Electrostatic interactions of poly (methyl methacrylate) colloids: deposition patterns of evaporating non-aqueous colloi
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ORIGINAL CONTRIBUTION
Electrostatic interactions of poly (methyl methacrylate) colloids: deposition patterns of evaporating non-aqueous colloidal droplets Mohamad Danial Shafiq 1,2
&
Franceska Waggett 1 & Nur Liyana Marissa Ismail 3 & Paul Bartlett 1
Received: 7 June 2020 / Revised: 20 September 2020 / Accepted: 11 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We generate controllable micrometer-range electrostatic interactions in a suspension by using a charge control additive: an anionic surfactant, dioctyl sodium sulfosuccinate (AOT), and an organic salt, tetradodecylammonium tetrakis (3,5-bis (trifluoromethyl)phenyl)borate (TDAT) in non-aqueous solvents. Both systems function via different mechanisms of altering the electrostatic interaction between poly (methyl methacrylate) (PMMA) colloids. For the AOT system, the particle surface charge is modified by the adsorption of charged and neutral AOT micelles on the surface, hence affecting the interactions between particles. The measured scaled surface potential is independent on the AOT concentration, so that the AOT-PMMA system approximates the constant surface potential (CSP) limit. For the electrolytic TDAT non-aqueous system, the screening length of the solution was altered due to the presence of free ions in the solution. This is confirmed by the conductivity and theoretical Debye length λD values. However, from the force measurement using the blinking optical tweezers (BOTs), it was revealed that the measured screening length κ−1, and the particle effective charge Zeff shows a non-monotonic dependence on the TDAT concentration. The deviation between these values revealed that at high TDAT concentrations, the classical DLVO theory-Debye-Hückel limit is no longer valid for the system. We relate the formation of clusters and aggregates formed in the bulk system with the deposition patterns of a colloidal droplet on a hydrophobically coated glass substrate. The drying of droplets containing monodisperse PMMA particles was studied by confocal microscopy. Keywords Electrostatic . Charge . Evaporation . Non-aqueous . Surface . Attraction
Introduction Since the 1940s, the Derjaguin Laudau Verwey and Overbeek (DLVO) theory has been widely assumed to summarize the overall interactions of a colloidal system governed by electrostatic repulsion and van der Waals attraction in an aqueous system. However, it is not clear yet if DLVO is applicable for colloidal interactions in non-aqueous solvents. Due to that, the evolvement of interaction theory for non-aqueous systems is
* Mohamad Danial Shafiq [email protected] 1
School of Chemistry, University of Bristol, BS8 1TS Bristol, United Kingdom
2
School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia Engineering Campus, 14300 Penang, Malaysia
3
Selangor, Malaysia
pivoted to the classical DLVO theory. The obvious contrast between the polar and non-polar solvents is the relative permittivity εr, where water has an εr value of up to 40 times larger than
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