Does Graphene Change T_g of Nanocomposites?

Abstract

The effect of the addition of graphene on the glass transition temperature (T 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 T g increase was found for a-PMMA nanocomposites made via in situ polymerization with TRG but not when a-PMMA was solvent blended with TRG. However, a T 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. T 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 in situ 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 T g of i-PMMA is 60 °C lower than a-PMMA, meaning that hydrogen bonds are stronger at the lower temperature. The T 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 T 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 in situ polymerization or chemically modified fillers yielded significant T g increases in graphene/polymer nanocomposites.

Studies on PLA grafting onto graphene oxide and its effect on the ensuing composite films

“…Accordingly, in the former case the cold crystallization peak, usually observed in the first heating DSC trace is considerably reduced or even suppressed which is in agreement with what is observed in our samples [64]. Moreover, it can be noticed that the glass transition temperature of the polymer was increased by 2e3 C. A recent literature review showed that generally the T g of graphene or GO/polymer nanocomposites is significantly increased (4 C or more) when using functionalized nanofillers, due to the enhancement of their interactions with the matrix [65]. In this view, the interaction of the prepared GO-g-PLA hybrid with the commercial PLA matrix seems to be substantial, even if the PLA chains are short and/or sparsely grafted on the nanofiller surface.…”

Amine-graphene oxide/waterborne polyurethane nanocomposites: effects of different amine modifiers on physical properties

“…However, in the opposite way, incorporating amine-GO nanoplatelets might cleave the original interaction between hard-and soft-segments and hence change the microphase structure in WPU matrix, which will lead to the shift of T g to low temperature. Therefore, the change of nanocomposites in T g compared with pure WPU is not obvious base on the above reciprocal inhibition mechanism [31].…”

Natural rubber/graphene oxide composites: Effect of sheet size on mechanical properties and strain-induced crystallization behavior

“…However, some published literatures show increases in the T g of the bulk polymer chains upon the addition of GO or graphene [53,54], while others report no obvious change in T g [39,47,55] or even decrease in T g [49]. A very recent study shows that only the covalent attachment of polymer chains onto graphene surface can produce significant restriction on the mobility of the bulk polymer and lead to an increase in the T g [56]. In our work, the variation of T g is in a very narrow region of 1-3°C, which may be considered to be essentially the same.…”