Dynamic adsorption process of sericin protein solutions

The dynamic surface tensions of sericin solutions at a given concentration and different pH values were measured by Wilhelmy plate method.Such curves were plotted according to the dynamic surface tension(γ_t) data in different pH,as surface pressure p versus adsorption time t,the relationship between surface pressure and time,r_tlgt,and ln(dp/dt)p. The curves were analyzed by using some experiential expressions to elucidate the dynamic adsorption behavior,through which the adsorption parameters were deduced of adsorption half-time(t_1/2,the time required for surface tension decreasing to the half of the equilibrium value),the constant controlling adsorption mode(n),the mean molecule area of the molecule occupied at the interface both in initial penetrated and anchored state(ΔA_1) and in rearranged and reoriented state(ΔA_2).The results indicated that the adsorption process of sericin protein is attributed to a model of diffusion-controlled adsorption kinetics.The conformational transformation of sericin protein molecules adsorbed at the surface undergoes two dynamic steps.The first is initial penetration and anchoring of the molecule from aqueous solution to the surface,and the other is the rearrangement and reorientation of the adsorbed molecule at the interface. The pH value of sericin solution has influences on the dynamic surface tension and the adsorbed molecule area.When pH value of sericin solution is smaller than the equipotential point of sericin protein,ΔA_1 and ΔA_2 are smaller;the dynamic surface tension is higher;and the adsorption rate becomes slower,in comparison with those in the pH value higher than the equipotential point.