Supramolecular temperature responsive assembly of polydopamine reduced graphene oxide

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Abstract

Supramolecular temperature responsive self-assembly of graphene colloidal systems is enabled by an amphiphilic structure incorporating polydopamine clusters on reduced graphene oxide flakes, without using temperature responsive polymers.

Abstract

Graphene oxide (GO) and reduced graphene oxide (rGO) colloidal systems can directly respond to environmental stimuli such as pH, ionic strength, and light by themselves, but not to temperature. Here we show that surface modification of rGO with polydopamine (PDA) leads to a temperature-responsive composite material, even though neither rGO nor PDA have intrinsic temperature responsiveness. Reducing GO with dopamine results in rGO/PDA flakes with hydrophilic PDA clusters attached to hydrophobic rGO domains, which mimics the amphiphilic structure of temperature responsive poly( N-isopropylacrylamide) (PNIPAM). The rGO/PDA flakes self-assemble at temperature higher than 30 °C, causing flake aggregation and precipitation in suspensions with concentration of 0.05 g L ⁻¹, which is reversible upon cooling, shaking, and re-heating. A solution-to-gelation transition occurs upon heating suspensions with concentration of 10 g L ⁻¹. Nacre-like films and porous monoliths are obtained by drying rGO/PDA suspensions at different concentrations. Films and porous monoliths obtained by drying suspensions that are previously self-assembled through heat have more compact structures compared to those obtained with suspensions that are not heated. Overall, this work introduces the concept of supramolecular temperature responsive assembly of nanomaterials (STRAN), i.e., that temperature response can be introduced in nanomaterials by combining non-responsive components that function cooperatively in supramolecules, whose interactions with solvents can be modulated by temperature changes, mimicking what happens in macromolecular systems such as PNIPAM. STRAN could be applied to nanomaterials beyond GO to develop responsive systems whose self-assembly in suspension and architectural features realized upon drying can be controlled by temperature.

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The rise of graphene.

A. K. Geim, K. S. Novoselov (2007)

Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

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Mussel-inspired surface chemistry for multifunctional coatings.

Haeshin Lee, Shara M Dellatore, William M Miller … (2007)

We report a method to form multifunctional polymer coatings through simple dip-coating of objects in an aqueous solution of dopamine. Inspired by the composition of adhesive proteins in mussels, we used dopamine self-polymerization to form thin, surface-adherent polydopamine films onto a wide range of inorganic and organic materials, including noble metals, oxides, polymers, semiconductors, and ceramics. Secondary reactions can be used to create a variety of ad-layers, including self-assembled monolayers through deposition of long-chain molecular building blocks, metal films by electroless metallization, and bioinert and bioactive surfaces via grafting of macromolecules.