| The investigation on the self-assembly of surfactants is an important part in the field of physical chemistry.Also,it nowadays is the focus and front subject of various interdiscipline subjects.Based on the synergistic effect of multiple noncovalent interactions,surfactant molecules can self-assemble into aggregates with different and ordered morphologies.Under certain conditions,self-assembled structures can further develop into multifunctional materials,such as different gels.Since the lack of precise and effective methods,we could not understand the mechanism of dynamic process for the self-assembly of surfactants.Combining experimental and theoretical studies,we can further investigate the formation and transformation mechanism of aggregate structures formed by surfactants in different solvents,especially in room-temperature ionic liquids(RTILs).These results have great guiding significance for the construction of functional materials by surfactants.The preparation of multifunctional gels through the self-assembly of surfactants has became the research hotspot.Among various gels,ionogels formed by amphiphilic molecules in RTILs possess superior performances,including good ionic conductivity and lubricative properties and so on,and they have attracted more and more attention.In this thesis,my work has centred on researches on self-assembly of surfactants and can be roughly divided into two parts.The first issue we focused on is micellar solutions formed by fluorinated surfactants in both water and RTIL.We investigated structures and thermodynamic and kinetic micellization by using technological methods such as 19F NMR and transmission electron microscope(TEM),as well as the molecular dynamics(MD)simulation.It is expected that these results could provide detailed and richer theory and discipline for molecular self-assembly of surfactants in solutions.In the second part of this thesis,we constructed various ionogels by dissolving surfactants in protic and imidazolium RTILs.The revelation of different supermolecular structures and the mechanism of structural transformation could provide better understanding for the self-assembly of surfactants in RTIL media.Meanwhile,the work expanded the application range of ionogel materials.The contents of this doctoral thesis are as follows:In Chapter ?,as for the research background of this thesis,we gave a comprehensive presentation from several aspects.Based on the basic conception of self-assembly,the classification,features and research significance of self-assembly have been summarized.Then we detailedly introduced important knowledge for surfactant physical chemistry,including the information of surfactants,theories of the aggregate formation,parameters of micelle formation,several types of aggregates as well as the important thermodynamics and kinetics in the micellization process.We summarized properties,applications of RTILs,as well as various aggregates formed in RTIL media.The construction,properties and recent important applications of ionogels were reviewed in detail.Finally,we presented the research purpose,contents and significance of the work.In Chapter ?,we investigated the micellization of a zwitterionic fluorinated surfactant(C9F19CF=CHCH2N(CH3)2(CH2)30S03,PDSPDA)in protic RTIL,ethylammonium nitrate(EAN),by using methods of 19F NMR,surface tension and freeze-fracture transmission electron microscope(FF-TEM).Based on results of surface tension measurements,we found that the micelle formation in present work is a mainly entropy-driven process at relatively low temperatures,while at high temperatures it is a mainly enthalpy-driven process.We successfully detected two types of signals on NMR time scale due to the slow exchange rate for surfactants between micelles and the bulk.The long lifetime of PDSPDA micelle is a comprehensive result of multi factors.Rare work has been reported concerning the kinetic micellization of surfactants in RTIL media,so the present work deepened this part.In Chapter ?,we performed deeper investigation on the micellar solution formed by a fluorinated surfactant,tetraethylammonium perfluorooctane sulfonate(TPFOS,C8F17SO3N(C2H5)4)in water.By using 19F NMR,we unexpectedly detected four signals for TPFOS,including one monomer signal and three micelle signals.Similarly,the result was caused by the slow kinetic exchange process in the system.The cryogenic transmission electron microscope(cryo-TEM)observations confirmed that there are three types of micelles:spherical micelles,toroidal micelles and wormlike/wormlike micelles with rings in end caps.From the viewpoint of thermodynamics,the process of micelle formation is mainly driven by the entropy term,indicating the unusually strong hydrophobic effect.MD simulation demonstrated that the large and hydrophobic counterion +N(C2H5)4 could diffuse into the core of micelles.The special distribution of couterions can explain both the intense hydrophobic interactions and the slow kinetic micellization process in the system.In Chapter ?,we constructed an ionogels through the self-assembly of a sugar surfactant in' EAN.The sugar surfactant used in present work is N-Octadecyllactobionamide(C18G2),which containing a disaccharide polar head.By using small angle X-ray scattering(SAXS)measurements and FF-TEM observations,we confirmed the effects of C18G2 concentration and temperature on microstructures,and revealed the formation and transformation mechanisms of different aggregates.We investigated the thermal reversible and rheological properties through SAXS,differential scanning calorimetry(DSC)and rheological measurements.Tribological results revealed that the lubricating properties of EAN can be effectively enhanced by the sugar surfactant,which could provide theoretical support for the construction and application of ionogel lubricants.In Chapter ?,a sugar surfactant containing gluconic acid,amino acid and hexadecyl was synthesized and dissolved into two imidazolium RTILs to prepare different ionogels.The stimuli-responsive properties have been investigated,and microstructures as well as their transformation mechanism were revealed by SAXS,FF-TEM,field-emission scanning electron microscope(FE-SEM)and X-ray diffraction(XRD)measurements.Rheological results indicated the good thixotropy of ionogels.Different microstructures of destroyed samples have been clearly observed from SEM.Both differences of rheological properties and microstructures contribute to the different tribological properties of ionogels formed in different RTILs.The revelation of the correlation of microstrcutures,rheological and tribological properties may provide important information for future applications of ionogel lubricants.In Chapter ?,we prepared ionogels through the self-assembly of pseudogemini surfactants in EAN.These ionogels showed high mechanical strength and thermal-reversible property.Synergistic effects of various noncovalent interactions including electrostatic interaction,hydrogen bond and solvophobic interaction,as well as aggregate morphologies have been investigated.The formation mechanism of different microstructures formed by pseudogemini surfactants in RTIL has been summarized.The work provided an important method for constructing ionogels.In Chapter ?,gelation behaviors of three cationic surfactants in protic and imidazolium RTILs have been investigated.The cation of three surfactants is 1-hexadecylpyridinium,and counterions are Br-,[FeCl3Br]-and[CeCl3Br]-.The corresponding surfactants are HB,HBFe and HBCe,respectively,and all of them formed lamellar structures in different RTILs.The size of imidazolium RTILs has great influence on the transformation temperature of ionogels,as has been revealed by DSC results.SAXS results indicated that the interlayer spacing of lamellar structures depends on the anion type of imidazolium RTILs.Further rheological measurements demonstrated that the mechanical strength of ionogels formed in imidazolium RTILs is closely connected with both sizes of anions and cations of RTILs.By using HBCe/EAN ionogel as the precursor,we obtained CeO2 nanoparticles with different sizes,which exhibiting good catalase mimetic activity. |
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