A Photoaddressable Liquid Crystalline Phase Transition in Graphene Oxide Nanocomposites

Abstract

The multifunctionality of graphene has the potential to unlock important developments in nanocomposite science. However, the manipulation of graphene without interfering with its unique properties and while controlling its spatial organization remains challenging. Here, the formation of a photoaddressable liquid crystalline (LC) solution through the stabilization of graphene oxide (GO) with photocleavable brushes is described. The LC behavior leads to the thermodynamic entrapment of GO into low aspect ratio domains that fail to display the properties typically predicted for graphene nanocomposites. The morphology and structural and electronic performance of these nanocomposites are regenerated through the brush cleavage, which controls the phase transition of the LC phase. These results show that kinetic control of graphene assembly can be an attractive tool toward the dynamic regulation of processable sol states and structured percolated networks for rational composite manufacturing.

Ultrafast Photo-Crosslinking of Thiol–Norbornene Opaque Silicone Elastomer Nanocomposites in Air

“…Above 0.5 wt % GO loading, the conductivity reaches a steady value around 4.27 × 10 –2 S/m, compared to conductivities typically around 1.0 × 10 –9 S/m for pristine silicones. Although the conductivity and percolation threshold depend on the molecular weight and chemical characteristics of the polymer matrix, , our values are well in agreement with those reported for other systems incorporating GO composites. Similarly, increasing the rGO wt % produced a linear improvement of the effective mechanical reinforcement in our composites, which suggests a good dispersion degree and an intimate interaction between the silicone matrix and rGO (Figure D).…”

“…Materials such as graphene and GO have relatively high extinction coefficients that are incompatible with photo-crosslinking in air, even for relatively thin films. GO has a substantially lower extinction coefficient than graphene; however, it requires a thermal reduction step in order to display useful conductive properties. , Owing to their excellent thermal stability, silicone elastomers are attractive matrices for the above application, as they enable GO dispersion before curing and can withstand the subsequent thermal reduction without GO re-agglomeration (Figure S5, Supporting Information). To investigate the incorporation of both materials within thiol–norbornene silicones, we supplemented our formulations with these nanomaterials and studied the gelation of formulations incorporating varying amounts of graphene and GO via photorheology (Figure A).…”

“…To enable the dispersion of hydrophilic GO in our photocurable PDMS formulation, we first functionalized GO with an NH 2 -containing PDMS copolymer (PAPMS- b -PDMS) following a protocol previously adapted by our group . 250 mL of a 5 mg/mL solution of the NH 2 –PDMS copolymer in DE was placed in a 500 mL glass bottle equipped with a magnetic stirrer.…”

“…To enable the dispersion of hydrophilic GO in our photocurable PDMS formulation, we first functionalized GO with an NH 2containing PDMS copolymer (PAPMS-b-PDMS) following a protocol previously adapted by our group. 31 250 mL of a 5 mg/mL solution of the NH 2 −PDMS copolymer in DE was placed in a 500 mL glass bottle equipped with a magnetic stirrer. 250 mL of a 1 mg/mL aqueous solution of GO (originally 4 mg/mL in distilled water) was carefully injected on top of the DE solution, and the two phases were stirred very gently for 12 h. After this time, the organic phase (top) became brown while the aqueous phase turned (bottom) transparent, indicating that the GO had been completely transferred from the aqueous phase to the organic phase by the electrostatic interaction between NH 2 −PDMS and the GO surface, rich in COO − groups.…”