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There is an increasing need for wireless autonomous micro electromechanical systems (MEMS) and microrobots that can perform various functions such as sensing, diagnosis, locomotion, actuation, implantation, material removal, manipulation, and localized drug delivery. A major problem with these systems is the production, storage, and transduction of power at the micro scale. In addition, these miniature devices cannot use existing battery packs that are commonly used to power electronic devices. These MEMS and microrobots need on-board power sources that are miniaturized to their size. Together with the energy of an external source, some basic functions of microrobots can be powered simultaneously. This study seeks to develop a theoretical framework based on a chemo-electromagnetic model for use in the design of microrobots with full energetic autonomy. We first conceive a microrobot design and derive its mathematical model; the design consists of an on-board fuel generator, electrochemical device, electromagnetic device, and a locomotion mechanism. Then we present numerical simulations to show the relationship between the consumption rate of the H2 source, power density, and angular and translational velocities at low Reynolds number. We find that power density decreases approximately linearly with the diameter, while the relative velocity with respect to the body-length is approximately inversely proportional to the size, making downscaling favourable for this class of untethered devices.

Titanium dioxide (TiO2) has attracted considerable attention in the field of (photo)electrocatalysis, optoelectronics, and sensors [1]. Although a great number of strategies for the synthesis of TiO2 structures exist, methods leading to one-dimensional (1D) structures are of great interest due to the benefits of higher surface area and ease of functionalization with external entities [2], like metal nanoparticles. Here electrospinning will be discussed as an attractive and versatile fabrication method to obtain high aspect ratio TiO2 (nano)fibers, which additionally allows the overlaying of several layers of TiO2 fibers. Such structures can form an open porous network, that allows maximizing surface-to-volume ratio and has benefits for light absorption in optoelectronic devices [3]. In this study, suspended nanoparticles of TiO2 in a polyvinylpyrrolidone (PVP)/ethanol solution are used for the formulation of active layers with electrospinning for applications in electrochromic (EC) devices. A coaxial nozzle is utilized to fabricate TiO2 fibers with spatially distributed metal (M) nanoparticles (Cu, Au, and Ag). The synthesized TiO2 fibers have anatase phase with 335±24 nm average diameter. Electrospun TiO2 and TiO2-M fibers on fluorine-doped tin oxide (FTO) glass substrates are tested for EC behavior by applying an external electrical potential. The response time of these fibrous structures is 10 seconds when cycling between ±3V. The color of the additively manufactured fibrous layers can be tuned from green (TiO2-Cu) to blue (TiO2-Au) or brown (TiO2-Ag) while maintaining a stable device structure over 150 cycles. Potentiostatic/galvanostatic measurements in half-cell configuration are carried out to understand the coloration and bleaching mechanism of the electrochromically active layers. It is hypothesized that the meso-porosity of the TiO2 fibers enhances the redox reaction kinetics when compared to that of thin films. Furthermore, attained coloration is attributed to the tailored optical absorption with nanoparticles decorating the fiber structure. This concept can pave the way to a more efficiently colored generation of optical windows.

A pillar array column (PAC) is a micro column which is fabricated by reactive ion etching of a silicon substrate and has non-porous pillars with a high degree of order in narrow flow channels. Compared to conventional spherical particles randomly packed in an empty column, the order of pillars is systematically designed to provide a higher efficiency due to a smaller van Deemter A term and higher permeability (Kv) attributed to higher external porosity. Therefore, PACs are expected to have a higher resolution and are promising candidates for the next generation chromatography columns. However, retention capacity (contributing to resolution) with PACs is low because pillars have a non-porous structure resulting in a low surface area. In order to achieve the same level of retention factor with PACs as with superficially porous particles which are currently drawing much attention in the market because of the high efficiency, electrochemical anodization was applied to grow porous shell layers of 300 nm (30 nm pores) on the surface of pillars with the diameter of 5 um and spacing (between pillars) of 2.5 um. A specific injection method (on-chip injection) was established, which enables a small amount of injection (a few nL) to minimize an influence of injection volume on a tiny PAC. Uniformity of the porous PACs were assessed by determining local height equivalent to a theoretical plate (HETP) along the channels, which appeared to be constant. On measuring the retention time as an indicator of the surface area, an increase in the surface area by a factor of about 30 compared to that of non-porous pillars was found as expected. On measuring the efficiency of a PAC with a commercial HPLC instrument, theoretical plate of about 100,000 with a retention factor of 2.2 under an isocratic condition and peak capacity of about 500 under a gradient condition were obtained at an extremely low pressure with a 1 m long PAC, which are ascribed to the increase in surface area.

