Studies On Aggregation Behaviors Of Bile Salt Surfactants In Deep Eutectic Solvents

The deep eutectic solvents(DESs)are the mixtures composed of two or three compounds at a suitable stoichiometric ratio via hydrogen bond.Similar to ionic liquids,DESs have the physicochemial properties such as low volatility,low flammability,wide electrochemical potential window and favorable solubility for various compounds,also called quasi-ionic liquids.DESs have attracted much attention owing to the simple preparation,low cost,biodegradable,in conformity with the development principle of green chemistry.As an important class of organic compounds,the surfactant can be widely used in the fields of production and life.For the purpose of further expanding the application range of surfactants,researchers are looking forward to finding the new potential solvent media for self-assembly.There have been now many reports to explore such aggregation behaviors of the conventional ionic surfactants in DESs.Usually,they form micellar aggregates.However,there have been rarely reports on eutectic gels.Bile salts(BSs)act not only as naturally anionic surfactants,but also as an important type of low-molecular-weight gelators(LMWG).Unlike the linear structure of conventional surfactants,BSs contain rigid steroidal skeletons with the facial amphiphilic structures.The presence of steroidal backbones induces BSs to present unusual interfacial aggregation behaviors and self-assembling mechanism.In addition,the luminescent gels can be constructed by the metal-coordination interaction between the carboxylate group of BSs and rare-earth metal ions.Based on the above background,the content of this thesis is designed to contain following two parts:1.The micellization and gelation behaviors of the bile salt:sodium deoxycholate(NaDC),were firstly studied in the common DESs,which were composed of choline chloride(ChCl)and urea or glycerol,called ChU or ChG,respectively.The critical micelle concentration(CMC)of NaDC in ChU was found smaller than that in ChG.And both of them was larger than that in water.The inorganic salt:LiCI was chosen to study its influence on the self-assembly behavior of NaDC in ChG.After adding LiCl(10 mM)to ChG,the CMC of NaDC was reduced,just like that observed in water.As an LMWG,NaDC could form gel in ChU but only precipitates in ChG.However,when adding large amounts of LiCl(100,200,400,600 mM)to ChG,NaDC could also induce gel formation,too.2.The luminescent gels through self-assembly of the sodium cholate and europium nitrate were firstly fabricated in three choline chloride(ChCl)-based DESs with urea or glycerol or ethylene glycol as hydrogen bond donor(HBD).The gel-ike nature of obtained eutectogels were confirmed by rheology measurements.Among them,the one formed in ChU was found to possess the strongest mechanical strength,while the weaknest one was in ChCl/ethylene glycol DES.The microstructure of gels in three DESs were characterized by scanning electron microscopy and the entangled fibers with diameters in between 50～80 nm were observed.All three eutectogels exhibited good photophysical properties.The one formed in ChG exhibited the longest luminescence lifetime and quantum efficiency,which were better than those observed in similar systems in water or ionic liquids.Fourier transformed infrared spectroscopy and small-angle X-ray scattering were used to analyze the gel formation mechanism.The luminescent gels were considered to have the lamellae structure,which were driven synergistically by metal coordination,hydrogen bonding and solvophobic interactions.The obtained results demonstrate the possibility to use DESs to regulate the aggregation behavior of surfactants or construct the lanthanide luminescent soft materials through the choice of hydrogen-bond donor molecules.