Simultaneous patterning of two different types of nanoparticles into alternating domains of a striped array of a polymer blend in a single spin-casting step

Abstract

A fast and convenient method is developed for simultaneously patterning inorganic nanoparticles with different optical, electronic or magnetic functionality to specific surface regions, by spin-casting onto microcontact printed substrates blend solutions in which the two nanoparticle types are functionalized with surface polymer brush layers of different surface energies. The process is based on phase separation of different nanoparticles based on their immiscible brush layers during spin-casting, with the underlying surface energy heterogeneity of the patterned substrate directing the different NP types to domains of different surface energies. Here, we specifically demonstrate the simultaneous localization of cadmium sulfide quantum dots (CdS QDs), addressed with a surface layer of polystyrene (PS), and silver nanoparticles (Ag NPs), addressed with a surface layer of poly(methyl methacrylate) (PMMA), onto the non-polar and polar surface domains, respectively, of hydrophilic glass patterned with hydrophobic octadecyltrichlorosilane (OTS) stripe arrays with micron-scale periodicities. In order to prevent gelation of solvent-swollen polymer-brush coated NPs during spin casting, which effects strong kinetic constraints on phase separation and localization, PS, PMMA or PS/PMMA homopolymer blends of sufficiently high Mw were added to the NP blends to increase the free volume between approaching NPs. The process parameters were fine-tuned to obtain control over defects in the obtained patterns.