Nanostructure of matrices for sulfur constructional composites: methodolody, methods and research tools

Complex of operational properties of sulfur-based and sulfur-extended building materials may lead both to economical efficiency of construction and to reduced load on the environment. The feasibility of the sulfur-extended materials is primarily caused by properties, availability and low cost of sulfur. Before the development of building material it is necessary to examine the supramolecular structure of the matrix in detail. Material science of sulfur is still with several ?white spots? which have to be filled with sound knowledge and reproducible data. New level of the research in constructional material science can be achieved with help of system analysis. The key prerequisite for successful application of system analysis in material science is the determination of primary interactions which, in turn, define applicable modeling methods. Several investigation methods can be used at the nanoscale level ? traditional experimental methods, quantum chemistry modeling, molecular dynamics. The methodology of research depends on objectives and also on acceptable values of time and resource consumption. Requirements for precision and reproducibility, together with demands for new scientific data must also be taken into consideration. In the present work we have presented different strategies of investigation: case for dominance of practice, case for high demands for new scientific data and the case for high demands for precision, reliability and reproducibility. The latest case is the preferable one, and it was used during investigation of the nanostructure of sulfur binder. Three different methods of research were applied: Raman spectroscopy, quantum chemistry simulation and molecular dynamics. It was demonstrated again that broadly available technical sulfur corresponds to orthorhombic allotrope; at the same time, comparative analysis of the Raman spectra reveals that bending of long sulfur chains in technical sulfur takes place in less constrained conditions. For the quantum chemistry computations three different software tools are used; the capabilities of accompanying pre- and post-processing tools are discussed. It is shown during analysis of quantum chemistry calculations that verification of the experimental Raman spectra should not be performed with results obtained for isolated S8 molecule. Results of simulation performed for the sulfur crystal are close to the experimental measurements; such correspondence is an important proof of conformity between lattices of real crystal and model. During molecular dynamics simulations it is found that such methods can successfully be used only on the spatial scales starting from 10 nm, whereas on the lower scale the quantum effects must be taken into account.