Surface Tension of Polyacrylamide in the Presence of Triton-100 Surfactant April J. Cartwright

1. Surface Tension of Polyacrylamide in the Presence of Triton-100 SurfactantApril J. Cartwright CONCLUSIONS Further narrowing of the CMC of 0.3% PAM using TX-100 concentrations from 100-125 ppm. Testing additional concentrations of PAMand determination of the cause of surface tension increase when no surfactant is present. Frame 1 – Surfactant molecules diffuse to the air/fluid interface. Low concentration of surfactant has little effect on surface tension. Frame 2 – Increasing concentration of surfactant causes decrease in surface tension. Frame 3– When surface of drop is fully loaded micelles, spherical bubbles of surfactant, form andno further change in surface tensionis observed. Amphiphilicmolecules have a hydrophobic tail region and hydrophillic head region. These molecules will orient to limit the interaction of the tail region with 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) http://www.attension.com/critical-micelle-concentration.aspx April J. Cartwright Determination of Critical Micelle Concentration of Triton X-100 in 0.3% PAM 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) As concentration of PAM in solution increased the initial surface tension decreased. Each solution reached an equilibrium surface tension around 71 mN/m. High variation in data is likely due to vibrations APPARATUS FABRICATION Problem: Elastic fluid bubbles are pulled back into the syringe when pressure is released. 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. Fill syringe with 1-½ ml PAM solution and attach to tubing. Dispense PAM into tubing, remove tubing, fill syringe with air, reattach tubing. Place syringe into pump and follow pump directions to set proper needle diameter and a flow rate of 50 ul/min. 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. Record data using tensiometer set for 1000 fast frames and 500 normal frames and analyze using the Young-Laplace equation. ACKNOWLEDGMENTS BACKGROUND GOALS 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. 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. http://www.attension.com/critical-micelle-concentration.aspx Dynamic Surface Tension of 0.3% PAM in the Presence of Triton X-100 FURTHER EXPERIMENTS MOTIVATION RESULTS 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. γ = surface tension Δρ = difference in density between fluids at interface g = gravitational constant Ro = radius of drop curvature at apex Β = shape factor ad defined through the Young – Laplace Equation 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 Polyacrylamide (PAM) High viscosity Non-Newtonian fluid Soluble in water Triton X -100 (TX-100) Nonionic surfactant High viscosity at room temperature Soluble in water 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 × Rocan be used where, β The surface tension changes over time caused by movement of TX-100 to the air/fluid interface. The 500 ppm sample shows no change in surface tension. Previous tests indicated CMC was between 10 ppm - 500 ppm TX-100. Range was narrowed to between 100 ppm – 125 ppm TX-100. The CMC is the point where the graph changes from a negative slope to zero slope ashighlighted by the blue box. Figure 1: Known as the pendant drop experiment, a single drop of fluid is suspended from a syringe needle for analysis. Three equations are used as shown to the right to determine the shape of the drop. Dx/ds = cosθ Dz/ds = sin θ D θ /ds = 2 Bz – sin θ /x Surface Tension in Solution of Varying PAM Concentration: 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. TENSIOMETRY PROCEDURE CRITICAL MICELLE CONCENTRATION CMC Zone