The friction and lubrication of polymers

1966 ◽  
Vol 291 (1425) ◽  
pp. 186-207 ◽  
Keyword(s):  
Water Film ◽  
Deformation Mode ◽  
Surface Films ◽  
Surface Layers ◽  
Adsorbed Films ◽  
Lubricating Layer ◽  
Local Pressures ◽  
Elastic And Plastic Deformation ◽  
Work Supports ◽  
Polar Polymer

This paper describes a study of the friction of a typical polar polymer, nylon, and a typical non-polar polymer, polyethylene. The friction of unlubricated surfaces varies with load and geometry in a manner that can be explained in terms of the multi-asperity model of Howell & Lodge (1954), modified to allow for a deformation mode that is intermediate between elastic and plastic deformation. Nylon is markedly plasticized by water and its effect as it diffuses into the bulk of the polymer has been studied using hardness measurements. Initially the water produces a softening restricted to the surface layers and this leads to a modest reduction in friction. After a protracted period the bulk softening of the polymer causes an increase in the area of contact (cf. Rubenstein 1961) and the friction again rises. If one of the surfaces is a hydrophilic substance such as glass a more marked reduction in friction occurs when water is introduced to the surface. There is strong evidence that this due to the formation of a weakly held water film, a few molecules thick, attached to the hydrophilic surface. The film survives because the local pressures are not too severe. For this reason water provides effective lubrication for glass sliding on polyethylene or rubber but not for glass on glass where the contact pressures are much higher. Long chain acids produce negligible plasticization of the polymers but lubricate by forming adsorbed surface films. They are not as effective on polymers as on metals and this work supports the view of Fox & Zisman (1952) that this is because the films are not fully condensed. Polyethylene surfaces are lubricated by surface films of oleamide or stearamide. These materials may also be incorporated, in small quantities, within the bulk of the polymer and can diffuse to the surface to provide an effective lubricating layer. Non-polar liquids and some silicones produce a small reduction in the friction of polymers; the effect is more marked if one of the surfaces is of glass (or metal). It is suggested that these liquids form weakly adsorbed films which survive the relatively gentle stresses at the contact regions and so reduce the amount of polymer-polymer or polymer-glass interaction.

Amorphous Solids, Small Particles and Thin Surface Films

1957 ◽  
Vol 1 ◽  
pp. 73-99 ◽  
Author(s):  
F. Schossberger
Keyword(s):  
Electroless Nickel ◽  
Surface Films ◽  
Fibrous Materials ◽  
X Ray Diffraction ◽  
Surface Layers ◽  
X Ray ◽  
Cold Rolled ◽  
Combination Of Methods ◽  
Diffraction Effects ◽  
The Relationship

AbstractA comprehensive chart is preserit of the X-ray diffraction effects of gas-and Uquid-like armorphous substances, small particle-size materials, mixtures of amorphous and crystalline compounds, sheetlike crystals, and fibrous materials.The relationship between the X-ray diagrams and chemical preparations as shown by typical examples from the field of the manufacture of active catalysts cadmium sulfide semiconductors, pour point-depressed lubricants, electroless nickel platings and metal-filled cellulose fibers.The investigation of thin surface layers formed by chemical reactions required the combination of electron and X-ray diffraction techniques. The usefulness of this combination of methods is demonstrated by a study of black stain formation on cold rolled annealed steel. By identifying the materials in the stain and determining the sequence in which they formed a reaction mechanism between steel surface and annealing-gas can be postulated.

scholarly journals Transferable Gaussian Attractive Potentials for Organic/oxide Interfaces

2021 ◽  
Author(s):  
Jérôme Rey ◽  
Sarah Blanck ◽  
Paul Clabaut ◽  
Sophie Loehlé ◽  
Stephan Steinmann ◽  
...  
Keyword(s):  
Electrostatic Interactions ◽  
Organic Molecules ◽  
Surface Films ◽  
Oxide Interfaces ◽  
Gaussian Potential ◽  
Adsorbed Films ◽  
Head Groups ◽  
Strong Structuration ◽  
The Common ◽  
Dynamics Simulations

Organic/oxide interfaces play an important role in many areas of chemistry, and in particular for lubrication and corrosion. Molecular dynamics simulations are the method of choice for providing complementary insight to experiments. However, the force fields used to simulate the interaction between molecules and oxide surfaces tend to capture only weak physisorption interactions, discarding the stabilizing Lewis acid/base interactions. We here propose an improvement of the usual molecular mechanics description (based on Lennard-Jones and electrostatic interactions) by addition of an attractive Gaussian potential between reactive sites of the surface and heteroatoms of adsorbed organic molecules, leading to the GLJ potential. The interactions of four oxygenated and four amine molecules with the typical and widespread hematite and γ-alumina surfaces are investigated. The total RMSD for all probed molecules decreases from 29.2 to 5.7 kcal/mol, and the corresponding percentage from 107.4 to 22.6% over hematite, while on γ-alumina the RMSD decreases from 21.5 to 7.6 kcal/mol, despite using a single parameter for all five chemically inequivalent surface aluminum atoms. Applying GLJ to the simulation of n-octadecanamine and N-tetradecyldiethanolamine adsorbed films on hematite and alumina respectively demonstrates that mobility of the surfactants is overestimated by the common LJ potential, while GLJ shows a strong structuration and slow dynamics of the surface films, as could be expected from the first-principles adsorption energies for model head-groups.

