Hydroxyethyl cellulose surface tension

The difference between hydrophobicities of the hydroxyethyl (HE) grouping and the hydroxypropyl (HP) unit is evident in the relative aqueous solution surface tensions(7,8) of the two cellulosic polymers in these comparative references the M.S. of the products is not equal. The dramatic influence of the more hydrophobic HP groupings on surface pressures is illustrated in Figure 2. 

The classic studies of Saunders( 17) demonstrated that in the presence of excess surfactant methyl cellulose (MC) would desorb from monodispersed polystyrene latices. MC is one of the most surface active water-soluble polymers (W-SPs) and it will readily dominate the surface pressure 7T (7T = cre - cr t where cr is the surface tension of water and is the surface tension of the aqueous polymer solution) of the aqueous solution. For example, hydroxyethyl cellulose (HEC) lowers the surface tension of water much less than MC or HPMC, and when the combination of HEC and MC or HPMC in water is studied, there is no notable influence of HEC on the surface pressure (Figure 2). 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

Nahringbauer, I. Dynamic surface tension of aqueous polymer solutions, I Ethyl(hydroxyethyl)cellulose (BERMOCOLL cst-103), /. Colloid Interface Sci., 176, 328,1995. 

In addition to solution viscosity, interfacial surface tensions have also been measured as a function of polymer concentration [7]. In general, the polyacrylamides did not significantly change the surface tension of water over the concentration range of interest. On the other hand, the hydroxyethyl celluloses did lower the interfacial surface tension of water by about 5 percent over the concentration range of interest. Other than solution viscosity and surface tension, all other physical properties of the solvent have been assumed to remain unchanged at the very low polymer concentrations used in these experiments. ... 

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