| In comparison to liquid lubricants,solid lubricants have more capacity to perform under harsh conditions such as high temperature and heavy pressure.Different organic and inorganic materials such as polytetrafluoroethylene(PTFE),polychlorotrifluoroethylene(PCTFE)and graphene oxide GO,tungsten sulfide WS2,molybdenum sulfide MoS2,manganese oxide MnO2,boron nitride BN,fluorine-based octadecylamine salt of decapentylfluorooctanoic acid,and LaF3 have been used for this purpose.Most of them are hazardous materials,emit harmful substances after degradation,and not suitable for environment and biological species.Eco-tribology is the study of science which deals with the solution of problems related to friction reducing systems or compounds and its negative impact on environment and health.In this view,silicone oil(SO)was considered as good choice because it is adaptive with living bodies,safe for humans,having good dielectric property,moisture resistance,and affordable market price.Borax,which is commonly used as a solid lubricant and lubricant additive in different systems related to industry and household items.Its use in metal wire drawing,cutting metal works,as a fluxing agent,additive in ceramic material and cosmetics is considerable.Due to these attributes,borax was tested for enhancing the tribological performance of SO and the results were quite good but low thermal stability didn’t let it to withstand against high temperature.Therefore,we were facing three big challenges and need to prepare a novel solid lubricant that comprises the following properties i)safe for health ii)highly thermally stable iii)perform better than borax in friction reduction with small amount.For finding better material,the highly thermally stable poly(methyl silsesquioxane)(PMSQ)with rigid silicone-oxygen-silicone core were prepared by methyl triethoxysilane(MTES)in micro and nano sizes and modified with different biobased long alkyl chains.These solid powder form PMSQ microparticles(P-MPs)and PMSQ nanoparticles(P-NPs)modified with oil form long alkyl chains,proved as excellent novel hybrid materials integrated with the solution of above-mentioned three challenges such as health-friendly,highly thermally stable,and after using their small amounts showed a low coefficient of friction(COF)to improve the tribological properties of SO.These synthesized five different modified PMSQs were tested in SO as a solid lubricant additive,their thermal and tribological performances were evaluated as mentioned in the given projects.In chapter 2 of thesis,the uniform-sized PMSQ microparticles(P-MPs)were prepared by the hydrolysis of MTES with narrow size distribution.The 11 carbon chains were prepared by hydrosilylation of bio-based ethyl 10-undecanoate with triethoxy silane and this hydrosilylation product(S2E11)was then grafted on P-MPs by condensation reaction followed by hydrolysis.The size distribution of P-MPs,hydrosilylation,grafting of S2E11 on microparticles,and their thermal stability was confirmed by differential light scattering(DLS)technique,fourier transform infrared(FTIR),H nuclear magnetic resonance(1H-NMR),scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS)and thermogravimetric analysis(TGA)respectively.The P-MPs modified by S2E11(MP-MPs)proved as a novel hybrid lubricant additive for improving the tribological performance of SO as the 0.4 wt%of MP-MPs showed the maximum COF reduction up to 58.4%and that of 0.4 wt%borax showed 42.7%,which means MP-MPs exhibited 15.7%better performance than borax and thus improved the tribological performance of SO.As a high thermally stable lubricant the MP-MPs showed 33%less weight loss than borax at 200℃.In chapter 3,the PMSQ nanoparticles(P-NPs)with good polydispersity index(PDI)values were prepared by tunning the stirring speed of reaction and amount of surfactant.These P-NPs were carefully modified with S2E11 and named as MP-NPs,then the PDI value,grafting of S2E11 on nanoparticles,and their thermal stability were confirmed by Zeta Nano Sizer,SEM,FTIR,EDS and TGA analysis respectively.The small size and large surface area of MP-NPs made these particles a better lubricant additive than their corresponding MP-MPs in SO.The maximum COF reduction of MP-NPs was 65.26%with 0.3 wt%which is 22.5%higher than borax and thus improved the tribological performance of SO.The MP-NPs showed good thermal performance by losing 32.3%less weight than borax at 200℃.In chapter 4,the bio-based oleic acid was changed to ethyl oleate(EO)by esterification and this EO was used to prepare 18 carbon chains by hydrosilylation reaction of triethoxy silane and named as S2EO.The P-MPs and P-NPs were modified with S2EO by condensation reaction and converted to novel hybrid lubricants named as P-MPs-S2EO and P-NPs-S2EO respectively.The grafting of 18 carbon chains on nano and microparticles and thermal stability was confirmed by FTIR,1H-NMR,SEM,EDS,and TGA analysis respectively.The maximum COF reduction of P-MPs-S2EO was 80.51%with 0.3 wt%and that of P-NPs-S2EO was 93.23%at 0.2wt%in SO.In comparison with borax,the maximum COF reduction of P-MPs-S2EO and P-NPs-S2EO was 37.97%and 50.51%higher respectively and both materials showed 32%less weight loss than borax at 200℃ and thus improved the tribological performance of SO.In chapter 5,the long 21 carbon chains were prepared by oleic acid through chlorination and amidation reactions which resulted as N-(3triethoxysilylpropyl)oleamide(OAm).The P-NPs were modified by OAm through condensation reaction and named as P-NPs-OAm.The grafting of long carbon chains on nanoparticles and thermal stability was confirmed by FTIR,SEM,EDS,and TGA analysis respectively.The maximum COF reduction of P-NPs-OAm was 57.63%with 0.2 wt%in SO which was 14.91%higher than borax and thus improved the tribological performance of SO.The highly thermally stable P-NPs-OAm showed 32.1%less weight loss than borax at 200℃.All these materials proved themselves as novel silsesquioxanes based hybrid materials for improving the tribological properties of SO in which P-NPs-S2EO was the best one. |
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