Conjugated organic molecules, such as oligo(p-phenylene vinylene) (OPV), have attracted considerable interest in the areas of organic semiconductors and optoelectronics. OPVs are planar molecules that are known to self-assemble into organogels—with a nanotape morphology—above a critical concentration in some solvents. However, these supramolecular structures are not stable at high temperatures, thus, limiting their practical applications.

Now, Ayyappanpillai Ajayaghosh and co-workers1 at the National Institute for Interdisciplinary Science and Technology, India, have shown that hybrid gels formed from OPVs and either single-walled or multi-walled carbon nanotubes, exhibit greater stability compared to OPV gels. “Usually if a foreign material is added to an organogel, the stability of the gel decreases,” says Ajayaghosh. “It’s challenging to prepare a hybrid gel with improved stability.” In addition, gelation is accelerated in the presence of the carbon nanotubes and occurs below the critical concentration observed for OPV gels.

“An advantage of our hybrid system is that the OPV-nanotubes can be easily dispersed in hydrocarbon solvents which may facilitate the formation of coatings, including superhydrophobic surfaces, on suitable substrates.” The higher stability and the enhanced elastic response of the hybrid OPV-nanotube gels are a result of the physical interactions between the components, rather than because of entanglement of the nanotubes. The strong, physical interaction between the OPV molecules and the carbon nanotubes is attributed to the interaction between the π-conjugated backbone of the organic molecules and π-structure of the carbon nanotubes.

Fig. 1: Transmission electron microscopy images of OPV-carbon nanotube composite gels.

According to Ajayaghosh, the carbon nanotubes are well-aligned within the composite gel and act as a reinforcing influence on the supramolecular nanotapes of OPV. From transmission electron microscopy images of the OPV-nanotube gel, the nanotubes were seen to be unbundled, fibre-reinforced nanotapes (Fig. 1).

“We now plan to use a variety of conjugated molecules to make composites and investigate whether OPVs can act as a mediator to disperse carbon nanotubes with other polymers to make higher strength composites,” says Ajayaghosh. “We will also probe the conducting properties of the composites.”