J. Zawała, M. Krzan, K. Małysa

Institute of Catalysis and Surface Chemistry Polish Academy of Sciences

ul. Niezapominajek 8, 30-239 Cracow, Poland

Influence of Surfactant on Initial Influence of Surfactant on Initial Accelerations, Shape and Velocity Variations Accelerations, Shape and Velocity Variations

of the Detaching Bubblesof the Detaching Bubbles

Cluster A Meeting, 22 September 2005, Poznań

Bubble MotionBubble Motion

INDUSTRY

flotation

foam fractionation techniques

biotechnology

waste water treatment

EVERYDAY LIFE

washing (detergents)

champagne

beer

QuestionsQuestions

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 solutionsBubble motion in surfactant solutions

Uniform coverage

eq

eq

35 cm

eqtop

u

Motion leads to disequilibrationof adsorption coverage

Motion leads to disequilibrationof adsorption coverage

terminal velocity

in = 0.075 mm

lamp = 100 Hz i 200 Hz

hsolution 35 cm

Experimental SET-UPExperimental SET-UP

PC

CCD camerasvideo

TV square glass column

stroboscopic lamp

syringe pump

Captured moviesCaptured movies

Detachment of the bubble in :

distilled water

stroboscop illumination frequency – 100 Hz

Captured moviesCaptured 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

x

t = 0.01 s or 0.005 s

L

x

dv dh dh,dv – horizontal and vertical diameter

Shape deformationsShape deformations

dh

dv

quantitative parameter characterizing the deformation degree of the bubble

Deformation ratio =

v

h

d

d

AccelerationsAccelerations

Stroboscop illumination frequency - 200 Hz

Initial acceleration

time [s]

0.00 0.01 0.02 0.03 0.04 0.05ve

loci

ty [

cm/s

]0

5

10

15

20

25

30

water pentanol 2*10-3 M

pentanol 5*10-3 M

c [M] a [cm/s2] sd

0 (water) 925 64

2*10-3 640 48

5*10-3 500 110

n-pentanol

distance from the capillary [ mm]0 50 100 150 200 250 300 350

velo

city

[cm

/s]

0

10

20

30

40

water1*10-4

5*10-4

1*10-3

1.5*10-3

3*10-3

5*10-3

VelocitiesVelocities

Low pentanol concentrations: 3 stages of the bubble motion

acceleration, deceleration and terminal velocity

n-pentanol

distance from the capillary [mm]

0 50 100 150 200 250 300 350

dh

/dv

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7n-pentanol

distance from the capillary [mm]

0 50 100 150 200 250 300 350

velo

city

[cm

/s]

0

10

20

30

40

distilled water

1*10-3 M

1.5*10-3 M

2*10-3 M

3*10-3 M

Shape pulsations vs. local velocitiesShape pulsations vs. local velocities

for low concentrations: CORRELATION

VelocitiesVelocities

n-octyltrimethylammonium bromide

distance from the capillary [mm]

0 50 100 150 200 250 300

velo

city

[cm

/s]

0

10

20

30

40

water5*10-4

1*10-3

5*10-3

1*10-2

2*10-2

4*10-2

n-pentanol

concentration [mol/dm3]

0.000 0.002 0.004 0.006 0.008 0.010 0.012

term

inal

vel

oci

ty [

cm/s

]

0

10

20

30

40

full immobilization of bubble surface

Adsorption coverageAdsorption coverage

VelocitiesVelocities

adsorption degree

0.0 0.2 0.4 0.6 0.8

term

inal

vel

oci

ty [

cm/s

]

0

10

20

30

40

n-pentanoln-octanoln-octyltrimethylammonium bromide

Effect of concentration on shape pulsationsEffect of concentration on shape pulsations

acceleration U max deceleration U terminal

1.10 - 1.22 1.29 1.25 - 1.14 1.06:vh dd

:vh dd 1.06

61 mm16 mmcapillary 2.5 mm 34 mm 84 mm 100 mm 157 mm 216 mm 322 mm7 mm

1). n-pentanol 1.5*10-3

1).

capillary 3.5 mm 7.5 mm 15 mm 33 mm 61 mm 84 mm 102 mm 162 mm 216 mm 325 mm

2). n-pentanol 5*10-3

2).

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 164 27) from Ministry of Scientific Research and

Information Technology is gratefully acknowledged

Participation in Cluster C Meeting was made possible by EC grant INCO-CT-2003-003355