Optically Transparent Composites Reinforced with Networks of Bacterial Nanofibers

Abstract

sist was spin-coated on the surface of PEG-modified silicon wafers. After exposure to UV light under a photomask, the wafers were immersed in developing solution and then etched via wet etching. The remaining photoresist was removed using acetone.Self-Assembly of Protein/Silica Nanoparticles in Microwells: The etched silicon wafer was rinsed three times with deionized water, followed by drying of the wafer with dry air. The wafer was immersed in a freshly prepared 1 mg mL ±1 solution of protein/silica nanoparticles for 6 h at room temperature. Then, the wafer was rinsed carefully in deionized water and sonicated in deionized water for 5 min to remove free nanoparticles.Atomic Force Microscopy (AFM) and Fluorescence Microscopy Measurements: The tapping mode AFM images were taken using a Digital Instruments Nanoscope IIIa DIMM AFM atomic microscope operating at room temperature with an image resolution of 256 pixels 256 pixels at a scan speed of 0.7±1.2 Hz in air. Light and fluorescence photographs were obtained using an Axiostar plus fluorescent microscope with a color charge-coupled device (CCD) camera and image-acquisition system. Mechanical reinforcement of optically functional materials is of significant interest to various industries due to the rapid expansion of related devices, such as displays. Nanocomposite materials with components less than one-tenth of a wavelength in size are free from scattering, making them acceptable for a variety of optical applications. [1,2] Since fibers could provide the desired mechanical reinforcement of optically functional materials, reinforcement using nanofibers of electrospun nylon-4,6 has been studied. An optically transparent composite was obtained at a fiber content of 3.9 %, [3] but an inevitable difficulty remains in the way of obtaining highfiber-volume composites without losing transparency. Herein we report the first example of a transparent composite reinforced with bacterial nanofibers. The composite is optically transparent at a fiber content as high as 70 %, with a low thermal-expansion coefficient (similar to that of silicon crystal) and a mechanical strength five times that of engineered plastics. These significant improvements in the thermal and mechanical characteristics of the composite are due to the web-like network of the semicrystalline extended chains of nanofibers, produced by the bacterium Acetobacter xylinum (Glucronobacter aceti). The nanofiber-network-reinforced polymer composite maintains its transparency. It is light, flexible, and easy to mould, thus making it an excellent candidate COMMUNICATIONS

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