Immigration and epidemiological studies provide evidence indicating the correlation of high ultraviolet exposure during childhood and increased risks of melanoma in later life. While the explanation of this phenomenon has not been found in the skin, a class of hair has been hypothesized to be involved in this process by transmitting sufficient ultraviolet rays along the hair shaft to possibly cause damage to the stem cells in the hair follicle, ultimately resulting in melanoma in later life. First, the anatomy of hair and its possible contribution to melanoma development, and the tissue optical properties are briefly introduced to provide the necessary background. This paper emphasizes on the review of the experimental studies of the optical properties of human hair, which include the sample preparation, measurement techniques, results, and statistical analysis. The Monte Carlo photon simulation of human hair is next outlined. Finally, current knowledge of the optical studies of hair is discussed in the light of their possible contribution to melanoma development; the necessary future work needed to support this hypothesis is suggested.
This paper investigates various experimental techniques of improving the optical properties as well as the electro-active characteristics of polyurethane polymer films for smart lens applications. Two experimental methods are used for preparing the films, the first consists of molding the polymer under various pressure and temperature conditions while the second is based on producing films of various thicknesses by the solvent casting method using tetrahydrofuran (THF) as solvent followed by a 100°C annealing in vacuum for 30min. Testing samples of 50 mm diameter are rigidly attached to circular frames and tested under applied field in the range of 30-80 kV/mm. The first method produces thicker and stiffer films with deformation response in the order of 0.8 mm; however, they are translucent. The second method results in thinner films with lower flexibility and reasonable electro-active response in the order of 0.3 mm. The transparency of the latter samples is excellent and closes the gap to produce a smart lens.
In this paper a model is postulated to describe the optical response of an electroactive polymer hydrogel due to applied electrical fields. This model consists of a series of several modules: an electrical module that identifies the relationship between the applied voltage/current, electrode location and material and applied electrical field; a chemical module that correlates the percentage monomer in the gel, percentage cross linker, solvent ionic strength and pH; a mechanical module that employs the output of the chemical module to calculate deformation, taking into consideration experimentally measured elastic and viscoelastic characteristics; an optical module that will incorporate results from the previous modules to yield important optical characteristics (such as focal length and refractive index). It is anticipated that ultimately this model will set the required voltage to produce particular optical characteristics. Using an elastic modulus of 2160 Pa, a Poisson's ratio of 0.33 and experimentally measured gel response force of 0.1 N has resulted in a mechanical module which fully describes the gel motion. This result is promising; however, the mechanical module is currently using elastic properties, whereas viscoelastic properties are ideally needed.
This paper summarizes some of the work done to investigate the environmental stability, optical properties and electroactive response of a polyethylene glycol diepoxypropyl ether (n9)(PEGDE) polymer, acrylic elastomer and polyurethane. The first one confirms piezoelectricity; however it is not suitable for optical applications due to color instability and loss of transparency with various environmental conditions; the second confirms electrostriction with
good transparency, while the polyurethane behaves with smaller mixed piezoelectric-electrostrictive response. The acrylic elastomer has demonstrated chemical stability with good optical properties for various environmental conditions
The primary purpose of this research is to create a flexible, self-sustaining gel with an optical transparency of over 70% for light in the range of 400 to 700 nanometers. Attention is focused on identifying and controlling the effect of crosslinker concentration and degree of neutralization on the polymer gel optical transparency, structural rigidity and electroactive response. Appropriate flexible and transparent electrodes suited for the present application are identified. Spectrophotometer tests indicate that there is a large gap between the spectra from crosslinker content of 175mg and 200mg (with an intensity difference of approximately 40% at 440nm).