ORCID Profile
0000-0002-0475-7858
Current Organisation
University of Leeds
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Publisher: Swiss Chemical Society
Date: 29-06-2011
Publisher: American Chemical Society (ACS)
Date: 07-09-2010
DOI: 10.1021/LA102912U
Abstract: Repulsive electrostatic double-layer forces are responsible for the stabilization of charged colloidal particles in the presence of adsorbed polyelectrolytes of opposite and high line charge densities. This mechanism is revealed by studies of electrophoretic mobility and colloidal stability performed with dynamic light scattering as a function of the polyelectrolyte dose and the ionic strength for two different types of latex particles and four different types of polyelectrolytes. The dependence of these quantities is very similar for bare charged latex particles and the same particles in the presence of the different oppositely charged polyelectrolytes. Positively charged particles in the presence of anionic polyelectrolytes behave analogously to negatively charged particles in the presence of cationic polyelectrolytes.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CP20654K
Abstract: Highly charged polyelectrolytes adsorbed on oppositely charged colloidal particles are investigated by electrophoresis and dynamic light scattering. The dependence of the adsorbed amount and of the hydrodynamic layer thickness on the molecular mass and the salt level is analyzed. The adsorbed amount increases with increasing salt level and decreases with increasing molecular mass. The hydrodynamic layer thickness is independent of the molecular mass at low salt levels, but increases with the molecular mass as a power law with an exponent 0.10 ± 0.01 at high salt. The same behavior was observed for different polyelectrolytes and substrates and therefore is suspected to be generic. Due to semi-quantitative agreement with computer simulations carried out by Kong and Muthukumar in 1998, the observed behavior is interpreted with conformational changes of single adsorbed polyelectrolyte chains.
Publisher: Walter de Gruyter GmbH
Date: 25-07-2012
Abstract: Colloidal stability and charging behavior of amidine latex particles in the presence of multivalent oligomers of acrylic acid was investigated by electrophoresis and light scattering. The data were interpreted quantitatively with the theory of Derjaguin, Landau, Verwey and Overbeek (DLVO) whereby the surface potentials were estimated from electrophoresis. Monomer leads to slow aggregation at low concentrations and to rapid aggregation at high concentrations, as characteristic for simple salts. The oligomers induce a charge reversal of the particles. Close to the isoelectric point (IEP) aggregation is rapid while the suspension becomes stable away from this point. At high oligomer concentrations, the aggregation becomes rapid again. The agreement between DLVO theory and experiment is good close to the IEP. At higher oligomer concentrations, the theory predicts larger stabilities than observed experimentally. While inter-particle forces seem to be well described by DLVO theory near the IEP, additional attractive non-DLVO forces are becoming relevant at higher concentrations.
Publisher: Elsevier BV
Date: 02-2013
DOI: 10.1016/J.JCIS.2012.09.058
Abstract: Charging and aggregation of negatively charged carboxyl latex particles in the presence of positively charged linear oligoamines containing 1-6 amine groups were investigated by electrophoretic mobility and dynamic light scattering. The oligoamines of low valence resemble simple inert salts and destabilize the suspensions by screening their charge. The oligoamines of higher valence induce overcharging at low concentrations, whereby destabilization is triggered by charge neutralization. At higher concentrations, destabilization is also induced by screening. The onset of first fast aggregation regime scales with the inverse six power of the valence in agreement with the Schulze-Hardy rule. The aggregation rates can be relatively well described by the DLVO theory which indicates that the interactions are governed by van der Waals and electrostatic double layer forces.
Publisher: American Chemical Society (ACS)
Date: 05-04-2012
DOI: 10.1021/LA300542Y
Abstract: The destabilization of charged colloidal suspensions is studied in the presence of polyelectrolytes and the corresponding oligomers. Two different systems are investigated, namely, negatively charged particles in the presence of polyamines and positively charged ones in the presence of polycarboxylates. Multivalent oligomers of low valence destabilize the particles by screening according to the Schulze-Hardy rule. Polyelectrolytes induce destabilization by overcharging. Both regimes can be observed for oligomers of intermediate valence. The stability data of any valence can be rather well described by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), indicating that the interactions are mainly governed by van der Waals and electrostatic double-layer forces.
Publisher: Swiss Chemical Society
Date: 27-11-2013
Abstract: The present article reviews recent progress in the measurement of aggregation rates in colloidal suspensions by light scattering. Time-resolved light scattering offers the possibility to measure absolute aggregation rate constants for homoaggregation as well as heteroaggregation processes. We further discuss the typical concentration dependencies of the aggregation rate constants on additives. Addition of simple salts containing monovalent counterions leads to screening of the electrostatic repulsion of the charged particles and a transition from slow to rapid aggregation. Addition of salts containing multivalent counterions may lead to a charge reversal, which results in a sequence of two instability regions. Heteroaggregation rates between oppositely charged particles decrease with increasing salt level. This decrease is caused by screening of the electrostatic attraction between these particles.
Publisher: American Chemical Society (ACS)
Date: 11-07-2011
DOI: 10.1021/LA201968B
Abstract: Positively charged amidine latex particles are studied in the presence of poly(acrylic acid) (PAA) with different molecular masses under neutral and acidic conditions by electrophoresis and time-resolved dynamic light scattering. Under neutral conditions, where PAA is highly charged, the system is governed by the charge reversal induced by the quantitatively adsorbing polyelectrolyte and attractive patch-charge interactions. Under acidic conditions, where PAA is more weakly charged, the following two effects come into play. First, the lateral structure of the adsorbed layers becomes more homogeneous, which weakens the attractive patch-charge interactions. Second, polyelectrolyte adsorption is no longer quantitative and partitioning into the solution phase is observed, especially for PAA of low molecular mass.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Amin Sadeghpour.