Interfacial interactions underpin phenomena ranging from adhesion to surface wetting. Here, we describe a simple, rapid, and robust approach to modifying solid surfaces, based on an ultrathin cross-linkable film of a random copolymer, which does not rely on specific surface chemistries. Specifically, thin films of benzocyclobutene-functionalized random copolymers of styrene and methyl methacrylate were spin coated or transferred, then thermally cross-linked on a wide variety of metal, metal oxide, semiconductor, and polymeric surfaces, producing a coating with a controlled thickness and well-defined surface energy. The process described can be easily implemented and adapted to other systems.
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.
Non-classical behaviour, brought about by a confinement that imposes spatial constraints on molecules, is opening avenues to novel applications. For example, carbon nanotubes, which show rapid and selective transport of small molecules across the nanotubes, have significant potential as biological or chemical separation materials for organic solvents or gaseous molecules. With polymers, when the dimensions of a confining volume are much less than the radius of gyration, a quantitative understanding of perturbations to chain dynamics due to geometric constraints remains a challenge and, with the development of nanofabrication processes, the dynamics of confined polymers have significant technological implications. Here, we describe a weak molecular-weight-dependent mobility of polymers confined within nanoscopic cylindrical pores having diameters smaller than the dimension of the chains in the bulk. On the basis of the chain configuration along the pore axis, the measured mobility of polymers in the confined geometry is much higher than the mobility of the unconfined chain. With the emergence of nanofabrication processes based on polymer flow, the unexpected enhancement in flow and reduction in intermolecular entanglements are of significant importance in the design and execution of processing strategies.
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