Synthesis Of Quaternary Ammonium Camphorsulfonate Plastic Crystals And Phase Behaviors Of N-C₂₈ And C₃₀ Under Nanoconfinement

Organic ionic plastic crystals?OIPCs?have gained considerable attention in the synthesis and applications in recent years,due to various electrochemical devices.Because of the accidents caused by the flammable electrolyte matries of liquid organic solvents,solid electrolytes have become a hot research topic.Organic ionic plastic crystals have special molecular structures,which are the candidates for solid state electrolytes in applications in electrochemical devices such as lithium batteries and dye-sensitised solar cells.In this paper,a series of quaternary ammonium camphor sulfonate organic ionic salts are prepared.These materials with plastic crystal phases were recognized using DSC,polarized light microscope,NMR and XRD.The heat capacities of one new plastic crystal material were measured in the liquid helium temperature region.The precision thermodynamic properties such as the phase transition temperature and enthalpy were obtained.Some single crystal structures were measured for the phases appeared during phase transformations.The conductivities of ions were measured by AC impedance method,which aims at exploration of the dominant factors of ion conduction?lattice or grain boundary defects?and the way to improve ion conductivities.The physical properties of materials in nanometer confinement often change greatly.Previous studies on the phase behaviors of materials in nanospace show that the phase transition temperature is associated with the pore size,interfacial interaction and pore morphology.The depression of phase transition temperatures often exhibits linear dependence on the inverse of pore diameter.However,quantitative estimates of the influence of the pore morphology and interfacial interaction are seldom described.In this paper,we studied the nanoconfinement effect on the phase behaviors of normal octacosane(n-C₂₈H₅₈,C₂₈)and triacontane(n-C₃₀H₆₂,C₃₀)using differential scanning calorimetry?DSC?and temperature-dependent powder X-ray diffraction?XRD?.When confined in the nanopores of controlled pore glasses?CPGs?,SG,SBA-15 and KIT-6.The main research contents and results are as follows:?1?Eleven organic ionic salts with high thermal stability have been synthesized.They were composed of camphor sulfonate anion?a large carbon frame as stator?and quaternary ammonium cation?as rotator?.Among them,three kinds of N₂₂₂₂-CPSO₃ and N₁₁₂₂-CPSO₃ with different configuration were found to have plastic phases.The ¹H NMR spectrum of N₂₂₂₂-CPSO₃ showed the half peak width decreases with the increasing temperature;the conductivitities of pure N₂₂₂₂-CPSO₃ increased with the increasing temperature;and the conductivity increased several times when doping of Cl^-and OH^-.The heat capacities and thermodynamic parameters were obtained using an adiabatic calorimeter.The ¹H NMR spectrum of N₁₁₂₂-CPSO₃ showed that the peak splitting is more obvious in the plastic phases,and plastic deformation was observed when applying mechanical pressure.The experiments provided some information for study of ionic conductivities for solid electrolytes.?2?C₂₈8 showed depressed melting points and solid-solid phase transition temperatures.The depression of phase transition temperatures,the degree of supercooling and enthalpies of phase transitions for C₂₈8 in the CPGs and SBA-15 exhibited a linear relationship with the inverse of the pore diameter.The phase transition temperatures for C₂₈8 in the pores also varied with the pore geometry,and the depression of melting points in one-dimensional pores?SBA-15?is 2.2 times of that in three-dimensional pores?CPGs?.In the CPG and SBA-15pores,the phase transition temperatures of C₂₈8 may not be affected by the changing interfacial interactions.Synchrotron radiation X-ray diffraction revealed that bulk C₂₈8 crystallized into a monoclinic structure at room temperature,while an orthorhombic phase was observed for C₂₈confined in the CPGs?50,100,and 300 nm?.And the surface layer of the alkane lamellar structure became rougher when the pore size decreased.Variable-temperature X-ray diffraction analysis demonstrated that the phase transformation sequences of C₂₈8 in the nanopores changed and were different to that of the bulk.At low temperatures,C₂₈8 in the CPGs and SBA-15 crystallized into an orthorhombic phase instead of the monoclinic structure of the bulk.At high temperatures,two new rotator phases,R_I and R_II,were observed in the pores of the CPG?24 nm?and SBA-15?14.4 nm?.The appearance of the new phases was attributed to the extra disorder in the packing of pore molecules in the interfacial layers.The phase behaviors of C₃₀0 in the nanopores are similar with those observed in the pore-confined C₂₈.The study is supposed to gain an improved insight into nanoconfinement effect on the phase behaviors of a representative normal alkane with a long alkyl chain.The knowledge of the melting and crystallization of alkyl chains in nanosized domains can provide important information for applications in liquid crystals,biomembranes,heat storage materials,etc.