Study Of The PH Responsiveness Of Amino Acid-based Surfactant Sodium Lauroylglutamate And Its Foam Characteristics

Surfactant is a kind of important chemical product, which is widely applied in many industrial and daily life products and the demand has been gradually increased. But large amounts of waste water and slag containing surfactants were discharged into soil and water, coursing affect on environment, which has recently attracted extensive social concern. Green surfactants have attracted attentions for their low toxicity and good degradability. Amino acid-based surfactants have attracted increasing attention nowadays as they are human friendly and less toxic comparing with traditional surfactants. Besides, they have many excellent properties such as good solubility, salt resistance and responsivity to pH derived from the special chemical structures which made them having good application prospection. By far, most of the investigations of N-acylamino acid-based surfactants are focus on their self-assembly in bulk phase while interfacial behavior and foaming properties of amino acid-based surfactant, which is actually extremely important in many applications are rarely reported. Meanwhile, studies about environmental responsiveness of amino acid-based surfactant used as foam stabilizer are scarce.In this thesis, the bulk phase aggregation and interfacial adsorption properties especially the foam properties of a kind of amino acid-based surfactant, Sodium lauroylglutamate (LGS) under the variety of pH were investigated. The mechanism was discussed thoroughly by combining experimental determination with theoretical molecular simulation methods. We also investigated the synergistic effect between polymers, such as LGS and methylcellulose, sodium alginate, and cationic surfactant Dodecyl trimethylammonium Bromide respectively. The knowledge based on our study might be useful in developing performance of amino acid derived surfactants in the application fields.This thesis is divided into three parts:In the first part, the molecular structures of Sodium lauroylglutamate (LGS) varied with pH and the interfacial and bulk phase properties under different pH conditions were investigated by acid-based titrated curve, Infrared Spectrophotometer, surface tension, rheometer and TEM measurement. The results showed that the LGS molecules at neutral pH arranged more tightly and decreased the surface tension. As pH decreasing, gel was formed and the gelating degree increased as the protonating degree increasing. Furthermore, the increased ratio of protonated to deprotonated carboxyl groups leads to a drastic increase in the Krafft point and a decrease in solubility.The second part focused on the foam properties of LGS solutions under different temperature and pH values. We measured the foamability, foam stability, liquid volume in the foam and liquid drainage using Foam Scan method. And the mechanism was discussed thoroughly by combining experimental determination with theoretical molecular simulation methods. At neutral pH, the LGS molecules arrayed more densely at the interface as the electrostatic repulsion interaction between the surfactant molecules decreased and the hydrogen bond interaction increased. So the bubble size was smaller and the stability of the foam was increased. At acidic pH, the foamability decreased and the foam stability increased due to generation of weak gel in the foam film. As pH further decreased, the gelating degree increased, and it was found that the foam films were very easy to break up following with liquid drainage leading to quicker collapse of the foam.The third part focused on the foam properties of complexed systems of LGS and water-soluble polymers, such as methylcellulose, sodium alginate, and cationic surfactant Dodecyltrimethylammonium Bromide respectively. The foam stability, dynamic surface tension and interfacial rheology of the mixtures were investigated. It was found that the synergistic effect between LGS and polymer was determined by the nature of polymer.