| Gemini Ionic Liquids?GILs?are a new category of ionic liquids and functional soft materials obtained by merging molecular framework similar to Gemini and ionic liquid molecular building block in the molecular design concept.The structure contains a couple of cations connected by covalent bonds and two separate anions.GILs possess the specificity of ionic liquids,higher thermal stability than traditional ionic liquids and excellent designability.Nevertheless,the main disadvantages of GILs were higher melting point?>100??and viscosity,and some GILs exhibit high viscosity even at high temperature,which can weaken the important characteristics of ILs and result in the reduction of mass transfer rate and the increase of transmission costs in the process of application.Therefore,whether to use the excellent designability of GILs to overcome the above-mentioned weaknesses has become one of the scientific problems that need to be overcomed under the premise of maintaining the molecular framework similar to Gemini and the excellent characteristics of ionic liquids.In this study,some efforts are undertaken to solve the above-mentioned bottleneck problems by constructing asymmetrical GILs,that is,their physicochemcal properties can be regulated through the selection and matching of various anions and cations to achieve the goal of lowering the melting point and controlling the properties of viscosity and solubility,providing a theoretical and practical basis for their use as solvents and functional materials.Secondly,the volumetric and viscosity properties of the solutions containing GILs,as well as the high solubility of sugars in GILs for their conversion,are also the basic data that must be reserved for the use of GILs in biomass processing.In addition,functional GILs,a novel GILs,possess some special functions or characteristics as surface activity and catalytic performance other than the properties of ILs by the means of introducing one or more appropriate functional groups on the anion and cation.In view of the above-mentioned scientific problems and application needs,the main research contents,results and conclusions in the study are as follows:Constructing asymmetrical GILs can be respected to significantly reduce their melting point and viscosity of GILs.Three asymmetrical GILs were consequently designed and synthesized with dicyandiamide as anions and trimethyl tertiary amine as a cationic precursor matched with 1-methylimidazole,pyridine and 1-methylpiperidine,respectively.Constructing asymmetrical Gemini ionic liquid surfactants may be also respected to take full advantages of the excellent properties of Gemini surfactants and ionic liquids.Four novel asymmetrical Gemini ionic liquid surfactants were also designed and prepared by matching long chain alkyl tertiary amines and n-alkylimidazole obtained by introducing a series of chain length linear alkyl groups on the imidazole ring.The structures of the obtained GILs were respectively determined by 1H NMR,13C NMR and elemental analysis.The physicochemical properties of pure dicyandiamide-based asymmetrical GILs,including melting point,density,viscosity,heat capacity and thermal stability,were systematically investigated.The results showed that the melting points were all lower than-70?.Density decreased linearly with elevating temperature and the coefficient of thermal expansion???,standard molar volume?Vm?,molecular volume?V?,standard entropy?S0?,lattice potential or crystal(UPOT)are obtained.Viscosity decreased with increasing temperature.Viscosity-temperature relationship can be quantitatively described by VTF and mVTF equations.The relationship between molar heat capacity and temperature is quantitatively modeled by polynomial equation.The corresponding thermodynamic functions(relative enthalpy,HT-H298.15 K and relative entropy,ST-S298.15 K)were determined.Thermal stability is higher and increased in the following order:[N111C3MIM][N?CN?2]2>[N111C3Py][N?CN?2]2>[N111C3MPi][N?CN?2]2.Thermal decomposition mechanism of dicyandiamide-based asymmetrical GILs was proposed and suggested.The experimental results show that the asymmetrical GILs have a lower melting point and a moderate viscosity for the reason that the asymmetry or structural difference becomes larger,and the anion,[N?CN?2]-,has a strong coordination ability together with delocalization of the charges,resulting in the reduction of Coulomb attraction between the anion and the cation.The idea of constructing asymmetrical GILs is proved to achieve the design and synthesis of GILs with lower melting point and viscosity.Asymmetrical GILs are usually mixed with molecular solvents