Surface properties lubricity

Plasma processing technologies ate used for surface treatments and coatings for plastics, elastomers, glasses, metals, ceramics, etc. Such treatments provide better wear characteristics, thermal stability, color, controlled electrical properties, lubricity, abrasion resistance, barrier properties, adhesion promotion, wettability, blood compatibility, and controlled light transmissivity. 

The recovery of petroleum from sandstone and the release of kerogen from oil shale and tar sands both depend strongly on the microstmcture and surface properties of these porous media. The interfacial properties of complex liquid agents—mixtures of polymers and surfactants—are critical to viscosity control in tertiary oil recovery and to the comminution of minerals and coal. The corrosion and wear of mechanical parts are influenced by the composition and stmcture of metal surfaces, as well as by the interaction of lubricants with these surfaces. Microstmcture and surface properties are vitally important to both the performance of electrodes in electrochemical processes and the effectiveness of catalysts. Advances in synthetic chemistry are opening the door to the design of zeolites and layered compounds with tightly specified properties to provide the desired catalytic activity and separation selectivity. 

An atom or molecule that approaches the surface of a solid always experiences a net attractive potential ). As a result there is a finite probability that it is trapped on the surface and the phenomenon that we call adsorption occurs. Under the usual environmental conditions (about one atmosphere and 300 K and in the presence of oxygen, nitrogen, water vapor and assorted hydrocarbons) all solid surfaces are covered with a monolayer of adsorbate and the build-up of multiple adsorbate layers is often detectable. The constant presence of the adsorbate layer influences all the chemical, mechanical and electronic surface properties. Adhesion, lubrication, the onset of chemical corrosion or photoconductivity are just a few of the many macroscopic surface processes that are controlled by the various properties of a monolayer of adsorbates. 

Early in the history of polytetrafluoroethylene, W. A. Zisman recognized its unusual surface properties, and the polymer now finds many uses because its low coefficient of friction eliminates the need for lubrication (Fitzsimmons and Zisman). Shooter and Thomas called attention to the remarkable resistance of polytetrafluoroethylene to seizure, and Bowden (1950) described use of composite structures. These and other investigations have been reviewed and summarized by Allan (1958) (also Allan and Chapman), who showed that the dependence of the coefficient of kinetic friction, fk, on the load in grams, W, is given by the following equation ... 

Abstract Polyolefins such as polyethylene, polypropylene and their copolymers have excellent bulk physical/chemical properties, are inexpensive and easy to process. Yet they have not gained considerable importance as speciality materials due to their inert surface. Polyethylene in particular holds a unique status due to its excellent manufacturer- and user-friendly properties. Thus, special surface properties, which polyethylene does not possess, such as printability, hydrophilicity, roughness, lubricity, selective permeability and adhesion of micro-organisms, underscore the need for tailoring the surface of this valuable commodity polymer. The present article reviews some of the existing and emerging techniques of surface modification and characterisation of polyethylene. 

Groszek, A.J. and Witheridge, R.E., Surface Properties and Lubricating Action of Graphite and M0S2, ASLE Trans., 14, 254, (1971). 

The performance of a soil-release finish depends upon its ability to provide a hydrophilic surface during the laundering process. Therefore any material deposited on the fibre surface that would reduce this necessary hydrophilicity should be avoided. Softeners, lubricants and other products that modify surface properties should be carefully investigated in laboratory trials before being used with fabrics treated with soil-release finishes. 

A useful side effect of the radiation and especially the plasma treatments is the cleaning of the fibre surface. Fibre lubricants, sizing agents, soil and other residuals are burned off This provides, combined with the creation of reactive radicals on the fibre surface, better wetting properties and a higher adhesion of coatings and laminations. Anti-felting finishes for wool are also achievable with plasma treatments. 

Milling can affect the adsorption of actives on the carrier surface by altering the surface properties of excipients. It was noticed that milled actives frequently failed blend uniformity criteria, but unmilled active batches consistently met the blend uniformity criteria. By adding lubricant magnesium stearate, the blending content uniformity of the milled batches can be significantly improved. A small amount of amorphous materials could affect the blending characteristics of a direct compression formulation. ... 

The atomic and molecular structure of tribological surfaces and lubricants under shear plays a crucial role in tribology. Unfortunately, techniques to probe nanostructure spectroscopically or optically simultaneously with tribological probing are limited. This limits the ability to draw conclusive structure-property relations for all but the most idealized macroscopic surfaces, such as those described here. 

Polyorganoslloxanes are probably the most widely used and studied class of "seml-lnorganlc polymers. There are a variety of Interesting and useful properties exhibited by these materials that make them worthy of study. For example, they exhibit high lubricity, low glass transition temperatures, good thermal stability, high gas permeability, unique surface properties, and low toxicity (1 ). 

As stated in Chapter 1, the chemical structure of the top surface layers of a solid determines its surface properties. If these top layers consist of the same chemical groups, then the surface is called chemically homogeneous, and if they consist of different chemical groups it is called chemically heterogeneous. The presence of two or more chemically different solid substances in a surface layer enormously multiplies the possibilities for variety in the types of surface, such as copolymer surfaces and catalysts having many different atoms at the surface. The chemical heterogeneity of a surface is an important property in industry affecting catalysis, adhesion, adsorption, wettability, biocompatibility, printability and lubrication behavior of a surface, and it must be determined analytically when required. 

Unique surface properties further distinguish silicones from other materials. The low surface tension of sihcone fluids makes them ideal for apphcations such as paper release agents, fiber lubricants, textile hand modifiers, mold release agents, antifouling materials, and water repellents. In fact, sihcones have been used in foam control and as anticaking aids, corrosion inhibitors, emulsifiers, lubricants, conditioners, and gloss enhancers—all because of their special surface properties, see also Polymers, Synthetic. 

A drilling mud must be able to suspend the cuttings, carry them to the surface, and lubricate the drill bit. The pseudoplasticity and yield point of PS-7 giam provide these properties. Also the compatibility with high levels of salt allow drilling muds to be prepared using brines or seawater. 

Finally, shear viscosity is strongly affected by the clay in the blends, especially at high PEN contents. A lubricating effect rather than a filler effect reveals the possibility that the clay is not well dispersed in the polymer blend, and migration of particles in the flow to the wall region can explain the observed reduction in shear viscosity. When MMT clay is mixed with crystallizable polymers such as polyesters, some processing problems arise because the crystallization process is modifled by nucleation effects induced by the nanoparticles. Moreover, these particles also influence the kinetics of transesteriflcation between PET and PEN, besides other factors such as the reaction time and extruder processing temperature. In Reference 72, a quaternary alkyl ammonium compound (Cl8) and MAH were used to modify the surface properties of the clay... 

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