Applications Of Urea In The Surfactant Systems

The present dissertation mainly deals with urea from three aspects: 1. Dimerization of urea molecules in surfactant systems It can be found that only the cationic surfactant CTAB micellar system is favorable to the existence of urea monomer. The result is caused by the location of urea molecules in CTAB micelle that provides the space and chance for the existence of urea monomer. However, the anionc surfactant SDS and non-ionic surfactant Triton X- 100 have no obvious effect on the dimerization of urea molecules. 2. Hydrotrope and hydrotrope-solubiization action of urea in CTAB/n- C5H11011/H20 system Urea is found to show hydrotrope action when the aqueous solubility of surfaetant is enhanced while it will show hydrotrope-solubilization action when the solubility amount of oil in 01W microemulsion and that of water in W/0 microemulsion are increased. Both the hydrotrope action and the hydrotrope- solubilization action of urea are selective so that they can only be found in catiomc surfactant CTAB system. The addition of urea in CTAB system with cosurfactant enlarges the 0/W and W10 areas in the phase diagram and expands the bicontinuous region by reducing the lamellar liquid crystal area. The results show that the hydrotrope-solubilization action of urea is in fact a structural 1~~.. transition from the lamellar liquid crystal phase to the isotropic phase with 0/W, WI0 and bicontinuous structure. 3. Disruption and Reformation of the Helical Structure of Bovine Serum Albumin in Urea solution Upon the addition of small amounts of sodium oleate (NaOL), the helicity of bovine albumin (BSA), lost in the urea denaturation, is mostly recovered. This Master Dissertation of Yangzhou University refolding of BSA is actually induced by the binding of a small amount of NaOL by a cross-linking function of oleic ions between a group of nonpolar residues and a positively charged residue located on different ioops of BSA. However, the reformation of the helical structure is not induced by the addition of the cationic surfactant CTAB and the nonionic surfactant Triton X- 100 in the above- mentioned solution...