Draining and Long Range Interaction in Polymer Solutions

Abstract

Poly (ethylene oxide) (PEO) is soluble in water as well as in several organic solvents, such as methanol, acetonitrile, chloroform and ethylene dichloride. High molecular weight PEOs are effectively flocculent in water. Effective sedimentation occurs over a broad pH range at low concentration of less than a few hundred ppm. Of the polymer suspension which is very effective coagulated include uranium ore slimes, phosphate slimes, and a variety of clays such as kaolin, montmorillonite and bentonite. At room temperature, aqueous solution of PEO is transparent. However, the concept of solubility of PEO in water and polar organic solvents in the object of some controversies. Indeed, while it is sometimes considered as molecularly dispersed, light scattering or viscosity experiments often reveal the presence of large aggregates. Polik and Burchard have shown that the aggregation in aqueous solution of low molecular weight PEO samples increases markedly upon heating but decreases above 600C. In contrast, Devanand et al are able to prepare free aggregate solutions, and the molecular weight dependencies of the molecular dimensions reveal a behavior of the polymer in good solvent, and have given an explanation by enhanced draining in coil extensively swollen by the effect of excluded volume. The relationship between excluded volume effect and draining in polymer has been studied extensively by Douglas and co-workers.in fact the agreement between the different experimental studies is rather poor and the influence of method of preparation and classification of the solution seems to be of paramount importance both in aqueous and in polar solvents. There have been a few viscometric and light scattering studies of PEO in water and non-aqueous solvents. However the agreement between in different experimental studies is rather poor. Devanand et al were able to prepare aggregate free solutions and have observed some extra-ordinary properties for PEO/H2O system. The exponent obtained from power law relation of both static and dynamic single chain parameters are representative of asymptotically good solvents. The local structure of the solvent and site specific interaction are shown not affect power law exponent as expected t. the actual value of A2, RG and RH are much larger than is typically found for linear flexible polymers in good solvent. The enormously high value for the ratios P=M A2[h] , r=RG/RH, Kg/[h] are good solvent system have been partially explained by enhanced particle draining in coil exclusively swollen by the effect of excluded volume . In contact to the above findings of Polik and Burchard have shown that aggregates of high and low density coexists with molecularly dispersed PEO . the high density particles are probably spherulities and the low density aggregates are non-crytilanie microgel particles, on heating the spherulities melt causing the weight fraction of micro gel to incr. The decreasing of A2 is consistent with the concept of hydrodynamic interaction, that is, the increase in the order of water molecules in the neighborhood of PEO. The aqueous PEO is only slightly influenced by the presence of globular aggregates.