The Effect of Surface Layers on Thin Foil Standards on the Accuracy of Quantitative E.D.S. Analysis

1982 ◽  
Vol 40 ◽  
pp. 484-485
Author(s):  
J.M. Brown ◽  
H.L. Fraser
Keyword(s):  
Data Analysis ◽  
Thin Foil ◽  
Surface Films ◽  
Surface Layers ◽  
X Ray ◽  
Thin Foils ◽  
Accurate Quantification ◽  
Effect Of Surface

Quantitative X-ray microanalysis of thin foils may be achieved either by calculation or by making use of standards. This paper, although advocating the use of pure elemental standards for accurate quantification, points out some of the problems involved in the choice of good standards. Specifically, the presence of surface films on as-prepared thin foil standards must be removed or accounted for during data analysis.

Paper 16: Solid Friction and Boundary Lubrication

1967 ◽  
Vol 182 (1) ◽  
pp. 262-280 ◽  
Author(s):  
D. Tabor
Keyword(s):  
Recent Work ◽  
Boundary Lubrication ◽  
High Vacuum ◽  
Strength Properties ◽  
Surface Films ◽  
Surface Cracking ◽  
Brittle Solids ◽  
Solid Friction ◽  
Boundary Films ◽  
Work Supports

During the last decade considerable progress has been made in our understanding of the contact between solid surfaces. Earlier work emphasized the plastic deformation and more recent work the elastic deformation of the surface asperities. However, when sliding occurs combined normal and tangential stresses in the contact zone greatly enhance the plastic régime. Broadly speaking, recent work supports the earlier view that friction is attributable to adhesion at the points of real contact and to the ploughing or tearing of one surface by asperities on the other. In high vacuum the surface films normally present can be removed either by heating or by repeated rubbing. As a result the adhesion, friction and wear can rise to very high values. However, even under very clean conditions some metallic pairs appear to show relatively weak adhesion. With non-metals similar processes occur but with brittle solids they are complicated by surface and sub-surface cracking. Here crystal orientation can be very important. With polymeric solids, where strength properties are rate and temperature dependent, marked variations in friction with speed and temperature are often observed. The more rigid the polymer the smaller the effect. In the field as a whole little work has been carried out on the interaction between the adhesion and the ploughing mechanisms. In the field of lubrication it is now apparent that a considerable amount of what was formerly termed boundary lubrication was probably elastohydrodynamic. However, recent studies show that elastohydrodynamic films can operate under more severe conditions if small quantities of surfactants are added. These do not affect the viscous properties of the lubricant but form protective surface films of molecular dimensions. During the last decade little work has been carried out on the formation, structure and strength properties of these boundary films. It remains an area of great importance.

Friction of clean metals and the influence of adsorbed films

1951 ◽  
Vol 208 (1094) ◽  
pp. 311-325 ◽  
Keyword(s):  
Room Temperature ◽  
Physical Adsorption ◽  
Surface Films ◽  
Metallic Contact ◽  
Adsorbed Films ◽  
Real Area Of Contact ◽  
Molecular Layers ◽  
Very High ◽  
Frictional Behaviour ◽  
Real Area

An experimental Study has been made of the frictional behaviour of thoroughly degassed metal surfaces. An apparatus is described, in which friction can be measured at any desired temperature up to 1200° C or more, either in vacuo or in a particular gas. It is found that when sufficiently clean metals are allowed to touch, even at room temperature, complete seizure occurs. Over the real area of contact the specimens adhere with the bulk strength of the metal, and this area increases greatly with continued sliding or attempted sliding. Various gases and vapours have been adsorbed on to the clean specimens, and their in­fluences on friction determined. These specific contaminants are most effective as lubricants where they can react with the metal to form a solid and chemically attached film which is several molecular layers in thickness. Otherwise the friction remains very high, although seizure is prevented. It is shown that physical adsorption may occur in addition, with a significant reduction in the friction. The results support the view that the friction of metals is due mainly to adhesion at the points of real contact, and is governed by the extent to which even the thinnest of surface films can reduce this metallic contact.

