Thin film morphologies of a 75.5
kg/mol polystyrene-block-polydimethylsiloxane (PS-b-PDMS) diblock copolymer
subject to solvent vapor annealing are described. The PS-b-PDMS has a double-gyroid morphology in bulk, but as a thin film
the morphology can form spheres, cylinders, perforated lamellae, or
gyroids, depending on the film thickness, its commensurability with
the microdomain period, and the ratio of toluene:heptane vapors used
for the solvent annealing process. The morphologies are described
by self-consistent field theory simulations. Thin film structures
with excellent long-range order were produced, which are promising
for nanopatterning applications.
A universal block copolymer pattern transfer method was demonstrated to produce Co nanostructures consisting of arrays of lines or dots from a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) diblock copolymer. Three processes were used: liftoff, a damascene process, and ion beam etching using a hard mask of tungsten, including a sacrificial poly(methyl methacrylate) layer under the PS-b-PDMS for the etch and liftoff processes. The ion beam etch process produced the most uniform magnetic arrays. A structural and magnetic comparison in terms of uniformity, edge roughness and switching field distribution has been reported.
We report a combined directing effect
of the simultaneously applied
graphoepitaxy and electric field on the self-assembly of cylinder
forming polystyrene-b-poly(dimethylsiloxane) block
copolymer in thin films. A correlation length of up to 20 μm
of uniaxial ordered striped patterns is an order of magnitude greater
than that produced by either graphoepitaxy or electric field alignment
alone and is achieved at reduced annealing times. The angle between
the electric field direction and the topographic guides as well as
the dimensions of the trenches affected both the quality of the ordering
and the direction of the orientation of cylindrical domains: parallel
or perpendicular to the topographic features. We quantified the interplay
between the electric field and the geometry of the topographic structures
by constructing the phase diagram of microdomain orientation. This
combined approach allows the fabrication of highly ordered block copolymer
structures using macroscopically prepatterned photolithographic substrates.
In this work, the self-assembly behavior and pH responsiveness of a triblock copolypeptide in aqueous media are demonstrated. The copolypeptide was composed of a central pH responsive poly(l-glutamic acid) (PGA), flanked by two hydrophobic poly(l-alanine) blocks (PAla) (PAla5-PGA11-PAla5). This system showed a pH-responsive transition from short tapes to spherical aggregates by increasing the pH, as a result of deprotonation of the PGA block and a conformational change from α-helix to random coil. Increasing the ionic strength to physiological conditions (0.15 M) has triggered fibrillar self-assembly through intermolecular hydrogen bonding of PAla end-blocks that form β-sheet nanostructures, in conjunction with charge screening of the central random coil PGA segments. At elevated concentrations a thermo-responsive free supporting hydrogel was obtained, consisting of rigid β-sheet based twisted superfibers, resulting from hierarchical self-assembly of the copolypeptide. Yet, morphological transformation of this nanostructure was observed upon switching the pH from physiological conditions to pH 4. An unexpected morphology constituted of α-helix-based giant nanobelts was observed as a consequence of the secondary peptide transitions.
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