화학공학소재연구정보센터
Macromolecules, Vol.27, No.18, 5037-5042, 1994
Bridging by Reversibly Adsorbed Telechelic Polymers - A Transient Network
In this work we study a model "network" formed by the reversible adsorption of telechelic polymers between two flat surfaces using the dynamic Monte Carlo technique on a cubic lattice. Chains of 50 segments are studied in an athermal solvent and in the weak overlap limit. The parameters varied are the end-adsorption energy (epsilon/kT) and separation of the surfaces (L). We investigate the effect of the adsorption energy and the surface separation upon the equilibrium bridging fraction and on the lifetime distribution of the bridges. The bridging fraction is seen to increase monotonically with adsorption energy and reaches a limiting value for strong adsorption; the bridging fraction decreases monotonically with increasing surface separation. The average bridging time increases exponentially, without limit, with the adsorption energy. The average bridging time is relatively insensitive to the spacing of the surfaces if the bridges are not stretched strongly compared to the rms end-to-end distance of free chains, and drops off steeply above a critical stretching rate. The fraction of bridges of a given lifetime falls exponentially with the lifetime. Accordingly the stress decay in the system after unit shear strain is also exponential. While the stress decay time is rather insensitive to the surface separation (below a critical stretch) the plateau modulus depends both upon the binding energy and the surface separation. The exponential dependence of the bridging lifetime allows a simple scaling of the time axis so that the normalized stress relaxation data for different binding energies fall on the same curve.