Post by williamplayer on Jan 23, 2014 12:09:09 GMT
Functionalized Graphene – poly Nanocomposites: Physical and Dielectric Properties
Abstract.
Chemically derivatized graphene/poly(vinyl alcohol) (PVA) nanocomposites were successfully fabricated by combination of solution processing and compression molding. SEM imaging combined with XRD measurements revealed that graphene platelets were fully incorporated into the polymer matrix after their chemical modification through adsorption of amphiphilic copolymer. The chemical functionalities onto the graphitic surface prevented particle aggregation and pro- vided compatibility with the polymer matrix. Thermogravimetric analysis demonstrated enhanced thermal stability for the composites containing modified graphenes at loading above 1 wt%. Differential scanning calorimetry thermograms showed that graphene nanoplatelets induced the crystallization of matrix with optimum loading at 2 wt%. Dielectric spectroscopy measurements showed enhanced electrical permittivity for the graphene oxide/PVA system, compared to the one of graphene/copolymer/PVA. This could be attributed to the formation of an insulating coating between graphite inclusions and PVA because of the presence of the copolymer
Introduction.
Polymer composites, filled by graphitic nanostruc- tures, have attracted increased attention owing to their unique mechanical, electric and optical properties. Nano-sized conductive fillers, including graphene nanoplatelets, can create a percolative network within the polymer matrix at a low weight fraction, while the presence of conductive nano inclusions within a polymer matrix could alter the permittivity of the composite systems resulting in enhancement of their energy storing capability. Nanoinclusions can be considered as a distributed network of nanocapacitors, which can be charged and discharged defining an energy storing process, at the nanoscale level. Graphene platelets, pre- pared via natural graphite exfoliation, have been widely used as a conducting filler in the fabrication of conductive polymer composites. Graphite has a layered crystal structure, in which the carbon atoms are strongly bonded on a two-dimensional network consisting of hexagons. Because the layers are bound by weak van der Waals forces, the idea of separating the bulk graphite into platelets consisting of few carbon layers having nanometer-scale thick- ness, or even into a single layer, has long been con- sidered as the goal for obtaining super-strong and conductive polymer composites. Different types of graphite nanoplatelets, such as thermally expanded graphite, graphene oxide (GO) and chemically modified graphene, have been used to make functional polymer composites. Chemical functionalization of graphene surface by either oxidation procedure or physical adsorption/grafting protocols have been found to be a feasible and effective means for improving the dispersion of graphenes in organic and/or aqueous media. In addition, the attached functional groups may enhance the interfacial interactions between the graphenes and the polymer matrix. The advantage of modifying the graphene surface by physical adsorption is that the structural integrity of the conjugated net- work remains unaltered, whereas formation of defects is observed after treatment of the graphitic nanostructures by oxidative conditions and/or graft- ing reactions.
To the best of our knowledge, there is no report on fabricating graphene/polymer composites by using non covalently modified pristine graphene nano- platelets. In addition, dielectric data such as dielectric permittivity, ac conductivity, and electric modulus have not been widely studied in graphene/ polymer composites. We show here a simple and environmentally friendly preparation of graphene/ PVA nanocomposites by incorporating amphiphilic block copolymer-modified graphenes into a PVA matrix using water as the compounding solvent. PVA is one of the most important commodity poly- mers due to its good mechanical and thermal properties. Its semi crystalline nature allows us to circumvent complexities of interpreting property changes associated with crystallization versus graphite addition. Here, we report a comparative study of PVA nano composites based on non covalently modified graphene sheets, GO, and pristine graphite. The effect of graphene content on the physical and dielectric properties of PVA/graphene nano composites is investigated. The effect of filler’s chemical functionalities as well as loading on various dielectric data (dielectric permittivity, ac conductivity, and electric modulus) was studied in detail.
Read Full Article: www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&ved=0CFEQFjAFOAo&url=http%3A%2F%2Fwww.expresspolymlett.com%2Fletolt.php%3Ffile%3DEPL-0002909%26mi%3Ddc&ei=XQPhUrPBKsbT7AavqICABg&usg=AFQjCNHvAWNp5poI_eVup8EQrTEho3AKKQ&bvm=bv.59568121,d.ZGU&cad=rja
Abstract.
