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Surface active agents have been successfully employed in numerous industrial, agricultural and biomedical applications for decades. Trisiloxane surfactants in particular have proved to be exceptionally effective as wetting enhancers; hence the name ‘superspreaders’. Since the early ‘90s these extraordinary surfactants have become an irreplaceable component in various products and processes. However, the true nature of their specific wetting behaviour has not been fully revealed and their underlying wetting mechanisms are still poorly understood despite substantial scientific interest during the last decades. In this thesis is an attempt to shed light on specific wetting and spreading behaviour of trisiloxane solutions. Commercial superspreader products were tested in various environments in order to get further insight into their performance in specific practical applications. Experimental investigation of wetting of superspreader solutions on surfaces of different hydrophobicity and comparison to that of a conventional surfactant revealed superiority of trisiloxanes. Exceptional interfacial activity was explained in terms of the specific chemical structure and ‘T’-shape of the molecule. However, sensitivity of the trisiloxane head to low pH and long-time ageing in aqueous environment was revealed. Performance of binary mixtures of commercial superspreaders and conventional surfactant was also assessed. Behaviour of trisiloxanes in the capillary action was studied. Finally, a comprehensive mathematical model for trisiloxane wetting, which incorporates diffusion as the governing factor of the wetting process, was developed.

The world is embarking into a fossil fuel free environment in which the predominant sources will be renewable and sustainable energies. Since renewable energy is usually associated with their intermittent nature, it is important to always have a backup source of energy in times of need and demand. For this, energy storage is an essential component of any renewable energy system. In times of high demand, where the sun is not shining and the wind is not blowing, the existence of a backup energy supply with easy and fast access is necessary. Thus, Thermal Energy Storage (TES) is one of the proposed solutions to aid in this mismatch in consumption and demand caused by the nature of the green technologies (Ali et al., 2020). TES can be an accompaniment of systems such as a Joule-Brayton cycle, Rankine cycle, a heat pump or even solar collectors. Other applications include systems which focus on heat waste recovery, steam generation for turbines, domestic uses and household heating. Energy from TES can be stored daily, monthly or seasonally. This determines the type and size of the system and whether it is a smaller scale domestic or large scale industrial project (Fang et al., 2017). In all cases, however, its main potential to serve as a tool that saves energy and mitigates climate change, keeping CO₂ emissions minimized, and helping countries meet their established environmental goals. Low grade TES is in increasing importance and therefore remains the focus of this thesis.