Lecture5-6

Of molecules with energy 1rn we expect n 3 because

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Unformatted text preview: of molecules with energy ~1/rn we expect n > 3 (because large-distance contributions should disappear). Dielectric constant ? Presence of other ions ! Example from lab: The vertical Brownian motion of glass sphere near glass cover slip is strongly affected by salt concentration. “Screening” of electrostatic interactions: Debye-Hückel theory Screening of interactions between charged (bio)molecules Debye-Hückel theory • number density of ions “i” at x given by Boltzmann distribution: z e x i x exp i kBT … electrostatic potential • must fulfill Poisson equation: d 2 zi ei 0 2 dx • The combination (“Poisson-Boltzmann equation”) has the simplified solution: x 0 e x • “Debye length” 1/: 0.304 0.176 0.152 NaCl nm for 1:1 electrolytes CaCl2 nm for 2:1 and 1:2 electrolytes MgSO 4 nm for 2:2 electrolytes (Israelachvili) for 0.1...
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This note was uploaded on 07/12/2011 for the course BIM 162 taught by Professor Heinrich during the Spring '11 term at UC Davis.

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