lecture12

lecture12 - 1 3.051J/20.340J Lecture 12 Biomaterials...

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3.051 J / 20 .340 J 1 Lecture 12: Biomaterials Characterization in Aqueous Environments High vacuum techniques are important tools for characterizing surface composition, but do not yield information on surface structure or chemistry in a water-based environment. Aqueous-based methods for surface characterization are limited. Here we will consider three common techniques: 1. water contact angle studies - surface reconstruction (a) - water absorption (b) - surface chemistry analysis 11 2 2 cos cos cos ff θ θθ =+ θ a droplet volume advancing receding θ θ r droplet volume advancing receding θ (a) (b) Cassie’s eqn: use to determine fraction of surface area of components 1 & 2 ( f 1 + f 2 = 1)
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3.051 J / 20 .340 J 2 2. in situ ellipsometry - degree of hydration of a film Ellipsometric angles Ψ and thickness ( d f ) & refractive index ( n f ) ( 3-layer model) f water water material material nf n f n =+ n water n f d f n sub where f water and f material are volume fractions.
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3.051 J / 20 .340 J 3 3. Atomic Force Microscopy (or Surface Force Microscopy): imaging method that exploits intermolecular interactions between a small (~atomic) probe and molecules on surface position sensitive photodetector He-Ne laser (Au-coated) Si, Si 3 N 4 , SiO 2 cantilever; spring const k~0.1-1N/m “atomic” Si, Si 3 N 4 , C tip sample surface piezoelectric transducer piezo-controlled sample stage Intermolecular potential curve short-range: ion-ion repulsion Long-range (attractive): van der Waals, H-bonding, electrostatic, dipole-dipole,… r U(r) Scan area: 1 × 1 nm 2 to 250 × 250 µ m 2 z-range: 8 µ m force range: 10 -13 -10 -6 N Force generated: U F z −∆ =
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3.051 J / 20 .340 J 4 Operation Modes 1. Contact mode (short-range) ¾
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This note was uploaded on 11/11/2011 for the course BIO 2.797j taught by Professor Matthewlang during the Fall '06 term at MIT.

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lecture12 - 1 3.051J/20.340J Lecture 12 Biomaterials...

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