Banca de DEFESA: Marcos Fabrício de Souza Aleixo Filho

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Marcos Fabrício de Souza Aleixo Filho
DATE: 11/01/2024
TIME: 15:00
LOCAL: Plataforma TEAMs
TITLE:

Rheological Characterization of Polar Drop Emulsions

KEY WORDS:

Magneto viscous effect, pseudoplasticity, polar droplets, magnetic emulsion, interfacial tension, stress relaxation, linear viscoelasticity.

PAGES: 170
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

In this dissertation, the rheological behavior of polar droplets emulsion is experimentally characterized through the use of a parallel disk rheometer equipped with a magnetic cell. The emulsions treated vary in terms of the ratio of viscosities be-tween the fluid inside the droplet and the surrounding liquid. In this context, four emulsions were generated, each with its defined viscosity ratio and different from each other, but all with the same drop volume fraction (5% v/v). Static microscopy tests were performed to determine the average diameter of the drops, as well as its polydispersity. When an external magnetic field was applied, the size distribution of the chains formed by the polar drops was also verified. Three experimental methodologies were used to characterize the rheological behavior of the emulsions. The first refers to tests under permanent shear conditions in the absence and presence of a magnetic field. With this, one can examine the behavior of the apparent viscosity and of the shear stress of the emulsions as a function of the shear rate and the intensity of the magnetic field. This allows the verification of the adherence of the rheological behavior of such fluids to generalized Newtonian fluid models. Furthermore, comparisons of viscosity behavior in the absence of an external magnetic field with Taylor's infinitely dilute emulsion model are performed. The second methodology concerns experimental tests with time dependent flows, in a step-strain impulse regime in the presence of a magnetic field. From this experimental analysis, for an emulsion with a fixed viscosity ratio, its stress relaxation functions dependent on the intensity of the applied external magnetic field were obtained. The associated relaxation times were calculated. The third methodology refers to oscillatory shear tests in the presence of an external magnetic field, in a linear viscoelastic regime. From this methodology, the viscoelastic modules were obtained for a polar emulsion with a defined viscosity ratio. Such material functions were obtained as a function of the frequency and intensity of the magnetic field in a condition of small deformations. The existence of elastic shear modulus was observed when the polar emulsion is placed in the presence of an external magnetic field, which indicates the presence of microstructure induced by dipolar interactions. It is also noted that the application of the magnetic field injects elasticity into the dynamic system of the emulsion, which is corroborated by the fact that non-zero relaxation times were obtained from experimental tests. Compatibility checks between the complex viscous modulus and apparent viscosity for equal values of frequency and shear rate are carried out and, based on this, the first normal stress difference is calculated using Laun's rule.

COMMITTEE MEMBERS:
Presidente - 1170729 - FRANCISCO RICARDO DA CUNHA
Interno - 2730343 - RAFAEL GABLER GONTIJO
Externo ao Programa - 3087995 - ANDRE VON BORRIES LOPES - UnBExterno à Instituição - GESSE ARANTES DE ROURE NETO