Study On Self-assembly Thickening And Rheological Behaviors In Mixed Systems Of Amino Acid-based/Zwitterionic Surfactants

In order to solve the difficult thickening problem of amino acid-based surfactants applied in personal cleaning products, the preparation and rheological behaviors of self-assembly thickening mixed systems of amino acid-based/zwitterionic surfactants were studied. The micellar aggregation and formation mechanism were discussed. Moreover, the preparation and performance of low surfactant content cleaning detergent systems were preliminarily investigated. Main conclusions were obtained as follows:1) Under certain conditions, the new self-assembly thickening mixed systems were obtained between cocamidopropyl betaine (CAPB) and sodium N-lauroyl sarcosinate (LD), or sodium N-cocyl alanine (SCA), respectively. The increase of carbon chain length of sodium alkyl sarcosinate led to viscosity increasing and foam height decreasing of mixed CAPB/LD systems. The mass ratio (CAPB:LD=8:4) was optimal for CAPB/LD systems. The effects of NaCl, pH, difference of raw materials on mixed system were illustrated. Furthermore, self-thickening mixed systems were obtained between LD and cocyl betaine (CB), or cocamidopropyl hydroxyl sulfo betaine (CHSB), dodecanamide hydroxyl sulfo betaine (DHSB), sodium lauroamphoacetate (SL), respectively.2) The viscoelasticity, thixotropy and network structure stability of mixed CAPB/LD systems were enhanced under certain conditions such as suitable mass ratio, increasing of carbon chain length of sodium alkyl sarcosinate, and appropriate betaines. CAPB/LD systems at different mass ratio had good shear-thinning properties. The flow curves of these systems well followed non-linear co-rotational Jeffreys model.3) The ability to reduce the surface tension of mixed CAPB/LD systems was better than that of a single surfactant. Reducing pH appropriately could significantly enhance the ability to reduce the surface tension. The effect of pH on microstructure of CAPB/LD micelles was proved by Cryo-TEM. The reason for forming viscoelastic systems of CAPB/LD> CAPB/SCA^CHSB/LD was illustrated by the isoelectric point mechanism.4) The charateristics of low surfactant content cleaning detergent systems were explicit. AES(EO)i/CAB and CAB/LD systems with low surfactant content were obtained. The possibility of forming viscoelastic systems by anionic/cationic surfactants was conformed. The effects of NaCl, difference of raw materials, active matter content on mixed systems were illustrated.This work was expected to provide rheological basis and new ideas for applications of amino acid-based surfactants in personal cleaning products. Meanwhile, this paper laid the foundation for reducing the active matter content of surfactants.