Polymer-wall interactions

The effect of polymer-wall interactions is an essential parameter that has to be studied in order to understand the conditions under which slip is triggered. To do so. 

Clearly, all these simulations of surface effects on polymer blends are very stimulating, but at this point they may be considered to be first steps only. The effect of long range polymer wall interactions" should also be considered. 

Figure 5. Temperature dependence of Xe-wall interactions for MCM-41 samples with various pore sizes. The data obtained from Xe adsorbed on silicalite (ref. 18), zeolite NaY (refs. 14, 16, 19) and on polymer surfaces (ref. 17) are also shown for comparison.

Falco RE, Wiggert DC (1980) Effects of dilute polymer solutions in vortexring/wall interactions — a mechanism of drag reduction Prog Astronaut Aeronaut 72 Viscous flow drag reduction (AIAA) 275... 

Polyelectrolytes are a substance class notoriously difficult to analyze. This problem also exists for Fl-FFF due to polymer-polymer or polymer-wall/mem-brane interactions. Benincasa and Giddings [59] completed a systematic study of ionic-strength effects in the application of Fl-FFF to both cationic and anionic polyelectrolytes over a broad molecular weight range. Poly(2-vinylpyridine) was effectively characterized in a 20 mM solution of nitric acid (pH 2), while the best results on poly(styrene sulfonate) were obtained in a dilute (6.5 mM) solution of... 

The carrier liquid can also influence the FFF results as it can alter solute-solute or solute-wall interactions as well as the extension of a polymer in solution [266]. This in turn influences the diffusion and retention of the sample. Limited efforts have been made to describe these phenomena so that their influence still cannot be quantitatively treated. The practical importance of solvent effects becomes clear for the example of proteins which can be switched from positive to negative polyelectrolytes by pH variation. In any case, the pH should be chosen outside the range of the isoelectric point to avoid adsorption problems. 

A specific pattern of sharkskin depends on polymer chemistry, molecular weight and MWD, and polymer-wall surface interaction [50, 51]. With a further increase of the shear rate, a spurt flow can be observed that results from pressure oscillations in the extruder [52]. At higher shear rates, gross melt fracture eventually occurs, with the extrudate coming out with an irregular pattern [45],... 

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