Diffusion of small molecules in a shape memory polymer
A. Marquardt, S. Mogharebi, K. Neuking, F. Varnik, G. Eggeler,
Volume: 51. Pages: 9792--9804
DOI: 10.1007/s10853-016-0213-0
Published: 2016
Abstract
The present work studies the diffusion of small molecules (acetone,
ethanol, and water) in a shape memory polymer (SMP) of type Estane
ETE 75DT3 (SMP-E), which represents a thermoplastic polyurethane.
The work aims at providing background information on the chemical
reaction between SMPs and small molecules which can limit the service
life of SMP actuators operating in harsh chemical environments. Weight
gain studies after immersion of plate specimens in liquid acetone,
ethanol, and water yield data which can be assessed on the basis
of analytical and numerical solutions of Fick's second law. The diffusion
coefficients which are obtained for 21, 30, and 40 {\textdegree}C
in the present study scale as D acetone > D
ethanol > D water.
The diffusion coefficients show Arrhenius types of temperature dependencies
with apparent activation energies of 33 (acetone), 59 (ethanol),
and 58 (water) kJ mol−1. The diffusion coefficients and the apparent
activation energies obtained in the present work are in reasonable
agreement with data which were reported for the reaction of the three
small molecules with similar polymers in the literature. It is not
straightforward to correlate differences in molecular mobility with
individual physical properties. The Hansen solubility parameter (originally
derived to explain solubility not mobility) qualitatively rationalizes
the observed differences.