RESUMEN
Polymer vesicles made from poly(isoprene-b-styrene-b-2-vinyl pyridine) (PI-b-PS-b-P2VP) triblock copolymer confined within the nanopores of an anodic aluminum oxide (AAO) membrane are studied. It was found that these vesicles have well-defined, nanoscopic size, and complex microphase-separated hydrophobic membranes, comprised of the PS and PI blocks, while the coronas are formed by the P2VP block. Vesicle formation was tracked using both transmission and scanning electron microscopy. A mesh-like morphology formed in the membrane at a well-defined composition of the three blocks that can be tuned by changing the copolymer composition. The nanoscale confinement, copolymer composition, and subtle molecular interactions contribute to the generation of these vesicles with such unusual morphologies.
Asunto(s)
Polímeros/química , Poliestirenos/química , Polivinilos/química , Piridinas/química , Óxido de Aluminio/química , Interacciones Hidrofóbicas e Hidrofílicas , Membranas Artificiales , Microscopía Electrónica de Transmisión , Peso Molecular , Dióxido de Silicio/químicaRESUMEN
Phase transitions of polymeric materials are accompanied by changes in density as a function of temperature. Being able to measure these changes in polymeric systems in one, two or three dimensions on the nanoscopic length-scale is a challenge, but it would provide a simple route to assess phase transitions in nanoscopically confined systems. It is shown that the measurement of the dielectric permittivity in the high frequency limit (in spectral regions not affected by dielectric dispersions) offers an effective and very sensitive means to assess density fluctuations, and hence phase transitions, in nanoscopic systems. The sensitivity of this approach is demonstrated by assessing the phase transition behavior of ferroelectric polymer nanowires confined within alumina membranes. No significant shifts in the Curie transition are observed down to pore diameters as small as 15 nm.
Asunto(s)
Nanocables/química , Polímeros/química , Óxido de Aluminio/química , Transición de Fase , Temperatura , TermodinámicaAsunto(s)
Óxido de Aluminio/química , Cloroformo/química , Cristalización/métodos , Nanoestructuras/química , Nanoestructuras/ultraestructura , Nanotecnología/métodos , Polímeros/química , Electrodos , Sustancias Macromoleculares/química , Ensayo de Materiales , Micelas , Conformación Molecular , Tamaño de la Partícula , Porosidad , Solventes/química , Propiedades de SuperficieRESUMEN
Dense, ordered arrays of <100>-oriented Si nanorods with uniform aspect ratios up to 5:1 and a uniform diameter of 15 nm were fabricated by block copolymer lithography based on the inverse of the traditional cylindrical hole strategy and reactive ion etching. The reported approach combines control over diameter, orientation, and position of the nanorods and compatibility with complementary metal oxide semiconductor (CMOS) technology because no nonvolatile metals generating deep levels in silicon, such as gold or iron, are involved. The Si nanorod arrays exhibit the same degree of order as the block copolymer templates.
Asunto(s)
Cristalización/métodos , Nanotecnología/métodos , Nanotubos/química , Nanotubos/ultraestructura , Polimetil Metacrilato/química , Poliestirenos/química , Silicio/química , Conductividad Eléctrica , Sustancias Macromoleculares/química , Ensayo de Materiales , Conformación Molecular , Tamaño de la Partícula , Semiconductores , Propiedades de SuperficieRESUMEN
The filling behavior of a room temperature solvent, perfluoromethylcyclohexane, in approximately 20 nm nanoporous alumina membranes was investigated in situ with small angle x-ray scattering. Adsorption in the pores was controlled reversibly by varying the chemical potential between the sample and a liquid reservoir via a thermal offset, DeltaT. The system exhibited a pronounced hysteretic capillary filling transition as liquid was condensed into the nanopores. These results are compared with Kelvin-Cohan theory, with a modified Derjaguin approximation, as well as with predictions by Cole and Saam.