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Technique for Measurement of Inter-Phase Line Tension in Langmuir Films

Technique for Measurement of Inter-Phase Line Tension in Langmuir Films. Lu Zou and Elizabeth K. Mann Kent State University Jacob M. Pugh and Andrew J. Bernoff Harvey Mudd College James C. Alexander and J. Adin Mann, Jr. Case Western Reserve Unviersity. Introduction.

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Technique for Measurement of Inter-Phase Line Tension in Langmuir Films

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  1. Technique for Measurement of Inter-Phase Line Tension in Langmuir Films Lu Zou and Elizabeth K. Mann Kent State University Jacob M. Pugh and Andrew J. Bernoff Harvey Mudd College James C. Alexander and J. Adin Mann, Jr. Case Western Reserve Unviersity

  2. 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

  3. 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% ?

  4. 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)

  5. Phase coexistence of 8CB 8CB Molecule At room temperature Surface pressure ~6.5mN/m

  6. Experimental set-up Brewster Angle Microscope StepperMotor 4-Roll Mill

  7. Experimental set-up (cont’) 4-Roll Mill b Laser beam a M domain 5mm a = 6.6 mm, b = 10.5 mm • Running speed ~0.2 revolutions per second • Running time ~5 seconds • Reynolds number ~16

  8. Experimental video At 30 frames per second

  9. Simulation Relative standard deviation Δλ/λ < 5% 90%Tbest Tbest 110%Tbest λ = Inter-phase line tension T = Characteristic relaxation time η’= Subfluid viscosity A = Total area

  10. 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.

  11. Profile of 8CB layers at air/water interface Line tension: λ= (5.90 mN/m) ΔL [Ref] L. Lejcek and P. Oswald, J. Phys. II France, 1 (1991) 931-937

  12. Result Relative standard deviation Small perturbation technique Relative Standard deviation in area Symmetric Difference Metric Mean value

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