We report on the possibility to realize submicrometer plate heights using chromatographic pillar array columns filled with radially elongated diamond-shaped pillars, even when using a relatively large interpillar distance (2.5 mu m) and axial pillar width (5 mu m). It is demonstrated that the use of high aspect ratio radially elongated pillars which are 15 times wider in the radial than in the axial direction can lead to a fivefold reduction of the minimal plate height compared to beds filled with pillars with a similar interpillar distance but with an aspect ratio around unity (cylinders and diamonds). This increase in performance can be attributed to a decrease in longitudinal dispersion, reflected by a reduction of the B-term by a factor of about 25. Experiments were conducted at room temperature, as well as at elevated temperature (70 degrees C), where the B-term band broadening is known to be more critical. The main advantage of radially elongated pillar beds is that they enable a drastic reduction of the footprint of pillar array columns, allowing design of very long channels with a minimum of turns. Under retained conditions, a four-component laser dye mixture could be separated over a distance of only 1.5 mm.

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In this work, we report the detection of proteins by means of simultaneous fluorescence and impedance measurements in a cyclo olefin polymer (COP) chip containing an ordered pillar array column, used for reversed-phase liquid chromatography, with integrated microband gold electrodes at the end of the channel.

High-resolution LC-MS for the characterization of intact proteins and peptides using poly (styren-co-divinylbenzene)monolithic capillary columns

Experimental investigation of Viscous Fingering in Micro-Pillar Array Columns

A cyclo-olefin polymer chip containing a column with an array of ordered pillars for pressure-driven liquid chromatography

A1.4m long pillar channel for complex chromatographic separations of nl sized samples

Improving the homogeneity of monolithic silica columns using 2D micro-pillar arrays

Pressure-driven Reversed-phase Chromatography in Microstructured Pillars with UV-VIS Absorbance Detection Using Microfabricated Waveguides

Using Microfabricated perfectly Ordered Pillar Array columns as an Alternative for the Conventional Packed Bed in HPLC

Microfabricated porous and non-porous pillar Arrays to boost the efficiency and separation speed of HPLC

An important bottleneck of pillar array columns designed for liquid chromatography is that small deviations of the target 'magical distance' at the sidewall region leads to detrimental sidewall effects, due to local differences of linear velocities at the sidewall region versus other locations in the pillar bed. In the present study, we demonstrate that a lateral elongation of the pillar significantly increases the tolerance for offsets of the magical distance. By shifting the sidewall distance 600 nm for 2 pillar aspect ratio (AR) designs (AR = 3 and 9), only minor sidewall effects on the measured plate heights could be observed for the AR=9 columns, while the plate height was roughly doubled when using the wrong versus the correct sidewall distance for the AR = 3 columns. Technologically, this constitutes a huge advantage because small deviations (order of 100 nm) between the set and the finally achieved value for the inter-pillar distance are very common using mid-UV lithography based etching processes. (C) 2014 Elsevier B.V. All rights reserved.

Availability and low cost of light alkanes make them interesting as feedstock for commercial fuels and chemicals. However, direct conversion of lower alkanes for such purposes is a challenging problem. A discussion covers the oxidative conversion of light alkanes in the presence of cold plasma in a microreactor; variables influencing products selectivities; characteristics of the plasma microreactor; formation of C-C bonds; and directly upgrading cheap low molecular weight alkanes to commercially useful fuels and/or feedstock materials for the chemical industry. This is an abstract of a paper presented at the 42nd Loss Prevention Symposium (New Orleans, LA 4/6-10/2008).

