Structural relaxation patterns of an optically labelled polymer at cryogenic temperatures

A specific conformational microstate of a doped polymer (poly(methacrylic acid)) is optically labelled by burning a narrow spectral hole into the absorption of the dopand molecule. The hole is then used in thermal cycling experiments as a highly sensitive probe for thermally induced structural relaxation processes. The temperature range investigated covers more than two orders of magnitude, namely from 520 mK to 60 K. Even at extremely low temperatures the polymer undergoes thermally activated relaxation processes as detected via the recovery and broadening of the hole. The relaxation pattern as a function of temperature can be modelled in a quantitative fashion. It is shown that the probability distribution of the conformational barriers is ∼ 1 √V. It seems that there is no lower cut-off barrier and that the distribution diverges for V→0.