Abstract:SummaryThe spatial distribution of electrical charges along the longitudinal axes of a polypropylene electret fiber was determined using Electrostatic Force Microscopy (EFM). EFM mapping on highly curved surfaces, such as those of polymeric fibers, is a challenging endeavour and most work reported in the scientific literature has been limited to single linescan analysis or flat specimens. Charged polymeric fibers, electrets, are extensively used in high performance filtration applications and methods to determ… Show more
“…Although it is not clear how this defect formed on the fibre, it appears that it did impact overall surface charge distribution, though at this stage we cannot distinguish between a loss of charge or its redistribution. These results contrast prior reports, which either did not show significant variation in surface charge [ 11 – 14 , 16 ] or attributed it to heterogeneity in the corona-discharge surface charging process [ 15 ]. Figure 6 EFM phase shift image collected using the two-pass lift technique.…”
Facemasks have been a critical line of defense in the Covid-19 pandemic and have been used for decades to reduce the inhalation of sub-micron aerosols, including bacteria, viruses and nano-materials. These facemasks leverage electrostatic charge properties of non-woven electret fibre mats to remove sub-micron aerosols. However, the topographical and electrostatic properties of these mats have not been well characterized at the nano-scale. In this study, we use atomic force microscopy (AFM) to examine the surface topography of the electret fibres within a commercial respirator fibre mat, use electrostatic force microscopy to map the electrostatic interactions emanating from these fibres, and use synchrotron X-ray scattering to probe polymer morphology. We find that within these mats the fibres exhibit significant heterogeneity in surface topography, electrostatic interactions and polypropylene phase composition. The surface topographies ranged from nano-smooth surfaces to ordered spherulitic structures. The electrostatic interactions varied across fibre length and circumference, and are only weakly correlated with surface topographical features. Finally, we use AFM to characterize fibres after filtering a NaCl aerosol and find that the deposited particles are heterogeneous in size and distributed over the fibre surfaces.
“…Although it is not clear how this defect formed on the fibre, it appears that it did impact overall surface charge distribution, though at this stage we cannot distinguish between a loss of charge or its redistribution. These results contrast prior reports, which either did not show significant variation in surface charge [ 11 – 14 , 16 ] or attributed it to heterogeneity in the corona-discharge surface charging process [ 15 ]. Figure 6 EFM phase shift image collected using the two-pass lift technique.…”
Facemasks have been a critical line of defense in the Covid-19 pandemic and have been used for decades to reduce the inhalation of sub-micron aerosols, including bacteria, viruses and nano-materials. These facemasks leverage electrostatic charge properties of non-woven electret fibre mats to remove sub-micron aerosols. However, the topographical and electrostatic properties of these mats have not been well characterized at the nano-scale. In this study, we use atomic force microscopy (AFM) to examine the surface topography of the electret fibres within a commercial respirator fibre mat, use electrostatic force microscopy to map the electrostatic interactions emanating from these fibres, and use synchrotron X-ray scattering to probe polymer morphology. We find that within these mats the fibres exhibit significant heterogeneity in surface topography, electrostatic interactions and polypropylene phase composition. The surface topographies ranged from nano-smooth surfaces to ordered spherulitic structures. The electrostatic interactions varied across fibre length and circumference, and are only weakly correlated with surface topographical features. Finally, we use AFM to characterize fibres after filtering a NaCl aerosol and find that the deposited particles are heterogeneous in size and distributed over the fibre surfaces.
“…To confirm peptide nanotube surface charge, enhanced-electrostatic force microscopy (EFM) maps charge distribution, − and Figure contains the topographical and EFM amplitude images of the mature K/pY peptide coassemblies. At maturity, each detected assembly is homogeneously negative (dark) along its entire length, identical to the pY assemblies .…”
Energetic insights emerging from the structural characterization of peptide cross-β assemblies have enabled the design and construction of robust asymmetric bilayer peptide membranes. Two peptides differing only in their N-terminal residue, phosphotyrosine vs lysine, coassemble as stacks of antiparallel β-sheets with precisely patterned charged lattices stabilizing the bilayer leaflet interface. Either homogeneous or mixed leaflet composition is possible, and both create nanotubes with dense negative external and positive internal solvent exposed surfaces. Cross-seeding peptide solutions with a preassembled peptide nanotube seed leads to domains of different leaflet architecture within single nanotubes. Architectural control over these cross-β assemblies, both across the bilayer membrane and along the nanotube length, provides access to highly ordered asymmetric membranes for the further construction of functional mesoscale assemblies.
“…This adsorption is driven by the electronic property of acid–base polymeric foams. Under acidic or basic conditions, these polymers can acquire charge by protonation or dissociation of functional groups, such as carboxyl, hydroxyl, and amine groups. − Although these polymers are hydrophilic in nature, they are able to switch from a hydrophilic surface to an oleophilic surface by the adsorption of oppositely charged oil droplets. − The oil field effluents contain crude oil microdroplets, which are highly stable due to the presence of anionic surfactants at the oil–water interface. − At a specific pH, if the adsorbent surface (i.e., foam surface) has a positive charge and the oil droplets have a negative charge, the droplets will be attracted to the adsorbent surface, switching the surface from hydrophilic to oleophilic (Figure ). ,,− To invoke switchable wetting, bulk pH can be varied to alter the surface charge polarity of the foam and oil droplets, enabling effective adsorption …”
Separation of toxic organic pollutants from industrial effluents is a great environmental challenge. Herein, an acid-base engineered foam is employed for separation of micro-oil droplets from an aqueous solution. In acidic or basic environments, acid-base polymers acquire surface charge due to protonation or dissociation of surface active functional groups. This property is invoked to adsorb crude oil microdroplets from water using polyester polyurethane (PESPU) foam. The physicochemical surface properties of the foam were characterized using X-ray photoelectron spectroscopy, inverse gas chromatography, electrokinetic analysis, and micro-computed tomography. Using the surface charge of the foam and oil droplets, the solution pH (5.6) for maximum separation efficacy was predicted. This optimal pH was verified through underwater wetting behavior and adsorption experiments. The droplet adsorption onto the foam was governed by physisorption, and the driving forces were attributed to electrostatic attraction and Lifshitz-van der Waals forces. The foam was regenerated and reused multiple times by simple compression. The lowest trace oil content in the retentate was 3.6 mg L, and all oil droplets larger than 140 nm were removed. This work lays the foundation for the development of a new class of engineered foam adsorbents with the potential to revolutionize water treatment technologies.
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