Synthesis,Self-assembly And Applications Of Rosin-Based PH-Responsive Surfactants

In the past decades,stimuli-responsive surfactants and its stimuli-responsive systems have drawn considerable attention.And pH-responsive surfactants have been paid more attention due to its simplicity,affordability,and variety and availability of the chemicals used.Besides,the preparation of green surfactants from natural products also is an important development direction of surfactants.Rosin is an abundantly biomass resource,its main ingredient is abietic acid.The molecule of abietic acid is composed of a large rigid tricyclic hydrophenanthrene structure,which is extremely hydrophobic.In addition,the molecular structure of abietic acid contains a carboxyl group and a conjugated double bond,it can be easily modified.Thus,rosin is an available raw material for the synthesis of green surfactants.The rosin rigid group has large molecular volume,complex molecular conformation and strong hydrophobic interaction which will inevitably have an influence on the surfactant surface activity,self-assembly,and application performance etc.Herein,using rosin as the raw material,differently rosin-based pH-responsive surfactants have been synthesized,the surface activity,the self-assembly ability,pH-responsiveness of the synthesized rosin-based pH-responsive surfactants and its applications in dispersion of single-walled carbon nanotubes(SWNTs)were studied respectively.The main research contents and results are as follows:(1)The synthesis and surface activity of a series of rosin-based pH-responsive surfactants containing a flexible alkyl chain,namely,sodium N-alkyl-maleimidepimaric carboxylate(Cn-MPA-Na,n=12,14,16).Cn-MPA-Na were synthesized from rosin though D-A bonus,amidation and acid-base neutralization.The structures of Cn-MPA-Na were characterized by IR,1H NMR,13C NMR,MS and elemental analysis.The surface tension method was used to investigate the surface activities of Cn-MPA-Na.The critical micelle concentration(cmc)value of C12-MPA-Na,C14-MPA-Na and C16-MPA-Na is 0.015,0.025 and 0.0031 mM,respectively,and the surface tension at cmc(ycmc)is 33.00,33.42 and 32.13 mN·m-1,respectively.The results show that the Cn-MPA-Na show strong aggregation ability and excellent surface activity.(2)The self-assembly for C12-MPA-Na and the mixture system of Cn-MPA-Na and cetyltrimethylammonium bromide(CTAB).The nanometer particle-size analyzer,rheology,cryogenic transmission electron microscopy(Cryo-TEM)and polarizing microscope were used to study the self-assembly of Cn-MPA-Na.Despite containing 36 carbon atoms,C12-MPA-Na shows good water solubility at room temperature.Spherical aggregates with diameters of 100?200 nm are formed by C12-MPA-Na when its concentration is above 0.10 mM.Annular wormlike micelles,threadlike wormlike micelles and common wormlike micelles are discovered at a concentration between 58 mM and 85 mM.And the Annular and threadlike wormlike micelles were rare reported.The phase behavior of the Cn-MPA-Na/CTAB(100 mM)system sequentially transforms from a viscoelastic solution to an aqueous surfactant two-phase system(ASTP),an aqueous surfactant three-phase system(AS3P),and an anisotropic homogeneous phase as the concentration of Cn-MPA-Na was continuously increased from 10 to 35 mM.The aggregates in the viscoelastic solutions are wormlike micelles.The microstructures in the upper phase of the ASTP are wormlike micelles,and in the lower phase are spherical and rod-like micelles.The aggregates in the upper and lower phases of the AS3P are wormlike micelles,and spherical and rod-like micelles,respectively.The aggregates in the middle phase of the AS3P and the anisotropic homogeneous phase are sponge-like micelles.The anisotropic homogeneous solutions show clear birefringence and Maltese cross liquid crystal were formed.The phase behavior and aggregates induced by changes in pH in C14-MPA-Na(16 mM)/CTAB(100 mM)system have been investigated.Viscoelastic solutions