Study On The Preparation And Properties Of Low Molecular Weight Hydrogels Formed By Rosin-based Surfactants

Low molecular weight hydrogels,an important class of soft materials,play an important role in the fields of material sciences,life sciences and medicine.Designing low molecular weight hydrogelators with novel structures is the core of preparing small molecular weight hydrogels.Due to the complexity of molecular self-assembly,it is a big challenge to design low molecular weight hydrogelators with suitable molecular structures and specific functions.In view of low molecular weight hydrogel systems,the gelators generally contain rigid hydrophobic structures and the interaction between hydrophobic groups serves as an important driving force for the self-assembly of molecules to form hydrogels.Therefore,by choosing suitable raw materials and adopting reasonable molecular design,it is expected to obtain a series of low molecular weight hydrogels with unique properties.Rosin is a featured forestry resource in China,and its main ingredient is abietic acid.The molecular structure of abietic acid contains a hydrophobic rigid group with a tricyclic diterpene structure,and the carboxyl group of abietic acid can be used as an active site for introducing other groups.In this thesis,the dehydroabietic acid,an important derivative of rosin,was taken as the raw material.By introducing flexible chains of different lengths,a series of novel rosin-based amine oxide surfactants were synthesized.The surface activity,the self-assembly ability and application performance were studied respectively.The main research contents and research results are as follows:?1?The synthesis and surface activity of a series of rosin-based amine oxide surfactant R-n-AO?n=6,8,10?were studied.Using dehydroabietic acid as the raw material,R-n-AO were obtained by amidation and oxidation reaction,and the products were purified by chromatography.The structure and purity of the product were characterized by ¹H NMR and high-resolution mass spectrometry.The structure and the purity of the target products were identified.The surface activity of rosin-based amine oxide surfactants was studied by surface tension method.The cmc values of 6-dehydroabietyl amido-N,N-dimethyl-hexylamine oxide?R-6-AO?,8-dehydroabietylamide-N,N-dimethyl-octylamine oxide?R-8-AO?and10-Dehydroabietyl amido-N,N-dimethyl-decylamine oxide?R-10-AO?were 0.601 mmol·L^-1,0.115 mmol·L^-1 and 0.035 mmol·L^-1,respectively,and the?_cmc values were 35.20 mN·m^-1,35.77 mN·m^-1 and 35.81mN·m^-1,respectively.The results indicated that R-n-AO had excellent surface activity,and the presence of rigid rosin acid groups produced strong intermolecular hydrophobic interaction,which endowed the surfactant strong aggregation ability.?2?The self-assembly of R-n-AO in aqueous solutions were investigated.Differential scanning calorimeter,rheometer,cryogenic transmission electron microscope,circular dichroism were used to investigate the self-assembly of R-n-AO.The results showed that by increasing the length of the flexible chain in the molecule structure,R-n-AO can assemble into aggregates with different morphologies,resulting in the formation of low molecular weight hydrogels with different properties.R-6-AO molecules formed left-handed chiral fibers with a cross-sectional diameter about 10 nm and a length greater over 2?m.The critical gelation concentration?CGC?of the hydrogel formed by R-6-AO was only 0.177 wt.%(4 mmol·L^-1),and the gel-sol transition temperature(T_gel-sol)was 35°C,which is the first reported rosin-based supramolecular hydrogel;R-8-AO molecules formed right-handed chiral wormlike micelles without any additives,which have a cross-sectional diameter of 5-6 nm and a length of more than 200 nm.The critical overlap concentration of R-8-AO was approximately 8 mM,and the zero-shear viscosity was highly exponentially dependent on the concentration.When the concentration was above 30 mmol·L^-1?1.4 wt.%?,the solution could be gelled;R-10-AO was assembled into a crisscross ribbon structure with a width of 50nm-150 nm.The twisting phenomenon of ribbon micelles can also be observed.The water could be gelled when the concentration was greater than 50 mmol·L^-1.?3?A new type O/W gel emulsions were prepared with R-6-AO as the emulsifier and the stabilizer,and n-dodecane as the oil phase.Optical microscopy,laser confocal microscopy,rheology,and low-temperature transmission electron microscopy were used to investigate the properties of gel emulsions.R-6-AO not only stabilized gel emulsions at concentrations above0.2 wt.%of the continuous phase,but also formed gel emulsions with the oil volume fraction freely adjustable between 2%and 95%.This property is obviously superior to that of the traditional high internal phase emulsions,where the volume fraction of the dispersed phase is higher than 74%.The gel emulsions show good thermal reversibility,and could also be prepared with different oil phases,which greatly expand the application range of gel emulsions.?4?Using R-6-AO as stabilizer,gel foams with high water content and high stability were prepared.The dynamic foam analyzer and cryogenic transmission electron microscope were used to investigate the properties of the gel foams.Taking a 10 mmol·L^-1 R-6-AO solution for example,the half-life of the generated foams was 12,800 min and 45 vol%water was trapped by the foam.The draining process was also slow.No liquid film drainage was observed even after about 2000 min.In contrast,the volume fraction of water in 10 mmol·L^-1sodium dodecyl sulfate?SDS?foam decreased from 20 vol%to 1 vol%within 18 min.The stability of the foams was closely related to the structure of the aggregates in the liquid film.By adjusting the initial preparation temperature,the equilibrium temperature of the foams and the pH value of the system,the microstructure of the aggregates in the liquid film can be effectively changed,leading to tremendous variation of the foam stabilities.?5?The wormlike micelles formed by R-8-AO were used as soft templates to prepare ultra-small gold nanoparticles.The properties of gold nanoparticles were investigated by ultraviolet-visible absorption spectroscopy and transmission electron microscopy.The results showed that gold nanoparticles were synthesized in-situ by irradiating mixed solutions of HAuCl4 and wormlike micelles formed by R-8-AO with UV light.The generated spherical gold nanoparticles exhibit a high degree of monodispersity with a particle size of only 3±1nm.In addition,the gold nanoparticles form a worm-like morphology,showing the important role of small molecule aggregation structure in directing the assembly of inorganic nanoparticles.