Diffusiophoresis of hydrophobic spherical particles in a solution of general electrolyte

Abstract

The present article deals with the diffusiophoresis of hydrophobic rigid colloids bearing arbitrary $\zeta$-potential. We derived the generic expression for the diffusiophoretic velocity of such a colloid exposed in an externally applied concentration gradients of general electrolyte solution. The derived expression takes into account the relaxation effect and is applicable for all values of surface $\zeta$-potential and hydrodynamic slip length at large $\kappa a$ ($\kappa a \ge ca. 50)$, where $\kappa^{-1}$is the thickness of the electric double layer and $a$ is the particle radius. We further derived several closed form expressions for particle velocity derived under several electrostatic and hydrodynamic conditions when the particle is exposed in an applied concentration gradient of binary symmetric (e.g., ), asymmetric (1:2, 2:1, 3:1, 1:3) and a mixed electrolyte (mixture of 1:1 and 2:1 electrolytes). The results for diffusiophoretic velocity are further illustrated graphically to indicate the mutual interaction of chemiphoresis, induced electrophoresis due to unequal mobilities of cations and anions of the electrolyte and the mechanism by which the sufficiently charged particle migrates opposite to the applied concentration gradient direction. Impact of hydrophobicity is further discussed.

Diffusiophoresis of Weakly Charged Fluid Droplets in a General Electrolyte Solution: An Analytical Theory

“…The background electrolytes are taken to be either binary valence-symmetric z : z electrolytes (e.g., KCl, NaCl, HCl, MgSo 4 , [CO­(NH 3 ) 6 ]­[Fe­(CN) 6 ]) or valence-asymmetric z 1 : z 2 electrolytes (e.g., Na 2 SO 4 , MgCl 2 , LaCl 3 , Li 3 [Fe­(CN) 6 ]) or a mixed solution of the above stated binary electrolytes. The readers are referred to Table 1 of the article by Samanta et al for physical parameters associated with the background electrolytic medium that includes the limiting conductance, scaled drag coefficient, and diffusion coefficient of various electrolyte ions, etc. We have treated the electrolytes as fully dissociated, and the consideration of weak electrolytes is beyond the scope of the present study, which may be considered as a future direction of research.…”

Dynamic Electrophoresis of a Hydrophobic and Dielectric Fluid Droplet

“…In addition, the droplets with lower dielectric constant media (e.g., oil–water emulsion , ) as well as droplets with higher dielectric constant media (e.g., mercury droplets suspended in aqueous media) are further considered. It is noteworthy to mention that the nanoscaled or microsized oil droplets ,, or colloidal particles often show hydrophobicity, and to elucidate the impact of hydrophobic behavior on the electrokinetic motion under an oscillatory electric field, we have presented the results considering a wide range of hydrodynamic slip lengths (e.g., several nanometers to micrometers). The frequency of an applied oscillatory electric field is varied up to 10 MHz. − The concentration of the background aqueous solution is varied from low to high so that the Debye–Hückel parameter spans up to 100.…”

The Control of the Expansion or Compression of Colloidal Crystals Lattice with Salt Solution

“…In an aqueous solution, even a slight concentration gradient of salt can lead to the autonomous and spontaneous migration of colloidal particles, which is a fascinating phenomenon referred to as the diffusiophoresis (DP) effect. This effect arises from the inherent surface charge of the colloidal particles and was initially observed by Derjaguin in capillary osmosis and film formation from latex depositions [ 20 , 21 , 22 , 23 , 24 ]. Recent investigations have already showed the utilization of diffusiophoresis and its associated diffusioosmosis (DO) effect to propel particles [ 25 , 26 , 27 ], as well as to separate and assemble particles [ 27 , 28 , 29 , 30 , 31 ].…”