at a pH larger than 1.41,opalescent blue solutions at a pH between 1.41 and 1.32 and ASTPs at a pH between 1.32 and 0.56 are formed sequentially.The microstructures in the viscoelastic solutions are worm like micelles that partially transform to vesicles in the opalescent blue solutions.The aggregates in the upper phase of the ASTP are vesicles and lamellar micelles,and in the lower phase are spherical micelles.The viscoelastic wormlike micellar solution and an ASTP can be reversed by alternating the pH.A pH-responsive ASTP are formed.Rich phase behaviors and variously different aggregates are formed by the Cn-MPA-Na(3)The dispersion of SWNTs in the C14-MPA-Na/CTAB viscoelastic wormlike micellar solutions.Ingeniously utilizing the strong viscoelasticity of wormlike micelles and the excellent dispersion of surfactant,SWNTs were hybridized into the C14-MPA-Na/CTAB viscoelastic wormlike micellar solutions.Cryo-TEM,UV visible near infrared(UV-Vis-NIR),near-infrared photoluminescence(NIR-PL)and UV-Vis spectroscopy were used to study the dispersion of SWNTs in the viscoelastic wormlike micellar solutions.The results shows SWNTs can remain dispersed for more than 6 months at pH 6.40.When the pH decreases to 1.11,the system of C14-MPA-Na/CTAB/SWNTs forms an ASTP,and SWNTs gather at the middle of two phases.The SWNTs can be recycled through a process of liquid separation(4)The synthesis and surface activity of another rosin-based pH-responsive surfactant,sodium N-azobenzene-maleimidepimaric carboxylate(Na-MPA-AZO-Na).Na-MPA-AZO-Na was synthesized using rosin as the starting material through D-A bonus,amidation,diazotization,coupling reaction and acid-base neutralization.The hydrophobic group of Na-MPA-AZO-Na is completely composed by rigid group.The structure of Na-MPA-AZO-Na was characterized by IR,1H NMR,13C NMR,MS and elemental analysis.The surface tension method was used to investigate the surface activities of Na-MPA-AZO-Na.The cmc at pH 9.31 and pH 12.35 is 0.010 and 0.64 mM,respectively,and the ycmc is 52.05 and 48.27 mN-m-1,respectively.The Na-MPA-AZO-Na shows strong aggregation ability,but its ability of decreasing surface tension is poor.(5)The self-assembly for Na-MPA-AZO-Na and the mixture system of Na-MPA-AZO-Na and CTAB.The polarizing microscope and dynamic surface tension were used to study the self-assembly of Na-MPA-AZO-Na at the interface of air/water.Abundant and stable foams are generated by Na-MPA-AZO-Na at pH 9.31,and less and unstable foams at pH 12.35,the multi cycle between foaming and deforming by altering aqueous pH between 9.31 and 12.35 can be obtained.And the pH-responsive foams show highly pH-responsive efficiency.The transition of aqueous pH from 12.35 to 9.31 leads to a Bola surfactant converts into a traditional surfactant,which provides a new inspiration in the construction of responsive system.The rheology and Cryo-TEM were used to studied the self-assembly of the mixture system of Na-MPA-AZO-Na and CTAB.When the pH is 2.62,the Na-MPA-AZO-Na/CTAB system can form viscoelastic solutions,the aggregates are wormlike micelles with a cross-sectional diameter of 10 nm.When the pH is 12.00,the Na-MPA-AZO-Na/CTAB system show poor viscoelasticity and the aggregates are spherical micelles and rod-like micelles.The wormlike micelles and spherical micelles can be transformed by altering the pH(6)The study of pH-responsive SWNTs dispersions prepared by Na-MPA-AZO-Na Cryo-TEM,UV-Vis-IR,TEM and Zeta potential were used to study the dispersion of SWNTs The SWNTs can be homogeneously and stably dispersed at pH 10.36,and aggregate at pH 5.35 The dispersion and precipitation of SWNTs can be easily achieved by changing the pH Importantly,due to the strong hydrophobic interaction and large molecular volume of the rosin rigid group,the precipitated SWNTs can be easily re-dispersed by adjusting the pH to 10.36 without sonication.The results provide a simple and efficient method for the dispersion and precipitation of SWNTs.