Negative Poisson's ratios in siliceous zeolite MFI-silicalite

Brillouin scattering measurements of the single-crystal elastic properties of the as-made zeolite silicalite vertical bar(C3H7)(4)NF vertical bar(4)[Si96O192]-MFI provides the first experimental evidence for on-axis negative Poisson's ratios (auxeticity) in a synthetic zeolite structure. MFI laterally contracts when compressed and laterally expands when stretched along x(1) and x(2) directions in the (001) plane (nu(12)=-0.061, nu(21)=-0.051). The aggregate Poisson's ratio of MFI, although positive, has an anomalously low value nu=0.175(3) compared to other silicate materials. These results suggest that the template-free MFI-silicalite [Si96O192] might have potential applications as tunable sieve where molecular discriminating characteristics are adjusted by application of stress along specific axes. (C) 2008 American Institute of Physics