A gradient combinatorial approach was used to examine the effect of substrate surface energy on the morphology and stability of films of a poly(isoprene-b-styrene-b-ethylene oxide) triblock copolymer that exhibits an alternating gyroid morphology in the bulk. Atomic force microscopy data across our surface energy (water contact angle) library suggest a transformation to predominantly surface parallel lamellae with an antisymmetric ordering. For substrate water contact angles below 70 degrees the film exhibited autophobic dewetting from an adsorbed half-period triblock copolymer monolayer at longer annealing times. X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure analysis along gradient specimens indicated that the substrate surface energy governed the composition profile of the monolayer, and this variation in chemical expression was key to whether the film was stable or autophobically dewet. These observations demonstrate that enthalpic interactions, in addition to entropic considerations, can play a major role in autophobic dewetting of block copolymer films.

The phase behavior of thin‐film blends of polystyrene (PS) and the random copolymer poly(styrene‐co‐4‐bromostyrene) (PBS) was studied with atomic force microscopy (AFM) and small‐angle X‐ray scattering (SAXS). Phase behavior was studied as a function of the PBS and PS degree of polymerization (N), degree of miscibility [controlled via the volume fraction of bromine in the copolymer (f)], and annealing conditions. The Flory–Huggins interaction parameter χ was measured directly from SAXS as a function of temperature and scaled with f as χ = f2χS–BrS [where χS–BrS represents the segmental interaction between PS and the homopolymer poly(4‐bromostyrene)] Simulations based on the Flory–Huggins theory and χ measured from SAXS were used to predict phase diagrams for all the systems studied. The PBS/PS system exhibited upper critical solution temperature behavior. The AFM studies showed that increasing f in PBS led to progressively different morphologies, from flat topography (i.e., one phase) to interconnected structures or islands. In the two‐phase region, the morphology was a strong function of N (due to changes in mobility). A comparison of the estimated PBS volume fractions from the AFM images with the PBS bulk volume fraction in the blend suggested the encapsulation of PBS in PS, supporting the work of previous researchers. Excellent agreement between the phase diagram predictions (based on χ measured by SAXS) and the AFM images was observed. These studies were also consistent with interdiffusion measurements of PBS/PS interfaces (with Rutherford backscattering spectroscopy), which indicated that the interdiffusion coefficient decreased with increasing χ in the one‐phase region and dropped to zero deep inside the two‐phase region. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 255–271, 2002

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