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, SiOx, whereas the dPS block extends into the PS matrix. For diblock copolymers having dPS degree of polymerization (DOP), NdPS < 200, the distance between grafted chains, D, is greater than Rg, radius of gyration of dPS, whereas for N dPS > 200, D is less than Rg. Thus, a crossover from a collapsed to a stretched conformation is expected near NdPS ≈ 200, which corresponds to the entanglement DOP of PS, Ne. Moreover, adsorption strongly increases as NdPS increases from values below to values above Ne. 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 SiOx surface is also investigated. In contrast to the strong adsorption on SiOx, 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 SiOx, hole growth is observed for films having NdPS < 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 NdPS increases. This result suggests that entanglements across the interface increase with increasing NdPS. The effects of triblock chain architecture and anchoring block molar fraction, fA, on thin film dewetting and block copolymer adsorption on SiOx are also investigated. Although chain architecture has a minor effect on dewetting, hole grow is detected when the anchoring block is short and fA < 4%. In comparison to the PS:diblock case, PS:triblock films show less adsorption suggesting that triblocks are less effective adhesion promoters. ^
Engineering, Materials Science
Ana Claudia Aragao de Almeida Costa,
"Thin film property modification via block copolymer adsorption"
(January 1, 2003).
Dissertations available from ProQuest.