Preparation And Performance Study Of Liquid Crystal Functionalized MWCNTs Composites

Pressure sensitive adhesive is sensitive to stress,which is widely used in packaging,electric insulation,health care,adhesive labels and marks etc.However,the poor mechanical properties and thermal conductivity make them unable to meet the requirements of modern special-purpose adhesive.One of developing direction is modifie pressure sensitive adhesive filled with carbon nanotubes having excellent mechanical and thermal performance.Whereas,because of the reunion in carbon nanotubes and the poor compatibility between carbon nanotubes and polymer,the effect of modifying polymer is not ideal.Liquid crystal has special anisotropy and excellent liquidity,which can effectively improve the dispersion of carbon nanotubes and their compatibility with polymer.Therefore,it is very important to synthesize liquid crystal modifying carbon nanotubes and prepare the high-performance liquid crystal/ carbon nanotubes composites used in modified polymer.In this paper,preparation and performances of various liquid crystals and liquid crystal/ carbon nanotubes filled polymer composites are studied.The main research contents include:(1)According to design,three synthetic biphenyl liquid crystal,4?-allyloxy-biphenyl-4-ol(AOBPO),4,4?-Diallyloxy-biphenyl(DABP),P-hydroxy benzoic acid biphenyl diester(PHBE),with diverse end groups were characterized by FT-IR and 1H-NMR.The results show that the synthesis of three liquid crystals(AOBPO?DABP and PHBE)existing different molecular structure was successful.(2)The mesomorphic range and morphology of liquid crystals was explored by DSC and POM.The results indicate that all of these liquid crystals are smectic thermotropic liquid crystal.At the same time,the mesomorphic ranges of AOBPO,DABP and PHBE respectively are 160-175?,140-159? and 145-156?.(3)Further exploration of CNTs orientation effects induced by liquid crystal,4-Cyano-4'-pentylbiphenyl(5CB),was made,through the analysis of electrooptical effect of 5CB under the different electric field.The experimental results elucidate that liquid crystal can provide a good orientation-induced environment for carbon nanotubes due to its excellent anisotropy features.When there was no voltage,the light intensity of 5CB having little change was 3.1617%.The long rod-shaped molecules of 5CB went perpendicular with incident light at the moment.However,the light intensity of 5CB appearing geometric neat structure reached 24.4148% when the applied voltage was regulated to 20 V.It was speculated that the molecules of 5CB were parallel to incident light by this time.(4)A series of characterization of four LC/CNTs composites were carried out,including FT-IR,Fluorescent spectroscopy,Raman spectroscopy,XRD,TGA,SEM and POM.The upshot is that AOBPO was used to functionalize carbon nanotubers via physical means and chemical means.However,DABP,PHBE and 5CB were connect with CNTs by ?-? interactions,respectively.Tubular structure of carbon nanotubes was no fundamental changes without damaging effects of the inherent properties of MWNTs.At the same time,benefiting from strong interactions,CNTs had good dispersibility,which was beneficial to play a role in terms of performance.(5)By means of Electronic tensile machine,Rheometer,Thermal Conductivity Meter and SEM,four kinds of LC-MWNTs mixed with pressure sensitive adhesive(PSA)as fillers to fabricate polymer composites,were used for the performance tests contrasting with those unmodified by LC.The experimental results show that the tensile strength of 5CB-MWNT/PSA was increased to 14.5238 MPa when the mass fraction of MWNTs was 1wt %,943% over that of MWNTs/PSA.When the mass fraction of MWNTs was 2wt %,the tensile strength of DABP-MWNTs/PSA was increased to 14.19 MPa,641% over that of MWNTs/PSA.On the other aspect,the thermal conductivity of the resin filled with the AOBPO-MWNTs,DABP-MWNTs,PHBE-MWNTs and 5CB-MWNTs were improved to be 0.4768 W/(m·K),0.4208 W/(m·K),0.6975 W/(m·K)and 1.2805 W/(m·k)at the mass fraction of 10%,respectively,which was enhanced more than 552% over that of neat PSA and 231% over that of MWNTs/PSA.Owing to reducing the viscosity of PSA composites and improving the dispersion of MWNTs mixed with liquid crystal,it was speculated that the energy consumption reduction of pressure sensitive adhesive composites makes it a significant boost in all aspects of performance.