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Open AccessArticle

Failure of Debye-Hückel Screening in Low-Charge Colloidal Suspensions

School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
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Colloids Interfaces 2018, 2(4), 51; https://doi.org/10.3390/colloids2040051
Received: 30 September 2018 / Revised: 17 October 2018 / Accepted: 18 October 2018 / Published: 22 October 2018
Derjaguin–Landau–Verwey–Overbeek (DLVO) theory remains the cornerstone of colloid stability. Electrostatic interactions dominate van der Waals attractions at large colloid-colloid separations h, unless strongly screened. Under these conditions, the potential U ( h ) between charged colloids is expected to be exponentially screened, U ( h ) exp ( κ h ) / h , with κ 1 = λ D where λ D is the classical Debye-Hückel screening length. By measuring the force between individual charged particles at dilute electrolyte concentrations (<mM) using optical tweezers, we tested experimentally the prediction κ 1 = λ D in a nonpolar solvent. At low salt concentrations, we found close agreement between the directly-measured decay length κ 1 and Debye-Hückel predictions. However, above a critical electrolyte concentration (≈450 μ M), we obtained significant discrepancies between measured and predicted screening lengths, with κ 1 λ D . In marked contrast to expectations, we found that the measured screening length κ 1 appears to grow as the ionic strength of the solution is increased. The origin of this discrepancy is discussed and the importance of considering the surface is highlighted. View Full-Text
Keywords: electrostatics; DLVO; optical manipulation electrostatics; DLVO; optical manipulation
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Waggett, F.; Shafiq, M.D.; Bartlett, P. Failure of Debye-Hückel Screening in Low-Charge Colloidal Suspensions. Colloids Interfaces 2018, 2, 51.

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