Polymers, Liquid Crystals and Supramolecular Structures Group

Professor G Ungar

Dipl. Ing., Zagreb; Magister, Zagreb; PhD, Bristol;

Reader

Research Interests

Two main research areas: The first area is the study of structure and phase behaviour of liquid crystalline (l.c.) and supramolecular polymeric, oligomeric and low molecular systems. Molecular organisation is investigated by diffraction and spectroscopy. Applying principles of self-assembly, new molecular architectures are designed and tested in collaboration with synthetic chemists. Current topics include molecular channel matrices, liquid crystalline dendrimers, novel thermotropic l.c. phases with 3-d periodicity ("micellar" and bicontinuous cubic and non-cubic), controlled shape supramolecular nano-objects, highly conducting polymer electrolytes (with Prof. Wright), columnar main chain polymers, novel l.c. transitions (e.g. nematic-nematic), re-entrant and incommensurate mesophases, structure of light-emitting l.c. polymers.

The second area of research is structure and morphology of semicrystalline polymers. In particular, monodisperse model polymers in the form of very long n-alkanes are studied. As a result of these studies the "self-poisoning" crystallization mechanisms has been proposed for flexible polymers. Furthermore, new layer structures and superlattices were discovered recently.

Potential applications of the research on l.c. and supramolecular systems, including molecular electronics, photonic bandgap crystals, controlled release agents, l.c. displays and speciality fibres.

The development of advanced instrumentation and analytical methods for x-ray scattering, specifically tailored for liquid crystal and polymer studies, plays a major part in the group's research. Quadrant and Image Plate low and wide angle scattering detectors, often associated with synchrotron facilities, are incorporated into purpose-built in-house equipment. Synchrotron experiments are also carried out where high source brilliance and high resolution are required. Real-time low-frequency-shift Raman spectroscopy was recently introduced, allowing studies of structure development in polymers. Small-angle neutron scattering (SANS) on selectively deuterated polymers is applied and, currently, real-time SANS is being developed for in situ studies of crystallization of polymers and other materials.

Teaching Interests

Structure of matter, polymers, liquid crystals and physical techniques.

Selected publications:

G Ungar, J Stejny, A Keller, I Bidd, M C Whiting, “The crystallization of ultralong normal paraffins: the onset of chain folding”, Science, 229, 1985, 386.

SD Hudson, H-T Jung, V Percec, W-D Cho, G Johansson, G Ungar and VSK Balagurusamy, “Direct visualization of individual cylindrical and spherical supramolecular dendrimers”, Science, 278, 1997, 449.

V Percec, C-H Ahn, G Ungar, DJP Yeardley, M Möller and SS Sheiko, "Spherical and cylindrical supermolecules from polymer backbones jacketed with quasi-equivalent dendritic coats", Nature, 391, 1998, 161.

G Ungar, PK Mandal, PG Higgs, DSM de Silva, E Boda and CM Chen, "Dilution wave and negative-order crystallization kinetics of chain molecules", Phys. Rev. Lett. 85, 2000, 4397.

G Ungar and X B Zeng, “Learning polymer crystallization with the aid of linear, branched and cyclic model compounds”, Chem. Rev., 101, 2001, 4157.

G Ungar, Y. Liu, XB Zeng, V Percec and W-D Cho,  “Giant supramolecular liquid crystal lattice”, Science, 299, 2003, 1208.

Tele: (44) (0)114 222 5457

g.ungar@sheffield.ac.uk