Relations between Dewetting of Polymer Thin Films and Phase-Separation of Encompassed Quantum Dots

Abstract

Incorporation of semiconductor quantum dots (QDs) at high densities in polymer thin films is promising for the development of nanoscale sensors, light-emitting diodes, and photovoltaic devices. However, inhomogeneous distribution and aggregation of QDs in polymers limit the applications of QD-polymer composites. We investigated the origin of the aggregation of CdSe-ZnS QDs in polybutadiene (PB) thin films and its relations with the dewetting of polymer thin films on inorganic surfaces. Microscale dewetting of PB thin films on glass surfaces resulted in the formation of honeycomb structures of PB, and nanoscale dewetting on the QD surface resulted in phase-separation and aggregation of QDs. The formation of the honeycomb structures of PB is attributed to phase-separation between PB and glass during the dewetting on the glass surface, and the aggregation of QDs is attributed to the phase-separation between PB and QDs during the dewetting on the QD surface. The honeycomb structures of PB are characterized using optical microscopy and atomic force microscopy (AFM) imaging, and the phase-separation and aggregation of QDs are characterized using transmission electron microscopy (TEM) imaging and inter-QD Förster resonance energy-transfer (FRET). FRET is confirmed from photoluminescence (PL) spectral shifts and decreases of PL intensity and lifetime of QDs. Without the phase-separation and aggregation of QDs, inter-QD FRET is unexpected under the selected densities of QDs; the calculated inter-QD distance (>60 nm) for a homogeneous distribution of QDs is beyond the Förster distance (<10 nm). The phase-separation and aggregation of QDs in PB thin films are further characterized based on a decrease of FRET from QD to rhodamine 590 (R590) with an increase in the density of QDs. The aggregation of QDs occurs because of the rejection of QDs by PB molecules during the release of recoiling energy, which is distributed among entangled polymer chains and between polymer chains and QDs in the thin films. In the current work, we characterized the nanoscale dewetting of PB on the surface of QDs, the phase-separation and aggregation of QDs in PB thin films, and the limit of close-packing of QDs in polymer thin films without aggregation that are valuable during the construction of QD and polymer-based thin-film devices.

Integrated PLGA–Ag nanocomposite systems to control the degradation rate and antibacterial properties

“…The improvements can include mechanical properties, heat resistance, flammability, gas permeability, and biodegradability of biodegradable polymers. 35,36 The use of inorganic nanoparticles with higher affinity/solubility for the polymer matrix can reduce phase separation processes which occur during polymer dewetting, thus avoiding the film structuring. linear and non-linear optical properties or biological activity.…”

Photoluminescence of CdSe and CdSe/ZnS quantum dots: Modifications for making the invisible visible at ensemble and single-molecule levels

“…In addition to the above physical parameters, Föster resonance energy transfer (FRET) and surface plasmon affect the photoluminescence of QDs [63][64][65][66][67][68][69][70][71]. For example, CdSe/ZnS QDs placed on the surface of Ag nanoparticles show reduced photoluminescence intensity and lifetime due to efficient energy transfer from photoactivated QD to Ag nanoparticles ( Figure 1A) [70].…”

Fluorescent Biocompatible Tactic PMMA-QDs Thin Films

“…The study of thin films is increasing to meet the demands in the miniaturization of devices, including transistors, sensors, photodetectors, LEDs, and nonvolatile memory devices. [1] The tacticity of a polymer comes from the way substituents are arranged on the polymer backbone in relation to the stereochemistry of adjacent chiral center. There are three different tacticities, namely atactic, syndiotactic, and isotactic.…”

“…Owing to its excellent optical and mechanical properties, PMMA has been a first-choice component for the preparation of inorganic-organic composites. [1,[4][5] Quantum dots (QDs) are semiconductor nanocrystals with bright, stable and size-tunable photoluminescence (PL). Incorporation of QDs at high densities in polymer thin films is promising for the development of nanoscale sensors, light-emitting diodes, and photovoltaic devices.…”