BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Specific Ion Effects in Colloidal Surface Forces  - Drew Parsons\,
  Assoc. Prof.\, University of Cagliari
DTSTART:20240425T103000Z
DTEND:20240425T113000Z
UID:TALK213049@talks.cam.ac.uk
CONTACT:Chris Richardson
DESCRIPTION:The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of the inte
 ractions\nof colloid particles has provided a useful framework for underst
 anding\ngeneral trends determining adsorption and aggregation of micro- an
 d\nnanoparticles. The point-charge (Poisson-Boltzmann or Debye-Hückel)\nt
 heory of electrolytes characterises the nature of the electrolyte\nsolely 
 by its pH and Debye length or ionic strength. So conventional\ntheory is i
 ncapable of predicting the ion-specific distinction\nbetween\, for instanc
 e\, NaCl and KCl solutions\, or between phosphate\nand citrate pH buffer s
 olutions. But ion-specific phenomena\n(Hofmeister effects) are ubiquitous\
 , and observed in protein\naggregration\, enzyme adsorption on nanoparticl
 es\, particle diffusion\ncoefficients\, charge reversal effects\, bubble c
 oalescence\, lipid\nself-assembly\, electrode capacitance.\n\nIon specific
 ity essentially arises from the distinct electron\nstructure of different 
 ions. We identify two competing consequences.\nOn the one hand\, electroni
 c polarisability drives ion dispersion\nforces [1]\, leading to adsorption
  of coions\, or excess adsorption of\ncounterions resulting in charge reve
 rsal [2].  On the other hand\, the\nsize of the electron cloud drives ioni
 c steric forces\, resulting in a\nlimit to the concentration of adsorbed i
 ons that results\, for\ninstance\, in a diminution of electrode capacitanc
 e [3].\n\nWe account for these effects as additional nonelectrostatic\ncon
 tributions to the total chemical potential of ions\, applied in a\nmodifie
 d Poisson-Boltzmann model. For basic development of the ideas\nwe use symm
 etry to simplify the geometry to 1D calculations. But\nimplementing the so
 lution using finite element methods\, we obtain a\nframework that will be 
 used to model the complex 3D geometries of\nporous electrodes and self-ass
 embled lipid crystal phases. One long\nterm aim is to predict the phase tr
 ansitions between hexagonal\, cubic\nand micellar phases relevant to\, for
  instance\, the physiology of RNA\n(COVID) vaccines.\n\nReferences\n\n[1] 
 Importance of Accurate Dynamic Polarizabilities for the Ionic\nDispersion 
 Interactions of Alkali Halides. D.F. Parsons\, B.W. Ninham.\nLangmuir 2010
 \, 26(3)\, 1816–1823. https://dx.doi.org/10.1021/la902533x\n\n[2] Buffer
 -specific effects arise from ionic dispersion forces.  D.F.\nParsons\, C. 
 Carucci\, A. Salis. Phys. Chem. Chem. Phys.\, 2022\, 24\,\n6544. https://d
 x.doi.org/10.1039/d2cp00223j\n\n[3] Thermodynamics beyond dilute solution 
 theory: Steric effects and\nelectrowetting. D. Tadesse\, D.F. Parsons. In:
  Encyclopedia of\nSolid-Liquid Interfaces (2024). https://dx.doi.org/10.10
 16/B978-0-323-85669-0.00137-9\n\n
LOCATION:Open Plan Area\, Institute for Energy and Environmental Flows\, M
 adingley Rise CB3 0EZ
END:VEVENT
END:VCALENDAR