Study On The Secondary Structure Of Polyethylene Oxide (PEO) And Sodium Alginate In Dilute Solution

In this paper,the traditional uncharged water-soluble polymer polyethylene oxi de(PEO-24 K: Malvin;PEO-20 K: Agilent Co)and the typical water-soluble pol yelectrolyte sodium alginate with negative groups were taken as the research objec t.The structure of two kinds of PEO and sodium alginate in dilute solution was studied by three detector coupled gel chromatograph(TDA-GPC),dynamic light sc attering(DLS)and rotational rheometer.The quantum distribution,Mark-Houwink curve,mean square radius of gyration(Rg),hydrodynamic radius(Rh)and so on were studied,and the chain conformation in dilute solution was analyzed.In addit ion,the molecular chain length(Lp)of sodium alginate was calculated.The effect s of salt concentration,pH and temperature on the secondary structure of dilute s olution of two polymers were investigated.The results show that:1.The molecular weight and molecular weight distribution of PEO-24 K are c onsistent with the parameters labeled in the commodity,and do not change with t he salt concentration,but the solution conformation changes significantly with the increase of the salt concentration in the solution.The conformational parameters o f PEO-20 K do not change with the concentration of salt in solution.2.The molecular weight of sodium alginate is about 290 K and its molecular weight distribution is 2.02 by TDA-GPC test.The result of the test deviates grea tly from that of the traditional calibration method.According to M-H curve and worm chain model,LP was calculated to be 5.88 nm.3.When sodium alginate dissolves in different solvents,the distribution of m olecular weight and molecular weight is basically the same.The intrinsic viscosity[?] and the hydrodynamic radius Rh decrease with the increase of salt concentrat ion,while Rg increases.Accordingly,the Rh also increases gradually.4.A small amount of acid will not change the conformation of the molecule,but when the amount of acid reaches the critical value(250 ml in the experimen t),sodium alginate will become insoluble precipitate,which can not be tested by TDA-GPC.With the addition of NaOH,the particle size of sodium alginate decre ased first and then increased.Rheometer tests show that sodium alginate molecular chains gain more energy with the increase of temperature,Brownian motion intens ifies and viscosity decreases.