Nanocomposite hydrogel with varying number of repeating oxyethylene units: Adjustable pore structure and thermo-responsibility

To explore the effect of varying number (n) of repeating oxyethylene units upon the structure, pore shape and property of nanocomposite hydrogels, three kinds of lyotropic liquid crystal molecules polyoxyethylene (n) alkyl ether (Brij-52/56/58) with same alkyl chain C16H33 and different number of oxyethylene units (CH2CH2O)n = 2,10,20) were severed as novel type of template to prepare Brij/Poly(NIPAm/LMSH) (TNH52/56/58) nanocomposite hydrogels base on monomer N-isopropylacrylamide (NIPAm) and inorganic nanoclay lithium magnesium silicate hydrate (LMSH). It was found that, as the number values (n) of oxyethylene units are 10 and 20, the transmittance values of pre-polymerization solution decrease significantly to nearly zero at 37 and 33 min, while keeps constant at around 5% as n = 2. With increasing the values of n from 2 to 10 and 20, the pore structure changes from honeycomb to interconnected and layered pore structure, and pore size decreases from 40 to 60 μm to 20-40 μm (layer space). As n = 10, the maximum swelling ratio (MSR) and water loss rates of prepared TNH56 nanocomposite hydrogel is the largest. The volume phase transition temperature (VPTTs) values still keep at 30-35 °C, but linear fitting data and endothermic peak width indicate that, as n is 10, nanocomposite hydrogel presents rapid thermo-responsibility. It has revealed that the adsorption between LMSH sheets and Brij molecules and template-like role play an important role in controlling the pore shape, swelling behaviour and temperature-sensitivity.