Landman, Marile2026-01-282026-01-282019-04-112018-06*A2019http://hdl.handle.net/2263/107663Thesis (PhD)--University of Pretoria, 2018.The polyisobutylene succinic anhydride (PIBSA) surfactants have been used for decades to attain kinetic stability in ammonium nitrate (AN) based emulsions. There are a number of studies concerned with the structure activity relationship and mechanism of surfactant rendered stability. However, the reported surfactant structures are inconsistent and a relation of structure to emulsion stability is yet to be established. This defined two main objectives of this thesis: to confirm the structure of PIBSA surfactants (the experimental study), and to establish a direct link between the structure and efficiency (the theoretical part). Experimentally, based on the detailed analysis of the precursors and by chromatographic separation, the structure of the most effective surfactant in the series, the monoethanolamine (MEA) adduct of PIBSA (PIBSA-MEA), was resolved in this study. The proposed structure is consistent with the products of the classic Alder-ene thermal maleation step, followed by the regioselective ring fission of succinic anhydride. By analogy, structures were assigned to surfactants branded as PIBSA-IMIDE and PIBSA-UREA. Based on the nuclear magnetic resonance structural assignments, a novel semi-quantitative method was developed; and the estimated content of the surfactants, relative to the unreacted materials in the industrial concentrates, was found to be below 27 mole percent. The theoretical study focused on the surfactant series with known efficacy: PIBSA-MEA, PIBSA-UREA, PIBSA-IMIDE and PIBSA-DEA. With practical application in mind, and based on our experimental results, model surfactants with a partly truncated side chain were used to study electronic structures with density functional theory (DFT), and to predict likely ionization states of the surfactants in the gas phase. The order of the calculated dipole moment, which was the highest in the amide-bearing surfactants (e.g. PIBSA-MEA and PIBSA-UREA), followed the experimental surface activity trend. Surface affinity of the untruncated surfactants with the simulated surfaces of aqueous ammonium nitrate, water, and growth faces of ammonium nitrate was then probed with Molecular Dynamics using condensed phase optimised Compass force-field. Surface adsorption energies were used to compare the efficacy. Discrimination between water and ammonium nitrate ions and the electrostatic interactions were found to be the key factors driving the values of the interaction energy within the surfactant-oxidizer system.en© 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.UCTDSurfactantsComputationalExcplosivesNMRDFTThesis97174565N/A