Technique for Measurement of Inter-Phase Line Tension in Langmuir Films
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Transcript of Technique for Measurement of Inter-Phase Line Tension in Langmuir Films
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Technique for Measurement of Inter-Phase Line Tension in
Langmuir Films
Lu Zou and Elizabeth K. MannKent State University
Jacob M. Pugh and Andrew J. BernoffHarvey Mudd College
James C. Alexander and J. Adin Mann, Jr.Case Western Reserve Unviersity
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Introduction• Line tension = free energy per unit length
• Line tension (2D) Surface tension (3D)
• Determine the shape, size and relaxation of surface domains
• Help us to understand the function of biological membrane systems
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Previous experiments & limitations• Small perturbations
(oval shape)– Theory: Two surface phases have identical properties
– Exp: Hard to measure accurately
• Large perturbations
(bola shape)– Theory: Exact shape does NOT matter.
– Exp: Measured line tensions scatter ~20%-30%?
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Our theory model
• Considering the coupling between the surface phases and the substrate
[Ref] J. C. Alexander, A. J. Bernoff, E. K. Mann, J. A. Mann Jr., J. M. Pugh, and L. Zou, J. Fluid Mech. (2006)
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Phase coexistence of 8CB
8CB Molecule
At room temperature
Surface pressure ~6.5mN/m
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Experimental set-upBrewster Angle
Microscope StepperMotor
4-Roll Mill
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Experimental set-up (cont’)
M
a = 6.6 mm, b = 10.5 mm
4-Roll Mill
• Running speed ~0.2 revolutions per second
• Running time ~5 seconds
• Reynolds number ~16
5mm
Laser beama
b
domain
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Experimental video
At 30 frames per second
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Simulation
Tbest90%Tbest 110%Tbest
λ = Inter-phase line tension
T = Characteristic relaxation time
η’= Subfluid viscosity
A = Total area
Relative standard deviation
Δλ/λ < 5%
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Conclusion
• We develop a new technique to measure the line tension of two surface-fluid phases at air/water interface.
• Compared with other models, it provides a more accurate and stable solution.
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Profile of 8CB layers at air/water interface
[Ref] L. Lejcek and P. Oswald, J. Phys. II France, 1 (1991) 931-937
Line tension: λ= (5.90 mN/m) ΔL
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Result
Small perturbation technique
Mean value
Symmetric Difference
Metric
Relative Standard deviation in area
Relative standard deviation
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