亲水表面以疏水性聚合物水溶液为润滑剂时的摩擦行为，发现具有多重相互作用的聚合物水溶液可在较低浓度下实现边界润滑。基于上述研究结果，在聚乙烯醇（PVA）中引入表面活性剂和甘油，结合制备基板，促进凝胶形成过程中的微相分离，获得了具有超低边界摩擦系数的PVA水凝胶。利用两性离子的强亲水性，制备了减阻防污水凝胶涂层。以上研究结果为制备超润滑摩擦体系提供了理论参考。本项目主要取得了以下研究进展：.① 观察到具有多重相互作用的聚合物水溶液体系的二次屈服现象。.② 观察到具有多重相互作用的聚合物水溶液体系的特殊弱应变过冲现象，即随着浓度增大，过冲锋向大应变移动。提出了该体系的结构模型，可很好得解释其特殊流变行为。.③ 对疏水型摩擦表面，以含疏水基团的聚合物水溶液为润滑剂时，疏水表面可吸附聚合物大分子，从而在极低浓度时，润滑剂即表现出优异的润滑效果。提出了润滑状态模型，获得边界润滑区摩擦系数、转变速率、流体动力润滑区摩擦系数等与润滑液浓度及基板粗糙度的标度关系。.④ 在PVA水凝胶制备过程中引入疏水链（表面活性剂），并结合非极性基板，采用冷冻解冻法制备了物理交联水凝胶，该水凝胶表现出极低的边界区摩擦系数。此外，该水凝胶还具有极佳的低温韧性。.⑤ 以具有聚电解质效应的聚合物（PAA）为第一网络，具有反聚电解质效应的两性离子SBMA为第二网络制备的双组分水凝胶PAA/PSBMA涂层，在不同介质（第二单体、水、盐溶液）中溶胀程度小，有效防止了其制备及使用过程中的脱落，且具有较好的力学性能和优异的防污减阻性能。. 以上研究结果丰富了高分子流变学关于疏水缔合、静电相互作用、亲水性等对高分子溶液黏弹行为影响的相关理论，揭示了水润滑体系中疏水缔合的作用，具有一定的理论意义，研究结果既为性能优异的仿生水润滑材料设计提供了理论依据，也可为改进非水润滑体系提供了参考。