Synthesis And Properties Of Novel Branched Alkyl Glycoside

As a typical kind of green surfactant,alkyl glycosides(APG)has attracted extensive attention because of their excellent properties showing good application potential in cosmetics,detergent,biomedicine,oil exploitation and other industries,and has become a hot research topic in recent years.By changing the structure of surfactants,the interfacial activity and application performance can be modulated.Studies have shown that the branched chain surfactants can achieve higher interfacial activity or better performance than traditional linear chain surfactants,but there is still no report on the synthesis and performance research of branched chain APG.The two reactants for the synthesis of APG,glucose and fatty alcohol,are water-soluble and oil-soluble,respectively,and their miscibility is an important factor restricting the conversion rate of alkyl glycosides synthesis.In this thesis,micellar catalytic systems was applied in the synthesis of glycosides by direct Fischer method,The reaction conversion can be increased to more than 95%,and the efficient synthesis of branched APG can be achieved under relatively mild conditions.The effects of branched APG hydrophobic chains on the behavior and properties of molecules at gas-liquid,liquid-liquid and solid-liquid interfaces were systematically studied by combining experimental tests with molecular simulation techniques,and the structure-performance relationships on foaming,emulsifying,and wetting were discussed.The contents and relevant conclusions of this thesis are as follows:(1)Synthesis,characterization and isolation of linear chain alkyl glycosides and branched alkyl glycosides.Using glucose as hydrophilic raw material,n-dodecyl alcohol and 2-butyloctanol as linear chain and branched chain hydrophobicity raw material,DBS A as dual-function catalyst.Two kind of alkyl glycosides with the same total carbon number in hydrophobic chains,n-dodecyl glycosides(A-Ⅰ)and 2-butyl-octanol branched chain alkyl glycosides(A-Ⅱ),were synthesized by combining micellar catalytic synthesis method and Fischer direct aglytization method,respectively.The optimum conditions were determined.The structures of the two products were analyzed by IR,MS and 1H NMR,demonstrated the synthesis of target products.Thin layer chromatography(TLC)and column chromatography were used to separate alkyl monoglycoside,diglycoside and triglycoside.(2)Study of the molecular behavior and properties of A-Ⅰ and A-Ⅱ at the gas-liquid interface.The measurement results of equilibrium surface tension and dynamic surface tension show that,compared with A-Ⅰ,branched alkyl glycoside A-Ⅱ has critical micelle concentration(cmc)and lower minimum surface tension(γcmc)with values of 8.70 mg/L and 2.65 mN/m,respectively,smaller ultimate adsorption capacity(Γmax)of 1.85×10-10 mol/cm2 and larger ultimate molecular area(Am)of 0.90 nm2.The gas-liquid interfacial arrangement behavior and interfacial generation energy of two APGs were investigated by molecular dynamics simulation,and the simulation results show that A-ⅠI can fully extend at the gas-liquid interface,the gasliquid interface generation energy is lower,and the polar group hydration is stronger,and the diffusion coefficient of water molecules within the interfacial layer is smaller.The bulk density of A-Ⅱ at the gas-liquid interface is small,and the thickness of the interface film is thin.The foam performance tests show that A-Ⅱ has better foaming ability than A-Ⅰ,while having lower static and dynamic foam stability than A-Ⅰ.Combined with the experimental results and simulation results,it is shown that the molecular behavior and activity of APG at the gas-liquid interface are significantly affected by tail chain branching.(3)Study of the molecular behavior and properties of A-Ⅰ and A-Ⅱ at the oil-water interface,investigate the effects of A-Ⅰ and A-Ⅱ solutions on the wettability of different solid surfaces.The oil-water interfacial tensions of the two APGs were measured using soybean oil,liquid paraffin and octane as the oil phases,respectively.The emulsification properties of the two APGs with liquid paraffin and octane were investigated.The experimental results show that A-Ⅱ is stronger than A-Ⅰ in reducing all three oil-water interfacial tensions at the same concentration.The emulsions formed by A-Ⅱ with liquid paraffin and octane are more stable,and A-ⅠI has better emulsifying ability.Molecular dynamics simulation was used to analyze the distribution behavior and interfacial energy formation of the two APGs at the n-octane-water interface.The simulation results show that the bulk density of A-Ⅱ at the oil-water interface is higher,and the interfacial energy formation of A-Ⅱ is lower,so the interfacial activity of A-Ⅱis higher.The contact angles of two APGs solutions on polypropylene(PP)plate,glass plate and stainless steel plate were measured.The results show that the contact angle between A-Ⅱsolution and PP plate was smaller at the same concentration.The branched tail chain enhances the interaction between APG and the hydrocarbon chain on the surface of PP sheet,more hydrophilic head groups were directed toward the aqueous solution,so A-Ⅱ improves the hydrophilicity of PP sheet surface more significantly.When the concentration is lower than cmc,the contact angles of A-Ⅱ and A-Ⅰ solutions with glass and stainless steel increase,and both can enhance the hydrophobicity of the two solid surfaces.When the concentration is higher than cmc,the contact angles of A-Ⅱ and A-Ⅰ solutions with glass and stainless steel decrease.Both APG solutions can improve the hydrophilicity of glass and stainless steel solid surfaces,and the former A-Ⅱ is more significant.In summary,in this thesis,linear chain APG and new branched APG with the same total carbon number of tail chain were synthesized by combining micelle synthesis method and Fischer method,The effects of branched hydrophobic chain on the molecular behavior and properties of APG on gas-liquid,oil-water and solid-liquid interfaces were investigated by combining experimental and molecular simulation methods.It was found that the new branched APG exhibited high foaming property and low stability in foam performance.This provides new possibilities for constructing green water-based foam systems and regulating foam performance.Meanwhile,branched APG has excellent performance in emulsification and wetting properties,and has certain application potential in the field of daily chemical,washing and oil extraction.