Nano-hybrid self-crosslinked PDMA/silica hydrogels

Abstract

We discovered that the free radical polymerization of N,N-dimethylacrylamide in water can lead, above a certain concentration, to gels without any added difunctional crosslinker. These so called ''selfcrosslinked'' hydrogels were prepared and their weak mechanical properties were improved by introducing silica nanoparticles. From swelling experiments performed at equilibrium in aqueous media, it was shown that silica particles behave as adhesive fillers and strongly interact with PDMA chains. These interactions are responsible for the reinforcement of mechanical properties. From initial elastic moduli, determined in the preparation state, we show that the elastic behaviour of these hydrogels mainly originates from entanglements and from physical crosslinks that can be controlled by the polymer concentration and the ratio between silica particles and polymer chains, respectively. The mechanical behaviour was characterized using: monotonic tensile tests, loading-unloading cycles at large strains and stress relaxation experiments in order to investigate long time behaviour. The introduction of silica highly increases the stiffness of the network without greatly reducing its extensibility, implying that strong interactions take place between PDMA chains and silica surfaces. Non-linear behavior was pointed out: softening at small deformations and hardening at high deformations which is related to finite chain extensibility. All these effects have been shown to strongly depend on the silica content. The analysis of hysteresis and residual strains induced by cycles, clearly indicate that contrary to chemical crosslinkers, hybrid interactions increase the dissipative process.Physico-chimie des Polym eres et des Milieux Dispers es, UMR 7615,

High frequency rheology of hybrid hydrogels using ultrasound transient elastography

“…Tensile tests were carried out and repeated as a standard test with a strain rate of 100 mm/min ( ε &~0.06s -1 ) at a room temperature. Tensile properties of nanosilica PDMA gels are seen to strongly depend on silica content [10], In the first part of the curve, at low strains (ε<0.03), the initial modulus E is defined and identified as the Young's modulus. Experimental Young's moduli are given in Table 2.…”

Structure investigation of nanohybrid PDMA/silica hydrogels at rest and under uniaxial deformation

“…In the case of hybrid hydrogels prepared by cross-linking polymerization of DMA in silica suspension, we have shown that the presence of silica nanoparticles greatly enhances the whole mechanical properties [17,[19][20] . Interestingly, both initial modulus, dissipation, nominal strain at break and fracture energy were seen to be simultaneously enhanced with increasing amount of silica.…”

Hydrogels with Dual Thermoresponsive Mechanical Performance

“…[1] Despite their wide potential in biomedicine and industry, [2,3] applications of these aqueous-based soft materials have long been restricted due to their intrinsic poor mechanical strength, mainly related to the high hydration level and low efficiency of dissipation process. Since the last 15 years, different efficient strategies have been developed to improve their mechanical properties with either introducing inorganic charges forming nanocomposites or hybrid hydrogels [4,5] or using smart macromolecular architectures such as double network systems, [6] slide-ring gels, [7] or tetra-PEG. [8] During the past few years, another mode of hydrogel reinforcement based on the universal concept of polymer phase separation has been developed.…”