Insight into (alkyl)methacrylate-based copolymer/sepiolite nanocomposite cryogels containing amino and sulfonic acid groups: Optimization of network properties and elasticity via cryogelation process

Abstract

(Alkyl)methacrylate-based copolymer/sepiolite nanocomposite gels containing amino and sulfonic acid groups have been prepared via (cryo) gelation of N,N-dimethylaminoethyl methacrylate (DMAEMA) and 2-acrylamido-2-methyl-propanosulfonic acid (AMPS) in the presence of fibrous clay mineral sepiolite (SEP). The morphology, thermal stability, compression performance, and swelling behavior of nanocomposite gels were systematically studied with various SEP contents. X-ray diffractometry results indicated that SEP had been participated in (cryo)gelation, and the resulting thermal stability and surface morphology were improved by the addition of inorganic clay SEP. Owing to dispersion of SEP, the prepared nanocomposite cryogels exhibited dramatic improvements on their elasticity while low water absorption capacity was maintained. The presence of low amount of SEP significantly enhanced the mechanical strength and the cross-link density of DMAEMA-based nanocomposite gels due to its fibrous morphology and crystalline structure acting as cross-links. Addition of 0.4% (w/v) SEP led to five-fold increase in the compressive modulus of nanocomposite cryogels. As SEP concentration in the feed was increased from 0 to 2.40% (w/v), the effective cross-link density in the nanocomposite matrix increased continuously from 2.84 to 22.9 × 103 mol/m3. The prepared nanocomposite gels showed enhanced swelling response and on-off switching characteristics in aqueous KBr solutions. The parameters of equilibrium swelling, initial swelling rate, diffusional exponent, and diffusion coefficient were evaluated and the swelling kinetics of the nanocomposite gels in aqueous KBr solution followed the pseudo second order model. Since DMAEMA and inorganic clay SEP were effectively combined in a nanocomposite network, the obtained results would expand the range of responsive properties and related industrial applications available to DMAEMA and SEP individually.