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Manufacture and stabilisation of highly concentrated emulsions using polyhedral oligomeric silsesquiozane nanomolecules
The subject of this current study concerns highly concentrated emulsions of the explosive grade. A distinguishing characteristic of these systems is a high internal to external phase volume ratio. The volume fraction of the aqueous phase of such an emulsion generally far exceeds the close packing limit. Continuous phase of the system is a supersaturated aqueous solution of ammonium nitrate inorganic salt. In combination with high internal phase concentration, this inevitably leads to the destabilisation of the system. The thermodynamic instability of such systems is attributed to two major factors: 1) crystallisation of dispersed phase and 2) coalescence of the individual droplets within the bulk. This poses a significant problem since destabilisation of the bulk emulsion in turn leads to partial or complete loss of sensitivity to detonation of the final product of which highly concentrated emulsion is the base. Since the invention of such types of bulk explosives, a considerable and on-going effort has targeted the improvement of the stability of these systems, with a scope primarily focused on the use of various surfactant agents with different properties as well as stabilising mixtures containing numerous surfactants. In recent years, a new approach has been explored: the stabilisation of highly concentrated emulsions with the use of solid fumed silica nanoparticles. This is a promising new field of study, already being implemented by manufacturers and actively developing. The focus of this present study is to investigate and lay the ground work for further research in the principally new approach towards the stabilisation of highly concentrated emulsions with the use of the polyhedral oligomeric silsesquiozane nanomolecules. These are unique compounds possessing hybrid inorganic-organic structures and properties, and carrying a range of advantages over currently implemented surfactants. As opposed to silica nanoparticles, these compounds are not solid particles but can be regarded as molecular silica. This investigation will focus on the general possibility of implementation of such compounds as stabiliser agents for emulsions in general, and highly concentrated emulsions of the explosive grade in particular, and the resultant effects on the stability. Effects on stability will be investigated both when used solely and in combination with common surfactants. In addition, stability both on shelf and under stress will be investigated within the framework of the study.