because of their high price when they are used as solvents.Therefore,the volumetric and viscosity properties of solutions containing GILs are the basic data necessary for further investigation of other thermodynamic properties and transfer properties.The behaviors of solutions of GIL+acetonitrile?MeCN?,GIL+methanol?MeOH?,GIL+ethanol?EtOH?and GIL+isopropanol?IPA?deviating from their ideal solutions were respectively evaluated from excess molar volume?VmE?and excess viscosity????within whole composition?x1?in the temperature range of 283.15 to 333.15 K.It is found that there is a negative deviation between the binary mixture and the ideal solution,and there exists a lowest value.The accumulation and filling of the polar organic solvents in the GILs network structure plays a leading role on the change of VmE.As for??,the solvation between solvent and GIL,the dispersive force and the hydrogen bonding force between different molecules are the main factors.The relationship between VmE-x1 and??-x1 can be regressed by the Redlich–Kister type models.The excess Gibbs free energy?G*E for the viscous flow of binary system indicates that there is a strong interaction between GIL and solvent molecules.The above results can provide particularly useful information for explaining the nature and strength of the mixed systems containing GILs from the level of intermolecular interactions and can also provide fundamental data and basis for the investigations of their industrial applications and solution thermodynamics of GILs.The advantages of GILs used in sugar conversion processes include high solubility in sugars,ease of recovery,and providing a relatively mild reaction environment as well as high selectivity and yield.The dissolution behavior of D-?+?-glucose and D-?-?-fructose in[N111C3MIM][N?CN?2]2,[N111C3Py][N?CN?2]2 and[N111C3MPi][N?CN?2]2 was systematically investigated.The results showed that the solubilities of D-?-?-fructose in all three GILs were higher than D-?+?-glucose,which is related to its structure and thermal property parameters.The strong hydrogen bond between the hydroxyl group in the monosaccharide molecule and the anion in the GILs molecule has the greatest influence on the solubility.At the same time,the positive charge delocalization degree in the cationic group and the Coulomb interaction strength between the cation and the anion can also have a considerable effect on the dissolution ability of GILs.The relationship between solubility and temperature can be respectively quantitatively described by Apelblat,?h,NRTL,Wilson and UNIQUAC models.The average deviation of the UNIQUAC model is less than 4%.The apparent thermodynamic functions(?0dissH and?0dissS)are positive,indicating that the dissolution is an endothermic,enthalpic-driving process.The dissolution process of monosaccharides in GILs was investigated.These results provide basic thermodynamic data for the recovery of GILs and the separation of products in the conversion of monosaccharides in GILs.Moreover,the established thermodynamic models provide a basis for the prediction of solubility at various tempertures and for the development and design of the processing of biomass feedstock.The surface activities and corrosion inhibition performance of Gemini ionic liquid surfactants[N11nC3CnIM][Br]2?n=10,12,14,16?were systematically investigated,together with the interactions between[N1112C3C12IM][Br]2 and bovine serum albumin?BSA?.Krafft temperatures of[N11nC3CnIM][Br]2 increase with the number of carbon atoms in the hydrophobic group,while the cmc values decrease.The measured?cmc is around 35 mN·m–1,indicating their good surface active performance.The value of?max decreases with the elevating temperature.The micelle formation processes of[N1110C3C10IM][Br]2,[N1112C3C12IM][Br]2 and[N1114C3C14IM][Br]2 are entropy-driven,while[N1116C3C16IM][Br]2 is enthalpic-driving process.Gemini ionic liquid surfactant is a mixed corrosion inhibitor mainly for suppressing the anode.With the addition of BSA,the cmc and?cmc of[N1112C3C12IM][Br]2/BSA system gradually increased and a complex is formed,leading to the decrease of the content of?-helical structure.Krafft temperatures of such surfactants are significantly lower than quaternary ammonium cationic surfactants.The values of cmc are12 order of magnitude lower than traditional cationic surfactants.Gemini ionic liquid surfactants have good corrosion inhibition properties and can change the conformation of protein.The above investigations have attempted to broaden the practical applications of asymmetrical GILs into the field of surfactants. |
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