Modified Hyperbranched Polyglycerol As Dispersant For Size Control And Stabilization Of Gold Nanoparticles And The Application In Hydrocarbon Fuels

With the development of hypersonic technology,higher requirements on cooling and combustion performance for hydrocarbon fuels has been put forward.It is a new strategy for the improvement of such liquid propellants to combine metal nanoparticles(NPs)with hydrocarbon fuels to prepare uniform and stable pseudohomogeneous nano fluids.However,because of the large surface area,the nano-sized metal particles are active and are prone to produce coagulation in hydrocarbon fuels.Therefore,how to make the metal NPs be highly dispersed into hydrocarbon fuels is a key practical problem.It has been known to modify the surface of the NPs can prevent the aggregations of metal NPs.In this work,modified hyperbranched polyglycerol(HPG)is used as new surface-modification reagent for Au NPs.The relationship between the size of Au NPs and the molecular weight of HPG is investigated.The dispersion stability of Au NPs in hydrocarbon fuels,and the roles of Au NPs in the thermal cracking and combustion of hydrocarbon fuels are examined.It is expected to provide new ideas for solving the aggregation problem of functional NPs in hydrocarbon fuels.The main contents and results are summarized as follows:HPG was synthesized by anionic ring-opening polymerization,then the hydroxyl groups in HPG molecules are esterified with glycidyl methacrylate(GMA)to form HPG-MA.From the "thiol-alkenyl" click reaction of dodecanethiol and HPG-MA,the DSHPG was formed.Au NPs were then modified with DSHPG to form Au @ DSHPG.The molecular structures and some physical properties of these products are characterized by NMR,UV-Vis,FTIR,DLS,TEM,DSC and TGA.The effect of relative molecular mass of HPG on the size of Au NPs was investigated.The results indicate that the diameters of Au NPs modified with the HPG molecular weights of 1123,3826 and 55075 are observed as 4.1 nm(Au @ DSHPG-1),9.7 nm(Au @DSHPG-2)and 15.1 nm(Au @ DSHPG-3),respectively.The dispersion stability of Au @ DSHPG in different solvents and hydrocarbon fuels was studied by UV-Vis spectroscopy.As an example,Au @ DSHPG-2 was dispersed as much as possible in toluene,ethyl ether,ethyl acetate,acetonitrile and water,the UV-Vis observation results indicated that the dispersion ability of Au@DSHPG-2 in nonpolar solvents(such as toluene and diethyl ether)was significantly higher than that in polar solvents(such as water and acetonitrile).It was proved the strong effect of DSHPG on the dispersion of Au NPs in solvents.To further reveal the relationship between the dispersion ability of Au@DSHPG and the solvent polarity,a series of Au@DSHPG-2-containing dispersion systems with the mixtures of toluene and acetonitrile as dispersants were prepared.The polarities of the dispersants were tuned by the ratios of two components.It was shown that the absorbance of Au @ DSHPG-2 decreased with the increase of acetonitrile,and that the weaker the polarity of the solvent,the more feasible dispersion of Au@DSHPG.After that,the stability properties of Au @ DSHPG in different hydrocarbon fuels,such as n-hexane,cyclohexane,n-octane,decalin,n-dodecane and n-Alkane,were investigated from the monitors of UV-Vis absorption against the sediment time.It could be observed that the coagulation ratios of Au @ DSHPG-2 in the six kinds of hydrocarbon fuels were less than 20%after 3600 h.The catalytic effects of Au @ DSHPG on the cracking of a kerosene based hydrocarbon fuel(8220)at different reaction temperatures(600?750 0C)were investigated.It was found that the heat sink,conversion ratio,gas yield and hydrogen yield of the hydrocarbon fuel were significantly improved with the addition of 5 ppm Au @ DSHPG-1.Furthermore,the effects of Au @ DSHPG and three types of hyperbranched polymer additives(palmitoyl chloride-grafted hyperbranched polyglycidol PHPG,polyamide-amine hyperbranched polymer PAMAM,and dithiol-modified hyperbranched polyglycidol DSHPG)on the combustion characteristics of the kerosene based hydrocarbon fuel 8220 and a high density hydrocarbon fuel HD01 were investigated in a bomb calorimeter under oxygen-poor conditions.It was shown that,with a proper addition quantity of Au @ DSHPG,PHPG,PAMAM or DSHPG,the burning rates of the hydrocarbon fuels could be observed to be promoted significantly.