Caiazza, Carla (2017) Use of advanced microscopy and microfluidics to study liquid process transformations in wormlike micellar systems. [Tesi di dottorato]

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Item Type: Tesi di dottorato
Lingua: English
Title: Use of advanced microscopy and microfluidics to study liquid process transformations in wormlike micellar systems
Creators:
CreatorsEmail
Caiazza, Carlacarla.czz@hotmail.it
Date: 9 December 2017
Number of Pages: 145
Institution: Università degli Studi di Napoli Federico II
Department: dep08
Dottorato: phd038
Ciclo di dottorato: 30
Coordinatore del Corso di dottorato:
nomeemail
Mensitieri, Giuseppegiuseppe.mensitieri@unina.it
Tutor:
nomeemail
Guido, StefanoUNSPECIFIED
O'Sullivan, DenisUNSPECIFIED
Guida, VincenzoUNSPECIFIED
Date: 9 December 2017
Number of Pages: 145
Uncontrolled Keywords: surfactants; wormlike micelles; shear banding; microfluidics; rheology; CFD; concentration gradients;
Settori scientifico-disciplinari del MIUR: Area 09 - Ingegneria industriale e dell'informazione > ING-IND/24 - Principi di ingegneria chimica
Date Deposited: 06 Jan 2018 02:49
Last Modified: 05 Apr 2019 10:10
URI: http://www.fedoa.unina.it/id/eprint/12102

Abstract

During the last decades, solutions of wormlike micelles have been successfully used in a number of diverse applications, for instance as proppants in oil industry, drag-reduction agents, heat-transfer fluids, and carrier in drug-delivery systems. One of the most extensive use of wormlike micelles is as additives in a wide variety of consumer goods, including hard-surface cleaners, dish-wash and laundry-detergents, body-soaps and shampoos. In fact, thanks to their reological properties, they act as thickener in such products, thereby ensuring the possibility to properly tune the viscoelastic behaviour of the final formulation. This is a particularly critical aspect for home-care and personal-care products, as high viscosity is desired to increase their stability, and to suspend particles, colorants and perfumes in the solution; on the other hand, elastic properties are required to ensure a proper dosage of the product, which otherwise couldn't flow through the pump of a dispenser, or would form filaments after being squeezed out of a bottle; finally, viscoelastic products appear more appealing to consumers. The widespread utilization of wormlike micelles is at the base of an huge industrial interest in understanding the flow-behaviour of these solutions. In fact, a constitutive model which describes these systems would allow a predictive analysis and modelling of the operation-units involved in manufacturing processes, such as pipes, tanks and static mixers, pumps and injector-nozzles, giving the possibility to predict industrially-relevant quantities, such as blending and pressure-drop. On the other hand, wormlike micellar systems generated a considerable interest in the basic research world, thanks to their rheological and flow-properties, characterized by the occurrence of several flow-instabilities, some of which haven't been observed in other complex fluids, and which look ubiquitous in such systems. In fact, due to the effect of the flow-deformation on the microstructure of the solution, wormlike micelles show a complex non-linear flow-behaviour even under very simple flow-conditions. Nowadays, many of these flow-induced phenomena have been extensively reported in a variety of systems, and studied by varying the physico-chemical parameters of the solution, the flow-conditions, and the analytical techniques. In spite of all these efforts, there is still no constitutive model which allows one to predict the onset of flow-instabilities under strong-flows. In fact, the physical nature of these phenomena have not been fully elucidated yet, and, even if several mechanisms have been proposed, the debate is still open. In this scenario, microfluidics has emerged in the last decade as a powerful tool to get a deeper insight into the flow-behaviour of wormlike micellar solutions. In addition to the well-known advantages allowed from this techniques - low costs, chemical consumption and experimental time, and small space required for the setup - microfluidic devices show features which make them an elite instrument to investigate wormlike micellar solutions, as the high confinement of the flow-geometry facilitates the onset of the surface-force driven instabilities; furthermore, they can easily be coupled with many optical techniques, enabling unique flow-visualization possibilities. Here, microfluidics is coupled with advanced microscopy, in order to get a deeper insight into the flow-behaviour of a wormlike micellar model system. Thanks to direct visualization of the flowing solution, the onset of flow-induced structuring has been detected, and its effects on the velocity-profiles have been analysed. The effects of confinement are then analysed by scaling the flow-geometry up to pilot-scale. On the other hand, a complete rheological characterization of the model system is reported. By matching several measurement-techniques, a new approach to high-shear rheology is implemented. The measurements so-obtained, together with a complete study of the wall-slip behaviour of the solution, are then used to model the flowing solution, by using the a software for computational fluid dynamics (CFD) analysis. The prediction of this analysis are then compared to experimental results. Lastly, the onset of demixing-phenomena has been detected in a complex microfluidic device, by coupling microfluidics, rotational rheometry, electrical-conductivity and dry-mass measurements.

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