The formation of surface films at the transition between mild and severe metallic wear

1963 ◽  
Vol 273 (1355) ◽  
pp. 466-483 ◽  
Keyword(s):  
Surface Film ◽  
Surface Films ◽  
Surface Layers ◽  
Severe Wear ◽  
Wear Process ◽  
High Speeds ◽  
Mild Wear ◽  
Oxide Particles ◽  
Heavy Loads ◽  
Micro Analysis

The conditions of sliding have been found in which a transition occurs between the régimes of mild and severe wear for a leaded brass (60/40 brass containing 2% lead) sliding on hardened steel without lubrication. At light loads, low speeds, and low temperatures, mild wear begins when sufficient time is available to establish a protective surface film by oxidation; in addition, mild wear also occurs at heavy loads, high speeds and high temperatures because of an increase in the rate of oxidation. The topography and composition of the films generated on the brass during mild wear have been examined by reflexion electron microscopy and X-ray micro-analysis. The presence of a relatively large proportion of iron oxide in the surface layers, originating from the steel, increases their hardness and, in turn, causes wear of the steel itself. The variation of the rates of mild wear with load and speed is complex and, in contrast to the severe wear process, there is no unique mechanism of wear. It is concluded that mild wear of brass results from the combined effects of intermittent metal-to-metal contact, abrasion by oxide particles, and flaking of the oxide layers from the surface.

scholarly journals On the structure and chemical activity of copper films, and the colour changes accompanying their oxidation

1922 ◽  
Vol 102 (716) ◽  
pp. 318-328 ◽  
Keyword(s):  
Surface Film ◽  
Complex Structure ◽  
Wave Length ◽  
Chemical Activity ◽  
Coarse Grained ◽  
Surface Films ◽  
Copper Films ◽  
Surface Layers ◽  
Fine Grained ◽  
Colour Changes

When the surface of a metal is exposed to the action of a gas with which it reacts chemically, brilliant colour phenomena are frequently produced. In some cases the colours are recognised as diffraction colours, produced by the scattering of light in the surface film, and not as simple interference effects. When this is found the film must have a more or less complex structure, fine grained compared with the wave-length of light, but of a coarse-grained granular nature compared with molecular magnitudes. The work of Beilby has drawn attention from other points of view to the complex structure which the surface layers of metals, or thin films of metals, may assume. It seems to be of considerable importance to correlate the chemical activity of such surface films with their structure, in view of the bearing this correlation may have on the problems of heterogeneous catalysis.

Part II. Friction of non-metals - Friction of diamond, graphite and carbon: the influence of adsorbed films

1952 ◽  
Vol 212 (1111) ◽  
pp. 485-488 ◽  
Keyword(s):  
Experimental Study ◽  
Plastic Deformation ◽  
Shear Strength ◽  
Large Scale ◽  
Physical Adsorption ◽  
Surface Films ◽  
Diamond Surfaces ◽  
Adsorbed Films ◽  
Carbon And Graphite ◽  
Frictional Behaviour

An experimental study has been made of the frictional behaviour of diamond, graphite and carbon which have been outgassed in vacuo . With carbon and graphite the friction rises to a high value when the surface films normally present are removed by outgassing. A small pressure of oxygen or water vapour restores the friction to its normal value. These results may be compared with Savage’s observations on the wear of graphite. This change is reversible on pumping out without heating, suggesting that a major factor is the physical adsorption of surface films. The friction of diamond surfaces in air is low, but on removing the surface films in vacuo it rises to a high value and the shear strength of the junction is comparable with the bulk strength of diamond. Large-scale seizure does not occur as with outgassed metals, since the deformation in the region of contact is elastic and the area of contact remains small. If the diamond slides on a metal such as platinum so that plastic deformation is possible, the area of contact becomes large and the friction is correspondingly increased.

scholarly journals 2-CHLORO-4-NITROANILINE ADSORPTION ON ACTIVE CARBON FROM 2-PROPANOL SOLUTIONS

2019 ◽  
Vol 62 (10) ◽  
pp. 84-88
Author(s):  
Nikolai Y. Sharonov ◽  
Anastasia A. Fedorova
Keyword(s):  
Adsorption Isotherms ◽  
Active Carbon ◽  
Heterogeneous Catalysts ◽  
Nitro Compounds ◽  
Pharmaceutical Products ◽  
Surface Films ◽  
Two Dimensional ◽  
Surface Layers ◽  
State Diagrams ◽  
Aromatic Nitro

Aromatic nitro compounds, such as nitro anilines and its halogen derivatives, are widely used in the industrial synthesis of dispersed azo dyes and some pharmaceutical products. For its preparation the processes of heterogeneous catalysis in various liquid media are used. One of the most important stages of catalysis, which in some cases determines its rate, is adsorption. The study of the nitro compounds adsorption from aqueous and non-aqueous solvents on the heterogeneous catalysts surface makes it possible to reveal the catalytic hydrogenation intimate mechanism features and the solvent influence on the hydrogenation process. In this work, we studied the 2-chloro-4-nitroaniline adsorption on active carbon from 2-propanol solutions at 293 and 313 K. Adsorption isotherms, two-dimensional state diagrams of the surface layers were obtained, and the isosteric heats of the process were calculated. The experimental adsorption isotherms are described in the framework of the volume filling of micropores for mesoporous adsorbents theory. The heat of adsorption is negative and decreases in absolute value with increasing degree of surface filling. On two-dimensional surface layers state diagrams the breaks presence, which corresponds to two-dimensional phase transitions, similar to second-order transitions in surface films. This fact indicates changes in the surface layers state with an increase in the degree of filling the coal surface with adsorbate, is observed.

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