Microphase-separated block copolymers were introduced as melts into nanoscopic cylindrical pores in alumina membranes via capillary action. The geometric confinement of both lamellar and cylindrical microdomain morphologies of styrene/butadiene block copolymers, PS-b-PBD, was investigated by transmission electron microscopy. Well-developed microphase-separated structures were formed within the resulting nanorods. Polymers that exhibit cylindrical microdomains in the bulk orient with cylindrical microdomains along the nanorod axis due to the preferential segregation of the PBD block to the walls of the pores. The period and packing of the microdomains differ from those observed in the bulk due to an incommensurability between the pore geometry and the natural period and hexagonal packing of the copolymer microdomains. With polymers exhibiting bulk lamellar morphology, confinement forces the formation of concentric cylinders oriented along the nanorod axis. The number of concentric cylinders depends on the ratio of the nanorod diameter to the equilibrium period of the copolymer. Because of the preferential segregation of PBD at the alumina surface, either PBD or PS can form the central core. These results indicate a method by which copolymer microdomains can be manipulated in a simple manner for the fabrication of isolated nanostructures.

Two polymer chains that occupy equal volumes when covalently linked together at one end self-assemble into an alternating lamellar morphology that has a characteristic period dictated by the molecular weight. When such copolymers are confined within alumina membranes that have cylindrical pores with diameters comparable to the repeat period, the interaction of the blocks with the confining walls and the imposed curvature induces a morphological transformation to relieve the constraints. Here, we show a lamella-to-toroid transition, captured through the dissolution of the surrounding membrane.

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Measurement of contact angles on super hydrophobic surfaces by conventional methods can produce ambiguous results. Experimental difficulties in constructing tangent lines, gravitational distortion or erroneous assumptions regarding the extent of spreading can lead to underestimation of contact angles. Three models were used to estimate drop shape and perceived contact angles on completely nonwetting super hydrophobic surfaces. One of the models employed the classic numerical solutions from Bashforth and Adams. Additionally, two approximate models were derived as part of this work. All three showed significant distortion of microliter-sized drops and similar trends in perceived contact angles. Liquid drops of several microliters are traditionally used in sessile contact angle measurements. Drops of this size are expected to and indeed undergo significant flattening on super hydrophobic surfaces, even if the wetting interactions are minimal. The distortion is more pronounced if the liquid has a lesser surface tension or greater density. For surfaces that are completely nonwetting, underestimation of contact angles can be tens of degrees. Our modeling efforts suggest that accurate contact angle measurements on super hydrophobic surfaces would require very small sessile drops, on the order of hundreds of picoliters.

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