Patterning phase separation in polymer films with dip-pen nanolithography.

We report a rapid-prototyping method for controlling nanoscale phase separation and pattern formation in conjugated polymer blend films using Dip-Pen Nanolithography (DPN). We use DPN to generate patterned alkylthiol monolayers with feature sizes down to 50 nm on gold surfaces and show how such patterns can nucleate the formation of lateral domains in blends of poly-3-hexylthiophene (P3HT) and polystyrene (PS) cast from solution. We show that this process can be used to probe phase nucleation at heterogeneous surface sites ranging in size from 50 to 750 nm, and that polymer features smaller than 150 nm in diameter can be achieved. We anticipate this method will be useful for studying polymer film responses to nanoscale surface fluctuations as well as for correlating nanoscale phase separation with optoelectronic processes in organic films used in light-emitting diode and photovoltaic devices.