Surface Tension of Polyacrylamide in the Presence of
Triton-100 Surfactant
April J. Cartwright
APPARATUS FABRICATION
• To determine the dynamic surface tension (DST) of an non-Newtonian fluid.
• To determine the critical micelle concentration (CMC) of an Non-Newtonian fluid.
• To develop a system which allows single drops of an elastic fluid to be analyzed using a
tensiometer.
RESULTS
Problem: Elastic fluid bubbles are pulled back into the syringe when pressure is released.
Surface Tension in Solution of Varying PAM Concentration:
75
Solution: As shown below a tubing apparatus was constructed which connected the needle
in the Attension Theta tensiometer to a syringe pump. The syringe pump held the
pressure on the bubble eliminating the need to hold the syringe. Images from the
camera were saved on a nearby computer for analysis.
MOTIVATION
74
•As concentration of PAM in
solution increased the initial
surface tension decreased.
73
72
Surface Tension (mN/m)
GOALS
•Each solution reached an
equilibrium surface tension
around 71 mN/m.
Surface tension is an intermolecular attractive force between adjacent molecules that
keeps fluids together at the air/fluid interface. Surface tension is a direct indicator of the
quality and purity of a fluid.
•High variation in data is likely
due to vibrations
Polyacrylamide is used in a number of consumer applications including wastewater
treatment, paper making, soil conditioning, and oil recovery. The gel is also used in
molecular biology as a medium for electrophoresis.
71
70
0.1%
PAM
0.2%
PAM
69
68
67
66
65
64
63
62
61
60
0
100
200
300
400
500
Time (s)
Dynamic Surface Tension of 0.3% PAM in the Presence of Triton X-100
75
TENSIOMETRY PROCEDURE
BACKGROUND
The shape of a drop hanging from a syringe needle is determined by several forces acting
on the drop including surface tension.
The equation γ = Δρ × g × Ro can be used where, γ = surface tension
Δρ = difference in density between fluids
β
at interface
Figure 1: Known as the
g = gravitational constant
pendant drop
Ro = radius of drop curvature at apex
experiment, a single drop
Β = shape factor ad defined through the
of fluid is suspended
Young – Laplace Equation
from a syringe needle for
CRITICAL MICELLE CONCENTRATION
Problem: What is the critical micelle concentration of TX-100 in 0.3% PAM?
Solution: Test a variety of concentrations of TX-100 in 0.3% PAM using same tensiometry
procedure. Analyze using a surface tension – concentration graph
Dx/ds = cos θ
Dz/ds = sin θ
D θ /ds = 2 Bz – sin θ /x
•Amphiphilic molecules have a
hydrophobic tail region and
hydrophillic head region.
Frame 2 – Increasing concentration of surfactant causes decrease in surface tension.
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Frame 3 – When surface of drop is fully loaded micelles, spherical bubbles of surfactant,
form and no further change in surface tension is observed.
ACKNOWLEDGMENTS
http://www.attension.com/critical-micelle-concentration.aspx
10ppmtx
50
100 ppm
•The 500 ppm sample shows
no change in surface tension.
45
500ppm
40
35
30
0
100
200
300
400
500
Time (s)
Determination of Critical Micelle Concentration of Triton X-100 in 0.3% PAM
80
•Previous tests indicated CMC
was between 10 ppm - 500
ppm TX-100.
•Range was narrowed to
between 100 ppm – 125 ppm
TX-100.
70
60
50
40
CMC Zone
30
20
0
1
10
75
100
125
250
500
1,000
Triton X-100 Concentration (ppm)
Frame 1 – Surfactant molecules diffuse to the air/fluid interface. Low concentration of
surfactant has little effect on surface tension.
•These molecules will orient to
limit the interaction of the tail
region with water.
1ppmtx
55
•The CMC is the point where
the graph changes from a
negative slope to zero slope as
highlighted by the blue box.
http://www.attension.com/critical-micelle-concentration.aspx
RESEARCH POSTER PRESENTATION DESIGN © 2011
PAM
Surface Tension (mN/m)
1. Fill syringe with 1-½ ml PAM solution and attach to tubing. Dispense PAM into tubing,
remove tubing, fill syringe with air, reattach tubing.
2. Place syringe into pump and follow pump directions to set proper needle diameter and a
flow rate of 50 ul/min.
3. Dispense PAM with pump until a small bubble forms. Turn off pump, bubble will continue
to grow. If needed, pressure from syringe pump can be slightly decreased by pulling
back on the pressure plate to stop the drop from enlarging.
4. Record data using tensiometer set for 1000 fast frames and 500 normal frames and
analyze using the Young-Laplace equation.
Triton X -100 (TX-100)
•Nonionic surfactant
•High viscosity at room temperature
•Soluble in water
•Surface tension will change
from the time of drop formation
until equilibrium is reached. This
is referred to as the dynamic
surface tension (DST)
•The surface tension changes
over time caused by
movement of TX-100 to the
air/fluid interface.
65
60
Polyacrylamide (PAM)
•High viscosity
•Non-Newtonian fluid
•Soluble in water
analysis. Three equations
are used as shown to the
right to determine the
shape of the drop.
Surface Tension (mN/m)
70
Dr. Nivedita Gupta, UNH Chemical Engineering Department
Dr. Steve Hale and Dr. Brad Kinsey, UNH RETE coordinators
National Science Foundation – Research Experience For Teachers (RET)
CONCLUSIONS
• Unique behavior was observed in PAM solutions without surfactants which will require
further investigation to determine the molecular cause.
• The CMC of TX-100 in O.3% PAM is between 100 and 125, above 125 no more surfactant is
able to distribute on the surface of a droplet and micelles will form on the interior.
• TX-100 will lower surface tension in PAM to a minimum of 31 mN/m, further additions of
surfactant are unable to cause further decrease.
FURTHER EXPERIMENTS
•Further narrowing of the CMC of 0.3% PAM using TX-100 concentrations from 100-125 ppm.
•Testing additional concentrations of PAM and determination of the cause of surface tension
increase when no surfactant is present.