We have developed a thermal insulation based on bi-component fibers that adapts to its thermal environment, providing greater insulation at low temperatures than at warmer temperatures. The analysis of bi-metallic strips done by Timoshenko [1] for strips of rectangular cross-section concluded that "…curvature is proportional to the difference in elongation of the two metals and inversely proportional to the thickness of the strip." We have extended Timoshenko's formulation and applied it to bi-component fibers of circular and triangular cross-sections. In each case, the curvature resulting from the balance of the axial forces and bending moments has been brought into a standard form inversely proportional to (A+Bn+C/n) where n is the ratio of the moduli and A, B, and C are functions of the geometry of the two components. An important consequence of this result is that for any "n" there is a maximum curvature where (A+Bn+C/n) is a minimum. We have used the process of melt-spinning to produce fibers with circular and triangular cross-sections, varying the proportion of the two components. The polymers used have widely different coefficients of thermal expansion. These fibers spontaneously form mats at room temperatures. The experimentally measured thickness changes are in good agreement with the analytical results for fiber bending. The most effective samples to date change thickness by more than 1.5% per degree C (30% over a temperature range from approximately 20 o C to 0 o C).

For the purpose of producing polymer ribbon/polymermatrix composites, we manufacture rectangular cross section ribbons directly by spinning from a rectangular die. A range of optical techniques, including the interferometric measurement of filament refractive index and characterization of composite optical performance through the modulation transfer function, are employed to quantify properties and guide system design. The interferometric measurements revealed that, compared with previous mechanically worked filaments, the die spun filaments have a more uniform optical path across the fiber. These measurements also enabled characterization of the filament's chromatic dispersion and allowed for matching the matrix refractive index across the visible spectrum. The results show that composites manufactured from rectangular die-spun ribbons have excellent optical properties with a significant optical performance improvement over previous work. POLYM. COMPOS., 39:2523-2534

We report on a new textile metamaterial created by adding metal wires directly into the polymer yarn. Split-ring resonator-like extended states are created. Simulations revealed that the extended states can be easily tuned via the geometry. Measurements of the transmittance spectrum as a function of the polarization angle in the low terahertz range were also performed and these peaks were ascribed to a polarization-dependent resonator model. The fabrics are viable candidates for flexible and deformable gigahertz and terahertz-enabled metamaterials.

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