Chemically derivatized graphene/poly(vinyl alcohol) (PVA) nanocomposites were successfully fabricated by combination of solution processing and compression molding. SEM imaging combined with XRD measurements revealed that graphene platelets were fully incorporated into the polymer matrix after their chemical modification through adsorption of amphiphilic copolymer. The chemical functionalities onto the graphitic surface prevented particle aggregation and pro- vided compatibility with the polymer matrix. Thermogravimetric analysis demonstrated enhanced thermal stability for the composites containing modified graphenes at loading above 1 wt%. Differential scanning calorimetry thermograms showed that graphene nanoplatelets induced the crystallization of matrix with optimum loading at 2 wt%. Dielectric spectroscopy measurements showed enhanced electrical permittivity for the graphene oxide/PVA system, compared to the one of graphene/copolymer/PVA. This could be attributed to the formation of an insulating coating between graphite inclusions and PVA because of the presence of the copolymer
Introduction.
Polymer composites, filled by graphitic nanostruc- tures, have attracted increased attention owing to their unique mechanical, electric and optical properties. Nano-sized conductive fillers, including graphene nanoplatelets, can create a percolative network within the polymer matrix at a low weight fraction, while the presence of conductive nano inclusions within a polymer matrix could alter the permittivity of the composite systems resulting in enhancement of their energy storing capability. Nanoinclusions can be considered as a distributed network of nanocapacitors, which can be charged and discharged defining an energy storing process, at the nanoscale level. Graphene platelets, pre- pared via natural graphite exfoliation, have been widely used as a conducting filler in the fabrication of conductive polymer composites. Graphite has a layered crystal structure, in which the carbon atoms are strongly bonded on a two-dimensional network consisting of hexagons. Because the layers are bound by weak van der Waals forces, the idea of separating the bulk graphite into platelets consisting of few carbon layers having nanometer-scale thick- ness, or even into a single layer, has long been con- sidered as the goal for obtaining super-strong and conductive polymer composites. Different types of graphite nanoplatelets, such as thermally expanded graphite, graphene oxide (GO) and chemically modified graphene, have been used to make functional polymer composites. Chemical functionalization of graphene surface by either oxidation procedure or physical adsorption/grafting protocols have been found to be a feasible and effective means for improving the dispersion of graphenes in organic and/or aqueous media. In addition, the attached functional groups may enhance the interfacial interactions between the graphenes and the polymer matrix. The advantage of modifying the graphene surface by physical adsorption is that the structural integrity of the conjugated net- work remains unaltered, whereas formation of defects is observed after treatment of the graphitic nanostructures by oxidative conditions and/or graft- ing reactions.
To the best of our knowledge, there is no report on fabricating graphene/polymer composites by using non covalently modified pristine graphene nano- platelets. In addition, dielectric data such as dielectric permittivity, ac conductivity, and electric modulus have not been widely studied in graphene/ polymer composites. We show here a simple and environmentally friendly preparation of graphene/ PVA nanocomposites by incorporating amphiphilic block copolymer-modified graphenes into a PVA matrix using water as the compounding solvent. PVA is one of the most important commodity poly- mers due to its good mechanical and thermal properties. Its semi crystalline nature allows us to circumvent complexities of interpreting property changes associated with crystallization versus graphite addition. Here, we report a comparative study of PVA nano composites based on non covalently modified graphene sheets, GO, and pristine graphite. The effect of graphene content on the physical and dielectric properties of PVA/graphene nano composites is investigated. The effect of filler’s chemical functionalities as well as loading on various dielectric data (dielectric permittivity, ac conductivity, and electric modulus) was studied in detail.
Read Full Article: www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&ved=0CFEQFjAFOAo&url=http%3A%2F%2Fwww.expresspolymlett.com%2Fletolt.php%3Ffile%3DEPL-0002909%26mi%3Ddc&ei=XQPhUrPBKsbT7AavqICABg&usg=AFQjCNHvAWNp5poI_eVup8EQrTEho3AKKQ&bvm=bv.59568121,d.ZGU&cad=rja