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| Author(s): |
Tatiana Porto dos Santos
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia de Alimentos |
| Defense date: | 2021-04-20 |
| Examining board members: |
Rosiane Lopes da Cunha;
Maria Claudia Cuellar Soares;
Lucimara Gaziola de la Torre;
Carolina Siqueira Franco Picone;
Márcio da Silveira Carvalho
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| Advisor: | Rosiane Lopes da Cunha |
| Abstract | |
The ability of formation and stability are fundamental attributes to be investigated during the development of emulsions aiming at technological applications. Notwithstanding, in other processes, such as fermentative and petroleum-related, in which the production or extraction of nonpolar compounds is triggered, the minimum stability of the emulsions inherent to the process is desirable in order to increase the oil recovery. In this sense, the evaluation of emulsion stability is of paramount importance to determine the optimized composition depending on the characteristics of the sought-after emulsion. Furthermore, unraveling the mechanisms of (de)stabilization would be of outmost value for the development of these important colloidal systems. In this light, strategies based on microfluidics were applied to the investigation of droplets (de)stabilization, since this technology can achieve both the formation of emulsions and their efficient separation of phases. Due to the above, the present study aimed to investigate the (de)stabilization of model emulsions (using conventional surfactants or tensoactive agents of fermentative systems as stabilizers) in microfluidic channels. In such devices, the applied strategies were mainly related to changes in the geometry and surface properties. However, the addition of external agents (aqueous solutions) was also performed to induce the destabilization even of the most stable emulsions. Therewith, it was possible to identify the main parameters related to the mechanisms of emulsion (de)stabilization, in addition to determining the flow conditions and set of channels most suitable for inducing this phenomenon. Overall, it was observed that glass microcapillaries were not efficient to evaluate the events of coalescence due to the 3D geometry, while planar channels (whose dimensions can be modified) were most suitable to assess the destabilization phenomena. Moreover, it was verified extreme difficulty in destabilizing emulsions (especially those with a high concentration of stabilizing agents) using microdevices inducing the contact between the droplets. Nonetheless, such destabilization was achieved through the forced injection of aqueous solution in concentrated droplets. Indeed, depending on the aqueous solution added (saline solution or water), varied mechanisms of destabilization were visualized (fracture, droplet burst on the channel surface and/or coalescence). Such mechanisms were also dependent on the surface properties of the microchannels (zeta potential and hydrophobicity). Therefore, understanding the role of the microchannel wall was essential to induce both formation and destabilization of the droplets, allowing modulating the kinetic stability of the emulsions. In general, it was found that charged stabilizing agents must have charges of the same signal as microchannels to allow droplets formation. In addition, the continuous phase of the emulsions must have the same nature (polar or nonpolar) as the channel surface. On the other hand, adherence of oil droplets on the device walls was observed on two occasions: (i) when the microchannels possessed both high hydrophobicity and reduced surface charges and (ii) when the emulsion droplets had opposite charges to those of the walls of the microchannels. Ultimately, this study allowed indicating the use of channels coupled in series to determine the stability of the droplets; however, it was emphasized that a prior understanding of the potential interactions between the droplets and the channels needs to be accomplished (AU) | |
| FAPESP's process: | 17/18109-0 - Development of an emulsion stability analyzer from microfluidics |
| Grantee: | Tatiana Porto dos Santos |
| Support Opportunities: | Scholarships in Brazil - Doctorate |