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Florida State University Libraries Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2019 Detecting Wormlike Micellar Microstructure Using Extensional RheologyRose Omidvar Follow this and additional works at the DigiNole: FSU's Digital Repository. For more information, please contact [email protected] FLORIDA STATE UNIVERSITY FAMU-FSU COLLEGE OF ENGINEERING DETECTING WORMLIKE MICELLAR MICROSTRUCTURE USING EXTENSIONAL RHEOLOGY By ROSE OMIDVAR A Thesis submitted to the Department of Chemical and Biomedical Engineering in partial fulfillment of the requirements for the degree of Master of Science 2019 Rose Omidvar defended this thesis on April 8, 2019. The members of the supervisory committee were: Hadi Mohammadigoushki Professor Directing Thesis Subramanin Ramakrishnan Committee Member Daniel Hallinan Committee Member The Graduate School has verified and approved the above-named committee members, and certifies that the thesis has been approved in accordance with university requirements. ii I dedicate this thesis to my family. iii ACKNOWLEDGMENTS I would first like to thank my advisor Dr. Hadi Mohammadigoushki, for all his continuous help and support throughout this study. His hard work and dedication to research has always been motivating me and I am thankful for the opportunity to work with him. I shall extend my special thanks to dear committee members for taking time and reading this manuscript and helping me improve my work with their valuable comments. Last but not least I would like to thank the department of Chemical and Biomedical engineering for their care and support. iv TABLE OF CONTENTS List of Tables ................................................................................................................................. vi List of Figures ............................................................................................................................... vii Abstract .......................................................................................................................................... ix 1. INTRODUCTION .......................................................................................................................1 2. LITERATURE REVIEW ..........................................................................................................13 3. EXPERIMENTAL REULTS .....................................................................................................24 APPENDIX A. CABER CALIBRATION ....................................................................................42 References ......................................................................................................................................51 Biographical Sketch .......................................................................................................................56 v LIST OF TABLES Table 3.1. List of surfactant solutions studied in this work together with measured and/or calculated rheological parameters ..................................................................................................29 Table A.1. List of Newtonian fluids together with their physical and rheological properties ......50 vi LIST OF FIGURES Figure 1.1. Two plate model ............................................................................................................2 Figure 1.2. Newtonian and non-Newtonian fluids ...........................................................................3 Figure 1.3. Maxwell model ..............................................................................................................5 Figure 1.4. Linear and non-linear viscoelastic regime in SAOS experiment ..................................7 Figure 1.5. Uniaxial extension .........................................................................................................7 Figure 1.6. Spherical micelle formation ........................................................................................10 Figure 1.7. Formation of viscoelastic wormlike micelles by addition of salt and surfactant ........10 Figure 2.1. Falling plate filament stretching rheometer .................................................................14 Figure 2.2. Filament stretching rheometer developed by Tirtaatmadja and Sridhar .....................15 Figure 2.3. Operating space of a filament stretching rheometer and the known instabilities .......16 Figure 2.4. Schematic diagram of capillary break-up extensional rheometer ..............................17 Figure 3.1. Capillary breakup extensional rheometer setup mounted on the optical table ........... 26 Figure 3.2. (a) Steady shear viscosity as a function of imposed shear rate for surfactant solutions. The inset shows the zero shear viscosity as a function of concentration. (b) Storage (G′) and loss (G′′) moduli as a function of angular frequency. The inset shows the shear relaxation time calculated by fitting an n-mode Maxwell model (solid curves) to the data. In (b), filled symbols correspond to the storage modulus and empty symbols denote the loss modulus .........................27 Figure 3.3. TEM images of the wormlike micellar solutions for (a) 1.1 wt % and (b) 3 wt % CTAT in de-ionized water ........................................................................................................................30 Figure 3.4. Filament thinning dynamics for surfactant solutions from the onset of experiments till breakup moment with hi= 1.3 mm and h= 4.2 mm. Images in top row indicate filament dynamics for a surfactant solution that contains 5 wt% CTAT and the bottom row corresponds to 0.8 wt% CTAT in water ...............................................................................................................................32 Figure 3.5. Filament diameter as a function of time for surfactant solutions along with the best fit to Eq. (3): (a) for dilute surfactant solutions, and (b) for more concentrated solutions. ................33 Figure 3.6. (a) Transient extensional viscosity as a function of Hencky strain for surfactant solutions and (b) Maximum Trouton ratio for surfactant solutions as a function of surfactant concentration ..................................................................................................................................35 vii Figure 3.7. Extensional relaxation time as a function of surfactant concentration. Inset shows the ratio of the relaxation times as a function of surfactant concentration ..........................................38 Figure A.1. CaBER setup. (a) Top view. (b) Side View ...............................................................42 Figure A.2. Transient evolution of the filament of a silicon oil as a function of time. tbr refers to the breakup time of the filament. ...................................................................................................44 Figure A.3. MATLAB code ...........................................................................................................45 Figure A.4. Example of edge detection code applied on an image ................................................46 Figure A.5. Detection of upper and lower edge location based on pixels .....................................47 Figure A.6. Example of a Diameter Vs. Time plot by MATLAB .................................................48 Figure A.7. Filament diameter as a function of time for three Newtonian fluids. Lines indicate the linear fit to the experimental data obtained by equation (2.4). ......................................................49 viii ABSTRACT Viscoelastic wormlike micelles are widely used in variety of industrial processes, and daily life applications such as food, paint, pharmacy, oil-field operations and others. Wormlike micelles usually contain surfactant and salts that are dissolved in water at high concentrations. These systems share many similarities with viscoelastic polymer solutions and follow similar scaling laws. However, unlike polymers, micellar chains have the ability to break and reform and for this reason they are also known as living polymers. Many of the above industrial applications, involve continuous shearing and extensional flows of wormlike micelles. Therefore, a fundamental understanding of micellar dynamics in shear and extensional flows is necessary for optimal design of such processes. Dynamics of viscoelastic wormlike micelles have been extensively studied under shear deformations. However much less is known about the behavior of these systems in predominantly extensional flows. Therefore, a fundamental understanding of micellar dynamics and morphological transitions in extensional flows is needed. In this project, we studied the nonlinear dynamics of a model wormlike micellar solutions using capillary breakup extensional rheometer (CaBER), shear rheology and Transmission Electron Microscopy (TEM). Wormlike micellar solutions contain cetyltrimethylammonium tosylate (CTAT) in deionized water over a wide range of surfactant concentrations. Steady shear experiments indicate that the shear relaxation time and the zero-shear rate viscosity increase as a function of surfactant concentration up to a critical threshold, beyond which shear relaxation time drops to smaller values, but zero shear viscosity approaches an asymptotic value. TEM images indicate that as surfactant concentration increases, the micellar length increases and beyond the critical concentration micelles become entangled and shorter in size. Our results indicate that at low surfactant
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