ABSTRACT
Neutrons produced by reactors and spallation sources, and x-rays produced by synchrotron sources, have wavelengths in the range of 0.1-1 nm, making the scattering experiments a powerful and versatile probe of nanoporous materials. In fact it is hard to „nd a comprehensive paper on some aspect of con„nement on the nm scale that does not include references to scattering measurements. A case in point is the excellent topical review of Alcoutlabi and McKenna1 dealing with the effects of size and con„nement on the melting temperature Tm (always depressed) and the glass transition temperature Tg (may increase, decrease, remain the same, or even disappear). Among other scattering results they refer to the work of Morineau et al.,2 who measured the density of con„ned liquid toluene through changes in the Bragg peak intensity in neutron diffraction measurements resulting from the change in contrast with the con„ned liquid. Whereas little or no changes were observed for con„nement in mesoporous silicates with pore sizes of 3.5 nm and above, a decrease in density and an increase of 30 K in Tg were observed upon con„nement in 2.4 nm pores. Alcoutlabi and McKenna also refer to the inelastic neutron scattering (INS) studies of Zorn et al.3 who observed a decrease in Tg on the con-„nement of salol in microporous silica glass together with a broadening of the relaxation spectra. These effects were discussed in terms of a cooperativity length scale that, since it cannot become larger than the con„ning dimensions, leads to an acceleration of the molecular dynamics compared with the bulk.
