Dhurjati S. K. Mudigonda

Tailoring the electrochromic properties of devices via polymer blends, copolymers, laminates and patterns

The ability to tune colour constitutes an important goal in the design of electrochromic devices. The majority of single electrochromic materials, whether inorganic or organic have a very narrow spectral colour change, however. Complex colours such as browns and tans that mimic natural vegetation and soils are not inherent to these materials. We have explored several strategies to achieve these colours including the use of copolymers that contain two distinct moieties, blends of polymers that have different colour changes, laminating two different polymers on the working electrode, and using fine patterns of two different materials to confuse the eye. We have constructed solid state electrochromic devices using ITO/Mylar substrates, a solid polymer electrolyte, a V2O5 counterelectrode and working electrodes that were made via one of the four methods outlined above. The colour changes of these devices were measured using spectrocolourimetry conforming to the CIE standard. The colour changes observed were similar to those of natural vegetation and soils.

Effect of Electrolytes on Performance of Electrochemical Capacitors Based on Poly[3-(3,4-difluorophenyl)thiophene]

Poly[3-(3,4-difluorophenyl)thiophene], MPFPT, electrochemically deposited onto carbon paper, was studied in electrochemical capacitors utilizing several tetraalkylammonium/acetonitrile electrolyte systems. Although the surface morphology of the polymer varied with the anion used for polymerization, an open and porous structure on cross section was obtained with all the electrolytes. The cycle stability of model Tee cell devices incorporating 1 cm 2 polymer electrodes was affected by both polymerization and cycling electrolytes. In general, electrolytes employing the tetraethylammonium cation yielded better cycle stability than those with tetramethylammonium cations. Devices with electrodes prepared and cycled in tetraethylammonium bis(trifluoromethane-sulfonyl)imide showed the best overall performance, Symmetric and asymmetric MPFPT devices were cycled up to 10,000 times retaining 50 and 70%, respectively, of their initial charge. In the case of the asymmetric device, little or no change in the capacity was observed after the first few hundred cycles.

Modifying the electrochromic properties of some novel non-conjugated polymers with pendant teraryl groups

Abstract A series of N-substituted-2-(5′-vinyl-2′-thienyl)-5-(2″-thienyl)pyrroles were synthesized and their electrochromic properties studied, Ia an attempt to tailor the observed color, copolymers of 5-vinylterthiophene and N-phenyl-2-(5′-vinyl-2′-thienyl)-5-(2″-thienyl) pyrrole were prepared using different stoichiometries. In another approach we synthesized copolymers of (i) N-vinylcarbazole and 5-vinylterthiophene and (ii) N-vinylcarbazole and N-phenyl-2-(5′-vinyl-2′-thienyl)-5-(2″-thienyl)pyrrole.