Determining Surface Tension Using The Pendant Drop Method

Department of Chemistry and Physics
Georgia Regents University
Determining Surface Tension Using
The Pendant Drop Method
Camille Miller, Jaleel Bolden, Zane Corder, Charlene Higdon
Faculty Advisor: Dr. Guerrero-Millan
Applications
Surface Tension
The energy required to decrease the surface area of a fluid
Y. Yuan, T. R. Lee. Surface science techniques. Springer Berlin Heidelberg, 2013. 3‐34.
Surface Tension
Sessile drops
lg cos (θC) = γsg− γsl
Experimental Setup
Image Processing
Original image
Edge Detected
Edge Plotted
A. Egatz‐Gomez, et al. RSC Advances 2(30) (2012)
Fitting
Literature: 38.6o Our code: 38.5o
Concentration
VSoap/VWater
Contact Angle
5mL/5mL
15.7
5mL/10mL
5mL/20mL
34.7
43.5
Droplet
Other Methods of Determination
Some instruments to measure surface tension:
Du Noüy Ring
Wilhelmy plate
Pendant drop method
Young Laplace Equation
Gravity
P  P0  ( ) gz
 1 sin   2
 
   ( )gz
x  R0
 R1
Capillarity
1
1 

P     
 R1 R2 
Young Laplace Equation
In dimensionless parametric form:
sin 
d
 2  Z 
dS
X
dX
 cos 
dS
dZ
 sin 
dS

( ) gR02
Boundary conditions:

X ( 0)  Z ( 0)   ( 0)  0

( ) gR02

Shape factor
Young Laplace Equation
In dimensionless parametric form:
sin 
d
 2  Z 
dS
X
dX
 cos 
dS
dZ
 sin 
dS

( ) gR02
Boundary conditions:

X ( 0)  Z ( 0)   ( 0)  0

( ) gR02

Shape factor
Young Laplace Equation
In dimensionless parametric form:
sin 
d
 2  Z 
dS
X
dX
 cos 
dS
dZ
 sin 
dS

( ) gR02
Boundary conditions:

X ( 0)  Z ( 0)   ( 0)  0

( ) gR02

Shape factor
Image Enhancement
Edge Detection
Finding Ro

How did we choose the number of
points at the bottom of the drop?
( ) gR02

Radius of curvature Ro (pixels)
Finding Ro
Number of points
Finding Ro
Needle diameter: 0.9 mm
Ro = 1.5 mm
Determining the shape factor
CC
Method 1:
Two diameters at
different heights

( ) gR02

Method 2:
Fitting the profile
Method 1: Measuring two diameters within the drop (DE and DS)
DE: Largest diameter in the drop
DS: Diameter DE to the drop apex
CC
DS = 56 px
DE = 85 px
2
 DS 
 DS 
DS
  0.5426 

 1.7713 
  0.12836  0.7577
DE
 DE 
 DE 
3
F. K. Hansen and G. Rødsrud, J. Colloid Interface Sci. 141 (1991)
Method 2: Fitting the whole profile
= 0.05 : 0.01 : 0.5
Method 2: Fitting the profile
Surface Tension Values γ (mN/m)
From
Literature
First Method
(DS DE)
Second Method
(fitting the profile)
72.75
73.18
73.47
Water /10 cSt Silicone oil
-
40.83
40.87
Glycerol /
10 cSt Silicone oil
-
29.19
29.40
Ethylene glycol /
10 cSt Silicone oil
-
18.98
15.74
Water / Air
Measuring the flow rate in electro-coflow
Experimental setup
Drop size measurement
If the same drop appears in several frames…
Monitoring the centroid position
Results
Thank you!