The water structure in the polymer network with LC-organisation

The water structure existing in (2-hydroxypropyl)cellulose-poly(acrylic acid)-water (HPC-PAA-H2O) hydrogel, exhibiting liquid crystalline (LC) organization of the polymer network (anisotropic hydrogel), was assessed by means of Raman spectroscopy. It was shown that the LC-network of HPC-PAA-H20 exerts significant influence on the structure of liquid water present in the hydration shells around polymer chains of the anisotropic hydrogel. Due to poor stability of LC-ordering of polymer network, observed in HPC-PAA-H2O) after its long-term water immersion, the process of crosslinking of the anisotropic hydrogel was considered. The results of Raman measurements revealed that, during immersion of HPC-PAA-H2O in calcium ions (Ca2+) solution, formation of a salt by poly(acrylic acid) of HPC-PAA-H2O and Ca2+ takes place. This results in crosslinking of the anisotropic hydrogel, leading -- in a consequence -- to significant improvement of its mechanical toughness, as well as to stability of LC-ordering of the investigated network in the swollen state. However, during crosslinking of the anisotropic hydrogel (by Ca2+), apart from formation of the salt by Ca2+ and PAA, the ions influence additionally the structure of the water existing in hydration shells round polymer chains of both polymer constituents (HPC and PAA) creating the anisotropic hydrogel network.