Study Of Physicochemical Properties Of Water-Soluablepolymer At Air Solution Interface

Recently, the physicochemical properties of water-soluable polymer at air solution interface and the interaction between small molecules and polymers in aqueous solution are attractive points of study in macromolecule solution and its interface. The study is of significance in understanding the physical phenomena and laws of condensed phase in quesi-two-dimensional space and the interaction of small molecules with macromolecules in solution. In the present thesis, we report the results of investigation on the thermodynamic properties, adsorption and desorption kinetics of polyethylene glycol (PEG) at air solution interface as well as the interaction of PEG with small molecules in aqueous solution.Based on careful analysis of surface tension and pressure isotherms, the properties, organization of PEG spared and adsorb films well as the conformation of PEG molecules at tihe air aqueous solution interface were studied under the different conditions.. The results showed that the PEG spread film at air solution interface is a monolayer with two dimensional characteristics, when the surface concentration of PEG under about 0.40mgm-2. The concentration dependence on the surface pressure of PEG monoelayers could be expressed by the scaling law in two dimentional space. In the monoelayer, PEG molecules attached at the air solution interface with a trainconformation. When the surface concentration of PEG was over 0.40mg m"2, PEG molecules at the interface might loop or tail into the aqueous subphese. Under the experiment conditions, PEG adsorb films at air solution interface were multi-layer fihns at the nearly same surface pressure of the spread fihns, the surface concentration and the monomer density of PEG in the adsorb fihns were higher than those in the spread fihns. Because the adsorption of PEG at air solution interface exhibited a non ideal characteristics, the Gibbs adsorption isotherm equation used for the adsorption thermodynamics of surfactant is no longer suitable for that of surface active macromolecules such as PEG very well.The properties of bulk solution exhibited obviously influence on the properties, organization, and molecule conformation both of PEG spread and adsorb films at absolution interface. At the thermodynamically unfavorable salt solution surface, the equilibrium surface pressure and monomer density of PEG spread and adsorb films increased with the increase of salt concentration, but the static Gibbs elasticity and the compressibility of the fihns decreased with the increase of salt concentration. At the salt solution surface, the zig-zig degree of PEG molecules was intensified and the molecular segments tended to immerse in adjacent air phase. On the contrary, at the thermodynamically favorable dimethylacetylamide (DMA) solution surface, the equilibrium surface pressure and the monomer density of PEG spread and adsorb fihns decreased due to the water structure destroyed by the strong polar of DMA and the increased solventibility of PEG. At the DMA solution surface, the static Gibbs elasticity of PEG surface spread and adsorb fihns increased with the increase of the DMA concentration, the fihns turn to be compressed easily and PEG molecules tended to loop or tail into the adjacent aqueous subphase. It was clear that the interaction of small molecules with PEG molecules in different solutions resulted in the varitions of thermodynamic properties and the state of PEG fihns at the absolution interface.On the discussion of adsorption and desorption kinetics, the dynamic surface tension of PEG solution was determined by the sweeping method to investigate the adsorption kinetics of PEG at air solution interface and the affecting factors on theadsorption kinetics. At the same time, the dynamic surface pressure of PEG spread films were measured under the condition of constant surface area to study the desorption kinetics of PEG at air solution interface and the effect of different factors on the desorption kinetics.The diffusion coefficients of PEG adsorption and desorption were calculated by the quan...