Formation and characterization of elongated micelles from protein-based biodegradable surfactants: effect of ph and co-surfactants

Abstract

An extensive study of mixed surfactant systems in aqueous environments is the focus of this thesis. Viscoelastic micellar solutions were studied in terms of mixing composition, pH, and surfactant properties. The preferred surfactant was sodium Cocoyl glycinate (abbreviated as SCGLY), an anionic surfactant considered to be based on amino acids. As a co-surfactant, several amphoteric (zwitterionic) and nonionic amphiphiles were used. The SCGLY does not show any micellar transition up to 20 wt % at room temperature. However, when the addition of cosurfactant at the appropriate concentration the mixed systems show slight elongation in the micelle and after that maintaining pH between 5.5-6.0 mixed surfactant systems show phase transition and give a viscoelastic gel-like structure due to the decreased effective cross-sectional area per surfactant molecule. This work first studied elongated wormlike micelles formed in a (binary) SCGLY/nonionic phase without any additions. A SCGLY is a Newtonian fluid that exhibits Newtonian behaviour in solutions that do not exceed the critical micelle concentration (CMC). The addition of nonionic co-surfactant like Cocamide diethanolamine (CDEA) or lauryl glucoside (LG) to the 6 wt % of SCGLY there were no visual changes in the systems but after a certain concentration reaches unidimensional micellar growth are occurs and maintain pH at 5.6 In the presence of elongated micelles that form a rigid network congealed with viscoelastic worm-like micelles. Therefore, viscoelastic solutions formed over a wide range of frequencies followed Maxwellian behaviour and are thought to be composed of transient networks of wormlike micelles. In addition, the same kind of behaviour shown by the SCGLY/zwitterionic like Cocoamidopropyl betaine (CAPB) or sodium Cocoamphoacetate (SCA) this mixed system also makes wormlike micelle at a particular concentration range. Anionic/nonionic and anionic/zwitterionic surfactant mixtures can form viscoelastic worm like micelles without adding salts or polymers. Next, the addition of one more co-surfactant in the anionic/nonionic system generates a new triple surfactant mixture as SCGLY/CDEA/LG. Here complete viscosity profile of the trial surfactant system was by changing the composition of all surfactants, in addition, rheological behaviour and phase behaviour were studied in a triple mixture of amphipathic molecules of SCGLY/CDEA/LG nonionic cosurfactants systems. Additionally, the presence of nonionic cosurfactants in SCGLY solution reduces the effective cross-sectional area of each amphipathic molecule, thereby favouring the growth of mono-dimensional micellar systems. As co-surfactants concentration increases, solution viscosity increases gradually. The pH should be maintained between 5.5-6.0 to increase the number of long micelles that form a stiff network of wormlike micelles. This will also increase the viscosity of the solution significantly. The elongated wormlike micelles that were formed exhibited viscoelastic characteristics with a single mode of relaxation and followed Maxwell's mechanical model as a consequence. Finally, we have studied the consequence of additives (salts and polymers) on the rheological behaviour of viscoelastic wormlike micellar solutions in a ternary mixed system of SCGLY/CDEA/LG. This amino-based surfactant system turns milky while the addition of salts due to the precipitation of the amino group, addition by using polymer such as Xanthan gum, carboxy methyl cellulose, acrylates in the same formulation systems turns in to highly viscoelastic gel formation. This type of final formulation is used for hair cleansing activities (smoothness and contact angle) and also compares our formulation with marketed brands. The light scattering method was used to govern the hydrodynamic radius and zeta potential of SCGLY in the presence of CDEA and LG. Furthermore, CDEA and LG have been discovered to alter SCGLY's foaming behaviour, skin mildness, emulsification, and cleaning characteristics. The research presented here could be a good way to change not only the rheology but also the foaming behaviour of the SCGLY-CDEA-LG mixed surfactant system.