CHAPTER 1 INTRODUCTION...1

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Bruno Whitehead
5 years ago
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1 Acknowledgement My most sincere thanks go to my advisor and mentor, Dr. Roe-Hoan Yoon. I thank him for introducing me to the wonders and frustrations of scientific research. I thank him for his guidance, encouragement and support during the development of this work. He has been teaching me all about self-discipline in laboratory work and in written scientific communication. I am indebted to my committee members: Dr. Gerald H. Luttrell, Dr. Rickey M. Davis, Dr. Demetri P. Telionis and Dr. Pavlos Vlachos. They have provided, with kindness, their insight and suggestions, which are precious to me. Especially, I thank Dr. Jan C. Eriksson for numerous helpful advices and inspiring discussions since his first visit to Virginia Tech in Dr. Eriksson has directly involved with many aspects of Chapter 6. I want to express sincere gratitude to Drs. Hans J. Müller and Rumen Krustev for the experimental training while I was a visiting student at the Max-Planck Institute of Colloids and Interfaces in Germany. I thank Ramanathan Muruganathan, Narayan C. Mishra and R. Emrich for their help, generosity, and friendship. I also thank Liqin Ge and Dr. Junbai Li for their kind help. Special thanks are due to Luis G. Cascão Pereira and Dr. Clayton J. Radke for kindly providing me the bike-wheel microcell and sharing information on related experimental details. Dr. William A. Ducker is gratefully acknowledged for allowing me to use the pendant drop apparatus in his laboratory. I also want to thank Tom Wertalik and Billy Slusser for their great technical support. I want to express my sincere gratitude to past and present members of the Center for Advanced Separation Technologies (CAST). Especially, I thank Jinming Zhang, Jinhong Zhang, Jialin Wang, Emilio Lobato, Baris Yazgan, Hubert Schimann, Chris Hull, and Carol Trutt for their support and friendship. I would like to express my eternal gratitude to my parents for their everlasting love and support. iii

2 Tables of Contents CHAPTER 1 INTRODUCTION MOTIVATION FOAM FILMS Charge of Air-Water Interface Foam Film Structure and Types DISJOINING PRESSURE Definition Thermodynamic definition Components of the disjoining pressure DISSERTATION OUTLINE REFERENCES...14 CHAPTER 2 HYDROPHOBIC FORCES IN THE FOAM FILMS STABILIZED BY SODIUM DODECYL SULFATE: EFFECT OF ELECTROLYTE...18 ABSTRACT INTRODUCTION COUNTERION BINDING MODEL EXPERIMENTAL SECTION Materials Experimental Method RESULTS DISCUSSION CONCLUSIONS REFERENCES...36 APPENDIX 2A...38 THIN FILM PRESSURE BALANCE TECHNIQUE A.1 Film Thickness Measurement A.2. Disjoining Pressure Measurement...41 APPENDIX 2B...42 THREE-DIMENSIONAL FOAM STABILITY MEASUREMENT...42 CHAPTER 3 ROLE OF HYDROPHOBIC FORCES IN THE THINNING OF THE FOAM FILMS IN THE PRESENCE OF SODIUM DODECYL SULFATE...43 ABSTRACT INTRODUCTION THEORETICAL METHODS Surface Potential at Air-Water Interface Determination of Hydrophobic Force Constant MATERIALS AND EXPERIMENTAL METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES...56 APPENDIX 3.A COMPARISON OF THE MAGNITUDE OF HYDROPHOBIC FORCE...58 APPENDIX 3.B THEORETICAL FITS OF FILM THINNING...59 CHAPTER 4 ROLE OF HYDROPHOBIC FORCE IN THE THINNING OF FOAM FILMS CONTAINING METHYL ISOBUTYL CARBINOL...61 ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES...75 iv

