The high water repellence of superhydrophobic surfaces is attributed to the limited contact area between the solid and water which is manifested by a high static water contact angle (WCA) and a low sliding angle. The solid-liquid interfacial energy can be minimized by engineering not only the chemistry but also the topography of the solid surface. [1,2] For example, epicuticular wax on the lotus leaf is an intrinsically hydrophobic material.[3] However, when nano-sized crystals of wax cover a micron-level rough surface, as is the case on the lotus leaf, the WCA is further enhanced to 1608, which is defined as superhydrophobic. [4][5][6][7][8] In this case, the water droplet forms a three-dimensional, discontinuous, triphasic (water-air-solid) contact line [9] that is relatively longer and less stable than such a line on a macroscopically smooth surface. Moreover, a nonhydrophobic material can also be rendered hydrophobic with a WCA well above 1508 by chemical modification, for example, through the incorporation of fluorine or silicone, as well as by increasing the roughness. [9][10][11][12][13][14] Such an extreme water repellence is highly attractive for novel industrial and practical applications: continuously clean buildings, windows, and outdoor decorations, stain-resistant fabrics, antifouling marine structures, and oxidation-resistant surfaces. [2,8,10] Currently, the production of superhydrophobic surfaces is based on time-consuming, expensive, and/or nonversatile processes, such as controlled crystallization, lithography, etching, and templating. [9][10][11][12][13]15] To mimic the topography of the lotus leaf and to achieve a high WCA, we fabricated a polymeric film surface with a high degree of roughness through a simple and practical electrospinning process.[16] Electrospun films consist of a continuous, nonwoven web of fibers (with diameters in the order of 1-1000 nm) and, depending on processing conditions, with polymer droplets either as isolated spheres (> 1 mm in diameter) or strung along a fiber. [17][18][19][20][21][22] The electrospun film is produced by applying an electrical bias from the tip of a polymer solution-filled syringe to a grounded collection plate. Along the trajectory of the extruded polymer fiber, most of the solvent evaporates, such that a mat of randomly aligned fibers collects and form a thin film. In addition to surface roughness, the film properties were optimized by chemical modification, such as the addition of fluorine to enhance and stabilize WCA values and the incorporation of crosslinking for solvent resistance. Our ability to engineer both the physical and chemical properties of the electrospun films enables flexibility in tuning the degree of hydrophobicity.A thermoset polymer was synthesized by first reacting acrylonitrile (AN) and a,a-dimethyl meta-isopropenylbenzyl isocyanate (TMI) in N,N-dimethylformamide (DMF), and then mixing the resultant poly(AN-co-TMI) with a perfluorinated linear diol (fluorolink-D) and tin(ii) ethyl hexanoate (T2EH) in DMF. The solution w...

a b s t r a c tSurface reactive P(St-co-GMA) copolymer and P(St-co-GMA)/MWCNT fibrous mats are placed onto a conventional carbon fiber/epoxy prepreg as interlayer reinforcing material. Experimental observations are used to demonstrate excellent epoxy wetting and structural compatibility of the interlayers chemically tuned for the epoxy matrix. Comparisons of increase in mechanical performance by incorporating P(Stco-GMA) and P(St-co-GMA)/MWCNT interlayers also show the contribution of MWCNT presence in the copolymer nanofibers. Flexural strength and stiffness of (0/0/0) and (90/0/90) laminates increase up to 17% when the nanocomposite interlayers are integrated. Cross-sectional SEM analyses of the failure surfaces suggest reinforcing ability of interlayers both against transverse cracking and delamination. Further examination for the delamination resistance is presented by the End Notched Flexure (ENF) tests. An improvement up to 70% in mode II strain energy release rate (G IIc ) is recorded for the laminates with nanocomposite interlayers. The resistance against transverse matrix cracking in the presence of interlayers is also elaborated. Charpy-impact and transverse-tension tests result in up to 20% and 27% increase in the impact energy absorbance and transverse tensile strength, respectively. Overall, the test results suggest that mechanical behavior of the laminates is enhanced by the nanofibrous interlayers chemicallytuned for epoxy crosslinking, with no weight penalty.

