Lubrication, polymer adsorption

Fig. 13 Velocity dependence of frictional stress for a soft gel sliding on a smooth adhesive solid substrate. The result is based on the molecular picture in Fig. 12, which considers the thermal fluctuation of adsorption and desorption of the polymer chain, (a) The elastic term of the frictional stress of a gel. See text for a description of parameter u. (b) Summation of the elastic term and the viscous term. When v -C Vf, the characteristic polymer adsorption velocity, the elastic term is dominant. At v 2> the viscose term is dominant. Therefore, transition from elastic friction to lubrication occurs at the sliding velocity characterized by the polymer chain dynamics. (Modified from figure 1 in [65])...

Chapter 1.15 by Marcus Muller describes the important problem of polymers at interfaces and in confined geometry. This topic is connected with polymer adsorption and wetting properties, as well as with the possibilities of controlling lubrication and wear. 

FIGURE 11.9 Schematic curve for the friction of a gel that is adhesive to the substrate in liquid. The friction is the sum of elastic force due to polymer adsorption and viscous force due to hydration of the polymer. At v Vf, the first component is dominant. At v Vf, the second component is dominant. Transition from elastic friction to lubrication occurs at the sliding velocity characterized by the polymer chain dynamics Vf = = T/ri/Jp. (Reprodnced from... 

Polymers at particle surfaces play an important role in a range of technologies such as paints, polishing, filtration, separations, enhanced oil recovery, and lubrication. In order to optimize these technologies, it is important to imderstand and control the adsorption, conformation, and role of surface molecular architecture in selective polymer adsorption. 

In summary, for metal surfaces in boundary lubrication, complex tribochemical reactions occur along with the physical/chemical adsorptions, which lead to the formation of surface hlms, consisting of reaction products, oxide layer, the mixture of particles and organometallic polymer, and perhaps a viscous layer. The surface hlms operate as a sacri-... 

Also carbon black markedly reduced melt processability (Table IX), particularly when fine particle size was used in soft ABS. This might be caused by the bonding between carbon black surfaces and polymer molecules or by the adsorption of low molecular weight lubricants on the carbon black surface. This suggests that coarse carbon black, especially low structure grades, should be used for the least loss of processability. 

The decrease in expansion seems to occur at moisture levels above 30°/o moisture for both cereal (starch-based) polymer systems, and protein (soy grits). This corresponds to a point on their adsorption curves where water activity rises rapidly with added moisture that is, at a level where the water added to a mix has little effect on primary hydration of polymers, but behaves as a diluent. In mechanical terms, this may be explained by proposing that at above levels of 25°/o-30% water plasticisation of the polymers is complete, and further added water acts as a lubricant, reducing the shear-induced temperature rise and particle damage necessary for the formation of homogeneous melts. 

Moisture is also an important factor that can affect the stability of candidate drugs and their formulations. Sorption of water molecules onto a candidate drug (or excipient) can often induce hydrolysis (see, e.g., Yoshioka and Cartensen 1990). In this situation, by sorbing onto the drug-excipient mixture, the water molecules may ionize either or both of them and induce a reaction. For example, we have found that a primary amine, when mixed with lactose, was apparently stable even when stored at 90°C for 12 weeks. However, when the experiment was carried out in the presence of moisture, extensive degradation by way of the well-known Mailliard reaction took place. Other properties such as crystal structure, powder flow, compaction, lubricity, dissolution rate and polymer film permeability may also be affected by moisture adsorption (Ahlneck and Zografi 1990). 

Corrosion inhibitors are substances whose introduction in small amounts into a corrosion system (aggressive medium, polymer coating, lubricating or packing material, etc.) produces noticeable corrosion abatement in metals. Cl are subdivided into adsorption and passivating Cl by their action mechanism. The former protect metals by affecting the kinetics of the electrode corrosion processes. The latter promote the formation of an oxide or other films on a metal product to transfer the metal into the passive state. 

Adsorption of polymers on a solid flat substrate is an important physical chemistry issue in many applications of polymers, such as composites, coatings, adhesion, lubricates, gel chromatography, wetting, colloidal stability, piping transportation. 

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