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CRYOPOROSIMETRY

CRYOPOROSIMETRY. 5.1. - Surface atoms have fewer inter-atomic bonds with respect to bulk ones. - They are characterized by higher energy contents. - Lattice break-down on crystal surface requires less energy with respect to bulk lattice break-down. E.

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CRYOPOROSIMETRY

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  1. CRYOPOROSIMETRY 5.1 - Surface atoms have fewer inter-atomic bonds with respect to bulk ones. - They are characterized by higher energy contents. - Lattice break-down on crystal surface requires less energy with respect to bulk lattice break-down. E It is based on the melting temperature (T) and enthalpy (Dh) reduction with crystal radius1(R). -This effect becomes relevant only when the number of surface atoms is not negligible compared to that of the bulk atoms (nano-crystals)2.

  2. 5.2 glv Vapour Liquid drop q gsv gsl Solid substrate YOUNG EQUATION3 Pure Substance q = 0 ===>

  3. R R = infinite TOLMANN EQUATION4 g = surface tension (N/m) (J/m2) g = surface tension (N/m) (J/m2) d = Tolmann length ≈ molecule diameter/3 d≈ 0.0681 nm for water

  4. 5.3 ice water β Three configurations can take place R Cylindrical mesh Rp Spherical mesh excess water no excess water Water iced inside a mesh (pore)1 Rp= mesh radius β= thickness of non-freezable water layer( R independent) R = nanocrystal radius = R-β

  5. Spherical mesh Cylindrical mesh, excess water Cylindrical mesh, with water in excess Zhang equation5

  6. Depends on pores geometry: for cylindrical pores for cubic or spherical pores Heating power provided by DSC melting temperature; Rp dependent Heating speed (experimental) Ice density; T dependent Thickness of liquid layer; calculated iteratively Melting enthalpy; evaluated according to Zhang5 Mesh size distribution6(dVf/dRp) by DSC experiments:

  7. Normalised Differential distribution Probability of finding a crystal or radius Rm

  8. 5.4 DSC RESULTS Water in excess EXAMPLE: SILICA

  9. DSC TRACE REFERRING TO WATER TRAPPED INSIDE NANO-PORES EXAMPLE: SILICA

  10. EXAMPLE: INTERPENETRATED NETWORK (ALGINATE-DEXTRAN METHACRYLATED ALGINATE CROSSLINKING: CaCl DEXTRAN METHACRYLATED CROSSLINKING: UV LAMP IRRADIATION

  11. D500MA30%

  12. REFERENCES • Brun, M., et al. J. de Chimie Physique, 1973, 70(6), 979. • Huang W.J., et al., Nature Materials, 2008, 7, 308. • Adamson, A.W., Physical Chemistry of Surfaces, 4° ed., John Wily & Sons, New York, 1982. • Tolman, R. C., Journal of Chem. Phys., 1949, 17, 333. • Zhang M., et al., Physical review B, 2000, 62(15), 10548. • Ishikiriyama K., et al., J. Colloid and Interface Science, 1995, 171, 92.

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