Session W18 - Computer Simulation II.
ORAL session, Thursday morning, March 15
Room 308-308, Washington State Convention Center
We study adhesion between a polymer melt and substrate due to chemically attached polymer chains on the substrate surface. We have performed extensive molecular dynamics simulations to study the effect of temperature, crosslink density, tethered chain density (\Sigma), tethered chain length (N_t), tensile pull velocity (v) and chain stiffness on the adhesive failure mechanisms of pullout and/or scission of the tethered chains. We observe a crossover from pure chain pullout to chain scission as N_t and v are increased. The value of N_t at which this crossover occurs is comparable to the chain entanglement length for the coarse-grained model used. Experiments and simulations have shown that the energy required to separate a polymer melt from a substrate increases considerably if the formation of large voids, or crazing can be initiated in the melt. The onset of crazing depends on the temperature and the interaction strength of the substrate with the melt. We also present data illustrating the additional effects of tethered chains on crazing mechanisms.