Esposito, Rodolfo (2023) Structural and dynamic study of the molecular mechanism of superspreading: towards the rational use of new eco-friendly wetting agents. [Tesi di dottorato]

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In the last years, an increasing attention towards environmental issues is steering the scientific and technological research. The need to protect human and environment health and to avoid the widespread use of substances obtained by non-renewable sources has prompted the research towards the discovery and development of new sustainable molecules characterized by high biocompatibility and biodegradability, obtained by a natural origin or a synthetic route based on green chemistry principles. In this framework, the present PhD thesis focuses on the physico-chemical characterization of sustainable eco-friendly surfactants and their use as spreading agents with the aim to exploit the acquired scientific and technological expertise for the rational design of eco-friendly wetting formulations. In the various chapters of this thesis, it was shown that bio-inspired glycosurfactants and natural glycolipids have physico-chemical features comparable to (or even better than) those of conventional surfactants, presenting at the same time a significantly improved ecological footprint. Great attention is posed on rhamnolipids, amphiphiles produced by Pseudomonas aeruginosa and nowadays available at a large scale thanks to optimized biotechnological production processes. The lower eco-toxicity of rhamnolipids compared to synthetic surfactants was preliminarily confirmed by a combination of biological assays. A deep and wide physico-chemical characterization of rhamnolipid behavior in aqueous solution highlighted on the one side features similar to those of conventional surfactants, such as the surface tension lowering and the supramolecular aggregation above a well-defined cmc, while on the other side specific properties were found, such as the co-existence of small micelles with larger aggregates even close to the cmc. More importantly, rhamnolipids were found to be a promising wetting agent, lowering the contact angle between aqueous solutions and a variety of solid supports much more effectively than synthetic surfactants. Importantly, rhamnolipids were found to co-micellize with both anionic and cationic surfactants. This capability is of great importance for applications in industrial formulations, in which the possibility to mix different surfactants offers the opportunity to design mixtures optimized for each specific tasks. Overall, the results presented in this thesis contribute to build a robust platform for the rationalization of the use of surfactants projected towards the design of a new-generation of “green” chemical formulations. Bio-inspiration could represent a strategy to face environmental issues, even though the production of the bio-inspired surfactants is still nonrenewable resource based. Biosurfactants at contrary offer several advantages, such as bio-sustainable production processes, reduced emissions, reduced environmental impact, high biodegradability, low toxicity and, particularly, excellent physico-chemical properties as wetting agents which definitely point to their implementation in chemical formulation industry.

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