Avossa, Joshua (2017) Imparting superhydrophobic properties through janus wrinkled silica-gel particles. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Resource language: English
Title: Imparting superhydrophobic properties through janus wrinkled silica-gel particles
Avossa, Joshuajoshua.avossa@unina.it
Date: 11 December 2017
Number of Pages: 126
Institution: Università degli Studi di Napoli Federico II
Department: dep08
Dottorato: phd038
Ciclo di dottorato: 30
Coordinatore del Corso di dottorato:
Mensitieri, Giuseppemensitie@unina.it
Branda, FrancescoUNSPECIFIED
Mensitieri, GiuseppeUNSPECIFIED
Date: 11 December 2017
Number of Pages: 126
Keywords: Superhydrophobic; wrinkled; particles, Janus
Settori scientifico-disciplinari del MIUR: Area 09 - Ingegneria industriale e dell'informazione > ING-IND/22 - Scienza e tecnologia dei materiali
Date Deposited: 08 Jan 2018 01:28
Last Modified: 15 Jan 2021 02:00
URI: http://www.fedoa.unina.it/id/eprint/12190

Collection description

In nature, superhydrophobicity is associated with a number of possible evolutionary benefits that may be bestowed upon an organism, ranging from the prevention of encumbrance by water droplets, self-cleaning and removal of particulates and potential pathogens, and even to antimicrobial activity. Superhydrophobicity is a surface related property, where droplets of water easily roll-off without stickicking or wetting the surface and can be achieved through hierarchical textured and low surface tension materials. The interest in this kind of behaviour comes from the possibility of exploiting superhydrophobic surfaces for many applications in different field (medical devices, infrastructures, fabrics, transports, etc.). In this PhD project (granted by Procter & Gamble), superhydrophobic surfaces were chosen as possible solution of a company’s problem related to the difficulty in emptying of plastic dispensers containing viscous liquid products. Therefore, a possible solution was to render the plastic surface superhydrophobic to reduce the drag and help the easy-emptying of the dispensers. We developed a new type of particles that can impart a superhydrophobic behaviour to the applied substrate. Janus wrinkled silica-gel particles combine all the aspects that are necessary to achieve superhydrophobic surfaces: enabling formation of hierarchical roughness and low surface tension (without using any fluorinated molecule, not allowed in the dispensers manufacturing). Such particles were applied to substrates by drop-casting and dip-coating methods, and through a camera we monitored the behaviour of different water solutions on particles coatings. Superhydrophobic surfaces have been obtained possessing high values of water contact angle and very low values of contact angle hysteresis (2°) and roll-off angle values (1.8°), which are close to zero. These results have been interpreted based on the multiple scales of hierarchical roughness that has been constructed by deposition of the particles. This thesis is divided in five chapters. In chapter 1, superhydrophobicity and how nature and man exploit this surface property are described so as methods to achieve such behaviour. Then, 10 the easy-emptying issue is discussed and the use of Janus wrinkled silica-gel particles as possible solution is motivated. Chapter 2 collects the theoretical backgrounds of this multidisciplinary project. Indeed, production of Janus wrinkled silica-gel particles involve different techniques and methods from different branches of science. Superhydrophobicity is described from a theoretical point of view: models and parameters that characterize the wettability of surfaces with regards to liquids are reported. Sol-gel method is briefly described, paying attention to the mesoporous particles formation mechanism. In the end, Pickering emulsion formation, necessary for Janus particles production, is described. In chapter 3, all the synthetic procedures are reported. The chapter is divided in paragraphs that reflects the multi-step synthetic procedure. First the synthesis of wrinkled silica-gel particles, then the formation of colloidosomes by Pickering emulsification of wrinkled particles, wax and water. Subsequently, the surface functionalization for obtaining Janus wrinkled particles. The characterization techniques are described in chapter 4, together with the apparatus used in this work and the sample preparations related to such characterization techniques. We used microscopic techniques as SEM, TEM and AFM for monitoring the structures of particles (SEM, TEM), the hierarchical roughness of the coatings (SEM, AFM) and the Janus nature of the particles (TEM). DLS and Zeta potential measurements were used for monitoring particles size and stability, especially in surfactant dispersions, necessary for Pickering emulsion preparation. ATR and XPS allowed evaluating the presence of functional groups (ATR, XPS) after each functionalization. Chapter 5 collects all the results of Janus wrinkled silica-gel particles: from the particles synthesis, to colloidosomes formation through Pickering emulsion, their functionalization and the particles application as coating on different substrates. In the end, the wettability properties results are reported to verify the excellence of this approach achieving superhydrophobic behaviour by Janus wrinkled silica-gel particles coatings.


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