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...

Deposition of tin-doped–indium-oxide (ITO) on unheated substrates via low energy processes such as electron-beam deposition can result in the formation of amorphous films. The amorphous-to-crystalline transformation was studied in this system using in situ resistivity, time resolved reflectivity, glancing incidence angle x-ray diffraction, and transmission electron microscopy. The resistivity of 180 nm thick In2O3(9.9 wt. %SnO2) was monitored during isothermal anneals at 125, 135, 145, and 165 °C. The dependence of the resistance on the volume fraction of crystalline phase was established using glancing incidence angle x-ray diffraction and a general two phase resistivity model for this system was developed. These studies show that, upon annealing, as-deposited amorphous ITO undergoes both a structural relaxation and crystallization. Structural relaxation of the amorphous material includes local ordering that increases the ionized vacancy concentration which, in turn, increases the carrier density in the material. Kinetic growth parameters were extracted from the data, which reveal that the relaxation of the amorphous structure occurs via a process that obeys a first order reaction rate law, while crystallization occurs via classical nucleation and growth with a growth mode parameter that is consistent with two- to three-dimensional transformation geometry. Both the relaxation and crystallization processes have an activation energy of approximately 1.3±0.2 eV. Time resolved reflectivity analysis of the electron beam deposited ITO reveals that there is a sharp and monotonic decrease in reflectivity during the anneal of the sample which is associated with the amorphous relaxation process.

Luminescent solar concentrators (LSCs) show promise because of their potential for low-cost, large-area, and high-efficiency energy harvesting. Stokes shift engineering of luminescent quantum dots (QDs) is a favorable approach to suppress reabsorption losses in LSCs; however, the use of highly toxic heavy metals in QDs constitutes a serious concern for environmental sustainability. Here, we report LSCs based on cadmium-free InP/ZnO core/shell QDs with type-II band alignment that allow for the suppression of reabsorption by Stokes shift engineering. The spectral emission and absorption overlap was controlled by the growth of a ZnO shell on an InP core. At the same time, the ZnO layer also facilitates the photostability of the QDs within the host matrix. We analyzed the optical performance of indium-based LSCs and identified the optical efficiency as 1.45%. The transparency, flexibility, and cadmium-free content of the LSCs hold promise for solar window applications.

No abstract