We
fabricated thermoplastic surfaces possessing extremely limited
water and oil wettability without employment of long-chain perfluoroalkyl
(LCPFA) substances. Namely, by taking advantage of the structure and
behavior of original oleophobic perfluoropolyether (PFPE) methacrylate
(PFM) molecular bottlebrush (MBB) additive we obtained polymeric surfaces
with oil contact angles well above 80° and surface energy on
the level of 10 mN/m. Those angles and surface energies are the highest
and the lowest respective values reported to date for any bulk solid
flat organic surface not containing LCPFA. We show experimentally
and computationally that this remarkable oil repellency is attributed
to migration of small quantities of the oleophobic MBB additives to
the surface of the thermoplastics. Severe mismatch in the affinity
between the densely grafted long side chains of MBB and a host matrix
promotes stretching and densification of mobile side chains delivering
the lowest surface energy functionalities (CF3) to the
materials’ boundary. Our studies demonstrate that PFM can be
utilized as an effective low surface energy additive to conventional
thermoplastic polymers, such as poly(methyl methacrylate) and Nylon-6.
We show that films containing PFM achieve the level of oil repellency
significantly higher than that of polytetrafluoroethylene (PTFE),
a fully perfluorinated thermoplastic. The surface energy of the films
is also significantly lower than that of PTFE, even at low concentrations
of PFM additives.
High concentration of carbon monoxide (CO) in the gas mixture entering the fuel cell can cause fuel cell poisoning, which can significantly reduce the life expectancy of the cell. To overcome this problem, we propose a new methodology based on the use of micro-cantilevers to detect minute concentrations of CO in a gas mixture. For this purpose, micro-cantilevers are coated with Copper Y (CuY) zeolite and utilized to selectively adsorb CO on their surface. It is shown that the adsorption of CO yields a measurable shift in the natural frequency of the micro-cantilevers, which can be directly correlated with the concentration of CO in the gas mixture. It is determined that the maximum adsorption capacity of the sensor occurs at 40 °C using CuY zeolite with 10 wt% Cu content. Furthermore, the shift in the natural frequency of the sensor is observed to increase as the thickness of the zeolite layer is increased up to a threshold value corresponding to about a quarter of the thickness of the micro-cantilever. At this point, a clearly measurable shift of about 275 Hz in the natural frequency of the micro-cantilevers is observed. While the maximum frequency shift occurs using a relatively thick zeolite layer, it is observed that, for the range of thicknesses considered, the maximum frequency shift per unit weight of CO adsorbed (sensitivity) decreases as the thickness of the zeolite layer is increased. The methodology proposed in this paper could pave the way towards the development of a portable and self-contained unit to monitor the concentration of CO in a mixture of gases.
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