Relations between Dewetting of Polymer Thin Films and Phase


Nano-bioanalysis Team, Health Technology Research Center, National Institute of AdVanced Industrial Science and Technology (AIST), 2217-14 Hayashi-cho...
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8184

J. Phys. Chem. C 2008, 112, 8184–8191

Relations between Dewetting of Polymer Thin Films and Phase-Separation of Encompassed Quantum Dots Ryodai Kanemoto,†,‡ Abdulaziz Anas,† Yusuke Matsumoto,†,‡ Rintaro Ueji,‡ Tamitake Itoh,† Yoshinobu Baba,†,§ Shunsuke Nakanishi,‡ Mitsuru Ishikawa,#,†,⊥ and Vasudevanpillai Biju*,†,⊥ Nano-bioanalysis Team, Health Technology Research Center, National Institute of AdVanced Industrial Science and Technology (AIST), 2217-14 Hayashi-cho, Takamatsu, Kagawa 761-0396, Japan, and Department of AdVanced Materials Science, Faculty of Engineering, Kagawa UniVersity, 2217-20 Hayashi-cho, Takamatsu, Kagawa 761-0396, Japan ReceiVed: NoVember 14, 2007; ReVised Manuscript ReceiVed: March 1, 2008

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 (