Polymer-like modes in shear mechanical spectra of phenylpropanols: The influence of hydrogen-bonded structures

We present a dielectric and shear mechanical study of 1-propanol and three phenylpropanols.

Contrary to other monoalcohols, the phenylpropanols do not show a bimodal behaviour in the their dielectric response, but a single, rather narrow process. Combined dielectric and light scattering spectra [Böhmer et al., J. Phys. Chem. B, 123, 10959] have shown that this single peak may be separated into a self- and a cross-correlation part, thus indicating that phenylpropanols do display features originating from hydrogen-bonded structures.

The shear mechanical spectra support that interpretation, demonstrating a subtle, yet clear, low-frequency polymer-like mode, similar to what is found in other monoalcohols. An analysis of the characteristic time scales found in the spectra show that shear relaxation is faster than the dielectric and that time scale separation of the dielectric Debye and alpha process is temperature independent and near identical in all the phenylpropanols.