16 research outputs found
Zwitterionic nanofibers of super-glue for transparent and biocompatible multi-purpose coatings
Here we show that macrozwitterions of poly(ethyl 2-cyanoacrylate), commonly called Super Glue, can easily assemble into long and well defined fibers by electrospinning. The resulting fibrous networks are thermally treated on glass in order to create transparent coatings whose superficial
morphology recalls the organization of the initial electrospun mats. These textured coatings are characterized by low liquid adhesion and anti-staining performance. Furthermore, the low friction coefficient and excellent scratch resistance make them attractive as solid lubricants. The inherent
texture of the coatings positively affects their biocompatibility. In fact, they are able to promote the proliferation and differentiation of myoblast stem cells. Optically-transparent and biocompatible
coatings that simultaneously possess characteristics of low water contact angle hysteresis, low friction and mechanical robustness can find application in a wide range of technological sectors, from
the construction and automotive industries to electronic and biomedical devices
Measurement and interpretation of contact angles in surface energetics and droplet impact.
Measurement and interpretation of contact angles in surface energetics and droplet impact
Healable Cotton–Graphene Nanocomposite Conductor for Wearable Electronics
Electrically
conductive materials based on cotton have important implications for
wearable electronics. We have developed flexible and conductive cotton
fabrics (∼10 Ω/sq) by impregnation with graphene and
thermoplastic polyurethane-based dispersions. Nanocomposite fabrics
display remarkable resilience against weight-pressed severe folding
as well as laundry cycles. Folding induced microcracks can be healed
easily by hot-pressing, restoring initial electrical conductivity.
Impregnated cotton fabric conductors demonstrate better mechanical
properties compared to pure cotton and thermoplastic polyurethane
maintaining breathability. They also resist environmental aging such
as solar irradiation and high humidity
Superoleophobic and conductive carbon nanofiber/fluoropolymer composite films
A solution-based, large-area coating procedure is developed to produce conductive polymer composite films consisting of hollow-core carbon nanofibers (CNFs) and a fluoroacrylic copolymer available as a water-based dispersion. CNFs (100 nm dia., length similar to 130 mu m) were dispersed by sonication in a formic acid/acetone co-solvent system, which enabled colloidal stability and direct blending of the CNFs and aqueous fluoroacrylic dispersions in the absence of surfactants. The dispersions were sprayed on smooth and microtextured surfaces, thus forming conformal coatings after drying. Nanostructured composite films of different degrees of oil and water repellency were fabricated by varying the concentration of CNFs. The effect of substrate texture and CNF content on oil/water repellency was studied. Water and oil static contact angles (CAs) ranged from 98 degrees to 164 degrees and from 61 degrees to 164 degrees, respectively. Some coatings with the highest water/oil CAs displayed self-cleaning behavior (droplet roll-off angles <10 degrees). Inherent conductivity of the composite films ranged from 63 to 940 S/m at CNF concentrations from 10 to 60 wt.%, respectively. Replacement of the long CNFs with shorter solid-core carbon nanowhiskers (150 nm dia., length 6-8 mu m) produced stable fluoropolymer-nanowhisker dispersions, which were ink-jetted to generate hydrophobic, conductive, printed line patterns with a feature size similar to 100 mu m. (C) 2011 Elsevier Ltd. All rights reserved
Surprising High Hydrophobicity of Polymer Networks from Hydrophilic Components
We report a simple and inexpensive
method of fabricating highly hydrophobic novel materials based on
interpenetrating networks of polyamide and polyÂ(ethyl cyanoacrylate)
hydrophilic components. The process is a single-step solution casting
from a common solvent, formic acid, of polyamide and ethyl cyanoacrylate
monomers. After casting and subsequent solvent evaporation, the in
situ polymerization of ethyl cyanoacrylate monomer forms polyamide-polyÂ(ethyl
cyanoacrylate) interpenetrating network films. The interpenetrating
networks demonstrate remarkable waterproof properties allowing wettability
control by modulating the concentration of the components. In contrast,
pure polyamide and polyÂ(ethyl cyanoacrylate) films obtained from formic
acid solutions are highly hygroscopic and hydrophilic, respectively.
