Study On Preparation And Properties Of Liquid Crystal Functionalized Graphene/Organosilicone Composites

Silicone material has excellent resistant to high/low temperature, radiation resistance, oxidation resistance, high permeability, weatherability, easy demoulding properties, hydrophobicity and physiological inert etc, so it has been widely used in chemical industry, construction, aerospace, electronics, medical and other fields. But its poor conductivity, inadequate mechanical properties and thermal conductivity made a new issue. Graphene with extremely high mechanical strength, excellent electrical conductivity and thermal conductivity make it an ideal nano filler for reinforcement of polymer. However, it is difficult to achieve ideal effect of graphene modified polymers because of the disadvantages such as easy aggregation of graphene and poor compatibility with polymers. Therefore, it is very important to improve the dispersion of graphene in organic silicon matrix and increase the interfacial interaction between graphene and organic silicon substrate. In this study, the functionalization of two kinds of liquid crystal molecules—biphenyl type liquid crystal,4'-allyloxy-biphenyl-4-ol(AOBPO) and polyester type liquid crystal,polyurethane-imide(PUI) on graphene were carried out, and the two kinds of liquid crystal functionalized graphene(LC-GNS) were characterized by fluorescence spectroscopy, FT-IR, Raman spectroscopy, XRD and TGA. Two kinds of LC-GNS/organosilicon nanocomposites were prepared by filling organic silicone with the two different LC-GNS respectively. In the curing process of silicone nanocomposites, two different ways of force field(shear force and normal force) were applied to LC-GNS, and the effect of liquid crystal induced graphene orientation on thermal conductivity and thermal conductivity of silicone material were studied. The results obtained are as follows:The tensile strength of AOBPO-GNS/organosilicon nanocomposite andPUI-GNS/organosilicon nanocomposite were increased to 7.66 MPa and 6.42 MPa when the mass fraction of GNS was 1.0%, 107% and 74% over that of GNS/organosilicon nanocompositerespectively. The elastic modulus of AOBPO-GNS/organosilicon nanocomposite and PUI-GNS/organosilicon nanocomposite were increased to 44.32 MPa and 36.32 MPa when the mass fraction of GNS was 2.0%, 192% and 140% over that of GNS/organosilicon nanocompositerespectively. The thermal conductivity of the resin filled with the AOBPO-GNS was improved to be 3.1056 W/(m·K) at the mass fraction of 15.0%,which was enhanced more than 38 times over that of neat silicone material and 123%over that of GNS/organosilicon nanocomposite. The thermal conductivity of the resin filled with the PUI-GNS was improved to be 1.3822W/(m·K) at the mass fraction of10.0%, which was enhanced more than 16.5 times over that of neat silicon resin and38% over that of GNS/organosilicon nanocomposite.Shear force was applied on the organosilicon nanocomposite during curing. The results indicated that the thermal conductivity of ladder heat cured AOBPO-GNS/organosilicon nanocomposite(15.0 wt% graphene, GNS/AOBPO=1:1)was 3.5113W/(m·K) increased by 14.62 times over that of GNS/organosilicon nanocomposite, and the electrical conductivity was 9.82×10-3S/m, increased by 43.2times over that of GNS/organosilicon nanocomposite. And the thermal conductivity of linear temperature cured PUI-GNS/organosilicon nanocomposite(10.0 wt% graphene,GNS/AOBPO=1 : 1) was 1.8045 W/(m·K), increased by 148% over that of GNS/organosilicon nanocomposite, and the electrical conductivity was 7.44×10-3 S/m,increased by 741% over that of GNS/organosilicon nanocomposite. It indicated that shear force field facilitated the orientation of the LC-GNS evidently, and the thermal conductivity and electrical conductivity of organosilicon nanocomposite were further improved.After normal force was applied on the organosilicon nanocomposite, the thermal conductivity of ladder heat cured AOBPO-GNS/organosilicon nanocomposite(15.0wt% graphene, GNS/AOBPO=1 : 1) under a normal force of 29.4N was3.1428W/(m·K), increased by 10.8 times over that of GNS/organosilicon nanocomposite, and the electrical conductivity is 7.61×10-3 S/m, increased by 34.3times over that of GNS/organosilicon nanocomposite. And the thermal conductivity of linear temperature cured PUI-GNS/organosilicon nanocomposite(10.0 wt% graphene,GNS/AOBPO=1:1) under a normal force of 9.8N was 1.4256 W/(m·K), increased by240% over that of GNS/organosilicon nanocomposite, and the electrical conductivity was 5.63×10-3 S/m, increased by 569% over that of GNS/organosilicon nanocomposite. It indicated that normal force field facilitated the orientation of the LC-GNS evidently, and the thermal conductivity and electrical conductivity of organosilicon nanocomposite were further improved.