Study On Interactions Between Polysiloxanes And Long-chain Alkanes

With the huge and rapid increase of people's demand on high performance materials,silicone materials have gradually come into people's vision.As it was known by all,organosilicon compounds and the polysiloxanes prepared by them possess good weather resistance,low temperature resistance,lubricity and dielectric properties,et al.Polysiloxanes also exhibit a small viscosity temperature coefficient and thus can be used at lower temperatures and last for longer time.Due to their excellent low temperature properties and complete miscibility with long-chain alkanes,this thesis intends to investigate the liquid-liquid interactions between polysiloxanes and long-chain alkanes,which is the foundation for studying the complex interactions among composions of diesel oil and polysiloxanes since diesel oil is consisted of many long-chain alkanes.To simply the complex system and facilitate to investige the“real” interactions between polysiloxanes and long-chain alkanes with numer of carbon atoms ranging from 10 to 14,the liquid-liquid phase equilibrium behavior of the binary system was studied.Since the crystallization phenomenon of diesel oil at lower temperature is mainly resulted from the precipitation of wax,therefore,the effect of polysiloxane on the melting ranges and heat of fusion of a complex mixture of wax crystals composed of long-chain alkanes was also investigated.This thesis is focused on the complex interactions between main components of diesel oil and polysiloxanes or polysiloxane oligomers and attempt to provide guidance for the research and development a series of silicone oil-based diesel pour point depressants.A combined density-viscosity analyzer system was used in this thesis to measure the density,viscosity and sound velocity data simultaneously.The thermodynamic data such as excess molar volume,thermal expansion coefficient,viscosity deviation,excess Gibbs free energy and isentropic compression coefficient deviation of the mixed system were derived from the measured data.With the classic Redlich-Kister equation and Legendre polynomial,experimental data were correlated by means of Eviews software.The reliability of these regressed parameters was verified and some possible interactions between the model molecules were analyzed and discussed.The thesis is consisted of the following four parts:In the first chapter,the composition and importance of diesel,the mechanism of diesel pour point depressant,the factors affecting diesel solidification,and the significance of reducing the freezing point of diesel were brifly introduced.Thenecessity of studying on liquid-solid equilibrium between silicone and wax crystals and the liquid-liquid equilibrium between silicone and long-chain alkanes were discussed in detail.In chapter two,the interactions between waxy components in diesel oil and silane compounds or polymers prepared by silane compounds were explored.A DSC was used to monitor the crystallization process and melting ranges of wax crystals affected by cyclosiloxanes or oligosiloxanes in non-isothermal processes.The effect of cyclosiloxanes or oligosiloxanes on the phase change process was compared with that of commercial polyacrylamide pour point depressants.The main factors affecting the crystallization or melting process were analyzed and discussed in detail.Effects of the type and amount of cyclosiloxanes or oligosiloxanes on the crystallization or melting process of wax crystals were thoroughly investigated.In the third chapter,the liquid-liquid phase equilibrium behavior of a binary mixture composed of a kind of cyclosiloxanes or oligocyclosiloxaneswith n-decane,n-dodecane,n-tridecane and n-tetradecane was studied.The influence of intermolecular forces,steric hindrance,and molecular packing on the excess properties of the solution wasanalyzed.The results indicated that with the increase in the number of carbons in the long-chain alkane,the steric hindrance increases,together with a decrease in the intermolecular forces among molecules in the mixed system.However,as the temperature decreases,the intermolecular bonds become tighter,which resulted in an increase in the intermolecular forces.In the fourth chapter,the liquid-liquid phase equilibrium of a quasi-binary mixed system composed of diesel oil and a cyclosiloxane or anoligosiloxane was investigated.By measuring the density,viscosity and sound velocity of the binary solution,thermodynamic data like molar volume,excess Gibbs free energy and viscosity deviation were calculated.The possible interactions between cyclosiloxanes,polysiloxanes and diesel were analyzed and discussed,which laid a theoretical foundation for the effect of cyclosiloxanes and polysiloxanes on the freezing point of diesel.