Surface mobility and slip of polybutadiene melts in shear flow

Molecular interpretation of the “stick–slip” defect of linear polymers

“…This assumption is confirmed by the data of Mhetar and Archer [31], obtained in simple shear between glass parallel plates: the average value of C ad is then 0.53, smaller than the one obtained with the data of Vinogradov et al [13] carried out with steel surfaces. This shows that the adsorption of the molecules on the wall depends on the nature of die material, which is generally admitted and has been well shown by the work of Wise et al [44].…”

“…Fig. 7 shows the variation of the experimental critical shear rate as function of molecular weight M w for the data of Vinogradov et al [13], Yang et al [10] and Wise et al [44]. These data can be fitted by a power law, showing that the critical shear rate is proportional to M −3.7 w .…”

Wall Slip Phenomena in Oil-in-Water Emulsions: Effect of Some Structural Parameters

“…and [6] are the areas under the flow curves obtained with rough and smooth surfaces, respectively, and consequently, S rel , is the relative difference between both flow curves. In such way, S rel gives zero for the nonslip condition and one for the hypothetical case of plug flow.…”

“…As Wise et al (6) have summarized, three different types of near-wall velocity profiles may appear: (a) "classical" wall slip, in which a discontinuity is found just at the boundary; (b) cohesive slip, where the slip plane is at a certain distance from the wall; and (c) wall depletion or lubrication, where the nonslip boundary conditions are not violated but shear rate is enhanced near the wall. At present, it is accepted that true slip at the wall does not occur during the flow of colloidal systems, and as Barnes (1) has pointed out, the term "wall depletion" is the most accurate way to describe this phenomenon.…”

Extrusion Defects and Flow Instabilities of Molten Polymers

“…In the first case, the usual steel surface of the tools could be replaced by a surface of lower energy. It has been proven at laboratory scale that dies in brass or covered with a special coating are able to greatly increase the flow rate without surface defects (Ramamurthy, 1986;Piau et al, 1995a;Hatzikiriakos et al, 1995;Wise et al, 2000;Kulikov and Hornung, 2004). Unfortunately, these surfaces are generally less resistant to abrasion and, to our knowledge, such use on an industrial scale is not actually developed.…”