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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:
zi ei 0 2 dx
• The combination (“Poisson-Boltzmann
equation”) has the simplified solution: x 0 e x • “Debye length” 1/:
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.
- Spring '11