Ground state analysis of a Hamiltonian that reflects the interaction between soft pentagonal rotors. While hard pentagons pack to give a 2x1 repeat (green curve), soft pentagons can order into at least three distinct additional structures. One of these, a 31/2 x 31/2 repeat (red curve), resembles the ordering experimentally observed in poly(2-ethylhexylfluorene). The blue curve is obtained in Monte Carlo simulations.

Atomic force microscope image of a poly(2-ethylhexylfluorene) thin film formed atop a rubbed polyimide substrate (rubbing direction is in the vertical). There is a fibrilar structure oriented along the rubbing direction.

This image represents a proposed 14/6 helix of the silicon backboned polymer, poly(di-n-butylsilane). The model consists of repeating dyad "deviant/transoid" conformational isomers. Unlike saturated hydrocarbons, in which only gauche and anti) conformations are present, polysilanes are characterized by up to five low energy conformations. The carbon, hydrogen and silicon atoms are denoted by grey, white and gold shaded spheres respectively.
Mapping of low energy conformational isomers in the poly(di-n-octylpolyfluorene) polymer. (Per monomer energy is referenced to that of the so-called beta isomer). Each symbol corresponds to a single, unique tested conformer. Alpha (blue), beta (green) and gamma (red) correspond to the proposed conformer families. Inset: Model of the beta type isomer highlighting side~chains self-assembly.
Blue emission from a polyfluorene light emitting diode (0.05 X 1.00 mm2) fabricated with a microfluidics applicator. The two insets depict the physical structure and layout of the device.
Fluorescence microscopy image from polyfluorene microspheres produced by dewetting on a liquid crystal substrate.
Polarized optical micrograph of Schlieren texture from polyfluorene drop and stripe formed by a microfluidics applicator.

 

MichaelWinokur, Professor
VITA

Welcome to the Winokur Group Web Site. We are a condensed matter physics research group specializing in structure studies and computer modeling of conducting polymer systems. We also dabble in spectroscopy and transport.
 
We are part of the Department of Physics at the University of Wisconsin.

Overview: Conjugated (aka conducting) polymers (CPs) now form the basis for a broad spectrum of new devices technologies (e.g., plastic transistors, organic photovoltaics, polymer light emitting diodes).  These fascinating materials combine many attributes traditionally found in inorganic semiconductors with those of soft condensed matter.  CPs in the solid-state undergo a hierarchical structural ordering spanning vastly different length scales.  Starting at molecular level are crucial questions involving a delicate balance of direct skeletal and side-group interactions and these dictate the near-neighbor conformational energy landscape.  Manipulation of the molecular architecture not only alters the observed electrical and optical properties of the polymer and but also influences supramolecular assembly patterns in the solid state. The rational design of these materials is limited by the incomplete understanding of the interplay between molecular architecture, supermolecular assembly and electronic/optical properties.  Our research focuses on experimental and modeling studies that elucidate key structure/property relationships.
 
University of Wisconsin
Department of Physics
1150 University Ave.
Madison, WI 53706


NSF supported research

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People: Current/Past members of the group

Questions or comments:
 E-mail (mwinokur @ facstaff.wisc.edu).

Last incremental update: 25-Jan-2007