James Peter Stokes

Charge Transfer Salts of Highly Oriented Fibers of Discotic Liquid Crystal HET-n

Abstract The charge transfer salt of highly oriented fibers of discotic liquid crystals of 2,3,6,7,10,11-hexa-alkoxytriphenylene (HET-n) and 2,3,6,7,10,11-hexa-alkanoyloxytriphenylene (HAT-n) can be made by a strand technique followed by a doping process. As a result, the bromine doped HET-5 fiber shows a conductivity of three orders of magnitude higher than that of the bromine doped HET-5 powder.

Synthesis of Δ2,2′-bithieno[3,4-d]-1,3-dithiole (DTTTF) and some of its charge-transfer salts

The title compound (DTTTF) was prepared by the coupling of the corresponding thieno-1,3-dithiolium salt, obtained from thieno-1, 3-dithiolane-2-thione synthesized from 3,4-dibromothiophen.

Synthesis and study of multiple cationic salts of hexamethoxytriphenylene (HMTP)

Abstract 2,3,6,7,10,11-Hexamethoxytriphenylene (HMTP) is known to exhibit multiple reversible oxidation states. We report on the synthesis and the physical properties of stable monocation, dication, and alloy salts between HMTP and ClO 4 − . The monocation salt, HMTP-ClO 4 , is a half-filled band, quasi one-dimensional semiconductor with a possible spin-Peierls transition at 240K. The dication is also found to be a semiconductor.

Weakly temperature dependent highly conducting polyquinoline based pyrolytic films

Abstract The vapour phase thermolysis of quinoline oligomers at 900 – 1200°C yields a new class of highly conducting organic polymer films. Both transmission electron microscopy and powder x-ray diffraction of the film showed an amorphous structureless appearance without any sign of the graphitic layer structure. These films exhibit a conductivity of higher than 400 S/cm at room temperature without doping and high stability under ambient conditions. The conductivity is weakly temperature dependent with a resistance ratio of R 29K /R 800K equal to 1.41, and a resistance maximum at 29K.

Percolation in oil‐continuous microemulsions

Percolation in oil continuous microemulsions containing surfactant covered water droplets demonstrate behavior significantly different from standard percolation phenomena. The hopping of charge carriers (anionic surfactants) on the cluster of water droplets which rearrange in time results in a dynamic (or ‘‘stirred’’) percolation that yields critical exponents and frequency scaling different from static percolation in systems with quenched disorder.

Viscous Fingering Instabilities in Porous Media

We study patterns formed by the viscous fingering instability in a porous media. When the displacing fluid preferentially wets the medium, the finger width is much larger than the pore size and, when normalized by the square root of the permeability, is found to scale with capillary number as Ca−1/2. While traditional theories based on Hele-Shaw geometry give this dependence for the most unstable wavelength, they are unable to explain the magnitude of the finger. We consider here the effect of a velocity dependent capillary pressure in addition to the more conventional static term, and suggest that it may control the scaling of the finger width on Ca. We demonstrate the existence of this dynamic capillary pressure, which offers new insight into the basic physics of the motion of a fluid interface in porous media.

Broadband noise in orthorhombic TaS3

We report experimental results on the broadband noise in sliding charge density wave conductor orthorhombic TaS3. We propose that the noise has its origin in the interaction of a deformable condensate with random impurities. The experimental results are in excellent agreement with a phenomenological model based on fluctuations in threshold field due to deformations of the sliding condensate. The amplitude of the noise is directly related to the dynamic coherence volume of these fuctuations.

High-Pressure Conductivity And Structure Of Hmtsf-TCNQ

Abstract Four-probe resistivity measurements on organic conductors have been extended to 6 GPa. The organic metal HMTSF-TCNO appears to undergo a phase transition to a three-dimen-sionaliy ordered conducting state near 4 GPa. X-ray and Raman scattering confirm the transition. Unexpectedly, the degree of charge transfer in HMTSF-TCNO is relatively insensitive to pressure.