Pseudo-Zero-Order Kinetics: Diffusion through a

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
This can be done by holding the
concentration gradient constant.
• 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
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
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
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
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
• 10% EVA (top
• 12% EVA (bottom
• 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
• Rate was faster
in first few hours
• Tested with 10%
EVA and 12%
accounts for
rates remain
• 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
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
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Dr. David Cincotta, Advisor
Alberto Rivera, Assistant
Dr. David Miyamoto, Director
New Jersey Governor's School in the Sciences and its Sponsors

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