The polymerization of ethyl cyanoacrylate in the presence of polyamide
promotes molecular interactions between the components, which reduce
the available hydrophilic moieties and render the final material hydrophobic.
The wettability, morphology, and thermo-physical properties of the
polymeric coatings were characterized. The materials developed in
this work take advantage of the properties of both polymers in a single
blend and above all, due to their hydrophobic nature and minimal water
uptake, can extend the application range of the individual polymers
where water repellency is required
High strain sustaining, nitrile rubber based, large-area, superhydrophobic, nanostructured composite coatings
Elastomeric superhydrophobic nanostructured composite coatings scalable to large areas are prepared by spray casting particle-polymer dispersions. The dispersions consist of nanostructured carbon black particles along with submicrometer-sized poly(tetrafluoroethylene) particles dispersed in nitrile rubber solution in acetone, with the goal to attain superhydrophobicity with minimal content of particle fillers. The coatings are applied on various flexible substrates, which are subsequently stretched uniaxially. Upon drying, water droplet roll-off (sliding) angle measurements are performed to quantify the self-cleaning ability of coated substrates being stretched uniaxially to 30% strain (coated silicone rubber) and 70% strain (coated polyester fabric). The coatings conform to the stretching of the substrates, while maintaining the self-cleaning property throughout this range. Self-cleaning is also maintained for cyclical stretching of coated substrates for strains 0–30% (coated silicone rubber) and 0–70% (coated polyester fabric) demonstrating the coatings’ functional recovery. Droplet roll-off angles below 10° reveal good self-cleaning ability for these coatings
Environmentally Benign Production of Stretchable and Robust Superhydrophobic Silicone Monoliths
Superhydrophobic
materials hold an enormous potential in sectors as important as aerospace,
food industries, or biomedicine. Despite this great promise, the lack
of environmentally friendly production methods and limited robustness
remain the two most pertinent barriers to the scalability, large-area
production, and widespread use of superhydrophobic materials. In this
work, highly robust superhydrophobic silicone monoliths are produced
through a scalable and environmentally friendly emulsion technique.
It is first found that stable and surfactantless water-in-polydimethylsiloxane
(PDMS) emulsions can be formed through mechanical mixing. Increasing
the internal phase fraction of the precursor emulsion is found to
increase porosity and microtexture of the final monoliths, rendering
them superhydrophobic. Silica nanoparticles can also be dispersed
in the aqueous internal phase to create micro/nanotextured monoliths,
giving further improvements in superhydrophobicity. Due to the elastomeric
nature of PDMS, superhydrophobicity can be maintained even while the
material is mechanically strained or compressed. In addition, because
of their self-similarity, the monoliths show outstanding robustness
to knife-scratch, tape-peel, and finger-wipe tests, as well as rigorous
sandpaper abrasion. Superhydrophobicity was also unchanged when exposed
to adverse environmental conditions including corrosive solutions,
UV light, extreme temperatures, and high-energy droplet impact. Finally,
important properties for eventual adoption in real-world applications
including self-cleaning, stain-repellence, and blood-repellence are
demonstrated
Superhydrophobic-Superhydrophilic Binary Micropatterns by Localized Thermal Treatment of Polyhedral Oligomeric Silsesquioxane (POSS)-Silica Films
Surfaces patterned with alternating (binary) superhydrophobic-superhydrophilic regions can be found naturally, offering a bio-inspired template for efficient fluid collection and management technologies. We describe a simple wet-processing, thermal treatment method to produce such patterns, starting with inherently superhydrophobic polysilsesquioxane-silica composite coatings prepared by spray casting nanoparticle dispersions. Such coatings become superhydrophilic after localized thermal treatment by means of laser irradiation or open-air flame exposure. When laser processed, the films are patternable down to similar to 100 mu m scales. The dispersions consist of hydrophobic fumed silica (HFS) and methylsilsesquioxane resin, which are dispersed in isopropanol and deposited onto various substrates (glass, quartz, aluminum, copper, and stainless