Thermoresponsive graphene nanosheets by functionalization with polymer brushes

We report the preparation of thermoresponsive graphene nanosheets functionalized by the polymer brushes. This approach involves the direct growth of thermoresponsive polymer brushes from functional graphene sheets (FGSs) by chemical modification with initiators followed by extension with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) through surface-initiated atom transfer radical polymerization. The highly controllable polymerization method affords the hybrid FGS-PDMAEMA with tailorable length of PDMAEMA brushes possessing the average molecular weight (Mn) ranging from 7.4 × 103 to 6.0 × 104 with low molecular weight distributions (Mw/Mn = 1.09–1.22). The resulting FGS-PDMAEMA was carefully characterized with a number of techniques, including elemental analysis, thermogravimetric analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy, all supporting the successful integration of polymer brushes onto the surface of FGS. Most importantly, we accomplished the reversible phase transfer of this hybrid FGS-PDMAEMA between aqueous and organic phases via temperature control by taking advantage of the thermoresponsive nature of PDMAEMA brushes. Moreover, the composite film prepared by depositing the suspensions of FGS-PDMAEMA demonstrated the facile control over the wettability upon temperature changes. This tailored control over dispersion in water, selective solubilization between aqueous and organic solvents, and wettability control upon temperature variation have a significant impact on the ability to improve properties of hybrid graphene-based materials. Because of the highly versatile and tunable properties of surface-initiated atom transfer polymerization, we anticipate that the general concept presented here offers a unique potential platform for integrating responsive polymers for graphene nanosheets for advanced electronic, energy, and sensor applications.