STRUCTURE AND DYNAMICS OF CONFINED H_2O AND D_2O IN CEMENT PASTE MATRIX STUDIED BY QUASIELASTIC AND INELASTIC NEUTRON SCATTERING

摘要

Understanding the state of hydration water in cements, the dynamics of water confined in nanopore structures, and the two-step dynamic process similar to the one in glasses and known as β- and α-relaxation is a topic of high fundamental interest in condensed matter physics. Aside from being theoretically challenging, it also has a broad range of applications. The results of a scientific research conducted in the frame of an international cooperation at the European Union Center of Excellence (CEX-IDRANAP) of IFIN-HH are given in this paper. Quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS) are very powerful tools for studying the dynamics and structure of condensed matter from simple liquids to the very exciting phenomena related to the supercooled state, nanostructure and fractal nucleation. QENS and INS experiments on hydrated cement pastes after a long aging time were performed using the TOF spectrometer DIN 2PI at IBR-2 reactor, JINR Dubna. Our experimental results confirmed the conclusions of the recent theoretical and MD simulation papers on the existence of supercooled water confined in the matrix structure of cement. A wave vector transfer Q dependence of the dynamic structure factor S(Q, ε) at constant energy transfers ε = hω revealed a nanometric structure where the water molecules were trapped in the nanoporous matrix. The water dynamics resembled the relaxing cage model. In the short term, the orientation of the water molecule considered was fixed by H-bonds (H-B) to its neighbors and the molecule performed harmonic oscillation around H-B. In the longer term, the bonds broke, the trap began to relax, and the molecule was able to reorient losing memory of its initial orientation. The relaxation dynamics suggested the existence of a fractal process.