3 CHAPTER 5 STABILITY OF FOAMS AND FOAM FILMS CONTAINING METHYL ISOBUTYL CARBINOL...78 ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES...89 CHAPTER 6 EFFECT OF CHANGING PH AND THE IONIC STRENGTH ON THE SURFACE FORCES IN SURFACTANT-FREE THIN AQUEOUS FILMS...91 ABSTRACT INTRODUCTION EXPERIMENTAL SECTION EXPERIMENTAL RESULTS THEORETICAL CONSIDERATIONS CONCLUSIONS REFERENCES...99 CHAPTER 7 EFFECTS OF SURFACE FORCES AND FILM ELASTICITY ON FROTH STABILITY ABSTRACT INTRODUCTION THEORETICAL MODEL MATERIALS AND EXPERIMENTAL METHODS Materials Foam Stability Measurement Film Thickness Measurement RESULTS AND DISCUSSION CONCLUSIONS REFERENCES VITA v

4 List of Tables Table 1.1 Chemical formulas of reagents..14 Table 2.1 The values of K 232 of Eq. [2.14] at different SDS and NaCl concentrations...29 Table 7.1 Various parameters for frothers vi

5 List of Figures Figure 1.1 Schematic of a thin foam film Figure 1.2. The counterion density and electrostatic potential with the aqueous region between two charged surfaces 5 Figure 2.1 Schematic presentation of the electrical double-layer at the air-water interface.20 Figure 2.2 Surface tensions of SDS solutions in presence and absence of NaCl...24 Figure 2.3 Adsorption isotherms for SDS..25 Figure 2.4 The Stern potential at the air-water interface as calculated using the counter ion binding model developed in the present work...25 Figure 2.5. Comparison of the surface potentials Figure 2.6 The surface excess ratio between the counterions (Na + ) and the surfactant ions (DS - ) as a function of SDS concentration in the presence and absence of NaCl..26 Figure 2.7 Equilibrium film thicknesses as a function of SDS concentration at 0, 0.4 and 1 mm NaCl; ph ; and 25±0.1 C.27 Figure 2.8 K 232 in Eq. [2.14] as a function of SDS concentration at 0, 0.4 and 1 mm NaCl.. 28 Figure 2.9 A disjoining pressure isotherm obtained at 0.1 mm SDS without NaCl..30 Figure 2.10 Disjoining pressure isotherms obtained in 10-4 SDS solutions at different NaCl additions..32 Figure 2.11 Surface area decay of SDS foams containing various concentrations of NaCl Figure 2.12 K 232 of Eq. [2.14] as a function of the fraction of the air/water interface covered by SDS Figure 2A.1 Schematic of Scheludko cell...38 Figure 2A.2 The intensity of light reflected from the two air/water interfaces of a foam film changes with time.. 40 Figure 2A.3 Equilibrium film thicknesses (H e ) versus SDS concentration.. 41 Figure 2A.4 Schematic of the experimental apparatus for measuring disjoining pressure isotherm.41 Figure 2B.1 Schematic drawing of pressure decay method..42 Figure 3.1 Surface tensions of SDS solutions in the presence and absence of NaCl.49 vii

