The present contribution
reports on a study aiming to find the
most suitable rubbing method for filling arrays of separated and interconnected
micromachined pockets with individual microspheres on rigid, uncoated
silicon substrates without breaking the particles or damaging the
substrate. The explored dry rubbing methods generally yielded unsatisfactory
results, marked by very large percentages of empty pockets and misplaced
particles. On the other hand, the combination of wet rubbing with
a patterned rubbing tool provided excellent results (typically <1%
of empty pockets and <5% of misplaced particles). The wet method
also did not leave any damage marks on the silicon substrate or the
particles. When the pockets were aligned in linear grooves, markedly
the best results were obtained when the ridge pattern of the rubbing
tool was moved under a 45° angle with respect to the direction
of the grooves. The method was tested for both silica and polystyrene
particles. The proposed assembly method can be used in the production
of medical devices, antireflective coatings, and microfluidic devices
with applications in chemical analysis and/or catalysis.
The present study investigated the use of a dedicated gas chromatography (GC) column (L = 70 cm, 75 μm deep, and 6.195 mm wide) with radially elongated pillars (REPs) as the second column in a comprehensive two-dimensional gas chromatography (GC × μGC) system. Three stationary phases [apolar polydimethylsiloxane (PDMS), medium polar roomtemperature ionic liquid (RTIL) based on monocationic phosphonium, and polar polyethylene glycol (PEG-1000)] have been coated using the static method at constant pressure or using an original vacuum pressure program (VPP) from 400 to 4 mbar. The best efficiency reached up to N = 62,000 theoretical plates for a film thickness of 47 nm at 100 °C for an iso-octane peak (k = 0.16) at an optimal flow rate of 4.8 mL/min. The use of the VPP improved the efficiency by approximately 15%. Efficiencies up to 28,000 and 47,000 were obtained for PEG-1000 and RTIL, respectively. A temperature-programmed separation of a mixture of 11 volatile compounds on a PDMS-coated chip was obtained in less than 36 s. The PDMS-, PEG-1000-, and RTIL-coated chips were tested as the second column using a microfluidic reverse fill/flush flow modulator in a GC × μGC system. The REP columns were highly compatible with the operating conditions in terms of flow rate and with more than 30,000 plates for the iso-octane peak. Moreover, a commercial solvent called white spirit containing alkanes and aromatic compounds was injected in three sets of columns in normal and reverse modes, demonstrating the great potential of the chip as a second-dimension separation column.
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