PSEUDO-ZERO-ORDER 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 Medicineo Agricultureo 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 re-

saturate the solution• Pseudo-zero-order

Polymer Membrane

Saturated Solution

Solid Citric Acid

Petri Dish

Water Basin

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 meter issue resulting in a few nonlinear curves

10% EVA Trials

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://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