Equilibrium and non-equilibrium dynamics of polymers confined in nanopores*

Polymers confined in nanopores are away from equilibrium in a temperature range above the glass temperature. The nonequilibrium dynamics of linear and star-shaped cis-1,4 polyisoprenes confined within nanoporous alumina was explored as a function of pore size, d, molar mass and functionality.  Two thermal protocols were tested; one resembling a quasi-static process (I), and another involving fast cooling followed by annealing (II). ² Both thermal protocols establish the existence of a critical temperature below which nonequilibrium effects set-in. The non-equilibrium phenomena in pores reflects the nonequilibrium configurations of the adsorbed layer that extent away from the pore walls. The equilibrium times depend strongly on temperature, pore size and functionality. Subsequently, we studied the adsorption kinetics of PI by following the evolution of the dielectrically active longest normal mode with in situ nanodielectric spectroscopy. The extremely slow kinetics reflect the fact that exchanging chains with the pore surface have to pass through several unfavorable configurations (e.g trains, loops). The molar mass dependence of the characteristic adsorption times was in good agreement with a scaling theory proposed by de Gennes and later refined by Semenov and Joanny. Polymer electrolytes in the same nanopores also show slow equilibration times and their origin can be traced to chain adsorption.