Glassy dynamics in one- and two-dimensional nanometric confinement - a comparision

Glassy dynamics of polymers (e.g. poly(methylphenylsiloxane) (PMPS) or poly(cis1,4-isoprene) (PI) ) is studied by broadband dielectric spectroscopy (BDS) in one-(1D)- and two-(2D)-dimensional nanometric confinement; the former is realized in thin layers having thicknesses down to 5 nm, the latter in unidirectional (length 50 m) nanopores with diameters varying between 4–8 nm. Based on dielectric measurements carried out in a broad spectral range at widely varying temperatures glassy dynamics is analyzed in detail in 1D and in 2D confinement. All the findings can be comprehended by considering the density of the polymer; in 1D it is assumed to be the same as in the bulk, hence the dynamic glass transition is not altered, in 2D it is reduced due to a frustration of packaging resulting in a higher free volume, as proven by ortho-positronium annihilation lifetime spectroscopy.