The formation of high aspect ratio organosiloxane fibers of nanodimensionality via the surface-induced vapor-phase polymerization of vinyltrichlorosilane is reported. We also demonstrate the versatility of our method by producing fibers of various densities, polydispersities, and lengths. Nanofibers were characterized using SEM, EDX, XPS, TOF-SIMS, and variable-angle FTIR. Advancing aqueous contact angle measurements were used to evaluate the nanofiber surface wettability.

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Abstract:This work describes a method for limiting internal losses of a luminescent solar concentrator (LSC) due to reabsorption through patterning the fluorescent dye doped coating of the LSC. By engineering the dye coating into regular line patterns with fill factors ranging from 20 -80%, the surface coverage of the dye molecules were reduced, thereby decreasing the probability of the re-emitted light encountering another dye molecule and the probability of reabsorption. Two types of fluorescent dyes with different quantum yields were used to examine the effects of patterning on LSC performance. The effect of various dimension and geometry of the patterns on the efficiency and edge emission of LSC are presented and analyzed.

Organic wavelength-selective mirrors are used to reduce the loss of emitted photons through the surface of a luminescent solar concentrator (LSC). A theoretical calculation suggests that application of a 400 nm broad reflector on top of an LSC containing BASF Lumogen Red 305 as a luminophore can reflect 91% of all surface emitted photons back into the device. Used in this way, such broad reflectors could increase the edgeemission efficiency of the LSC by up to 66%. Similarly, 175 nm broad reflectors could increase efficiency up to 45%. Measurements demonstrate more limited effectiveness and dependency on the peak absorbance of the LSC. At higher absorbance, the increased number of internal re-absorption events reduces the effectiveness of the reflectors, leading to a maximum increase in LSC efficiency of ~5% for an LSC with a peak absorbance of 1. Reducing re-absorption by reducing dye concentration or the coverage of the luminophore coating results in an increase in LSC efficiency of up to 30% and 27%, respectively.

We report the application of solution- and vapor-phase siloxane-based methods for tailoring the surface chemistry/properties of highly porous, nanostructured thin films fabricated using glancing angle deposition (GLAD). The GLAD technique produces high surface area films consisting of isolated columns and provides complete control over the film/column morphology. In the present study, the chemical tunability of a variety of metal oxide GLAD films was investigated using solution-based and vapor-phase surface functionalization methodologies. The surface properties and structures of the treated and untreated films were investigated using scanning electron microscopy (SEM), advancing aqueous contact angle measurements, cyclic voltammetry, and X-ray photoelectron spectroscopy (XPS). Results indicate that the surface chemistry of metal oxide GLAD films could be tailored by either method; however, chemical reactivity depends strongly on the metal oxide film material. Chemical tunability is demonstrated through the covalent tethering of numerous chemical moieties onto the exposed and interior surfaces of metal oxide GLAD films of varied structural motifs. Through careful choice of surface modifier, the present derivatization methods afford a full range of aqueous wettability from hydrophilic to superhydrophobic without compromising film structure. These functionalized, nanoconstructed films demonstrate a high degree of tunability over both structural and surface properties, making them well suited for diverse applications such as optical filters or sensors.