Jerome Nash and Prof. Kendra Erk

1. Utilizing rheological methods to examine mechanical properties of a triblock copolymer at the water/oil interface Jerome Nash and Prof. Kendra Erk School of Materials Engineering , Purdue University, West Lafayette, IN USA Introduction and Motivation Inadequate cleansing of contact lenses can lead to many problems for contact lens wearers such as eye irritation and eye infections. Clear Care® Cleaning & Disinfecting Solution utilizes a unique cleaning process that exploits the rheological properties of Pluronic 17R4 to remove dirt and debris from the surface of contact lenses, while also allowing water to adsorb to the contact’s surface for a more comfortable fit. [1] This goal of this research was to study adsorption and rheological mechanics of this non-ionic, triblock copolymer and determine the concentration and deformation strains that maximize the rheological abilities of Pluronic 17R4. Experiments were conducted at the water/hexadecane interface and the adsorption and viscoelastic properties of the interface were measured via methods of pendant drop tensiometry and dynamic oscillation with drop shape analysis software. Interfacial Tension Overview Interfacial Molecular Layer at Low and High Surface Pressures • Surface Pressure Study Results • Objective: Assess effect of increasing Pluronic concentration • Protocol: • 4 samples prepared in solutions of increasing Pluronic17R4 concentration • Static pendant drops of solutions were aged for 30 minutes in hexadecane oil • Maximum Surface Coverage: • R = Gas constant • T = Temperature (K) • = Surface pressure • cB = Bulk concentration • Maximum Surface Coverage for System: • = 6.03x10-4 mol/m2 • Summary: ↑ Pluronic 17R4 concentration » ↑ Interfacial layer surface pressure (↓ interfacial tension) • Dynamic Oscillation Study Results • Objective: Evaluate trends in viscoelasticity as deformation rate increases. • Protocol: • Static pendant drops of solutions were aged for 30 minutes in hexadecane oil • Oscillatory strains conducted over a range of frequencies (0.01Hz to 1Hz) • E’ = Elastic Response (open), E” = Viscous Response (closed) Adapted from Ramè-Hart Instrument co., http://www.ramehart.com/surface_tension.htm/ • Interfacial Tension represents the force exerted on the molecules located at the interface between two immiscible liquids • The water strider (shown above) relies on the high surface tension of water to move on the surface of streams and ponds without sinking • Hydrophilic polyethylene oxide and hydrophobic polypropylene oxidePluronic 17R4 conformation • MW: 2700 g/mol • Surface pressure depends on concentration of molecules Summary:↑ deformation rate » ↑ viscous response, ↓ elastic response; ↑ bulk concentration » ↓ E’ and E” difference Conclusions and Implications The methodologies utilized in this study allowed for an comprehensive analysis of the mechanical and rheological properties of Pluronic 17R4. Surface pressure analysis revealed that increasing the concentration of Pluronic 17R4 results in higher surface pressures, to a maximum surface coverage of approx. 6.03x10-4mol/m2. Oscillation experiments showed that Pluronic 17R4 forms the most elastic interfacial layer under 0.5 Hz perturbations. The rheological information obtained can be used to improve qualitative and empirical product design of Clear Care® Cleaning & Disinfecting Solution. References [1] http://www.clearcaresolution.com/lenscare_clearcare.shtml [2]Miller, R. (2010). Rheology of interfacial layers. Colloid Polymer Science, 288, 937–950. [3] Ivanov, I., Danov, K., Ananthapadmanabhan, K., & Lips, A. (2005). Interfacial rheology of adsorbed layers with surface reaction: On the origin of the dilatational surface viscosity. Advances in Colloid and Interface Science, Volumes 114–115, Pages 61–92. Drop Shape Analysis Overview Static pendant drop and dynamic oscillation methods were used to determine the properties of the interfacial layer. The contact angle goniometer used and interfacial orientation of Pluronic 17R4 are shown below. Contact Angle Goniometer Pendant Drop Schematic CAPILLARY DROP