Cryostructuring of polymer systems. XXVI. Heterophase organic–inorganic cryogels prepared via freezing–thawing of aqueous solutions of poly(vinyl alcohol) with added tetramethoxysilane

Abstract

Composite heterophase organic-inorganic hybrid cryogels of poly(vinyl alcohol) (PVA) containing silica constituents were prepared and studied. Such constituents were formed in the course of hydrolytic polycondensation (sol-gel process) of tetramethoxysilane (TMOS) introduced in to the aqueous polymer solution prior to its freezethaw treatment. It was shown that moderate (over the range of À15 to À308C) freezing, then frozen storage, and subsequent thawing of the water/PVA/TMOS systems resulted in the formation of macroporous composite cryogels filled with dispersed silica particles (discrete phase). The continuous phase of such gel materials represents the supramolecular PVA network, which is supposed to be additionally cured with the silicon-containing oligomeric cross agents formed from TMOS in the course of hydrolytic polycondensation. The incorporated silica components influenced the morphology of cryogels. The effects of significant increase in gel strength and heat resistance with increasing TMOS concentration in the initial feed and with thawing rate decreasing have also been observed.

Cryostructuring of polymer systems. XXX. Poly(vinyl alcohol)‐based composite cryogels filled with small disperse oil droplets: A gel system capable of mechanically induced releasing of the lipophilic constituents

“…If the polymeric chains of the continuous phase are cross‐linked with auxiliary agents by additional stable hydrogen bonds, apart from their “own” PVA‐PVA H‐bonding, this causes a significant increase in the toughness of composite materials. This effect was recently observed for organic–inorganic hybrid PVA cryogels prepared via combination of cryotropic gelation and sol‐gel techniques 22. It was also revealed that the rigidity of composite PVACGs grew considerably when ion‐exchange resins in a strong acidic or alkaline form were used as fillers, since such resins are capable of ionizing PVA hydroxyl groups thus facilitating the formation of tight ionic contacts between the continuous (PVA cryogel) and discrete (filler) phases 23, 24.…”

“…Apparent instantaneous shear modulus ( G 0 ; characterizes the elastic properties of the material) and shear modulus for the 30‐min‐loading ( G 30 ; reflects the plastic behaviour of the material) were determined with the technique used for the characterization of rheological behavior of diverse nonfilled and filled PVA cryogels and described in detail in Refs 6, 19–22, 31…”

“…Gel fusion temperatures ( T f ) were determined as described elsewhere 7, 8, 22, 23. In brief, the sealed polyethylene tube, where cryogel with metal ball at the bottom has been formed, was placed upside down into a water bath.…”

Conducting Nanocomposite Polymer Foams from Ice‐Crystal‐Templated Assembly of Mixtures of Colloids

“…[13] Hybrid organic-inorganic cryogels were prepared by an in situ sol-gel reaction of tetramethoxysilane in an aqueous solution of poly(vinyl alcohol) prior to the templating procedure by freezing. [14] Zhang et al [15,16] showed the fabrication of aligned porous polymeric structures by directional freezing of polymer solutions, in a few cases in presence of dispersed nanoparticles.…”

Poly(vinyl alcohol) Cryogel Formation Using Biocompatible Ice Nucleating Agents

“…A number of detailed investigations have been carried out to understand various factors that control the properties and the structure of the PVA cryogel. Others, and particularly, Lozinsky and his colleagues have published a lengthy series of papers focusing on various parameters in PVA cryogelation, such as rate of chilling, number of freeze–thaw cycles, influence of additives, and etc . In general, it has been shown that the porosity and properties of PVA cryogel are influenced by the molar mass of PVA employed, initial polymer concentration, freezing temperature, cooling rate, freezing time, thawing rate, and the number of freeze/thaw cycles …”