P. K. Sudeep

Kinetically trapped co-continuous polymer morphologies through intraphase gelation of nanoparticles.

We describe an approach to prepare co-continuous microstructured blends of polymers and nanoparticles by formation of a percolating network of particles within one phase of a polymer mixture undergoing spinodal decomposition. Nanorods or nanospheres of CdSe were added to near-critical blends of polystyrene and poly(vinyl methyl ether) quenched to above their lower critical solution temperature. Beyond a critical loading of nanoparticles, phase separation is arrested due to the aggregation of particles into a network (or colloidal gel) within the poly(vinyl methyl ether) phase, yielding a co-continuous spinodal-like structure with a characteristic length scale of several micrometers. The critical concentration of nanorods to achieve kinetic arrest is found to be smaller than for nanospheres, which is in qualitative agreement with the expected dependence of the nanoparticle percolation threshold on aspect ratio. Compared to structural arrest by interfacial jamming, our approach avoids the necessity for neutral wetting of particles by the two phases, providing a general pathway to co-continuous micro- and nanoscopic structures.

Nanoparticle Stripes, Grids, and Ribbons Produced by Flow Coating

Multicomponent and robust structures of quantum dots, in the form of stripes and grids, are produced by a simple flow coating method giving unprecedented control over macroscopic architectures from nanoscopic components. Crosslinking and lift-off of stripes lead to free-floating structures of nanoparticles that are flexible, robust, and fluorescent.

PEGylated silicon nanoparticles: synthesis and characterization.

Silicon nanoparticles were prepared and functionalized with alkene-terminated poly(ethylene oxide) to impart amphiphilic solution properties to the particles.

Polymer‐Nanoparticle Composites: Preparative Methods and Electronically Active Materials

The field of nanoparticle‐polymer composites is attractive from the standpoint of integrating the key features of both polymers and nanoparticles into hybrid or composite materials. Nanocomposites geared towards electronic and photophysical targets comprise an intriguing subset of the field, and benefit from interdisciplinary efforts in nanoparticle and polymer synthesis, along with methodology that provides the dispersion, orientation, and/or the assembly of nanoparticles and nanorods within a polymer matrix.

Polarization-Driven Stark Shifts in Quantum Dot Luminescence from Single CdSe/oligo-PPV Nanoparticles

We demonstrate polarization-induced spectral shifts and associated linearly polarized absorption and emission in single CdSe/oligo-(phenylene vinylene) (CdSe/OPV) nanoparticles. A mechanism for these observations is presented in which charge separation from photoexcited ligands results in a significant Stark distortion of the quantum dot electron/hole wavefunctions. This distortion results in an induced linear polarization and an associated red shift in band-edge photoluminescence. These studies suggest the use of single quantum dots as local charge mobility probes.

Linear Dipole Behavior in Single CdSe-Oligo(phenylene vinylene) Nanostructures

We report on linearly polarized absorption and emission from individual (4.3 nm) CdSe quantum dots whose surfaces are coordinated with monodisperse oligo-phenylene vinylene ligands. Shown previously to suppress quantum dot blinking, we demonstrate here that the electronic interaction of photoexcited ligands with the quantum dot core is manifested as a strong polarization anisotropy in absorption (M = 0.5), as well as distinct linear dipole emission patterns from the quantum dot core. Further, there is a correlation between the quantum dot emission moment and polarization orientation corresponding to the absorption maxima that is manifested as fluctuations in emission moment orientation in the X-Y plane. The observed polarization effects can be switched off by tuning the excitation away from the ligand absorption band. We propose a mechanism based on exciton dissociation from the photoexcited ligand, followed by the pinning of electrons at the quantum dot surface. The resulting Stark interaction is sufficiently strong to break the 2D degeneracy of the emission moment within the dot, and may therefore account for the linear dipole emission character.

Directional Absorption and Emission in Hybrid Polymer-Quantum Dot Nanostructures Studied by Scanning Probe and Fluorescence Microscopy

The optical properties of hybrid organic/quantum dot nanostructures, probed at the single molecule limit by scanning probe and fluorescence microscopy, reveal novel and highly directional absorption and emission characteristics, ideal for polarization-based switching applications.