Agglomeration in dimethyl sulfoxide and water binary System: A comprehensive study through thermodynamics, vibrational spectroscopy, quantum mechanical calculations and morphology

Some nano- or micro-sized agglomerates with different morphologies in the dimethyl sulfoxide (DMSO) and water binary system at different molar fractions were characterized using Scanning Electron Microscope (SEM) and Dynamic Light Scattering (DLS) for the first time. Four fundamental clusters with the composition of [(DMSO)₂], [(DMSO)₃], [(DMSO)₂ ∙ H₂O] and [(DMSO)₃ ∙ H₂O] were identified through the combination of quantum mechanical calculations and vibrational spectroscopy. These clusters act as seeds for the growth of agglomerates both in pure DMSO and in DMSO-water binary mixtures. According to SEM images, the morphology of the agglomerates varies with the molar fraction, wherein two main kinds were observed, viz. one growing from the center and spreading out to the surrounding, and the other growing into a chain-like structure. Inter-cluster and/or inter-agglomerate interactions are responsible for the molar fraction dependence of density, viscosity and other related thermodynamic properties. The present work is the first to study the morphology of agglomerates in the DMSO-water binary system and the first to propose the essential roles played by four dominant clusters in the agglomerating process.