Jian-Min Yuan

Organophosphorus acid anhydrolase (OPAA) was successfully nanoencapsulated, in-situ, into both silica and organic-modified silica following the low volume shrinkage, non-surfactant templated sol-gel process with D-fructose and poly(ethylene glycol) as the pore-forming agents. By varying the concentration of the template or the concentration of the starting materials, the pore parameters were tuned to have high surface area of 500-800 m(2)/g, large pore volume from 0.2-0.8 cm(3)/g, and pore diameters ranging from 2-6 rim. As a result, the enzyme remained active in the nanoencapsulated form in both aqueous and mixed aqueous-organic solvents and was reusable by employing a simple regeneration procedure of buffer wash. The immobilization of OPAA in mesoporous materials significantly increased the stability of OPAA against the denaturation in the presence of organic solvents. For a remarkable example, the organically-modified gel sample in 20% acetone significantly retained enzyme activity up to similar to 90% in comparison with aqueous solution.

Smart textiles with integrated fiber optic sensors have been studied for various applications including in-situ measurement of load/deformation on the textiles. Two types of silica multimode optical fibers were successfully integrated into 4/4 Twill-woven and Plain-woven textiles along the warp direction of the textile structures for sensing of applied load conditions. The sensing mechanism is based on the MPD (Modal Power Distribution) technique, which employs the principle of intensity modulation based on modal power redistribution of the propagating light within multimode fibers caused by external perturbations. In the presence of transverse load applied to an integrated optical fiber, the redistribution of the modal power is an indication of the applied load. The spatial modal power redistribution was clearly recorded as a function of the optical intensity profile. Based on the uni-axial tensile test results, the relationship between the mechanical behavior of the textile and the output of the embedded fiber-optic sensor was established and understood. It is clearly demonstrated that the sensitivity and dynamic range of this type of intensity-based sensor is determined by the interaction between the fabric yarns and optical fibers, which are closely related with the textile structure and the type of optical fiber.

Smart textiles are defined as textiles capable of monitoring their own health conditions or structural behavior, as well as sensing external environmental conditions. Smart textiles appear to be a future focus of the textile industry. As technology accelerates, textiles are found to be more useful and practical for potential advanced technologies. The majority of textiles are used in the clothing industry, which set up the idea of inventing smart clothes for various applications. Examples of such applications are medical trauma assessment and medical patients monitoring (heart and respiration rates), and environmental monitoring for public safety officials. Fiber optics have played a major role in the development of smart textiles as they have in smart structures in general. Optical fiber integration into textile structures (knitted, woven, and non-woven) is presented, and defines the proper methodology for the manufacturing of smart textiles. Samples of fabrics with integrated optical fibers were processed and tested for optical signal transmission. This was done in order to investigate the effect of textile production procedures on optical fiber performance. The tests proved the effectiveness of the developed methodology for integration of optical fibers without changing their optical performance or structural integrity.

On-fiber optical sensors, designed with chromogenic materials used as the fiber modified cladding, were developed for sensing environmental conditions. The design was based on the previously developed on-fiber devices. It is known that the light propagation characteristics in optical fibers are strongly influenced by the refractive index of the cladding materials. Thus, the idea of the on- fiber devices is based on replacing the passive optical fiber cladding with active or sensitive materials. For example, temperature sensors can be developed by replacing the fiber clad material with thermochromic materials. In this paper, segmented polyurethane-diacetylene copolymer (SPU), was selected as the thermochromic material for temperature sensors applications. This material has unique chromogenic properties as well as the required mechanical behaviors. During UV exposure and heat treatment, the color of the SPU copolymer varies with its refractive index. The boundary condition between core and cladding changes due to the change of the refractive index of the modified cladding material. The method used for the sensor development presented involves three steps: (a) removing the fiber jacket and cladding from a small region, (b) coating the chromogenic materials onto the modified region, and (c) integrating the optical fiber sensor components. The experimental set-up was established to detect the changes of the output signal based on the temperature variations. For the sensor evaluation, real-time measurements were performed under different heating-cooling cycles. Abrupt irreversible changes of the sensor output power were detected during the first heating-cooling cycle. At the same time, color changes of the SPU copolymer were observed in the modified region of the optical fiber. For the next heating-cooling cycles, however, the observed changes were almost completely reversible. This result demonstrates that a low-temperature sensor can be built by utilizing the chromogenic SPU copolymer as the modified cladding material.

Advanced ceramic composites with complex architecture have stimulated interest in innovative embedded fiber optic sensors for in-situ real-time characterization of the structure. Careful selection of a compatible optical fiber material and an inexpensive signal detection technique are most critical factors for successful incorporation of these embedded sensors. The focus of this paper is two-fold. The first reports on the development of a novel optical waveguide consisting of sapphire fiber core and polycrystalline alumina cladding, and how can these fibers be embedded into ceramic composites. The second aspect of this paper is devoted to the application of a novel inexpensive and sensitive signal detection technique, namely, the spatial intensity modulation technique to sapphire optical fibers. This technique is applicable to multimode fibers. It is based on modal power distribution modulation under external perturbations. A theoretical model has been developed to correlate variations in the modal power within multimode optical fibers to the changes induced in the state of the hosting material. Numerical results obtained from the model are shown to be in agreement with experimental observations. This paper provides a novel means to characterize high temperature composites using multimode sapphire optical waveguides.

Embedded fiber-optic sensors offer an attractive method for real-time in-situ characterization of composite materials. The present work is directed toward the development of an appropriate optical waveguide and sensing technique for high temperature ceramic applications. The waveguide consists of a sapphire optical fiber core and polycrystalline alumina cladding. The sensing technique is based on spatial intensity modulation induced within multimode optical fibers. This paper presents a brief description of the optical waveguide fabrication, a theoretical model for spatial intensity modulation (SIM) and experimental verification of SIM in sapphire fibers.