Biomedical subjects

Ali Dhinojwala

Publications and source records attributed to Ali Dhinojwala.

3 recordsLinked to original sources

PubMed2003

Observation of novel liquid-crystalline phase above the bulk-melting temperature.

In this paper, we show that a noncrystalline but ordered smectic-like phase exists above the bulk-melting temperature (T(m)) at poly(n-alkyl acrylates)-air interface. The surface ordered phase is one monolayer thick and undergoes a sharp transition from order to disorder 10 degrees C above T(m) for n=22. The presence of a surface phase that does not exist in the bulk has important implications in the design of thermally responsive adhesives.

Journal Article↗

PubMed2003

Relaxation of a rubbed polystyrene surface.

The relaxation dynamics of a rubbed polystyrene (PS) surface have been characterized using infrared-visible sum frequency generation spectroscopy (SFG). The SFG results were compared with previous relaxation of retardation measurements, and the results show that the rubbed PS surface has the same T(g) as the bulk where T(g) is defined as tau(T(g))=5 s, however, the surface has a lower activation energy (deltaE) and a larger stretching exponent (beta(KWW)) than bulk PS. This indicates that the surface region relaxes more quickly than the bulk. The thickness of this region of lower deltaE and larger beta(KWW) is estimated to be roughly 12 nm.

Journal Article↗

PubMed2002

Probing polymer/polymer interfaces.

Infrared-visible sum frequency generation spectroscopy (SFG) has been used to study the interface between poly(vinyl-N-octadecylcarbamate-co-vinyl acetate) (Comb) and deuterated or hydrogenated polystyrene (dPS or hPS) films. Strong methyl symmetric and Fermi resonance bands associated with the alkyl side chains of the Comb polymer are observed in the SFG spectra. In addition, for Comb/hPS spectra, symmetric and asymmetric vibration modes of phenyl groups are observed. The presence of asymmetric modes indicates the phenyl rings are tilted with respect to the interface normal.

Journal Article↗