One of the key issues associated with the utilization of block copolymer (BCP) thin films in nanoscience and nanotechnology is control of their alignment and orientation over macroscopic dimensions. We have recently reported a method, solvent vapor annealing with soft shear (SVA-SS), for fabricating unidirectional alignment of cylindrical nanostructures. This method is a simple extension of the common SVA process by adhering a flat, crosslinked poly(dimethylsiloxane) (PDMS) pad to the BCP thin film. The impact of processing parameters, including annealing time, solvent removal rate and the physical properties of the PDMS pad, on the quality of alignment quantified by the Herman's orientational factor (S) is systematically examined for a model system of polystyrene-block-polyisoprene-block-polystyrene (SIS). As annealing time increases, the SIS morphology transitions from isotropic rods to highly aligned cylinders. Decreasing the rate of solvent removal, which impacts the shear rate imposed by the contraction of the PDMS, improves the orientation factor of the cylindrical domains; this suggests the nanostructure alignment is primarily induced by contraction of PDMS during solvent removal. Moreover, the physical properties of the PDMS controlled by the crosslink density impact the orientation factor by tuning its swelling extent during SVA-SS and elastic modulus. Decreasing the PDMS crosslink density increases S; this effect appears to be primarily driven by the changes in the solubility of the SVA-SS solvent in the PDMS. With this understanding of the critical processing parameters, SVA-SS has been successfully applied to align a wide variety of BCPs including polystyrene-block-polybutadiene-block-polystyrene (SBS), polystyrene-block-poly(N,N-dimethyl-n-octadecylammonium p-styrenesulfonate) (PS-b-PSS-DMODA), polystyrene-block-polydimethylsiloxane (PS-b-PDMS) and polystyrene-block-poly(2-vinlypyridine) (PS-b-P2VP). These results suggest that SVA-SS is a generalizable method for the alignment of BCP thin films.
When
hydrolyzable cations such as aluminum interact with solid–water
interfaces, macroscopic interfacial properties (e.g., surface charge and potential) and interfacial phenomena (e.g., particle adhesion) become tightly linked with the
microscopic details of ion adsorption and speciation. We use in situ atomic force microscopy to directly image individual
aluminum ions at a mica–water interface and show how adsorbate
populations change with pH and aluminum activity. Complementary streaming
potential measurements then allow us to build a triple layer model
(TLM) that links surface potentials to adsorbate populations, via
equilibrium binding constants. Our model predicts that hydrolyzed
species dominate the mica–water interface, even when unhydrolyzed
species dominate the solution. Ab initio molecular
dynamics (AIMD) simulations confirm that aluminum hydrolysis is strongly
promoted at the interface. The TLM indicates that hydrolyzed adsorbates
are responsible for surface-potential inversions, and we find strong
correlations between hydrolyzed adsorbates and particle-adhesion forces,
suggesting that these species mediate adhesion by chemical bridging.
Bicontinuous mesoporous carbon films are fabricated by cooperative self-assembly of phenolic resin and amphiphilic triblock copolymer via an order-order transition from cylinders to gyroid. The film morphology is strongly influenced by the details of processing, including age of the resol, resol : template ratio, and the solvent vapor annealing process.
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