Does Graphene Change <i>T</i>_g of Nanocomposites?

The effect of the addition of graphene on the glass transition temperature (<i>T</i>_g) of polymers was investigated, first with poly­(methyl methacrylate) and then with an extensive literature review. Isotactic (i-PMMA) and atactic PMMA (a-PMMA) were blended with pristine graphene (PG) and thermally reduced graphene (TRG). A <i>T</i>_g increase was found for a-PMMA nanocomposites made via <i>in situ</i> polymerization with TRG but not when a-PMMA was solvent blended with TRG. However, a <i>T</i>_g increase was found for TRG solvent blended into i-PMMA and a smaller increase for PG with i-PMMA. Nearly all the increase occurred at the lowest loading, 0.25 wt %, with little change at increased graphene concentration. <i>T</i>_g increases due to interfacial interactions between matrix polymers and fillers. Physical blending such as solvent processes cannot provide enough interaction at the interfaces, whereas chemical blending processes such as <i>in situ</i> polymerization can yield strong covalent bonds. However, i-PMMA molecules can align on graphene sheets at the interface, creating more interaction between i-PMMA and graphene than a-PMMA. Also, the <i>T</i>_g of i-PMMA is 60 °C lower than a-PMMA, meaning that hydrogen bonds are stronger at the lower temperature. The <i>T</i>_g increase of TRG/i-PMMA is higher than that of PG/i-PMMA due to more oxygen functionalities on TRG than on PG to act as interfacial interaction sites. A broad literature survey agrees with our PMMA results. We found no changes in <i>T</i>_g for graphene/polymer nanocomposites synthesized via physical blending processes such as solvent or melt blending, except for blending with strongly polar polymers. In contrast, chemical blending processes such as <i>in situ</i> polymerization or chemically modified fillers yielded significant <i>T</i>_g increases in graphene/polymer nanocomposites

Influence of Functionalized Graphene Sheets on Modulus and Glass Transition of PMMA

Influence of Functionalized Graphene Sheets on Modulus and Glass Transition of PMM

Interfacial Rheology and Structure of Tiled Graphene Oxide Sheets

The hydrophilic nature of graphene oxide sheets can be tailored by varying the carbon to oxygen ratio. Depending on this ratio, the particles can be deposited at either a water–air or a water–oil interface. Upon compression of thus-created Langmuir monolayers, the sheets cover the entire interface, assembling into a strong, compact layer of tiled graphene oxide sheets. With further compression, the particle layer forms wrinkles that are reversible upon expansion, resembling the behavior of an elastic membrane. In the present work, we investigate under which conditions the structure and properties of the interfacial layer are such that free-standing films can be obtained. The interfacial rheological properties of these films are investigated using both compressional experiments and shear rheometry. The role of surface rheology in potential applications of such tiled films is explored. The rheological properties are shown to be responsible for the efficiency of such layers in stabilizing water–oil emulsions. Moreover, because of the mechanical integrity, large-area monolayers can be deposited by, for example, Langmuir–Blodgett techniques using aqueous subphases. These films can be turned into transparent conductive films upon subsequent chemical reduction