The high water repellence of superhydrophobic surfaces is attributed to the limited contact area between the solid and water which is manifested by a high static water contact angle (WCA) and a low sliding angle. The solid-liquid interfacial energy can be minimized by engineering not only the chemistry but also the topography of the solid surface. [1,2] For example, epicuticular wax on the lotus leaf is an intrinsically hydrophobic material.[3] However, when nano-sized crystals of wax cover a micron-level rough surface, as is the case on the lotus leaf, the WCA is further enhanced to 1608, which is defined as superhydrophobic. [4][5][6][7][8] In this case, the water droplet forms a three-dimensional, discontinuous, triphasic (water-air-solid) contact line [9] that is relatively longer and less stable than such a line on a macroscopically smooth surface. Moreover, a nonhydrophobic material can also be rendered hydrophobic with a WCA well above 1508 by chemical modification, for example, through the incorporation of fluorine or silicone, as well as by increasing the roughness. [9][10][11][12][13][14] Such an extreme water repellence is highly attractive for novel industrial and practical applications: continuously clean buildings, windows, and outdoor decorations, stain-resistant fabrics, antifouling marine structures, and oxidation-resistant surfaces. [2,8,10] Currently, the production of superhydrophobic surfaces is based on time-consuming, expensive, and/or nonversatile processes, such as controlled crystallization, lithography, etching, and templating. [9][10][11][12][13]15] To mimic the topography of the lotus leaf and to achieve a high WCA, we fabricated a polymeric film surface with a high degree of roughness through a simple and practical electrospinning process.[16] Electrospun films consist of a continuous, nonwoven web of fibers (with diameters in the order of 1-1000 nm) and, depending on processing conditions, with polymer droplets either as isolated spheres (> 1 mm in diameter) or strung along a fiber. [17][18][19][20][21][22] The electrospun film is produced by applying an electrical bias from the tip of a polymer solution-filled syringe to a grounded collection plate. Along the trajectory of the extruded polymer fiber, most of the solvent evaporates, such that a mat of randomly aligned fibers collects and form a thin film. In addition to surface roughness, the film properties were optimized by chemical modification, such as the addition of fluorine to enhance and stabilize WCA values and the incorporation of crosslinking for solvent resistance. Our ability to engineer both the physical and chemical properties of the electrospun films enables flexibility in tuning the degree of hydrophobicity.A thermoset polymer was synthesized by first reacting acrylonitrile (AN) and a,a-dimethyl meta-isopropenylbenzyl isocyanate (TMI) in N,N-dimethylformamide (DMF), and then mixing the resultant poly(AN-co-TMI) with a perfluorinated linear diol (fluorolink-D) and tin(ii) ethyl hexanoate (T2EH) in DMF. The solution w...

We present a strategy for stabilizing the morphological integrity of electrospun polymeric nanofibers by heat stimuli in situ crosslinking. Amorphous polymer nanofibers, such as polystyrene (PS) and its co-polymers tend to lose their fiber morphology during processing at temperatures above their glass transition temperature (T g ) typically bound to happen in nanocomposite/structural composite applications. As an answer to this problem, incorporation of the crosslinking agents, phthalic anhydride (PA) and tributylamine (TBA), into the electrospinning polymer solution functionalized by glycidylmethacrylate (GMA) copolymerization, namely P(St-co-GMA), is demonstrated. Despite the presence of the crosslinker molecules, the electrospinning polymer solution is stable and its viscosity remains unaffected below 60 8C. Crosslinking reaction stands-by and can be thermally stimulated during post-processing of the electrospun P(St-co-GMA)/PA-TBA fiber mat at intermediate temperatures (below the T g ). This strategy enables the preservation of the nanofiber morphology during subsequent high temperature processing. The crosslinking event leads to an increase in T g of the base polymer by 30 8C depending on degree of crosslinking. Crosslinked nanofibers are able to maintain their nanofibrous morphology above the T g and upon exposure to organic solvents. In situ crosslinking in epoxy matrix is also reported as an example of high temperature demanding application/processing. Finally, a self-same fibrous nanocomposite is demonstrated by dual electrospinning of P(St-co-GMA) and stabilized P(St-co-GMA)/PA-TBA, forming an intermingled nanofibrous mat, followed by a heating cycle. The product is a composite of crosslinked P(St-co-GMA)/PA-TBA fibers fused by P(St-co-GMA) matrix. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44090.

Green composites of poly(lactic acid) (PLA) and waste cellulose fibers (WCF) were produced by using a facile technique comprising high-shear mixing within relatively short processing times that facilitates the ease of processing of such materials and ensures the homogeneous dispersion of such fibers in thermoplastics due to shear rates as high as 5200 rpm. Key parameters, such as optimal concentrations, homogeneous dispersion, direct and indirect mechanical contributions of the fibers, interfacial interactions, and crystallinity of the PLA matrix, were examined for the sustainable production of PLA/WCF green composites with enhanced stiffness, strength, toughness, and impact resistance. Briefly, around one-fold, 50%, and 20% increase in the elastic modulus, tensile strength, and impact strength of PLA, respectively, were achieved by the addition of 30 wt % WCF. In addition, an 87% increase in the impact strength of PLA was also achieved by the incorporation of 5 wt % WCF.

No abstract

We demonstrated a facile method to produce perfectly hydrophobic surfaces (advancing and receding angles both 180°) via electrospraying. When a copolymer of styrene and a perfluoroacrylate monomer was electrosprayed in good solvents, surfaces composed of micrometer size beads were formed and fairly low threshold water sliding angles could be achieved. Addition of high boiling point poor solvents to the solutions resulted nanoscale roughness on the beads due to a possible phase separation that occurs in a predominantly poor solvent environment. However, sliding angles were not zero even on the nanoscale roughness dominated topographies achieved by this method. On the other hand, when the electrospraying process parameters were set such that micrometer size hills of nanoscopically rough beads were formed, 0° sliding angles were measured. Videos of droplets recorded and the adhesive forces measured during a contact and release experiment revealed that these dual scale rough surfaces were indeed perfectly hydrophobic. Application of the method with other binary good solvent-poor solvent systems also resulted in perfect hydrophobicity. Overall results showed how the differences in surface topology affected the wettability of surfaces within a very narrow range between perfect and extreme hydrophobicity (advancing and receding angles both close to 180°).

The effect of poly(ethylene oxide) (PEO) soft segment molecular weight (Mn= 2000, 4600, 8000 g mol−1) molecular mobility and segmental dynamics of a series of polyurethane–urea copolymers (PU) was investigated by dielectric relaxation spectroscopy.