Team 5 Project in Chemistry: Pseudo-Zero-Order Kinetics Across a Polymer Membrane Using a Saturated 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
Advisor: David Cincotta
Assistant: Alberto Rivera
ABSTRACT
Controlled-release kinetics involves the diffusion of molecules across a polymer membrane at a constant rate. In a zero-order rate of diffusion, molecules diffuse across a membrane at a rate independent of the concentration of molecules on either side of the membrane. Molecules diffuse by dissolving into the membrane when they collide with the surface. As concentration decreases, collision frequency and diffusion rate also decrease, making it difficult to achieve zero-order kinetics. For practical applications, zero-order release may be modeled with a pseudo-zero-order release mechanism. A pseudo-zero-order release mechanism was attempted by saturating a citric acid solution and allowing it to diffuse through polymer membranes made of either polyethylene with 10% vinyl acetate (10% EVA), or polyethylene with 12% vinyl acetate (12% EVA). Previous research has shown that 10% EVA is adequate for the diffusion of polar substances, such as citric acid. The concentration of the citric acid solution was kept constant by the addition of additional solid citric acid, which continuously dissolved into solution as aqueous citric acid diffused across the membrane. Most of the experiments performed used 10% EVA membranes. The release mechanism consisted of petri dishes loaded with saturated citric acid solution and solid citric acid. The petri dishes were covered with polymer membranes and propped on the surface of a water reservoir to allow for diffusion. The results indicated that pseudo-zero-order release is possible using this method. Future studies may include refining the experiments described in this paper to achieve more consistent data by altering the membranes or developing a mathematical model of the diffusion rate as a function of one variable.