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, ∼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.