Article pubs.acs.org/JPCC
Forces between Negatively Charged Interfaces in the Presence of Cationic Multivalent Oligoamines Measured with the Atomic Force Microscope Mohsen Moazzami Gudarzi, Gregor Trefalt, Istvan Szilagyi, Plinio Maroni, and Michal Borkovec* Department of Inorganic and Analytical Chemistry, University of Geneva, Sciences II, 30 Quai Ernest-Ansermet, 1205 Geneva, Switzerland ABSTRACT: The colloidal probe technique was used to accurately measure forces between water−solid interfaces of negatively charged latex particles in aqueous solutions of linear, cationic oligoamines of different valence up to roughly +4. These measurements were realized between pairs of particles with the atomic force microscope. Monovalent and divalent amines behave as simple electrolytes, and the forces are dominated by double layer repulsion at low concentrations and van der Waals attraction at high concentrations, as suggested by the classical theory by Derjaguin, Landau, Verwey, and Overbeek (DLVO). Additional attractive non-DLVO force of a short range can be evidenced, and its origin is attributed to hydrophobic interaction between the surfaces. Trivalent and tetravalent oligoamines induce a charge reversal and equally an additional attractive non-DLVO force. The charge reversal originates from the adsorption of these oligoamines to the particle surface. The additional non-DLVO force is more long-ranged than the ones observed in the presence of amines of low valence. This additional attraction is probably related to ion−ion correlations, existing surface heterogeneities, and the chainlike nature of the amines investigated.
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INTRODUCTION Forces acting between charged interfaces in aqueous suspensions represent a central question in material sciences and environmental engineering. Such forces control the formation of green bodies in ceramic processing, flow of particle suspensions, formation of particle aggregates in wastewater treatment, or particle deposition to surfaces.1−5 These forces can be modified through various additives, including salts, polymers, or polyelectrolytes.6−17 Among those, salts containing multivalent ions are of particular interest, as they may induce particle aggregation at substantially lower salt concentrations than monovalent ones. Such multivalent ions may include various metal ions, metal ion complexes, but equally short oligomers of polyelectrolytes.6−12 The accurate measurements of forces between water−solid interfaces remained elusive for a long time. The breakthrough came with the invention of the surface forces apparatus, which still offers unsurpassed distance resolution.18−20 More recently, additional techniques to directly measure surface forces became available, such as total internal reflection microscopy (TIRM),21,22 optical tweezers combined with videomicroscopy,10,23,24 and atomic force microscopy (AFM).14,25,26 TIRM and optical tweezers offer an excellent force resolution, but their distance resolution remains limited to a few nanometers. The AFM can be used to measure forces involving colloidal particles by means of the colloidal probe technique, either in the sphere−plate or in the sphere−sphere geometry. The latter technique offers a subnanometer distance resolution, © XXXX American Chemical Society
and with modern AFMs, a good force resolution can be obtained as well. Currently, the colloidal probe technique can be routinely used to measure forces involving colloidal particles down to about 1 μm in diameter.11,12,14,27 On the other hand, the theory of forces between charged water−solid interfaces has a long history. The cornerstone represents the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), which was developed more than half a century ago.28 This approach suggests that forces between two interfaces have two main contributions, namely, an attractive van der Waals force and a repulsive double layer force. Subsequently, this approach was refined by considering more precise models of the respective interactions. The calculation of van der Waals forces may consider retardation or include effects of surface roughness.28−30 Double layer forces may be obtained not only on the basis of Debye−Hückel theory but also from Poisson−Boltzmann (PB) theory, and they may include effects of charge regulation.31−33 More recently, it was suggested that the PB approach may break down due to neglect of ion−ion correlations or finite size of the ions.34−36 Forces involving colloidal particles can be obtained from the plate−plate geometry by means of the Derjaguin approximation.28 In recent years, there was a substantial interest whether other ionic properties, besides their valence, are relevant in Received: May 8, 2015 Revised: June 4, 2015
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DOI: 10.1021/acs.jpcc.5b04426 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C Table 1. Ionization Properties for the Oligoamine Cations Used mole fraction and ionization constantb name
a
methylamine, N1 CH3NH2 ethyelenediamine, N2 H2NCH2CH2NH2 diethylenetriamine, N3 H2NCH2CH2NHCH2CH2NH2 triethylenetetramine, N4 H2N(CH2CH2NH)2CH2CH2NH2 pentaethylenehexamine, N6 H2N(CH2CH2NH)4CH2CH2NH2
+1
+2
+3
+4
+5
+6
>0.99 10.63
