5 research outputs found
Image Charge Effects on the Formation of Pickering Emulsions
Vigorous mixing of an aqueous particle dispersion with
oil usually
produces a particle-stabilized emulsion (a “Pickering emulsion”),
the longevity of which depends on the particles’ wetting properties.
A known exception occurs when particles fail to adsorb to the oil–water
interface created during mixing because of a strong repulsion between
charges on the particle surface and similar charges on the oil–water
interface; in this case, no Pickering emulsion is formed. Here, we
present experimental evidence that the rarely considered electrostatic
image force can cause a much bigger hindrance to particle adsorption
and prevent the formation of Pickering emulsions even when the particle
interaction with the interface charge is attractive. A simple theoretical
estimate confirms the observed magnitude of this effect and points
at an important limitation of Pickering emulsification, a technology
with widespread industrial applications and increasing popularity
in materials research and development
Poly(3-hexylthiophene) Nanotube Array Surfaces with Tunable Wetting and Contact Thermal Energy Transport
Solution casting using a sacrificial template is a simple technique to fabricate vertical arrays of polymer nanotubes. However, because of their close proximity and high aspect ratios, large capillary forces cause nanotubes to cluster as the array dries; researchers often use special drying techniques to avoid this clustering. Here, we exploit the clustering of regioregular poly(3-hexylthiophene) (rr-P3HT) nanotubes in a unique template etching process to create surfaces that exhibit tunable wetting and contact thermal energy transport. Vertical arrays of rr-P3HT nanotubes are cast from solution in nanoscale alumina templates, and a solution etching process is used to partially release the nanotubes from the template. The clustering of rr-P3HT nanotube tips upon template etching produces hierarchical surface structuring with a distinct pattern of interconnected ridges, and the spacing between the ridges increases with increased template etch times. These changes in morphology cause the water contact angle to increase from 141° to 168° as the etch time is increased from 4 to 12 min. When assembled into an interface, the morphological changes cause the thermal contact resistance of the vertical rr-P3HT nanotube arrays to increase linearly at a rate of approximately 6 mm<sup>2</sup>·K/W per 2 min etch interval (after 6 min of etching is surpassed). The effective thermal conductivity of the rr-P3HT nanotube arrays is 1 ± 0.2 W/mK independent of the etch time, which is approximately 5 times higher than the bulk rr-P3HT film value
High Thermal and Electrical Conductivity of Template Fabricated P3HT/MWCNT Composite Nanofibers
Nanoporous alumina
membranes are filled with multiwalled carbon nanotubes (MWCNTs) and
then polyÂ(3-hexylthiophene-2,5-diyl) (P3HT) melt, resulting in nanofibers
with nanoconfinement induced coalignment of both MWCNT and polymer
chains. The simple sonication process proposed here can achieve vertically
aligned arrays of P3HT/MWCNT composite nanofibers with 3 wt % to 55
wt % MWCNT content, measured using thermogravimetric methods. Electrical
and thermal transport in the composite nanofibers improves drastically
with increasing carbon nanotube content where nanofiber thermal conductivity
peaks at 4.7 ± 1.1 Wm<sup>–1</sup>K<sup>–1</sup> for 24 wt % MWCNT and electrical percolation occurs once 20 wt %
MWCNT content is surpassed. This is the first report of the thermal
conductivity of template fabricated composite nanofibers and the first
proposed processing technique to enable template fabrication of composite
nanofibers with high filler content and long aspect ratio fillers,
where enhanced properties can also be realized on the macroscale due
to vertical alignment of the nanofibers. These materials are interesting
for thermal management applications due to their high thermal conductivity
and temperature stability
Enhanced Molecular Order in Polythiophene Films Electropolymerized in a Mixed Electrolyte of Anionic Surfactants and Boron Trifluoride Diethyl Etherate
We synthesized polythiophene (PTh) films on stainless
steel electrodes
using chronoamperometry in boron trifluoride diethyl etherate (BFEE)
electrolyte with anionic surfactants. The presence of the anionic
surfactants in BFEE reduced the oxidation potential of thiophene and
increased the oxidation current during electropolymerization. The
measured in-plane electrical conductivity of PTh films synthesized
in the presence of anionic surfactants was up to 300% higher than
that of films synthesized under similar conditions without surfactants.
The observed increase in conductivity reflects the improved order
and packing of polymer chains revealed by X-ray diffraction
Green Light-Triggered Photocatalytic Anticancer Activity of Terpyridine-Based Ru(II) Photocatalysts
The
relentless increase in drug resistance of platinum-based
chemotherapeutics
has opened the scope for other new cancer therapies with novel mechanisms
of action (MoA). Recently, photocatalytic cancer therapy, an intrusive
catalytic treatment, is receiving significant interest due to its
multitargeting cell death mechanism with high selectivity. Here, we
report the synthesis and characterization of three photoresponsive
Ru(II) complexes, viz., [Ru(ph-tpy)(bpy)Cl]PF6 (Ru1), [Ru(ph-tpy)(phen)Cl]PF6 (Ru2), and [Ru(ph-tpy)(aip)Cl]PF6 (Ru3), where, ph-tpy = 4′-phenyl-2,2′:6′,2″-terpyridine,
bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, and aip
= 2-(anthracen-9-yl)-1H-imidazo[4,5-f][1,10] phenanthroline, showing photocatalytic anticancer activity.
The X-ray crystal structures of Ru1 and Ru2 revealed a distorted octahedral geometry with a RuN5Cl
core. The complexes showed an intense absorption band in the 440–600
nm range corresponding to the metal-to-ligand charge transfer (MLCT)
that was further used to achieve the green light-induced photocatalytic
anticancer effect. The mitochondria-targeting photostable complex Ru3 induced phototoxicity with IC50 and PI values
of ca. 0.7 ÎĽM and 88, respectively, under white light irradiation
and ca. 1.9 ÎĽM and 35 under green light irradiation against
HeLa cells. The complexes (Ru1–Ru3) showed negligible dark cytotoxicity toward normal splenocytes (IC50s > 50 μM). The cell death mechanistic study revealed
that Ru3 induced ROS-mediated apoptosis in HeLa cells
via mitochondrial depolarization under white or green light exposure.
Interestingly, Ru3 also acted as a highly potent catalyst
for NADH photo-oxidation under green light. This NADH photo-oxidation
process also contributed to the photocytotoxicity of the complexes.
Overall, Ru3 presented multitargeting synergistic type
I and type II photochemotherapeutic effects