Surface Morphology And Friction Properties Of Polymer Elastomer

Polymer friction materials are widely used in high-end manufacturing,electronic information,transportation,building energy conservation,aerospace,national defense and other fields due to their excellent properties such as light weight,high strength,temperature resistance,corrosion resistance.At present,with the expansion of the application field of polymer friction materials,higher and higher requirements have been put forward for the varieties and properties of polymer friction materials.Up to now,polymer friction materials have been paid much attention to at home and abroad.Friction is a very common phenomenon in daily life and industry,which is controlled by the processes occurring on the thin surfaces layers of objects in moving contact.And tribology is a science and technology that studies the relative motion of interacting surfaces,and therefore covers friction,wear and lubrication,a big topic and of great importance to all of us.In the dissertation,mainly in order to achieve high-efficiency lubrication and low friction and wear of polymer elastomer as the goal,through the regulation of the surface morphology of polymer friction pair materials,the investigation of polymer chain behavior in lubricants,and the study of the friction characteristics of the whole friction system,the reasons for the decrease of friction coefficient in the tribology system are obtained,and the theoretical mechanism is deduced,which can provide very effective guidance for the application of polymer materials in various fields.These results would provide new strategies for the development of polymer materials in the field of tribology.The main research contents and conclusions of this dissertation can be divided into the following aspects:Firstly,here a model incompatible blend system,PS/PMMA is employed to elucidate troublesome heterogeneous morphology formation.Thus,coupling of the two processes with features in different scales leads to a hierarchical topography that includes the Voronoi cellular division as the primary structure and the intracellular nonlinear distribution as the secondary structure.In-situ observation shows that the morphology changed from homogeneous deposition with scale less than 10 microns to self-organized cellular pattern with scale of more than 100 microns after the fluid flow is involved.The cellular morphology is attributed to the flow-field guided deposition of sequentially generated precipitates.The coupling of phase separation and fluid convection results in the hierarchical morphology.Isolated modulation of either micro or meso-scale in the hierarchical morphology could be carried out via adjusting phase interaction or the convection disturbance correspondingly.The tribological properties of the films with corresponding surface morphologies under different blending ratios were also characterized.Secondly,we established a friction system composed of stainless steel ball and styrene-ethylene-butylene-styrene block copolymer(SEBS),an elastomer that adsorbs poly(vinyl alcohol)molecules onto its surface to form an interfacial layer for friction.Poly(vinyl alcohol)(PVA)aqueous solution,as commonly seen in our daily life playing a role to artificial tears,is a type of lubricant.It is for the first time found that degree of hydrolysis(DH)of PVA plays a critical role in determining the coefficient of friction(COF)during the friction.Upon employing fully hydrolyzed PVA aqueous solution as lubricant,the friction coefficient is at least one order of magnitude higher than that at partially hydrolytic PVA.It is proposed that such excellent lubrication effect is attributed to rapid adsorption of PVA chains to the SEBS substrate,forming a stable and perfect surface layer containing abundant water molecules upon movement of the friction pair,which has the function of bearing and reducing friction.At last,tribological behaviors related to the nanometer-scale architectures of styrene-ethylene-butylene-styrene triblock copolymer(SEBS)films were studied.In this chapter,the influence of surface morphology and the elastoplastic transformation of SEBS film on lubrication property is discussed emphatically.It is found that in the friction system composed of stainless steel ball on SEBSs film,the friction coefficient is affected by the hardness and modulus of SEBS elastomer under the condition of deionized water lubrication,while under the lubrication conditions of polyvinyl alcohol aqueous solution,the change of friction coefficient was determined by the microscopic surface parameter of the SEBS substrate.That is to say,the occurrence of this friction phenomenon is dominated by the micro-nano topography and has no direct relation with the macroscopic surface roughness.The microstructure of SEBS samples plays a decisive role in the friction performance.The reversal of the friction properties under the two lubrication conditions is mainly attributed to the micro-phase separation caused by the difference of the composition ratio of the soft and hard segments on the surface of the SEBS substrate,which determines the physicochemical property distribution of the SEBS surface and the mechanical properties of the friction pair materials.