Synthesis And Properties Of Novel Organosiloxane Room-Temperature Ionic Liquids

Surface active ionic liquids (SAILs), a class of organic salts that incorporate the advantages of surfactants and ionic liquids, have been applied in enzymatic catalysis, lubricants, heat-transfer fluids, and gas storage, among other applications. N-alkyl ILs, such as imidazolium and pyridinium salts are currently the most prominent class of SAILs. However, their surface activities are low and melting points are high, which restrict the applications of SAILs. Thus, it is a challenge to design ILs that incorporate progressively more lipophilic structure while keeping their melting points below room temperature. And the investigations can enrich the species of SAILs and also establish the basis for their applications in different fields.In this thesis, a series of novel organosiloxane room-temperature SAILs (RT-SAILs), with different substituent groups, siloxanes, chain length of the counter anions, numbers of counter anions, were designed and synthesized. And their adsorption properties, aggregation behavior in aqueous solutions were investigated.The dissertation includes six parts as follows:In chapter 1, the properties and aggregation behavior of siloxane surfactants are summarized. The development, properties and applications of ILs are reviewed, and the progress of SAILs in recent years is outlined. The significance of this dissertation and the research content are also pointed out at the end of this part.In chapter 2, three amino trisiloxane RT-SAILs, [Si(3)N-CA(n) n=1, 2,3], were synthesized and characterized by FT-IR, NMR, and elemental analysis. Their surface activitiy was investigated through measurements of surface tension and conductivity. The results reveal that all of them are highly surface active and can reduce the surface tension of water to about 20 mN/m. Their aggregation behavior in aqueous solution was carried out by dynamic light scattering (DLS), transmission electron microscopy (TEM) and cyro-Transmission Electron Microscopy (Cyro-TEM). Multilamellar vesicles are the most frequently obtained self-assembled structures in aqueous solution, and the number of the vesicles increases with an increase of the chain length of the carboxylate anions. Moreover, the formation of vesicles was explained by molecular packing parameter.In chapter 3, three novel 1:1 type two amino trisiloxane RT-SAILs, [Si(3)N(2)-CA(n) n=1,2,3], were synthesized and characterized. Their surface activity and aggregation behavior in aqueous solution were systematically investigated through measurements of surface tension, conductivity, transmission electron microscopy and dynamic light scattering. The results show that the substituent length has certain effects on the adsorption behaviors of organosiloxane RT-SAILs in aqueous solution. Two transition points were found in their surface tension curves, which implied a different aggregation process compared to conventional SAILs. Combined with the analysis of molar conductivity plots, it can be drawed that ion pairs were formed at the relatively low concentration. Comparing with [Si(3)N-CA(n) n=1,2,3], which has a shorter substituent length, [Si(3)N(2)-CA(n) n=1,2,3] have the lower CAC values. And they can self-assemble into vesicles in aqueous solution.In chapter 4, the synthesis and properties of three 1:2 type two amino trisiloxane RT-SAILs, [Si(3)N(2)-2CA(n) n=1,2,3], were discussed. Appearance of the SAILs shows that the melting points of them increases with an increase of the counter anion chain length. Surface activity measurements indicate that the number of counter anions has certain effects on the adsorption behaviors of organosiloxane RT-SAILs in aqueous solution. The CACs of [Si(3)N(2)-2CA(n) n=1,2,3] are obveriously lower than that of [Si(3)N(2)-CA(n) n=1,2,3], which have the less number of counter anions. Aggregation behavior studies reveal that the aggregates formed in Si(3)N(2)-2CA(1) and Si(3)N(2)-2CA(2) solutions are observed to be small spherical aggregates, while those formed in Si(3)N(2)-2CA(3) solutions are found to be large necklace-like aggregates. It is possible to induce a morphology transition by a judicious choice of the structure of the counterion within this family of RT-SAILs.In chapter 5, three novel 1:1 type two amino tetrasiloxane RT-SAILs, [Si(4)N(2)-CA(n)n=1,2,3], were synthesized and characterized. The surface tension measurements provided the critical aggregation concentration (CAC) and the surface tension at the CAC (γcac).It can be found that siloxane has certain effects on the adsorption behaviors of organosiloxane RT-SAILs in aqueous solution. Comparing with [Si(3)N-CA(n) n=1,2,3], [Si(4)N(2)-CA(n) n=1,2,3] can form ion pairs at the relatively low concentration, and they have the lower CAC values. Aggregation behavior studies reveal that the aggregates formed in Si(4)N(2)-CA(1) are observed to be small spherical aggregates, while those formed in Si(4)N(2)-CA(2) and Si(4)N(2)-CA(3) solutions are found to be vesicles. Moreover the formation of vesicles can be confirmed by the encapsulation of bromophenol blue.In chapter 6, the synthesis and properties of three 1:2 type two amino tetrasiloxane RT-SAILs, [Si(4)N(2)-2CA(n) n=1,2,3], were discussed. The static surface tension of the aqueous solutions indicates that all of them are highly surface active and can reduce the surface tension of water to about 20 mN/m. Comparing with [Si(4)N(2)-CA(n)n=1,2,3], [Si(4)N(2)-2CA(n) n=1,2,3] don’t form ion pair at the relatively low concentration. The dynamic surface tension results show that the time required to attain the equilibrium surface tension increases with the chain length of the carboxylate anions, indicating the difficulty of adsorption at the air/water interface. And their kinetic model of adsorption is consistent with a mixed kinetic-diffusion adsorption mechanism. With a combination of DLS data, TEM measurements, formations of vesicles in [Si(4)N(2)-2CA(n) n=1,2,3] solutions appear to occur at a concentration above the CAC.