Using silicon microfabrication technology, microchemical devices have been constructed for the purpose of conducting heterogeneously catalyzed multiphase reactions. The motivation behind the design, the fabrication approach, and the experimental characterization are presented for two classes of devices. The first design involves multiple parallel channels with integrated filter structures to incorporate standard catalytic materials. These catalysts are in the form of finely divided porous particles in a packed-bed arrangement. The second device involves the incorporation of porous silicon as a catalyst support, in the form of a thin layer covering microstructured channels. These microstructured channels simulate the structure of a packed bed and enhance mass transfer relative to an open channel. The ability to incorporate features at the tens-of-microns scale can reduce the mass-transfer limitations by promoting mixing and dispersion for the multiple phases. Directly integrating the catalyst support structures into the channels of the microreactor allows the precise definition of the bed properties, including the support's size, shape and arrangement, and the void fraction. Such a design would find broad applicability in enhancing the transport and active surface area for sensing, chemical, and biochemical conversion devices. Reaction rates for the gas-liquid-solid hydrogenation of cyclohexene using the integrated catalyst with porous silicon as a support compare favorably to those rates obtained with the packed-bed approach. In both cases, the mass transfer coefficient is at least 100 times better than conventional laboratory reactors.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFiller and Percolation Behavior of Ionic Aggregates in Styrene-Sodium Methacrylate IonomersJoon-Seop Kim, Rebecca J. Jackman, and Adi EisenbergCite this: Macromolecules 1994, 27, 10, 2789–2803Publication Date (Print):May 1, 1994Publication History Published online1 May 2002Published inissue 1 May 1994https://pubs.acs.org/doi/10.1021/ma00088a021https://doi.org/10.1021/ma00088a021research-articleACS PublicationsRequest reuse permissionsArticle Views633Altmetric-Citations125LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
This paper describes a method for fabricating microfluidic devices in a photodefinable epoxy (SU-8). This technique is compatible with, and complementary to, conventional fabrication techniques. It allows microstructures formed in SU-8 to be bonded to produce sealed microfluidic channels. A micromixer fabricated entirely in SU-8, using this technique, for performing liquid-phase reactions is shown to be suitable for visible spectroscopy. This fabrication method also allows the incorporation of materials that are often difficult to integrate. By fabricating hybrid devices that incorporate quartz windows, we demonstrate that these devices are compatible with organic solvents and that in situ ultraviolet detection in a microfluidic system is possible.
This paper describes a procedure for making topologically complex three-dimensional microfluidic channel systems in poly(dimethylsiloxane) (PDMS). This procedure is called the "membrane sandwich" method to suggest the structure of the final system: a thin membrane having channel structures molded on each face (and with connections between the faces) sandwiched between two thicker, flat slabs that provide structural support. Two "masters" are fabricated by rapid prototyping using two-level photolithography and replica molding. They are aligned face to face, under pressure, with PDMS prepolymer between them. The PDMS is cured thermally. The masters have complementary alignment tracks, so registration is straightforward. The resulting, thin PDMS membrane can be transferred and sealed to another membrane or slab of PDMS by a sequence of steps in which the two masters are removed one at a time; these steps take place without distortion of the features. This method can fabricate a membrane containing a channel that crosses over and under itself, but does not intersect itself and, therefore, can be fabricated in the form of any knot. It follows that this method can generate topologically complex microfluidic systems; this capability is demonstrated by the fabrication of a "basketweave" structure. By filling the channels and removing the membrane, complex microstructures can be made. Stacking and sealing more than one membrane allows even more complicated geometries than are possible in one membrane. A square coiled channel that surrounds, but does not connect to, a straight channel illustrates this type of complexity.
Bringing an elastomeric phase mask into conformal contact with a layer of photoresist makes it possible to perform photolithography in the near field of the mask. This technique provides an especially simple method for forming features with sizes of 90–100 nm in photoresist: straight lines, curved lines, and posts, on both curved and planar surfaces. It combines experimental convenience, new optical characteristics, and applicability to nonplanar substrates into a new approach to fabrication. Nanowire polarizers for visible light illustrate one application for this technique.
This letter describes a method for producing in-fiber gratings that reduces the effects of mechanical and optical instabilities limiting other methods. In this technique, opaque lines formed on the outside of the fiber using a procedure known as microcontact printing, serve as an amplitude photomask for exposure to ultraviolet light. Long-period fiber optic attenuators formed by ths technique demonstrate its advantages.
This article describes a near-field photolithographic method that uses an elastomeric phase mask in conformal contact with photoresist. The method is capable of generating ∼90 nm lines in commercially available photoresist, using broadband, incoherent light with wavelengths between 330 and 460 nm. Transfer of these patterns into silicon dioxide and gold demonstrates the integrity of the patterned resist.
Fourier transform infrared (FT-IR) spectroscopy in a multiple internal reflection (MIR) geometry is integrated with silicon-based microreactors to allow detection of a wide range of chemical species while taking advantage of inexpensive batch fabrication techniques applicable to silicon substrates. The microreactors are fabricated in silicon and glass using standard microfabrication and selective etching techniques. The small ( approximately 1 cm side) reactor size provides access to nearly the full mid-IR frequency region with MIR-FT-IR, allowing us to probe both solution-phase and surface-bound chemical transformations. The wide applicability of this approach is demonstrated with two representative test cases: kinetics of acid-catalyzed ethyl acetate hydrolysis and amidization of surface-tethered amine groups.
