Optical Properties of Electrospun Nanofiber Substrates
- PDF / 142,926 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 29 Downloads / 254 Views
1240-WW10-05
Optical properties of electrospun nanofiber substrates J. Lynn Davis, Howard J. Walls, Karmann C. Mills, Kim Guzan, Robert Yaga, and David S. Ensor RTI International PO Box 12194 Research Triangle Park, NC 27709-2194 U.S.A. ABSTRACT Light impinging upon electrospun nanofiber substrates encounters a complex media where a multitude of factors controls the transmittance and reflectance of light through the structure. The chemical composition of the nanofiber plays a significant role in that it determines the index of refraction of individual fibers. However, the surrounding media (e.g., air, encapsulating polymer, etc.) also plays an equally important role. In addition, physical effects such as fiber diameter, fiber morphology, fiber packing density (i.e., structure void volume), and substrate thickness play a large role in determining the light management properties of nanofibers. Our research has demonstrated that the transmittance and reflectance of undoped nanofibers can be adjusted through proper manipulation of these factors. For example, similar electrospinning formulations can produce either highly transmitting or highly reflecting light structures depending upon fabrication parameters that impact the final properties of the nanofiber substrates. In addition, a degree of wavelength dependent reflectance and transmittance can be imparted simply by adjusting the physical properties of the nanofibers to promote preferential light scattering below selected frequencies. This paper provides an overview of various factors impacting the light management properties of nanofiber substrates and the importance of controlling these factors to meet end-use applications. INTRODUCTION Light incident upon a material can be either absorbed, transmitted, or reflected depending upon the composition and structure of the material. This is especially important at the nanoscale, since feature size and spacing can have a significant impact upon the optical properties of the materials. For example, polymeric structures made from spheres and rods have been formed into a variety of optical structures often with unexpected benefits. The exceptionally brilliant white appearance of some species of beetles has been shown to arise from randomly oriented nanofibers (~ 250 nm in diameter) found on the animal’s scales. The contrast in refractive index between the nanofibers and the surrounding dielectric material creates efficient scatterers of visible radiation, and can produce an exceptionally bright, high whiteness appearance in layers as thin as 5 µm. This thickness is reported to be two orders of magnitude thinner than synthetic systems of equivalent whiteness [1]. Manipulation of nanofiber surface morphology has also been shown to produce nanofiber substrates that have variations in transmittance with wavelength [2]. In addition, the reflectance of nanofibers deposited on polyurethane foams can provide a potential light shield against photodegradation of the underlying urethane [3]. Nanofibers are interesting optical structure
Data Loading...