High Speed Shear-Driven Flows Through Micro-Structured 1D-Nano-channels

The ever-growing complexity of samples which need to be processed in e.g., environmental and biomedical/biochemical research, demand higher efficiencies of analytical techniques. Liquid chromatography (LC), mass spectrometry, among others, are analytical techniques that revolutionized the way in which chemical composition of samples of e.g., the environment, food, our body, etc. are measured. The miniaturization of LC columns has led to the use of chip columns. Up till now the efficiency of LC has been improved by reducing the size of monodisperse spherical particles, which are randomly packed in high pressure columns, and simultaneously increasing the operating pressure. To achieve a more groundbreaking progress, a paradigm shift from randomly packed beds of microparticles to perfectly ordered microparticles, is needed. This can be made possible by the latest advances in nano-meter precision positioning and material micromachining technology. The chromatographically most optimal ordered arrangement of these microparticles is proposed by using a layer-by-layer manufacturing strategy. Each layer of particles is collected using a vacuum-driven, micro-structured collection and deposition tray, and arranged with an array of precisely positioned suction holes capable of reversibly holding the particles. In our current study we model 10 micron sized particles. The microparticles travel from a bottom plate before sticking to the suction holes at the top of the system. The velocity of the airflow in the system is an important parameter which determines if the particles will detach from the bottom surface and it also determines the particle’s trajectory. To this end some preliminary simulations have been performed with the COMSOL Multiphysics® using its laminar flow and particle tracing interface. However, the particle tracing module assumes that particles are point masses, i.e. their shape and volume are not taken into account. This is considered to be a shortcoming, since the particles in our system influence the flow field around them and inherently the flow field for neighboring particles. To this end we will study a 2D system with two solid circular objects positioned in a rectangular channel as depicted in the attached figure. We will use the laminar flow interface of the COMSOL Multiphysics® to study the influence of the following parameters on the force exerted on these two solid objects due to the flow around them: the distance d of the second circular object to the right boundary of the system, the inlet velocity and the angle α between the two centers of the circular objects. This will enhance our knowledge on the influence of particles on one another. Currently we are studying the movement of these particles using the laminar flow and fluid structure interaction interface of the COMSOL Multiphysics® We expect that as the distance d decreases, the right boundary will exert a greater force on the second object, i.e. it pushes the object away from the right boundary. The fluid structure interaction should give us more insight what will happen with both particles hereafter. Ultimately this study will enable us to create a monolayer of particles.

The present paper reports on the experimental difficulties encountered when trying to realize the full potential of shear-driven chromatography in nanochannels. While it theoretically offers the possibility to yield over 10,000 plates per centimetre in a few seconds, the practical realization of this potential requires a detector miniaturisation that is carried to the extreme combined with very high sampling rates. In the present study, a charge coupled device camera and a photomultiplier tube combined with pinhole were tested as detector. Despite the fact that the photomultiplier tube could offer a higher sampling rate and a better sensitivity, the charge coupled device turned out to be better suited for the current set-up because of inevitable problems with the stray-light transported through the glass channel wall. The chemistry of the separation surface was additionally studied getting more homogenous coating, thus higher separation efficiency. Having also carried out a number of mechanical improvements, it is now possible to measure separations at a distance of 8mm downstream from the injection point. This is four times further downstream than ever before while realizing a four components mixture separation in less than 1.5s, with a plate generation velocity of about 2000-7000 plates per second depending on the sample.

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An optical injection system used for optimalization studies of high aspect ratio LC pillar array

Shear-driven flows through nano-channels uniformly packed with a micro-structured pillar region.

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Hydrodynamic chromatography of polystryrene microparticles in micropillar array columns