Abstract
Cellulose is a glucose polymer and the most abundant biological material on earth. Because it is biodegradable and yet water insoluble, cellulose has been pursued in the past as a scaffold or base structural material for medical applications, sensors, and optical devices. Patterning of two cellulose polymers, cellulose acetate and cellulose acetate butyrate, by photoablative lithography at 172 nm has been demonstrated and is reported here. This 3D subtractive process yields complex micro- and nanostructures and optical components, including sinusoidal gratings and waveguides. Having a depth precision of 15 nm and requiring no photoresist or solvents, vacuum-ultraviolet photoetching of cellulose polymer films proceeds at a constant rate of ∼0.8 μm/h for depths of up to and beyond 25 μm when the intensity of the flat lamp is 10 mW cm−2. A polydimethylsiloxane (PDMS) microimprinting process, in which photoetched cellulose serves as a negative master mold for PDMS, provides feature sizes as small as 0.5 μm and allows for optical structures such as gratings to be integrated with microfluidic devices while eliminating the existing necessity of fabricating Si molds in a cleanroom environment.
Highlights
Cellulose is a biodegradable polymer consisting of D-glucose monomers linked by glycosidic β 1–4 bonds to form linear macromolecules
We report here the patterning of organosoluble cellulose acetate (CA) and cellulose acetate butyrate (CAB) polymer films by photoablative contact lithography with flat lamps emitting at 172 nm in the vacuum-ultraviolet (VUV) spectral region
It is difficult to overstate the importance of this result because previous experiments with other polymers, including PMMA, acrylonitrile butadiene styrene (ABS), and polyvinyl acetate (PVA), observed a trench depth limit of ∼1.5 μm.[23]
Summary
Cellulose is a biodegradable polymer consisting of D-glucose monomers linked by glycosidic β 1–4 bonds to form linear macromolecules. Processing from the melt is not feasible, and the subtle interplay between hydrophilic and hydrophobic interaction forces in the supramolecular structure renders cellulose insoluble in water and common organic solvents. These factors scitation.org/journal/apm impede or preclude efforts to process bulk cellulose by dissolution and subsequent molding. A potential strategy to overcome such barriers is to convert cellulose into soluble derivatives amenable to further chemical or mechanical processing and, if required, subsequently, converted back to cellulose With this approach, homogenous cellulose-based thin films can be fabricated reproducibly and with low surface roughness,[15,16] both of which are essential for advanced material applications such as photoresists
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