Time−Temperature Superposition for Viscoelastic Properties of Regioregular Poly(3-hexylthiophene) Films

Abstract

Shear moduli were determined for chemically polymerized and solvent cast regioregular poly(3-hexylthiophene) films, using thickness shear mode acoustic wave resonators. The results are strikingly different to those for electropolymerized regiorandom poly(3-hexylthiophene) films. The time scale of the measurement was varied directly by use of higher harmonics of the acoustic wave resonator and indirectly via temperature. The significant variations in shear modulus with effective time scale can be "normalized"onto a stress master relaxation curve by using the concept of time-temperature superposition; this is the first time this has been demonstrated for electroactive films. The shift factors required to effect this normalization do not follow the classical Williams-Landel-Ferry (WLF) equation developed for long-range backbone motions of bulk polymers. Instead, they follow an Arrhenius-like behavior, commonly used to describe secondary motions of polymer side-chains. The activation enthalpy associated with this is independent of applied potential, is the same as for as cast (undoped) films, and is similar to that for rotation about a carbon-carbon single bond. These all point to the hexyl side-chains as the origins of the observed phenomena, consistent with the "melting point" separating two temperature-dependent phases and with the different molecular packing arrangements that would necessarily apply to regioregular and regiorandom materials.

Electrochemical and viscoelastic evolution of dodecyl sulfate-doped polypyrrole films during electrochemical cycling

“…As Figure 8-Route I shows, the PPy-DS film undergoes successive swelling and shrinking cycles during the redox process. In addition, a dehydration process of cations for freshly prepared films has been reported during anodic potential sweep due to the lower porosity of PPy-DS film in a relatively shrunken state [38]. As for route II which is explored in this work, the volumetric change capability of the film can become poorer upon cycling, and the solvation shell of cation at -0.6 V is removed during the cycling process.…”

“…The real component (G´) describes the energy storage capability of the polymer chains and the imaginary part (G") is associated with the energy dissipation of the film due to irreversible deformation of polymer chains [38] .…”

“…at -0.6V. It has been revealed that the G´ is correlated with the film stiffness, while G" is a measure of the film viscosity [12,38]. The progressively increased G´ and decreased G" suggest that the periodical cycling renders the PPy-DS film stiffer and less viscous.…”

Viscoelastic study of conducting polymers using quartz crystal microbalance

“…This work has shown that the QCM provides the opportunity to detect viscoelastic properties of the deposited layer. Several studies have been conducted by Hillman and co-workers on polythiophene [4][5][6][7][8][9][10][11][12][13] . Their work had been carried out using a QCM device working with an impedance system.…”

Detection of flexibly bound adsorbate using the nonlinear response of quartz crystal resonator driven at high oscillation amplitude

“…The value of its acoustic resistance should be taken at main resonance. It is defined by losses and storage moduli of the film, which may be solvated depending on applied potential [15] in case of redox polymers. It also depends on the surface roughness of interface with liquid [16].…”