Thermoreversible gelation of regioregular poly(3-hexylthiophene) in xylene

Regioregular poly(3-hexylthiophene) (P3HT) produces thermoreversible gel in xylene; The gel is brownish-red in color. SEM and TEM studies indicate the presence of fibrillar network. WAXS and electron diffraction pattern indic ate the presence of P3HT crystallites in the gel; The gels exhibit a first- order phase transition when heated in DSC. A time-dependent UV-vis study in dicates that gelation in this system is probably accompanied by two differe nt processes, e.g., (1) coil-to-rod transformation and (2) aggregation of r ods to form the crystallites producing the gel. The gelation rate (t(gel)(- 1)) measured from the test tube tilting method is analyzed using the equati on t(gel)(-1) = f(C) f(T), where Ac) = phi (n), phi being the reduced overl apping concentration and n is an exponent. The average "n" value determined is 0.52, which indicates that three-dimensional percolation is a suitable model for this gelation. The gelation rate is analyzed according to the Flo ry-Weaver theory of coil-to-helix transition, and the free energy of activa tion (DeltaF) for the coil-to-rod transformation is found to be 23.7 kcal/m ol. It is also analyzed using the theory of fibrillar crystallization in so lution, and the free energy of formation of critical size crystalline nucle us (DeltaG*(dil)) is found to be 37.5 kcal/mol. The conductivity of the dri ed P3HT gel becomes enhanced by similar to 10 times that of the cast film i n the undoped state, but in the doped state there is an similar to 50-fold increase.