Swelling and mechanical behavior of ionised networks of copolymers of N-isopropylmethacrylamide with an ionic comonomer, sodium methacrylate (mole fractions x S ¼ 0-0.1), and a crosslinker, methylenebisacrylamide, was investigated in water as a function of temperature and in aqueous NaCl solutions (c NaCl ¼ 10 À5 -1 M) at 23 C; small-angle neutron scattering (SANS) was used for structure investigation. On heating, a continuous decrease in the swelling degree in water, Q, was observed; increasing x S shifts the temperature of transition from the swollen to collapsed state, T tr , to higher values. On subsequent cooling, the temperature T tr was independent of x S . This means that in the collapsed state clusters of ions are formed and these microsegregates remain stable at low temperatures; the presence of clusters is supported by SANS results. The expected decrease in the swelling in aqueous NaCl solutions, Q s , with increasing NaCl concentrations, c NaCl , was observed. The decrease in Q with T and the decrease in Q s with c NaCl are accompanied by an increase in equilibrium shear modulus of gels. The experimental swelling behavior was analyzed using the theory of polyelectrolyte networks in which repulsion of charges on the chain and finite chain extensibility were considered.

The swelling and mechanical behaviour of ionized networks of N-isopropylacrylamide with an ionic comonomer, (2-acrylamidoethyl)trimethylammonium chloride (mole fractions x S = 0-0.1), in the presence of a crosslinker, N,N'-methylenebisacrylamide, was investigated in water as a function of temperature and in aqueous NaCl solutions (c NaCl = 10 -5 − 1 M) at 23 °C. On heating, a continuous decrease in the swelling degree in water, Q w , was observed; increasing x S shifts the volume transition temperature, T tr , (from the swollen to collapsed state) to higher temperatures. The expected decrease in the swelling degree, Q, with increasing NaCl concentration in aqueous NaCl solutions was observed and two shrinking regions in ionic gels were found. The decrease in Q w with increasing temperature and the decrease in Q with increasing c NaCl are accompanied by an increase in equilibrium shear modulus of gels, so that the mechanical behaviour of gels is predominantly determined by the swelling degree. The experimental swelling behaviour could be, in the first approximation, described by the theory of polyelectrolyte networks in which repulsion of charges on the chain and finite chain extensibility were considered.

No abstract

No abstract

No abstract