Thin film property modification via block copolymer adsorption

Using low-energy forward recoil spectrometry and neutron reflectivity, diblock and triblock copolymer adsorption from a polystyrene, PS, matrix to the substrate is investigated. The diblock copolymers are poly(deuterated styrene-block-methyl methacrylate), dPS-b-PMMA, and poly(deuterated styrene-block-dimethyl amino ethyl methacrylate), dPS-b-PDMAEMA. The PMMA and PDMAEMA blocks readily adsorb to silicon oxide, SiO_x, whereas the dPS block extends into the PS matrix. For diblock copolymers having dPS degree of polymerization (DOP), N_dPS < 200, the distance between grafted chains, D, is greater than R_g, radius of gyration of dPS, whereas for N _dPS > 200, D is less than R_g. Thus, a crossover from a collapsed to a stretched conformation is expected near N_dPS ≈ 200, which corresponds to the entanglement DOP of PS, N_e. Moreover, adsorption strongly increases as N_dPS increases from values below to values above N_e. Using only the adsorbing block-substrate interaction as a fitting parameter, self-consistent mean-field, SCMF, predictions are in good agreement with experimental results. The dPS-b-PMMA adsorption from a PS matrix to an amine-terminated SiO_x surface is also investigated. In contrast to the strong adsorption on SiO_x, PMMA adsorption to the amine-terminated surface must compete with the PS matrix chains. Thus, the interfacial width between the PS chains and the non-adsorbing dPS block is broader on the amine-terminated surface. In agreement with this result, PS:dPS-b-PMMA films on amine surfaces show hole growth suppression, whereas on SiO_x, hole growth is observed for films having N_dPS < P, where P represents the DOP of PS matrix. Tack tests of dPS-b-PMMA in contact with a PS melt show that adhesion improves as N_dPS increases. This result suggests that entanglements across the interface increase with increasing N_dPS. The effects of triblock chain architecture and anchoring block molar fraction, f_A, on thin film dewetting and block copolymer adsorption on SiO_x are also investigated. Although chain architecture has a minor effect on dewetting, hole grow is detected when the anchoring block is short and f_A < 4%. In comparison to the PS:diblock case, PS:triblock films show less adsorption suggesting that triblocks are less effective adhesion promoters.