【作者】 胡新亮；

【导师】 杜淼；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2008， 硕士

【摘要】 采用冷冻解冻法制备了物理交联的PVA水凝胶,并通过其与各种基板在水中和高分子溶液中的摩擦,考察了基板表面能、正压力、滑动速率、高分子（PEO）水溶液浓度以及高分子的分子量对PVA水凝胶摩擦行为的影响。利用凝胶摩擦的吸附—排斥模型以及标度理论对实验结果进行了分析。研究表明对于具有吸附行为的摩擦体系,其粘弹—流体润滑转变区域均在10^-3～10^-2m/s之间,且随正压P的增加,摩擦机理发生改变时的滑动速率—v_f向高速区域移动。以转变区域为分界线,当滑动速率v低于该区域时,不同v下,摩擦应力f对P的敏感性变化不大,且凝胶与基板间相互作用的差异并未影响f对P的敏感性。而当v高于该区域时,f对P的敏感性增大。在低v下,f随基板表面能γ的变化并不明显。随着v的增大,f随γ的增大而逐渐增大。在摩擦机理未发生改变时,f对γ的敏感度随着v的增大而增大。v_f随γ的增大而向高速区移动。当PVA凝胶浸入到PEO水溶液中,因渗透压而发生体积收缩。相同浓度下,PVA凝胶在分子量低的PEO-5水溶液中压缩模量增大,而在分子量高的PEO-400水溶液中,压缩模量变化不明显。在稀溶液中,PVA凝胶的压缩模量变化很小;而当浓度达到c^*以上时,在低分子量PEO水溶液中,PVA凝胶的压缩模量显著增大。PVA凝胶在PEO的c^*溶液中进行摩擦时,由于PEO线团会阻止PVA凝胶的blob与摩擦基板表面的吸附,使其在低v时的f比在水中摩擦时低,且未出现明显f峰值点;高v时,f主要来源于溶剂润滑层流体的粘性流动,其f与在水中的f基本相同。摩擦行为的不同与在PVA凝胶和摩擦基板间形成的受限空间中的PEO线团的粘弹响应有关。在低滑动速率区域,PVA凝胶的f随浓度的增加而降低,亚浓溶液中（c＞c^*）的f明显小于稀溶液中（c＜c^*）的f。高速滑动区域,浓度影响较小。在亚浓溶液中,由于PEO分子链间的相互交叠甚至缠结,使得在较低的滑动速率下即可形成流体润滑层,f的变化与PEO亚浓溶液的剪切应力随剪切速率的变化相近。更多还原

【Abstract】 We get the physically cross-linked PVA hydro-gel by the freezing-thawing method, and study the effect of factors on the PVA hydro-gel friction,such as sliding velocity（v）, normal pressure（P）,surface free energy（γ）,concentration（c）of PEO aqueous solution and its molecular weight（M_w）,by PVA hydro-gel sliding on various substrates in pure water and PEO aqueous solution.We analyze the experimental results by using the attraction-repulsion model and the scaling theory.When PVA hydrogel slides on glass surface in water,which has a little attraction with the gel,the sliding velocity（v）shows great influence on frictional stress（f）.We find that at a certain velocity（v_f）the friction mechanism changes and the f-v curve shows the S-shape.In low sliding velocity region,the friction comes from the elastic force of the deformation of the adsorbed polymer chain,and f increases with the enhancement of v.In fast sliding velocity region,the friction mainly comes from the viscous flow of solvent layer.By changing the substrate,we get that the fin low sliding velocity region raise slightly with the increase of surface free energy（γ）,in which highγmeans strong interaction between PVA gel and the substrate.With the increasing of v, f raise remarkably with the enhancement ofγ.At the same time,the elastic-hydrodynamic transition velocity（v_f）move toward high sliding velocity region with the increase ofγ.fincreases with P due to its intensification on the adsorption of gel with the substrate.In slow sliding velocity region,the interaction between PVA gel and substrate shows little influence on the sensitivity of f to P.The v_f of the systems will increase with the increase of normal pressure.In PEO aqueous solution,the PVA hydro-gel would lose some water due to the osmotic pressure,which changes the physical property of the gel,such as modulus and volume.Also,the PEO molecules in the solution would prevent the adsorption of gel with the substrate,which makes f decreases comparing with that in pure water. Comparing the friction behavior in pure water with in PEO c aqueous solution,we find that f is almost reduced one order in PEO c^* aqueous solution when v is low,and we can’t see the obvious friction mechanism transition.In c＜c^* region,f decreases with the increase of the concentration of PEO aqueous solution in low sliding velocity.However, with the increase of sliding velocity,the effect of PEO on friction diminishes,and all the friction curves superpose with the friction curve in pure water at velocity higher than 10^-2m/s.In this case,the frictional behavior of PVA gel is also related to the viscoelastic response of the PEO coil in the confined space between PVA gel and substrates.In c＞c region,a PEO layer is easy to form even in the slow sliding region, in which the frictional behavior is determined by the viscoelastic properties of the semidilute PEO aqueous solution.更多还原