steel). The coatings are characterized by advancing, receding, and sessile contact angle measurements before and after thermal treatment to delineate the effects of HFS filler concentration and thermal treatment on coating wettability. SEM, XPS and TGA measurements reveal the effects of thermal treatment on surface chemistry and texture. The thermally induced wettability shift from superhydrophobic to superhydrophilic is interpreted with the Cassie-Baxter wetting theory. Several micropatterned wettability surfaces demonstrate potential in pool boiling heat transfer enhancement, capillarity-driven liquid transport in open surface-tension-confined channels (e.g., lab-on-a-chip), and select surface coating applications relying on wettability gradients. Advantages of the present approach include the inherent stability and inertness of the organosilane-based coatings, which can be applied on many types of surfaces (glass, metals, etc.) with ease. The present method is also scalable to large areas, thus being attractive for industrial coating applications
Water-Based, Nonfluorinated Dispersions for Environmentally Benign, Large-Area, Superhydrophobic Coatings
Low-cost, large-area,
superhydrophobic coating treatments are of high value to technological
applications requiring efficient liquid repellency. While many applications
are envisioned, only few are realizable in practice due to either
the high cost or low durability of such treatments. Recently, spray
deposition of polymer–particle dispersions has been demonstrated
as an excellent means for producing low-cost, large-area, durable,
superhydrophobic composite coatings/films; however, such dispersions
generally contain harsh or volatile solvents, which are required for
solution processing of polymers as well as for dispersing hydrophobic
nanoparticles, thus inhibiting scalability due to the increased cost
in chemical handling and environmental safety concerns. Moreover,
such coatings usually contain fluoropolymers due to their inherent
low surface energy, a requirement for superhydrophobicity, but concerns
over their biopersistence has provided an impetus for eliminating
these chemicals. For spray coating, the former problem can be overcome
by replacing organic solvents with water, but this situation seems
paradoxical: Producing a highly water-repellent coating from an aqueous
dispersion. We report a water-based, nonfluorinated dispersion for
the formation of superhydrophobic composite coatings applied by spray
on a variety of substrates. We stabilize hydrophobic components (i.e.,
polymer, nanoparticles) in water, by utilizing chemicals containing
acid functional groups (i.e., acrylic acid) that can become ionized
in aqueous environments under proper pH control (pH > 7). The functional
polymer utilized in this study is a copolymer of ethylene and acrylic
acid, while the particle filler is exfoliated graphite nanoplatelet
(xGnP), which contains functional groups at its periphery. Once spray
deposited and dried, the components become insoluble in water, thus
promoting liquid repellency. Such coatings can find a wide range of
applications due to their benign processing nature as well as the
variety of substrates on which they can be deposited
Self-Cleaning Organic/Inorganic Photo-Sensors
We present the fabrication of a multifunctional,
hybrid organic–inorganic
micropatterned device, which is capable to act as a stable photosensor
and, at the same time, displaying inherent superhydrophobic self-cleaning
wetting characteristics. In this framework several arrays of epoxy
photoresist square micropillars have been fabricated on n-doped crystalline
silicon substrates and subsequently coated with a polyÂ(3-hexylthiophene-2,5-diyl)
(P3HT) layer, giving rise to an array of organic/inorganic p–n
junctions. Their photoconductivity has been measured under a solar
light simulator at different illumination intensities. The current–voltage
(<i>I</i>–<i>V</i>) curves show high rectifying
characteristics, which are found to be directly correlated with the
illumination intensity. The photoresponse occurs in extremely short
times (within few tens of milliseconds range). The influence of the
interpillar distance on the <i>I</i>–<i>V</i> characteristics of the sensors is also discussed. Moreover, the
static and dynamic wetting properties of these organic/inorganic photosensors
can be easily tuned by changing the pattern geometry. Measured static
water contact angles range from 125° to 164°, as the distance
between the pillars is increased from 14 to 120 μm while the
contact angle hysteresis decreases from 36° down to 2°