title: Small angle neutron scattering on an absolute intensity scale and the internal surface of diatom frustules from three species of differing morphologies.
abstract: The internal nanostructure of the diatoms Cyclotella meneghiniana, Seminavis robusta and Achnanthes subsessilis was investigated using small angle neutron scattering (SANS) to examine thin biosilica samples, consisting of isotropic (powder) from their isolated cell walls. The interpretation of SANS data was assisted by several other measurements. The N2 adsorption, interpreted within the Branuer-Emmet-Teller isotherm, yielded the specific surface area of the material. Fourier transform infrared (FTIR) and Raman spectroscopy indicates that the isolated material is amorphous silica with small amounts of organic cell wall materials acting as a filling material between the silica particles. A two-phase (air and amorphous silica) model was used to interpret small angle neutron scattering data. After correction for instrumental resolution, the measurements on two SANS instruments covered an extended range of scattering vectors 0.0011 nm(-1) < q < 5.6 nm(-1), giving an almost continuous SANS curve over a range of scattering vectors, q, on an absolute scale of intensity for each sample. Each of the samples gave a characteristic scattering curve where log (intensity) versus log (q) has a -4 dependence, with other features superimposed. In the high-q regime, departure from this behaviour was observed at a length-scales equivalent to the proposed unitary silica particle. The limiting Porod scattering law was used to determine the specific area per unit of volume of each sample illuminated by the neutron beam. The Porod behaviour, and divergence from this behaviour, is discussed in terms of various structural features and the proposed mechanisms for the bio-assembly of unitary silica particles in frustules.
authors: Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW, 2232, Australia, cjg@ansto.gov.au.
authors: C J
authors: CJ
authors: Garvey
authors: M
authors: M
authors: Strobl
authors: A
authors: A
authors: Percot
authors: J
authors: J
authors: Saroun
authors: J
authors: J
authors: Haug
authors: W
authors: W
authors: Vyverman
authors: V A
authors: VA
authors: Chepurnov
authors: J M
authors: JM
authors: Ferris
mesh_terms: D002473:Cell Wall / Q000737:chemistry*; D017377:Diatoms / Q000166:cytology*; D033363:Neutron Diffraction; D053838:Scattering, Small Angle; D012822:Silicon Dioxide / Q000737:chemistry; D013045:Species Specificity; D013499:Surface Properties
chemical_list: D012822:Silicon Dioxide
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