2 research outputs found
Gyroid Nanoporous Membranes with Tunable Permeability
Understanding the relevant permeability properties of ultrafiltration membranes is facilitated by using materials and procedures that allow a high degree of control on morphology and chemical composition. Here we present the first study on diffusion permeability through gyroid nanoporous cross-linked 1,2-polybutadiene (1,2-PB) membranes with uniform pores that, if needed, can be rendered hydrophilic. The gyroid porosity has the advantage of isotropic percolation with no need for structure prealignment. Closed (skin) or opened (nonskin) outer surface can be simply realized by altering the interface energy in the process of membrane fabrication. The morphology of the membranes’ outer surface was investigated by scanning electron microscopy, contact angle, and X-ray photoelectron spectroscopy. The effective diffusion coefficient of glucose decreases from nonskin, to one-sided skin to two-sided skin membranes, much faster than expected by a naive resistance-in-series model; the flux through the two-sided skin membranes even increases with the membrane thickness. We propose a model that captures the physics behind the observed phenomena, as confirmed by flow visualization experiments. The chemistry of 1,2-PB nanoporous membranes can be controlled, for example, by hydrophilic patterning of the originally hydrophobic membranes, which allows for different active porosity toward aqueous solutions and, therefore, different permeability. The membrane selectivity is evaluated by comparing the effective diffusion coefficients of a series of antibiotics, proteins, and other biomolecules; solute permeation is discussed in terms of hindered diffusion. The combination of uniform bulk morphology, isotropically percolating porosity, controlled surface chemistry, and tunable permeability is distinctive for the presented gyroid nanoporous membranes
Transfer of Direct and Moiré Patterns by Reactive Ion Etching Through Ex Situ Fabricated Nanoporous Polymer Masks
We present a conceptually simple
approach to nanolithographic patterning utilizing ex situ fabricated
nanoporous masks from block copolymers. The fabricated block copolymer
(BC) masks show predictable morphology based on the correlation between
BC composition and bulk properties, independent of substrates’
surface properties. The masks are prepared by microtoming of prealigned
nanoporous polymer monoliths of hexagonal morphology at controlled
angles; they appear as 30–60 nm thick films of typical dimensions
100 μm × 200 μm. Masks cut perpendicular to the cylindrical
axis show monocrystalline hexagonal packing of 10 nm pores with a
principal period of 20 nm. We demonstrate the transfer of the hexagonal
pattern onto silicon by means of reactive ion etching through the
masks. In addition, patterns of elliptic and slit-like holes on silicon
are obtained by utilizing masks cut at 45° relative to the cylinder
axis. Finally, we demonstrate the first transfer of moiré patterns
from block copolymer masks to substrate. The nanoporous masks prepared
ex situ show outstanding long-range order and can be applied directly
onto any flat substrate, eliminating the need for topographic and
chemical surface modification, which are essential prerequisites for
the conventional procedure of block copolymer directed self-assembly.
The demonstrated elliptic and moiré pattern transfers prove
that the proposed ex situ procedure allows us to realize nanolithographic
patterns that are difficult to realize by the conventional approach
alone