Letter pubs.acs.org/NanoLett Geometric Control of Rippling in Supported Polymer Nanolines

ABSTRACT: We study the swelling behavior of finlike polymer line gratings supported on a rigid substrate and show that the edge-supported polymer laminae undergo a rippling instability with a well-defined ripple wavelength λ transverse to the plane of the solid supporting substrate and a ripple amplitude that monotonically decreases from its maximum at the free-edge. These ripple patterns develop due to inhomogeneous compressive strains that arise from the geometric constraints that progressively suppress swelling near the supporting substrate where the laminae are clamped. By experimentally examining the influence of swelling strain and pattern geometry on the observed rippling instability, we find that the ripple wavelength λ scales with line width w for sufficiently long gratings, which is consistent with a simple theory. These trends were validated for polymer nanoline test patterns having w between (50 to 250) nm and a height-to-width aspect-ratio in the range 0.5 to 5. Our results suggest that line geometry, rather than material properties, governs the onset of rippling and suggest simple rules for their control

Well-Ordered Polymer Melts with 5 nm Lamellar Domains from Blends of a Disordered Block Copolymer and a Selectively Associating Homopolymer of Low or High Molar Mass

The use of short chain block copolymer melts as nanostructured templates with sub-10 nm domains is often limited by their low segregation strength (χN). Since increasing molar mass to strengthen segregation also increases the interdomain spacing of block copolymer melts, it is more desirable to increase the Flory−Huggins segment−segment interaction parameter, χ, to produce strong segregation. We have recently shown that poly(oxyethylene−oxypropylene−oxyethylene) block copolymer melts can undergo disorder-to-order transition when blended with a selectively associating homopolymer that can hydrogen bond with one of the blocks. Here, we study the effect of the molar mass of poly(acrylic acid) in the range 1−13 times that of the copolymer on the segregation of a 6.5 kg/mol poly(oxyethylene−oxypropylene−oxyethylene) copolymer melt. The neat copolymer is disordered, and the addition of poly(acrylic acid) resulted in a well-ordered lamellar morphology with an interdomain spacing of 10 ± 1.0 nm. Using small-angle and ultrasmall-angle X-ray scattering, we found that the blends remain well ordered at 80 °C over the entire range of homopolymer chain lengths. A small increase in the interdomain spacing of the lamellae and an order−order transition from lamellae-to-cylindrical morphology was observed in all blends as a function of increasing homopolymer concentration. The trends observed in experiments were validated by self-consistent field theoretical simulations