Surface Elasticity and Viscosity from Oscillating Bubbles Measured by Automatic Axisymmetric Drop Shape Analysis

Area of Science:

• Surface chemistry
• Polymer science
• Rheology

Background:

• Understanding interfacial properties of polymers is crucial for material science.
• Previous methods for measuring surface dilatational properties were limited.
• Video image analysis offers a promising approach for dynamic interfacial studies.

Purpose of the Study:

• To enhance a pendant/sessile drop instrument for measuring oscillating drops and bubbles.
• To analyze dilatational surface elasticity and viscosity of polymers at the air-water interface.
• To investigate the adsorption and surface properties of ethylhydroxyethyl cellulose (EHEC) and two poly(oxyethylene)-poly(oxypropylene) ABA block copolymers (PE6200, PE6800).

Main Methods:

• Utilized an enhanced pendant/sessile drop instrument with video image analysis.
• Measured oscillating drops and bubbles at rates up to 25 pictures per second.
• Analyzed sinusoidal oscillations to determine dilatational surface elasticity and viscosity.

Main Results:

• Polymers EHEC, PE6200, and PE6800 exhibited surface pressures of 20-30 mN m-1.
• Surface elastic moduli ranged from 4 to 30 mN m-1, with low viscous moduli (0-6 mN m-1).
• Elastic moduli increased with frequency; concentration dependency varied with polymer solubility, correlating with molecular orientation.

Conclusions:

• The enhanced instrument effectively measures dynamic surface properties of polymers.
• Polymer solubility and molecular orientation significantly influence surface elasticity and viscosity.
• Diffusional transport may explain higher viscous modulus observed for PE6200.