Compression elastic modulus of neutral, ionic, and amphoteric hydrogels based on N‐vinylimidazole

Abstract

Several hydrogels of N-vinylimidazole and sodium styrenesulfonate have been prepared by radical cross-linking copolymerization in aqueous solution, using N,N 0 -methylene-bisacrylamide as crosslinker. Depending on composition, these hydrogels were neutral, amphoteric, cationic or anionic. Compression-strain measure-ments were performed on samples as-synthesized and swollen in deionized water or in acid aqueous solutions, with and without salt. It was thus found that the cross-linking densities determined by compression measurements on assynthesized sam-ples are in good accordance with those calculated by means of the model of polymer networks with pendant vinyl groups. A non-Gaussian parameter (b) was introduced to explain that the elastic moduli (G) of samples swollen at equilibrium are larger than predicted by the Gaussian model. The b values of the neutral or ionized systems increase with swelling and fall into a single curve, which denotes a common behav-ior. Swelling has two opposite effects on G; on the one hand G decreases because the polymer volume fraction diminish and the system shifts from the affine limit to the phantom one; on the other, b increases and contributes to increasing G. The balance of those two opposite effects determines the variation of G with swelling. The possi-ble contribution of ionic crosslinks to m e for the polyampholyte and for the polycation wearing divalent counteranions was discussed.A peculiar system is poly(sodium styrenesulfonate), whose cross-linking density is much lower than expected.

Salting-in effect of ionic liquids on poly(N-vinylimidazole) hydrogels

“…The degree of conversion for the different specimens used here was 79 %, the degree of cross-linking ν e =0.069 mol/L and the average molecular weight for the chains between adjacent knots M c = 1.8 10 4 g/mol [34]. The polymer volume fraction in the relaxed state, i.e., just after synthesis, was v 2r =0.242 [4].…”

“…The total comonomer concentration in the feed was C T = 3.93 mol/L (approximately 40 wt%) and the crosslinker concentration was 0.063 mol/L (approximately 2 wt%). This sample, here called PVI, was previously denoted as PVI40(2) [32][33][34]. The protocol followed in the synthesis and purification was as previously reported [34].…”

Elasticity Study of PAAm-κ C Composite Prepared in Various κ C Content and Measured at Several Temperatures

“…They show the typical curvature at the smallest range of deformation that is generally assigned to imperfect geometry of the surface of the gel specimen [5]. The elastic modulus was determined by linear regression, as the slope of such plots as given in Eq.…”

“…• C. The modulus was calculated by means of the model polymer networks [5]. In addition, it was observed that compressive elastic modulus presented lower values at all temperatures for 1 (w/v)% of κC content gel composite, showing a minima at 40…”

“…The elastic modulus was found to increase exponentially with total comonomer concentration, and the modulus passed through a maximum as the crosslinking agent was increased. Compression elastic modulus measurements of neutral, ionic and amphoteric hydrogels based on N-vinylimidazole were performed [5]. A non-Gaussian parameter (β) was introduced to explain that the elastic moduli (G) of samples swollen at equilibrium are larger than predicted by the Gaussian model.…”