E. Chmela

Design and fabrication of a hydrodynamic chromatography chip

A chromatography chip is presented in which the analysis is performed by polymer separation entirely based on geometry. Design and fabrication are discussed for a chip incorporating an injection structure and a separation channel. The injection is characterized by fluorescence measurements. Chromatographic performance was shown by separation of fluorescein and 26 nm fluorescent particles.

Local anodic bonding of Kovar to Pyrex aimed at high-pressure, solvent-resistant microfluidic connections

Local anodic bonding of a common Kovar alloy to Pyrex is presented. This technique is ideally suitable for temperature-, solvent- and pressure-resistant microfluidic connections. In this paper we mainly concentrate on the stress problems occurring during and after bonding. Because of the different thermal expansion coefficients of Kovar and Pyrex a structure is added in order to release the thermal stresses induced during bonding. Optimum bonding conditions in vacuum on Pyrex and on a Pyrex-Si bonded wafer pair are investigated. In the latter case bonding for 3 h at 250 °C and 1.5 kV results in a high-quality bond.

A differential viscosity detector for use in miniaturized chemical separation systems

We present a micromachined differential viscosity detector suitable for integration into an on-chip hydrodynamic chromatography system. The general design, however, is applicable to any liquid chromatography system that is used for separation of polymers. The micromachined part of the detector consists of a fluidic Wheatstone bridge and a low hydraulic capacitance pressure sensor of which the pressure sensing is based on optical detection of a membrane deflection. The stand-alone sensor shows a resolution in specific viscosity of 3/spl times/10/sup -3/, in which specific viscosity is defined as the increase in viscosity by a sample, relative to the baseline viscosity of a solvent.

A low hydraulic capacitance pressure sensor for integration with a micro viscosity detector

A design is presented for a micromachined differential viscometer, that is suitable for integration into a planar hydrodynamic chromatography system (HDC) for polymer analysis. The viscometer consists of four equal flow restrictions and two pressure sensors, connected in a Wheatstone bridge configuration. Since this viscometer requires an ultra-low hydraulic capacitance differential pressure sensor, a pressure sensor is presented of which the internal volume displacement was reduced considerably compared to commercially available sensors. An optical method was used to detect membrane deflections with a magnitude of approximately 0.01 nm. This method lead to a linearity of 1% over the measured pressure range and a resolution of 2 Pa. With this pressure sensor integrated into the viscosity detector, viscosity measurements were performed on the viscosity difference of ethanol and water.

A Micro Viscosity Detector for Use in Miniaturized Chemical Separation Systems

A novel micromachined differential viscosity detector is presented that is suitable for integration with an on-chip hydrodynamic chromatography system. Viscosity detection is demonstrated using a prototype that shows a resolution in the specific viscosity of 3.0*10−3.

A Micro Viscosity Detector for a Planar Hydrodynamic Chromatography (HDC) System

A design is presented for a micromachined differential viscometer, suited for integration in a planar Hydrodynamic Chromatography System. The viscometer consists of four equal flow restrictions and two pressure sensors, connected in a Wheatstone bridge configuration.

Failure mechanisms of pressurized microchannels, model and experiments

Microchannels were created by fusion bonding of a Pyrex and a thermally oxidized silicon wafer. The maximum pressure which can be applied to these channels was investigated. In order to find the relation between this maximum pressure, channel geometry, material elasticity and bond energy, an energy model was developed. It was shown that the model is substantiated by the pressure data, from which it could be calculated that the effective bond energy increased from 0.018 J/m/sup 2/ to 0.19 J/m/sup 2/ for an annealing temperature ranging from 310/spl deg/C to 470/spl deg/C.

HDC-chip: an integrated micromachined separation system for polymers and particles

Development of a novel on-chip HDC system for analytical separation of (bio)polymers and particles is presented, consisting of an extremely shallow separation channel with integrated injection, fabricated using silicon and glass microtechnology. Successful sample injections and separation tests are shown.