Geopolymers have received a lot of attention in the recent years, due to their technological properties, such as low weight, mechanical resistance, and extreme versatility. They are obtained through a polycondensation reaction from silico-aluminate raw materials, with the aid of basic solutions containing cations such as Na, Ca, and/or K. They have an amorphous or semi-crystalline structure, which strongly depends on the synthesis conditions (type and amount of activator, pH and calcination temperature). The local structure of geopolymers is usually studied by means of solid state NMR, but it may also be useful to understand more about the relationship between the very local (as shown by NMR) and the medium-range structure. They both can be obtained by means of total scattering measurements (either X-ray or neutron), with the EPSR (Empirical Potential Structure Refinement, Soper et al. 2007, and references therein) approach. There are only 4 papers in the literature using the total scattering approach (3 by the same group, see White et al, from 2010 to 2013), mainly studying geopolymers local structure as a function of temperature, concentrating mainly on the onset of crystallisation and on the fully crystallised sample. They showed that there is a strong dependence on the presence of Na or of K in their samples. No paper is reported for EPSR approach on the amorphous or semi-crystalline geopolymer, which is in fact the most interesting one for the possible practical applications. Geopolymers with various Si/Al ratios, balanced by means of Na or K cations, were synthesized; some of them were functionalized, through the replacement of some of the inorganic silicon with 3aminopropyl-substituted silicon (with various degrees of replacement). The samples were analysed by means of high-energy X-ray total scattering (at the beamline ID11@ESRF in Grenoble), and the corresponding Pair Distribution Functions (PDF) were produced. A preliminary analysis was performed, by comparing the PDFs and by evaluating the main cation-oxygen distances.
Soper, AK, 2007 J. Phys.: Condens. Matter, 19, 415108 http://dx.doi.org/10.1088/0953-8984/19/41/415108
White, Claire E.; Provis, John L.; Bloomer, Breaunnah; Henson, Neil J.; Page, Katharine, Physical Chemistry Chemical Physics (2013), 15(22), 8573-8582.
White, Claire E.; Provis, John L.; Proffen, Thomas; van Deventer, Jannie S. J., Journal of the American Ceramic Society (2010), 93(10), 3486-3492.
White Claire E; Provis John L; Bloomer Breaunnah; Henson Neil J; Page Katharine, Physical chemistry chemical physics : PCCP (2013), 15(22), 8573-82.