Controllable organization of quantum dots into mesoscale wires and cables via interfacial block copolymer self-assembly

This paper describes morphology control and characterization of interfacial properties for the synergistic self-assembly of polymer-stabilized CdS quantum dots (QDs), referred to as PS-CdS, with polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers at the air-water interface. This spontaneous process yields various hierarchical one-dimensional (1D) QD/polymer hybrid structures with widths commensurate with optical wavelengths, similar to 300 nm, including wires, cables, branched wires, and rings incorporated along the lengths of cables. Control over predominant hybrid assemblies is achieved by varying the PS-CdS/PS-b-PEO blend composition and the concentration of the spreading solution, with higher PS-CdS fractions resulting in more uniform distributions of QDs throughout hybrid structures and higher spreading concentrations giving rise to a greater predominance of 1D structures relative to circular dots and island aggregates. Compression isotherms of QD/polymer assemblies at the air-water interface reveal that interfacial behavior of aggregates is also dependent on the spreading conditions and blend composition; for all spreading concentrations, a maximum is observed in plots of the limiting area vs PS-CdS weight fraction in the blends, suggesting a competition between the conformational effects of PS-b-PEO dilution and PS-CdS addition. In addition, we describe a mechanism of formation for QD/polymer assemblies, based on AFM data of structures obtained at the highest spreading concentration, in which self-assembly is initiated by dewetting of the evaporating polymer solution from the air-water interface.