Cocoon-in-Web-Like Superhydrophobic Aerogels from Hydrophilic Polyurea and Use in Environmental Remediation

Abstract

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.

Versatile Aerogel Fabrication by Freezing and Subsequent Freeze‐Drying of Colloidal Nanoparticle Solutions

“…Interestingly,f or the higher NP concentrations,the shape of the frozen colloid resembles the shape of the resulting aerogel ( Figure 2C). Therefore,o ur new cryogelation method is advantageous in comparison to conventional aerogels (and xerogels) resulting from lyogelated gels,w hich are frequently accompanied by syneresis [2,4,7,11,21,22] (i.e.t he gels are usually smaller than the colloid liquid). Therefore,o ur new cryogelation method is advantageous in comparison to conventional aerogels (and xerogels) resulting from lyogelated gels,w hich are frequently accompanied by syneresis [2,4,7,11,21,22] (i.e.t he gels are usually smaller than the colloid liquid).…”

Synthesis and biomedical applications of aerogels: Possibilities and challenges

“…polyurea [144], polyimides [145], polyamide [146], polyacrylonitriles [127], polyurethanes [147], polystyrene [148], polybenzoxazine [149], poly(dicyclopentadiene) [150], etc.…”

“…On the other hand, some industrial applications of aerogels [158] demanded highly flexibility and foldability, which cannot be attainable by the polymer-cross-linked silica aerogels. Leventis et al reported the synthesis of a highly flexible aerogel from polyurea and poly urethane [144,159,160]. They concluded that macroscopic flexibility is indirectly correlated with the molecular properties of the monomer.…”

Superhydrophobic polyimide aerogels via conformal coating strategy with excellent underwater performances

“…[1][2][3][4] Over the past years, most of the research works focused on the silica and metal-oxide aerogels. [5][6][7][8] Recently, a variety of new aerogels have been synthesized, such as organic polymer-based aerogels, [9][10][11][12] supramolecular aerogels, [13][14][15] hybrid aerogels, 16,17 and graphene aerogels. 18,19 Organic polymerbased aerogels including polyaimide, 20 polyurethane, 21 and cellulose aerogels 22,23 have attracted increasing interests due to their outstanding mechanical properties.…”