PSEUDO-ZEROORDER KINETICS:
DIFFUSION THROUGH A POLYMER
MEMBRANE USING A SATURATED
SOLUTION RESERVOIR SYSTEM
Jan-alfred Aquino | Christopher Chen |
Yanglu Chen | Zachariah DeGiulio |
Katherine Dong | Christina Floristean |
Michelle Guo| Alexandra Kapadia | Robert
Kolchmeyer | Erik Massenzio | Adam
Richardson | Jessica Xu
Dr. David Cincotta | Alberto Rivera
Controlled Release
• Zero-order kinetics
• Rate independent
of concentration
• Does not often
occur in nature
• Applications:
o Medicine
o Agriculture
o Cosmetics
Pseudo-Zero-Order Kinetics
Fick's Law:
A pseudo-zero-order system would
achieve a constant rate of release,
but would not be independent of
concentration.
This can be done by holding the
concentration gradient constant.
Hypothesis
• IF: An apparatus is made that
•
•
allows for diffusion of a saturated
solution into a body of water
across a membrane
THEN: Pseudo-zero-order diffusion
should be observed
Maintain a constant
concentration gradient
Polymer Membrane
• Repeating structural
units of monomers
• Amorphous structures
•
more easily allow
diffusion than crystalline
structures
Ethylene-vinyl acetate
o 10% EVA
o 12% EVA
Choosing Citric Acid
• Solid at room temperature
• Chosen over maleic acid
and sodium chloride
• Conductivity & pH probe
• Continuously measured
•
over longer periods of
time
Most consistent results
Citric acid
Maleic acid
Experimental Design: Saturated
Solution Reservoir System
•
•
•
•
Saturated solution of citric acid added to petri dishes
Solute passes through the membrane
Additional solid citric acid added to continuously resaturate the solution
Pseudo-zero-order
Water Basin
Petri Dish
Saturated Solution
Solid Citric Acid
Polymer Membrane
Final Setup
Experimental Design
Design Features:
Water-tight petri dishes
Petri dish supports
Maximize water and
solution contact with
the membrane
Surface area
optimization
Uniform water level
with respect to the
petri dish
•
•
•
•
•
Results - The Diffusion of Citric Acid
across a 10% EVA Membrane
Results – The Diffusion of Citric Acid Across
10% and 12% EVA Membranes
• With additional
solute
• 10% EVA (top
graph)
• 12% EVA (bottom
graph)
• Suspected pH
10% EVA Trials
meter issue
resulting in a few
nonlinear curves
12% EVA Trials
Results – The Diffusion of Citric
Acid Solution Across 12% EVA
• 12% EVA with 2g solid
• Trials with 2g extra solid are zero order
Discussion
• Rate was faster
in first few hours
• Tested with 10%
•
•
EVA and 12%
EVA
Polarity
accounts for
permeation
Reproducible
rates remain
elusive
Conclusion
• Achieved pseudo-zero-order
kinetics with reservoir system
• Polar likes polar: Citric acid
•
•
•
diffused through 12% EVA more
effectively than 10% EVA
Novel method for modeling a
controlled-release system
Data was supportive of
hypothesis
More needs to be done to
conclusively accept or refute
the hypothesis
Future Studies
• Explore alternate methods of
measuring diffusion
• Solute embedded in polymer
• Biodegradable polymers
• Solute with lower solubility
• Mathematical models based
•
on parameters of polymer
membrane and solute
Generalized curve fits
References
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Available from : http://goldbook.iupac.org/P04937.html
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Available from : http://www.sciencedirect.com/science/article/pii/S001191641000144X
Acknowledgements
Dr. David Cincotta, Advisor
Alberto Rivera, Assistant
Dr. David Miyamoto, Director
New Jersey Governor's School in the Sciences and its Sponsors