Friction polymer adsorption

The molecular meaning of b is best seen from the second or third equality of Eq. (3). In other words, b is explicitly related to the steady shear melt viscosity q and depends on the chain-chain interactions near the melt/wall interface as quantified by the friction coefficient p. In the limit of no polymer adsorption or in absence of interfacial chain entanglements due to the coil-stretch transition, P involves an interfacial viscosity q , which is as small as the viscosity of a monomeric liquid and independent of the molecular weight Mw p=qj/a, where a is a molecular length. Thus at the stick-slip transition, the molecular weight dependence of b arises entirely from q in Eq. (3). 

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])...

YanX, Perry SS, Spencer ND, Pasche S, De Paul SM, Textor M, et al. Reduction of friction at oxide interfaces upon polymer adsorption from aqueous solutions. Langmuir 2004 20 423-8. 

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... 

However, to date, almost all of the artificial organs (artificial hearts, blood vessels, hips and knees, etc.) have been constructed from hard and dry materials. These artificial organs, to some extent, have successfully served as substitutes for real organs, but are still far from satisfactory. For example, artificial hips and knees made of metals and ceramics, which are hard and dry materials, lack the shockabsorbing function and have a high frictional resistance against sliding motion [3]. Another example is artificial blood vessels. Blood blots occur in artificial blood vessels made of polymers due to protein adsorption at the surface of the blood vessel wall [4]. 

Using this C picture, the elastic force produced by the stretching of a single chain is /ei — FvTb/, the total number of chains per unit area is wo = and among these chains, only a fraction Tb/( tb + ff) are in an adsorbing state. The frictional stress due to the adsorption of polymer chains is given as [48, 65] ... 

On strongly adhesive substrates (Fig. 14b, c), friction increases with the substrate hydrophobicity in the low-velocity region, showing a weak velocity-strengthening, and a dramatic friction transition at around v = 10 m/s. This value is one order lower than the characteristic velocity of the polymer chain Vf = /Tf. The friction behavior is satisfactorily described by the repulsion-adsorption model below the transition region The friction transition is explained in terms of the elastic... 

This extends the previous work (I ) In which the Lennard-Jones type surface potential function and the frictional function representing the Interfaclal forces working on the solute molecule from the membrane pore wall were combined with solute and solvent transport through a pore to calculate data on membrane performance such as those on solute separation and the ratio of product rate to pure water permeation rate in reverse osmosis. In the previous work (1 ) parameters Involved in the Lennard-Jones type and frictional functions were determined by a trial and error method so that the solutions in terms of solute separation and (product rate/pure water permeation rate) ratio fit the experimental data. In this paper the potential function is generated by using the experimental high performance liquid chromatography (HPLC) data in which the retention time represents the adsorption and desorption equilibrium of the solute at the solvent-polymer interface. 

Numata K, Sato S, Fujita M, Tsuge T, Iwata T, Doi Y (2007) Adsorption effects of poly(hydroxybutyric add) depolymerase on chain-folding surface of polyester single crystals revealed by mutant enzyme and frictional force microscopy. Polym Degrad Stab 92 176-183 Ohura T, Kasuya K, Doi Y (1999) Cloning and characterization of the polyhydroxybutyrate depolymerase gene of Pseudomonas stutzeri and analysis of the function of substrate-binding domains. Appl Environ Microbiol 65 189-197... 

The essential point is that such an adsorption process markedly influences the hydrodynamic and electrical properties of the interface. Figure 3.16 is a schematic representation of the structure formed polymer chains with fixed charges extend out of the solid surface to an average distance d = b — a in this region, the fluid can move, although with an increased viscosity because of the hydrodynamic resistance of the polyelectrolyte layer (also called hydrogel layer). To take this into account, a friction term — yv is included in the Navier-Stokes equation. 

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