6 Figure 3.2 The ratio between the surface excesses for the Na + and DS - ions as a function of SDS concentration in the presence of 0.3 M NaCl and absence of NaCl..49 Figure 3.3 Kinetics of film thinning at 10-5 M SDS...50 Figure 3.4 Kinetics of film thinning at 10-4 M SDS and M NaCl Figure 3.5 Kinetics of film thinning at a) M SDS and 0.3 M NaCl; b) M SDS and 0.3 M NaCl Figure 3.6 Effect of SDS concentration on K 232 at 0.3 M NaCl Figure 3.7 Effect of SDS concentration on the film lifetime (τ) and the critical rupture thickness (H cr ) at 0.3 M NaCl...54 Figure 3.8 K 232 versus (Γ s +Γ c ) -1 as a function of SDS concentration in the absence and presence of 0.3 M NaCl...55 Figure 3A.1 Hydrophobic force in foam films containing 0.3M NaCl; ( ), 10-4 M SDS with P c =49.6 Pa; ( ) M SDS with P c =71.4 Pa. The solid line is the expected van der Waals attraction Figure 3B.1 Kinetics of film thinning at 5x10-7 M SDS and 0.3 M NaCl 59 Figure 4.1 Kinetics of film thinning at a) 10-5 M MIBC and 0.1 M NaCl; b) M MIBC and 0.1 M NaCl; c) M MIBC and 0.1 M NaCl.. 65 Figure 4.2 Effect of MIBC concentration on K 232 at 0.1 M NaCl..67 Figure 4.3 Effect of MIBC concentration at 0.1 M NaCl on the lifetimes of foam ( ) and film ( ) Figure 4.4 Effect of MIBC concentration on the critical rupture thickness (H cr )..69 Figure 4.5 Effect of film elasticity (E) on the film lifetime ( ) and the foam lifetime ( ) at various concentrations of MIBC at 0.1 M NaCl...71 Figure 4.6 The hydrophobic force constants, K 232, determined from the film thinning data, are plotted as a function of Γ -1 s.74 Figure 5.1 Static surface tension of MIBC solutions as a function of concentration...81 Figure 5.2 Surface excess of MIBC as a function of bulk concentration Figure 5.3 Equilibrium film thickness as a function of MIBC concentration in the presence of 5x10-5 M NaCl...83 Figure 5.4 Disjoining pressure isotherm of MIBC at varying concentrations in the presence of 5x10-5 M NaCl..84 Figure 5.5 The lifetime of three-dimensional foams measured using shake tests as a function of MIBC concentration in the present of 5x10-5 M NaCl. The error bar denotes the maximum data scattering range Figure 5.6 Effect of MIBC concentration on film elasticity (E) viii

7 Figure 5.7 The effects of MIBC concentration on the critical rupture pressure of single films (taken from Figure 5.4), lifetime of three-dimensional foams (taken from Figure 5.5), and film elasticity (E) (taken from Figure 5.6) Figure 5.8 Effects of MIBC concentration on the stability of foams measured by the shake tests: ( ), τ I, the time it took for the appearance of liquid surface for foams in the presence of 5x10-5 M NaCl; ( ), τ II, the time it took until only the isolated bubbles became visible for foams in the presence of 0.1 M NaCl Figure 6.1 Effect of the NaCl concentration on the lifetime of thin films formed in a Scheludko cell with inner radius of 1.0 mm. The dotted line is hypothesized on the basis of the observation that the lifetime of a thin film formed from pure water is less than 1 second Figure 6.2 The influence of ph-changes on the equilibrium film thickness (H e ). Thin aqueous films were formed using a Scheludko cell with the radius 1.0 mm. The error bars show the maximal measuring errors. 95 Figure 6.3 The estimated surface potential (ψ 0 ) shown as a function of ph. The filled circle represents the predicted surface potential (= mv) from the measured equilibrium film thickness at ph 6.2 (=133 nm) using Eq. [6.9]. The empty circle represents the measured ζ-potential (= mv) at ph Figure 6.4 The estimated hydrophobic force constant (K 232 ) in Eq. [6.9] as a function of ph at 10-5 M NaCl. 98 Figure 6.5 The area per (negative) surface charge plotted vs. ph..99 Figure 7.1 Surface tension as a function of frother concentration Figure 7.2 Film elasticity (E) calculated using Eq. [7.6] for various frothers: pentanol, MIBC, octanol, and PPG Figure 7.3 Foam stability (τ) as a function of frother concentration 108 Figure 7.4 Foam stability (τ) as a function of film elasticity (E).109 Figure 7.5 Disjoining pressure (Π) as a function of equilibrium film thickness (H e ) at ph ix

Hydrophobic Forces in the Foam Films Stabilized by Sodium Dodecyl Sulfate: Effect of Electrolyte

Langmuir 2004, 20, 11457-11464 11457 Hydrophobic Forces in the Foam Films Stabilized by Sodium Dodecyl Sulfate: Effect of Electrolyte Liguang Wang and Roe-Hoan Yoon* Center for Advanced Separation Technologies,