Cocoon-in-web-like Superhydrophobic Aerogels From Hydrophilic Polyurea and Use in Environmental Remediation
Polyurea (PUA) develops H-bonding with water and is inherently hydrophilic. the water contact angle on smooth dense PUA derived from an aliphatic triisocyanate and water was measured at θ = 69.1 ± 0.2°. Nevertheless, texture-related superhydrophobic PUA aerogels (θ′ = 150.2°) were prepared from the same monomer in one step with no additives, templates, or surfactants via sol-gel polymerization carried out in polar, weakly H-bonding acetonitrile. Those materials display a unique nanostructure consisting of micrometer-size spheres distributed randomly and trapped in a nanofiber web of the same polymer. Morphostructurally, as well as in terms of their hydrophobic properties, those PUA aerogels are analogous to well-studied electrospun fiber mats incorporating particle-like defects. PUA aerogels have the advantage of easily scalable synthesis and low cost of the raw materials. Despite large contact angles and small contact areas, water droplets (5 μL) stick to the aerogels surface when the substrate is turned upside-down. That so-called Petal effect is traced to H-bonding at the points of contact between the water droplet and the apexes of the roughness of the aerogel surface. Monoliths are flexible and display oleophilicity in inverse order to their hydrophobicity; oil fills all the available open porosity (94% v/v) of cocoon-in-web like aerogels with bulk density ρb = 0.073 g cm-3; that capacity for oil absorption is >10:1 w/w and translates into ∼6:1 w/v relative to state-of-The-Art materials (e.g., graphene-derived aerogels). Oil soaked monoliths float on water and can be harvested off.
N. Leventis et al., "Cocoon-in-web-like Superhydrophobic Aerogels From Hydrophilic Polyurea and Use in Environmental Remediation," ACS Applied Materials and Interfaces, vol. 6, no. 9, pp. 6872-6882, American Chemical Society (ACS), Jan 2014.
The definitive version is available at http://dx.doi.org/10.1021/am500685k
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