Nanoparticle Self-assembly Assisted by Polymers: The Role of Shear Stress in the Nanoparticle Arrangement of Langmuir and Langmuir-Blodgett Films

Abstract

We propose to use the self-assembly ability of a block copolymer combined with compression-expansion cycles to obtain CdSe quantum dots (QDs) structures of different morphology. The methodology proposed consists in transferring onto mica mixed Langmuir monolayers of QDs and the polymer poly (styrene-co-maleic anhydride) partial 2 buthoxy ethyl ester cumene terminated, PS-MA-BEE, previously sheared by 50 compression-expansion cycles. Results indicate that the shear stress takes out nanoparticles at the air-water interface from metastable states and promoted a new equilibrium state of the Langmuir monolayer, then it was transferred onto mica by the Langmuir-Blodgett (LB) methodology and the morphology of the LB films was analyzed by Atomic Force Microscopy and Transmission Electron Microscopy measurements. Our results show that when the amplitude strain increases the QDs domain size decreases and the LB film becomes more ordered. The dynamic of the monolayer relaxation after cycling involves at least three timescales which are related to the damping of surface fluctuation, raft rearrangement and component movements inside each raft. Brewster Angle Microscopy allowed visualizing in situ the raft rearrangement at the air-water interface.