Solution Performances And Applications Of Pyrrolidone Headgroup-based Surfactants

The long chain N-alkyl-2-pyrrolidone surfactants have good biodegradability and surface activity,and have a wide application prospect in the fields of personal care,biomedicine,agricultural additives and so on.N-alkyl-2-pyrrolidone and a series of polybasic acids were used to construct a variety of pyrrolidone cationic surfactants in the form of non-covalent.The surface chemical properties of these pyrrolidone cationic surfactants and their applications in thickening of amino acid surfactants were systematically investigated.PartⅠ:Single chain and gemini pyrrolidone cationic surfactants were synthesized by using N-octyl-2-pyrrolidone（C8P）,N-dodecyl-2-pyrrolidone（C12P）,monobasic acid（hydrochloric acid,acetic acid）and dicarboxylic acid HOOC（CH₂）_nCOOH（n=1,2,3,4）in the form of non-covalent,respectively.The structure of the surfactants was characterized by FT-IR and ¹H NMR.The effects of the hydrop H值obic chain length and the linker chain length on the solution behavior of the surfactant were investigated by measuring the surface tension curve of the solution.The results show that the critical micelle concentration（CMC）of C12P series single chain pyrrolidone cationic surfactants is higher than that of C12P,but is about one order of magnitude smaller than that of C8P series single chain pyrrolidone cationic surfactants.Compared with single chain surfactants,the CMC and maximum surface excess(Γ_max)of gemini surfactants decrease.The linker length has little effect on the C8P series.For C12P series,the CMC decreases with the increase of the linker chain length.It is also found that when the volume of C12P is about twice that of the strong acid（concentrated hydrochloric acid,concentrated sulfuric acid）,the gel is formed and the system has high viscoelasticity.PartⅡ:A series of pyrrolidone citrate surfactants（HCA-nC8P/HCA-n C12P,n=1,2,3）were fabricated by non-covalent bonding with tricarboxylic acid（citric acid）and N-alkyl-2-pyrrolidone surfactants（C8P,C12P）at different molar ratios（1:1,1:2,1:3）.The structure of the surfactants was confirmed by FT-IR,¹H NMR,differential scanning calorimetry（DSC）and electrical conductivity.The purity of the surfactants met the requirements of the study of the surface behavior of the solution.The experimental results of solution surface tension show that,with the increase of the molar ratio of C8P/C12P to citric acid,except HCA-1C12P,CMC gradually decreases,Γ_max decreases,and the average minimum adsorption area(A_min)occupied by each molecule on the solution surface increases.The solubility of pyrrolidone citrate surfactants in water also shows a trend from high to low.They have a good wetting effect on the surface of the oil-wet paraffin,and with the increase of n,the oily wetting becomes stronger.When applied to the thickening of amino acid surfactants（sodium lauroyl sarcosine）,it is found that the viscosity could be increased significantly at a lower concentration of HCA-nC8P/HCA-n C12P.PartⅢ:Follow up from PartⅡ,the effect of pyrrolidone surfactants on the thickening of sodium lauroyl sarcosine（SLSar）in aqueous solution was studied systematically.The effects of mass fraction of total surfactants,the addition amount of C8P/C12P,p H and temperature on the viscosity of the system were investigated.The results show that the viscosity of SLSar/water/Cn P system reaches a high viscosity of 10⁴～10⁵ Pa·s with the increase of mass fraction of C8P/C12P at high concentration of total surfactants（including 30wt%SLSar）.The system forms a transparent gel which could be inverted.The structure is a hexagonal liquid crystal determined by polarizing microscope and small angle X-ray scattering（SAXS）.When the mass fraction of total surfactants is 15wt%,with the mass ratio of C12P to SLSar increasing,the viscosity of the system increases continuously.First,the system forms wormlike micelles,and then becomes cloudy and viscous,forming lamellar liquid crystal.In addition,proper p H and low temperature are beneficial to the formation of wormlike micelles,which is conducive to adjusting the viscosity of amino acid surfactants according to actual needs.