96 research outputs found
Switching Anionic and Cationic Semi-Permeability in Partially Hydrolyzed Polyacrylonitrile:A pH-Tunable Ionic Rectifier
Membrane materials with semipermeability for anions or for cations are of interest in electrochemical and nanofluidic separation and purification technologies. In this study, partially hydrolyzed polyacrylonitrile (phPAN) is investigated as a pH-switchable anion/cation conductor. When switching from anionic to cationic semipermeability, also the ionic current rectification effect switches for phPAN materials deposited asymmetrically onto a 5, 10, 20, or 40 ÎŒm diameter microhole in a 6 ÎŒm thick polyethylene-terephthalate (PET) film substrate. Therefore, ionic rectifier behavior can be tuned and used to monitor and characterize semipermeability. Effects of electrolyte type and concentration and pH (relative to the zeta potential at approximately 3.1) are investigated by voltammetry, chronoamperometry, and impedance spectroscopy. A computational model provides good qualitative agreement with the observed electrolyte concentration data. High rectification effects are observed for both cations (pH > 3.1) and anions (pH < 3.1) but only at relatively low ionic strengths
Electrochemiluminescence reaction pathways in nanofluidic devices
Nanofluidic electrochemical devices confine the volume of chemical reactions to femtoliters. When employed for light generation by electrochemiluminescence (ECL), nanofluidic confinement yields enhanced intensity and robust luminescence. Here, we investigate different ECL pathways, namely coreactant and annihilation ECL in a single nanochannel and compare light emission profiles. By high-resolution imaging of electrode areas, we show that different reaction schemes produce very different emission profiles in the unique confined geometry of a nanochannel. The confrontation of experimental results with finite element simulation gives further insight into the exact reaction ECL pathways. We find that emission strongly depends on depletion, geometric exclusion, and recycling of reactants in the nanofluidic device
Facile fabrication of microperforated membranes with re-useable SU-8 molds for organs-on-chips
Microperforated membranes are essential components of various organ-on-a-chip (OOC) barrier models devel- oped to study transport of molecular compounds and cells across cell layers in e.g. the intestine and blood-brain barrier. These OOC membranes have two functions: 1) to support growth of cells on one or both sides, and 2) to act as a filter-like barrier to separate adjacent compartments. Thin, microperforated poly(dimethylsiloxane) (PDMS) membranes can be fabricated by micromolding from silicon molds comprising arrays of micropillars for the formation of micropores. However, these molds are made by deep reactive ion etching (DRIE) and are expensive to fabricate. We describe the micromolding of thin PDMS membranes with easier-to-make, SU-8 epoxy photoresist molds. With a multilayer, SU-8, pillar microarray mold, massively parallel arrays of micropores can be formed in a thin layer of PDMS, resulting in a flexible barrier membrane that can be easily incorporated and sealed between other layers making up the OOC device. The membranes we describe here have a 30-ÎŒm thickness, with 12-ÎŒm-diameter circular pores arranged at a 100-ÎŒm pitch in a square array. We show application of these membranes in gut-on-a-chip devices, and expect that the reported fabrication strategy will also be suitable for other membrane dimension
A simulation framework for the modeling of adsorption related noise phenomena in electrochemical sensors
Understanding Transient Ionic Diode Currents and Impedance Responses for AquivionÂź Coated Microholes
Ionic Diode Characteristics at a Polymer of Intrinsic Microporosity (PIM) | Nafion âHeterojunctionâ Deposit on a Microhole Poly(ethylene-terephthalate) Substrate
Ionic diode phenomena occur at asymmetric ionomer | aqueous electrolyte microhole interfaces. Depending on the applied potential, either an âopenâ or a âclosedâ diode state is observed switching between a high ion flow rate and a low ion flow rate. Physically, the âopenâ state is associated mainly with conductivity towards the microhole within the ionomer layer and the âclosedâ state is dominated by restricted diffusion-migration access to the microhole interface opposite to the ionomer. In this report we explore a âheterojunctionâ based on an asymmetric polymer of intrinsic microporosity (PIM) | Nafion ionomer microhole interface. Improved diode characteristics and current rectification are observed in aqueous NaCl. The effects of creating the PIM | Nafion micro-interface are investigated and suggested to lead to novel sensor architectures
Ionic Diode and Molecular Pump Phenomena Associated with Caffeic Acid Accumulated into an Intrinsically Microporous Polyamine (PIMâEAâTB)
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