Friction humidity dependence

Humidity Dependence of Friction on Water-Soluble Semicrystalline Polymers... 

Figure 3. Humidity dependence of friction on crystalline and amorphous components of (a,c) PVOH and (b) gelatin films like those in Figures lb and 2b. In (c) the humidity-dependence offriction on amorphous PVOH is further contrasted at four...

Fig. 27—Friction and adhesion forces measured on AFM show different dependences on reiative humidity (from Ref. [23]).

The friction coefficient is expected to depend on the normal pressure which is quite high (of order hundreds of kilobars) surface roughness surface homogeneity and humidity (or other environmental factors). As a result, a is not known, so a quantitative model is not possible, but the expected qualitative behavior is clear. 

The stiffness of a fabric can be objectively determined as the average of the flexural rigidities (in warp and weft direction). These depend on the shear modulus and the coefficient of friction both are influenced by swelling and, therefore by humidity. 

The actual coefficient of friction of a molybdenum disulphide film will depend on the integrity of the film, contact pressure, temperature, humidity, film thickness and presence of contaminants. For a pure, smooth, dense, properly-oriented film at high contact pressure in a clean, dry atmosphere in unidirectional sliding, coefficients of friction as low as 0.02 have been reported. With impurities, poor orientation, humidity and low pressure, the coefficient of friction may be as high as 0.3. 

The increased risk of hand eczema seems to depend on multiple factors. Exposure to common irritating factors, wet work, detergents, chemicals, dirt and mechanical friction are the most common causes for the development of hand eczema at work. Exposure to airborne allergens or irritants can also lead to dermatitis. In addition, working at jobs in which there are changes in temperature and humidity or working in ways that lead to extensive sweating increase risk of dermatitis. 

Metal workers are exposed to numerous exogenous factors that play a substantial role in tbe development of allergic as well as irritant contact dermatitis (ICD). Even though nickel is regarded as the most frequent source of all reported metal allergies [i], metal-work fluids (MWFs) are the most important cause of irritant hand dermatitis. Other factors such as metal dust, friction, pressure, heat and humidity also contribute to the irritation of the skin [2]. However, the metal industry is a wide fleld, and exposure may vary widely depending on the kind of job and the type of metal industry. 

The proportionality factor/is called the friction coefficient. Its value depends on mechanical parameters and the presence or not of a lubricant on chemical parameters such as humidity, oxide films, chemical additives and on materials parameters such as hardness, ductility and microstructure. 

Frictional forces and coefficients of Diction depend to a considerable extent on relative humidity, or in extreme cases on the presence of water. We are distinguishing between three conditions for frictional measurements ambient (65% RH), wet-with-water (www, the fiber is taken directly from the bath to the friction measurement), and wet-in-water (wiw, friction measurement in a liquid bath). There is also a significant effect of the nature of the capstan material. Hard rubber produces a higher coeffieient of frietion than aluminium, an effect that is more pronounced in the wet state (41). Similarly, the surface of the hair, especially its hydrophilicily, affects its frictional behavior. Bleaehing and permanent-waving treatments increase frictional forces (40). In both eases, seission of disulfide bonds in the outer layer of the cuticle leads to a softening of the surface, resulting in an increase in the area of real contact. 

We have stndied the macroscopic frictional properties of high-density polymer brushes prepared by surface-initialed ATRP of methyl methacrylate (MM A) [31] and hydrophilic methacrylates [32, 33] from silicon substrates. Friction tests were carried out using a stainless steel or glass ball as the sliding probe under a normal load of 100 MPa from the viewpoint of practical engineering applications. This chapter reviews the macroscopic frictional properties of polymer brushes under a high normal load, the dependence of solvent qnaUty, the effect of humidity on hydrophilic brnsh, and wear resistance, and we compare these with alkylsilane monolayers. 

A hand-held device called a triboelectric pen is commercially available from Wolfson Electrostatics. This operates on the phenomenon of the frictional electrical charge that develops when the plastic material is rubbed. Each pen is designed to distinguish selected pairs of polymers e.g. PP and ABS. The particular advantage here is the simplicity and portability of the method. It is claimed to have success rates of 90-98% depending on the relative humidity [10]. 

We present a quantitative study of frictional properties of pure self-assembled monolayers (SAMs) of alkanethiols as a function of chain length and mixed SAMs of dodecanethiol and 11-mercapto-l-undecanol as a function of surface composition on Au (111) using atomic force/friction force microscopy (AFM/FFM). The lateral and normal forces were calibrated in situ using a combined two-slope and added-mass method. Molecular dynamics simulations were also carried out to interpret the chain length dependence of frictional properties of alkanethiols. We then extended the in situ force calibration method to the mixed SAMs and investigated the effects of chemical nature and relative humidity on the frictional properties. Friction coefficients were plotted as a function of surface composition with different relative humidity. Such a plot could serve as a reference in determining surface composition in a nanoscale domain by measuring its friction coefficient. 

Figure 4. Scan velocity dependence of friction at discrete humidities on amorphous...

Sensitivity to friction is highly dependent on the method of measurement. The most important factors influencing the final results include the material of the plate surface and the peg, speed of the peg sliding, and humidity. These factors are very difficult if not impossible to compare making results of various authors hardly ever directly comparable. 

The wear and degradation of DLC overcoats on a hard disk is a complex process, dependent not only on the head-to-disk material interface but also the environment in which the disk drive operates. Heat and humidity play an important role. Marchon et al. [19,20] have shown that friction and wear rates of amorphous carbon films are dependent on the at-... 

Static electricity (cleaning) The electric charge that is built up on an insulator surface, typically by friction and the charge separation associated with the friction. The amount of charge buildup depends on the conductivity of the surfaces and the humidity. Static charge buildup can be a problem with blow-drying insulating surfaces with un-ionized air. 

Polymeric materials exhibit a great deal of sensitivity to the environmental conditions (tanperature, humidity, gases, liquids, etc.). Not only are friction and wear sensitive to the operating environment, they are often more sensitive than bulk properties. Temperature affects friction of polymers in the same way as the complex modulus and other mechanical properties. Studies of both nylon and elastomers have shown that the coefficient of friction will transform in the same manner as storage and loss modulus. The coefficient of friction dependence of nylon on temperature is shown in... 

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