J. Zawała , M. Krzan, K. Małysa

1. Institute of Catalysis and Surface Chemistry Polish Academy of Sciences ul. Niezapominajek 8, 30-239 Cracow, Poland Cluster A Meeting, 22 September 2005, Poznań Influence of Surfactant on Initial Accelerations, Shape and Velocity Variations of the Detaching Bubbles J. Zawała, M. Krzan, K. Małysa

2. Bubble Motion • EVERYDAY LIFE • washing (detergents) • champagne • beer • INDUSTRY • flotation • foam fractionation techniques • biotechnology • waste water treatment

3. Questions • What determine the bubble velocities? • How important is the type and concentration of the surfactant for: • accelerations of the bubble? • local velocities of the bubble? • terminal velocities of the bubble? • minimum adsorption coverages needed to full immobilization of bubble interface? • Is there any relation between velocity variations and deformation of the bubble?

4. Velocity of the rising bubble is very sensitive for presence of surface active substance >10 % adsorption coverage can diminish bubble velocity 2 x Bubble motion in surfactant solutions • What affects bubble motion? • viscosity of the continous phase • density • surface tension • properties of gas\liquid interface

5. G < Geq top s h u terminal velocity Geq Motion leads to disequilibration of adsorption coverage 35 cm Geq Uniform coverage

6. hsolution» 35 cm TV square glass column Fin = 0.075 mm nlamp = 100 Hz i 200 Hz video CCD cameras stroboscopic lamp PC syringe pump Experimental SET-UP

7. Captured movies Detachment of the bubble in : distilled water stroboscop illumination frequency – 100 Hz

8. Captured movies Detachment of the bubble in : 1.5 M pentanol solution stroboscop illumination frequency – 100 Hz

9. dv dh dh,dv – horizontal and vertical diameter L – distance from the capillary Dx – distance between two subsequent positions of the bubble Dx L Velocity= Dt = 0.01 s or 0.005 s Measurements

10. Deformation ratio = dv dh Shape deformations quantitative parameter characterizing the deformation degree of the bubble

11. Initial acceleration pentanol 2*10-3 M water pentanol 5*10-3 M Accelerations Stroboscop illumination frequency - 200 Hz

12. Velocities Low pentanol concentrations: 3 stages of the bubble motion acceleration, deceleration and terminal velocity

13. Shape pulsations vs. local velocities for low concentrations: CORRELATION

14. Velocities

15. full immobilization of bubble surface Adsorption coverage

16. Velocities

17. 1.25 - 1.14 1.06 1.29 1.10 - 1.22 d d d d : : h h v v 1). capillary 2.5 mm 61 mm 84 mm 216 mm 322 mm 7 mm 157 mm 16 mm 34 mm 100 mm deceleration acceleration U max U terminal 1.06 2). 325 mm capillary 3.5 mm 7.5 mm 15 mm 33 mm 84 mm 102 mm 162 mm 216 mm 61 mm 2). n-pentanol 5*10-3 1). n-pentanol 1.5*10-3 Effect of concentration on shape pulsations

18. CONCLUSIONS • Initial acceleration and terminal velocity of the bubble decreases with increasing concentation of surface active substances • Presence of maximum at the bubble velocity profiles is an indication that dynamic structure of adsorption layer was not yet established there • Shape variations - „Indicators” of establishment of dynamic structure of the adsorption layer (steady state non-equilibrium distribution of the surfactant adsorbed) • Lower adsorption coverages needed in the case of nonionic surface active substances for immobilization of the bubble interface

19. ACKNOWLEDGEMENTS Partial financial support: (grant 3 T09A 164 27) from Ministry of Scientific Research and Information Technologyis gratefully acknowledged Participation in Cluster C Meeting was made possible by EC grant INCO-CT-2003-003355