MONTE-CARLO SIMULATION OF THE ADSORPTION FROM A NONSELECTIVE SOLVENT OF SYMMETRICAL TRIBLOCK COPOLYMERS WITH STICKY END BLOCKS

The adsorption of symmetric triblock copolymers from a nonselective so lvent on an impenetrable surface has been studied by a lattice Monte C arlo simulation method. The triblock copolymers are A(NA)B(NB)A(NA) wi th N-A=10, 5 less than or equal to N-B less than or equal to 40, and s urface interaction parameters -1.5 less than or equal to epsilon less than or equal to-0.5, where A is the adsorbing block and B is the nona dsorbing block. The concentration, expressed as the volume fraction, i s varied over the range 0.012 less than or equal to c less than or equ al to 0.143. This report describes the adsorption isotherms and the ki netics of the adsorption in;he simulations. At short times, the adsorp tion is diffusion controlled. Good approximations to the Langmuir adso rption isotherm are observed for the equilibrium adsorbed amount, Gamm a and surface coverage of the adsorbing block, theta(A). The results a re compared with recent simulations for diblock copolymers. The adsorb ed amount is less for the diblock than for the triblock copolymers at low concentration. The surface coverage by the adsorbing block is the same for both cases at weak surface adsorption. The surface density pr ofiles are also obtained and compared. The adsorbed number of chains p er unit area (sigma) and surface coverage for triblock copolymers unde r: weak adsorption conditions are found, respectively, to scale accord ing to the relationship sigma, theta(A) similar to 1/beta(2), where be ta=(N-B/N-A)(3/5), which implies the importance of the nonadsorbing bl ock size for the adsorption features of triblock copolymers. These res ults confirm the experimental observation reported recently by Dorgan et al. [Macromolecules 26, 5321 (1993)]. (C) 1997 American Institute o f Physics.