Silica phase formed by sol–gel reaction in the nano- and micro-pores of a polymer hydrogel

Abstract

ElsevierPlazas Bonilla, CE.; Gómez-Tejedor, JA.; Perilla, JE.; Gómez Ribelles, JL. (2013). Silica phase formed by sol-gel reaction in the nano-and micro-pores of a polymer hydrogel. Journal of Non-Crystalline Solids. 379:12-20. doi:10.1016/j.jnoncrysol.2013. Corresponding author José L. Gómez Ribelles .E-mail address: jlgomez@ter.upv.es AbstractHybrid composites consisting in a hydrogel matrix with silica micro-and nano-particles reinforcement were produced and characterized. The strategy proposed in this work to obtain these composites consisted in a two-step synthesis, being the polymer network formation the first step. Porous poly(hydroxyethyl acrylate) polymer network was produced via free radical polymerization. Monomer and crosslinker were diluted in a varying amount of ethanol that controls the porosity of the resulting network. Polymeric microstructure drives the absorption of a silica precursor solution and the further distribution of the inorganic phase which was formed "in situ" in part occupying the pores and in part in the form of nanoparticles distributed in the polymer phase.Composites with silica content up to 60% by weight were obtained. In the case where the silica phase was continuous, samples maintained their integrity after eliminating the organic phase by pyrolysis. Water absorbed in the gel was able to crystallize, at least in Clara E. Plazas Bonilla, Journal of Non-Crystaline Solids 379 (2013) 12-20 2 part, when the silica content was below 30% by weight. Interestingly, for higher silica content the glass transition of the polymer phase was suppressed as well. Compliance was determined by indentation experiments. A continuous decrease in compliance was observed as filler content increased. Improvement of bioactivity of the material in simulated body fluid was also assessed. The synthetic route proposed allowed obtaining a family of composite hydrogels with variable properties. HighlightsA procedure to synthesize an interconnected silica nanophase in a previously formed polymer hydrogel.Silica nano-and micro-domains formed in a polymer nano-and micro-porous hydrogel by a sol-gel reaction.Hybrid materials with up to 60% by weight silica content in which both silica and organic phases are continuous.

Organic-inorganic bonding in chitosan-silica hybrid networks: Physical properties

“…In previous studies we have shown that the silica coating of the pore walls of polymeric porous membranes through in situ sol–gel yields hybrid materials with interesting mechanical and water sorption and permeation properties . Chitosan–silica blends were also tested as fillers of polymer membranes showing mechanical reinforcement and enabling the tuning of mechanical properties by varying the ratio chitosan–silica in the coating .…”

“…In previous works, we have proposed a novel strategy for the preparation of hybrid porous materials performing sol–gel reactions using silica precursors inside the pores of polymeric high‐interconnected porous membranes, obtaining a homogeneous thin layer upon the pore walls of the membrane . The silica layer deposited highly reinforced the polymer, for that reason we also produced a tuneable reinforced hybrid material filling the pores of the membrane with a blend of chitosan–silica network .…”

“…These hybrids typically consist of nanoparticles of bioactive glasses, hydroxyapatite, silica, or other ceramics dispersed in polymer matrices . Sol–gel developed materials have shown the versatility of this methodology to create different structures for bone tissue repair …”

Hybrid Polycaprolactone/Silica Porous Membranes Produced by Sol‐Gel

“…It was shown in previous papers that sol‐gel reaction taking place while the sol is confined in the pores of a polymer could yield a variety of silica phase micro or nanostructures depending on the capacity of the precursor to penetrate into the polymer matrix and on the catalyst used. Thus, sol‐gel reaction performed into a microporous membrane of poly(hydroxyethyl acrylate) yields a non‐porous composite with a silica phase consisting in interconnected nano and micro‐domains because silica is in part formed into the nanopores of the hydrogel and in part in the macropores of the membrane, and silica interconnectivity collapses any remaining empty spaces. When silica is formed into the pores of a polycaprolactone membrane the polymer is not swollen by the precursor solution and silica is formed as a coating of the pore walls if sol‐gel reaction is performed at low pH or as dispersed microparticles loosely adhered to each other or the pore walls if performed at high pH …”

“…In this type of measurements where a controlled time‐dependent compression force is applied the obtained force‐penetration curves allow the evaluation of the material Compliance . Following the analysis of Hayes with the procedure described in ref the creep compliance of a sample with thickness h intended by a stiff flat‐ended cylindrical indenter with radius α could be evaluated from the load ( F ) ‐ penetration ( w ) curve through the Eq. (6): where k is a non‐dimensional parameter which depends on the ratio, α/h , and the Poisson coefficient of the material, ν .…”