Study Of Polyampholyte Gels And Supramolecular Gels Formed By Non-covalent Interactions

Ionically crosslinked gels are novel non-covalent bond gels.The electrostatic attraction of high density between negatively and positively charged groups on polymer chains makes the polymer chains capable to form stable junction zones which maintain the ordered structure inside the ionically crosslinked gels.An ionic complex of anionic and cationic monomers was obtained by protonation of(N,N-diethylamino)ethylmethacrylate (DEAM) with acrylic acid(AA).Free radical copolymerization of the ionic complex and acrylamide(AAm),yielded the ionically crosslinked polyampholytic gel electrolytes [poly(AAc-DEAM-AAm),designated as PADA]using water or organic solvents.The investigation indicated PADA hydrogels that were prepared in water exhibited peculiar erosion phenomenon under non-contact direct current electric fields.The erosion rate of PADA gels was related to the voltage of electric field,the concentration of salt solution,pH value of buffer solution,the molar ratio of anionic/cationic monomers,valence of ion and so on.For instance,the erosion rate increased with an increase of voltage or the concentration of salt solution.The erosion kinetics revealed that the erosion rate of PADA gels was almost invariable in experiments.The PADA organogel electrolytes that were prepared in two types of organic solvents (propylene carbonate(PC) and the mixture of PC,ethyl methyl ether(DME) and dioxolane (DOL)(3:1:1,v/v,designated as PDD)) containing a lithium salt(LiClO₄,1mol/L) exhibited good thermal stability.The impedance analysis at temperatures ranging from -30 to 75℃indicated that the ionic conductivities of the PADA gel electrolytes were rather close to those of liquid electrolytes.The temperature dependence of the ionic conductivities was found to be in accord with the Arrhenius equation.Moreover,the ionic conductivities of PADA gel electrolytes increased with an increase of the molar ratios of cationic/anionic monomers.The ionic conductivities of PADA gels prepared in PDD were higher than those of PADA gels prepared in PC only.The electrochemical windows of PADA gel electrolytes measured by cyclic voltammetry were in the range from -1 to 4.5V(vs.Li/Li⁺).The impedance analysis of the PADA organogel electrolyte that was prepared in a solvent mixture of ethylene carbonate(EC),dimethyl carbonate(DMC) and ethyl methyl carbonate(EMC)(1:1:1,v/v) containing 1 mol/L of LiPF₆ indicated that the ionic conductivity of the polyampholytic gel electrolyte was rather close to that of solution electrolytes in the absence of a polymer at the same temperature.The temperature dependence of the conductivity was found to be well in accord with the Arrhenius behavior. The formation processes of the solid electrolyte interphase(SEI) formed in both gel and solution electrolytes during the cycles of charge-discharge were investigated by cyclic voltammetry,electrochemical impedance spectroscopy and field emission scanning electron microscopy.The results indicate that the SEI formed in the gel electrolyte showed a rough surface consisting of smaller solid depositions.1,3:2,4-di-p-methylbenzylidene sorbitol(MDBS) is a small organic molecule that is capable of inducing self-assembly in a wide variety of organic solvents and of forming organogels.In this paper,we present a novel approach to tune the network architectures of organogels by utilizing geometric confinement while varying the gelator concentration. Self-assembly of MDBS in propylene carbonate(PC) is investigated in a series of microchannels with widths varying from 20 to 80μm and the gelator concentration varying from 2 to 7 wt%.We demonstrate by optical microscopy,scanning electron microscopy (SEM),polarized microscopy and transmission electronmicroscopy(TEM) that a transition from fibrillar structure to sheaflike spherulite structure occurs when(a) the channel width is increased for fixed gelator concentrations and(b) gelator concentration is increased for fixed channel widths.A phase diagram is built based on these observations.The thermal properties of the organogel are measured by differential scanning calorimetry(DSC) to verify the structural difference obtained under confined and unconfined conditions and the structure stability.Our results provide a novel strategy to control the topological structure of self-assembled systems and to modify their thermal properties via geometric confinement.