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Metachromatic Materials

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Final progress rept. 01 Jun 2001-13 Nov 2002

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The primary goal of the work performed under this contract was to study the feasibility of using metal nanoparticles as contrast agents ink in full-color, flexible, reflective, low-power, electronic displays. The concept is based on the tunability of the plasmon absorption peak in metal nanoparticle ensembles. Well-separated, nanometer-sized fragments of Au, Ag, or Cu have intense plasmon absorptions in the visible part of the spectrum. The extinction coefficient, the frequency of maximum absorbance, and the full width at half maximum of the plasmon peak all depend on the sizes of the nanoparticles. As the nanoparticles increase in size from 2 to 20 nanometers, the peak becomes sharper and more intense. The spectral position of the peak remains relatively unchanged over this size range. As particles are brought into close proximity--less than 3 diameters between their respective centers--the position of the plasmon peak red-shifts, leading to a dramatic change in color. The magnitude of the shift and the color change is proportional to the extinction coefficient of the nanoparticles. Because larger particles have larger extinction coefficients and smaller widths at half maximum, they are expected to be best-suited for metachromatic color-changing applications. To prove the possibility of using this plasmon shift in an electronic display, the authors set out to develop a scheme to electrically control the distribution of and distances between metal nanoparticles in soft matrices. One of the most intriguing possibilities was the use of supported bilayer lipid membranes BLMs as two-dimensional fluids to confine the nanoparticles without completely eliminating their mobility. Previous studies at Stanford University showed that BLMs could be patterned under certain conditions and that the patterning resulted in diffusional barriers to molecules attached to the membranes. The authors set out to reproduce these results in their laboratory. 5 figures, 13 refs.7

Subject Categories:

  • Physical Chemistry
  • Electrical and Electronic Equipment
  • Plasma Physics and Magnetohydrodynamics

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