Dip coating, which provides many degrees of freedom – for example, withdrawing motion, solution properties, evaporation conditions and suspension chemistry – to control the deposition process, has been used to pattern the π-conjugated polymers. The combination of aged solution, chemically patterned substrate and dip-coating process has made it possible to deposit poly(3-hexylthiophene) (P3HT) and orientate the nanowires at desired locations.

It is widely accepted that on a chemically patterned substrate the solution-substrate interactions guide the solvent to the desired locations. Different wettabilities on the substrate cause the liquid to flow out of the lyophobic areas and into the lyophilic areas. However, the team found that the difference in the receding contact angles of the toluene solution rather than the toluene-substrate interaction determines the distribution of P3HT solution on the n-octadecyltrichlorosilane (OTS) patterned Si/SiOx substrate during the dip-coating process.

In combination with this thickness fluctuation of the thin liquid film, the size of P3HT aggregates in the solution, which changes during the ageing process, also determines the local structures in the two areas.

The researchers presented their work in the journal Nanotechnology.