Monte Carlo simulation of polymer welding

Monte Carlo Modelling of random polymer chains, course grained onto a cubic F lattice, provides the ability to monitor the long range relaxation proce sses and the dynamic parameters of chains up to 400 units long. The model, described and verified by Haire et al. (Haire KR, Carver TJ, Windle AK. A M onte Carlo model for dense polymer systems and its interlocking with molecu lar dynamics simulation. Computational and Theoretical Polymer Science 2000 ; in press), is here applied to the study of molecular parameters in the vi cinity of different types of surface and also to the process of polymer wel ding, whereby adhesion between two adjacent surfaces is achieved by the int erpenetration of chains which are across the surface. The model demonstrates that a surface distorts the conformation of chains a djacent to it to give an oblate molecular envelope, that the concentration of vacant sites and chain ends increases near to the surface and that the d ensity of points representing the centres of mass of the chains increases i n the sub-surface regions. These results confirm earlier predictions and pr ovide additional confidence in the model. Modelling of the welding process leads to the parameter intrinsic weld time , t(w), which is the time from initial perfect contact of the surfaces to t he achievement of a weld within which the chain conformation is indistingui shable from the bulk. After the initial period in which the mating surfaces roughen, the welding proceeds according to the t(1/4) law predicted by rep tation theory. The time to a given level of interdiffusion across the bound ary is proportional to the chain length I, a comparatively weak dependence, while t(w) is proportional to l(3), a strong dependence. This is the same dependence on length as for the relaxation time of the chain end-to-end vec tors. In fact, the agreement between the relaxation time, measured on the m odel of the bulk, and t(w) is surprisingly close, at least for the monodisp erse polymers investigated here. (C) 2000 Elsevier Science Ltd. All rights reserved.