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

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

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?

What affects bubble motion?  viscosity of the continous phase  density  surface tension  properties of gas\liquid interface 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

Uniform coverage  eq 35 cm  eq top u Motion leads to disequilibration of adsorption coverage Motion leads to disequilibration of adsorption coverage  terminal velocity 

 in = mm lamp = 100 Hz i 200 Hz h solution  35 cm Experimental SET-UP PC CCD cameras video TV square glass column stroboscopic lamp syringe pump

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

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

Measurements L – distance from the capillary  x – distance between two subsequent positions of the bubble Velocity =  t = 0.01 s or s L xx dvdv dhdh d h,d v – horizontal and vertical diameter

Shape deformations dhdh dvdv quantitative parameter characterizing the deformation degree of the bubble Deformation ratio =

Accelerations Stroboscop illumination frequency Hz Initial acceleration water pentanol 2*10 -3 M pentanol 5*10 -3 M c [M]a [cm/s 2 ]sd 0 (water) * *

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

Shape pulsations vs. local velocities for low concentrations: CORRELATION

Velocities

full immobilization of bubble surface Adsorption coverage

Velocities

Effect of concentration on shape pulsations acceleration U max deceleration U terminal : vh dd : vh dd 61 mm 16 mm capillary2.5 mm 34 mm 84 mm 100 mm 157 mm 216 mm322 mm 7 mm 1). n-pentanol 1.5* ). capillary3.5 mm7.5 mm 15 mm33 mm 61 mm 84 mm102 mm162 mm216 mm 325 mm 2). n-pentanol 5* ).

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

ACKNOWLEDGEMENTS Partial financial support: (grant 3 T09A ) from Ministry of Scientific Research and Information Technology is gratefully acknowledged Participation in Cluster C Meeting was made possible by EC grant INCO-CT