Charge-driven co-assembly of polyelectrolytes across oil-water interfaces
Monteillet, H. ; Hagemans, F. ; Sprakel, J.H.B. - \ 2013
Soft Matter 9 (2013)47. - ISSN 1744-683X - p. 11270 - 11275.
controlled flocculation - opposite charge - small particles - emulsions - membranes
We report a simple strategy to co-assemble oppositely charged polyelectrolytes across oil–water interfaces; this allows the accumulation of an electrostatic complex at the interface of species that are not surface active by themselves. To this end, we use a new, oil-soluble anionic polymer, poly-(fluorene-co-benzothiadiazole-co-benzoic acid), in combination with a cationic polyelectrolyte that is dissolved in the aqueous phase. When only one of the two charged components is present, no positive adsorption is observed in interfacial tension measurements; by contrast, when both polyelectrolytes are present, in the oil and water phases respectively, a rapid decrease of the interfacial tension is observed, indicating co-adsorption of the cationic and anionic polyelectrolytes. The complexation strength can be tuned through changes in both ionic strength and pH. Confocal microscopy and co-localization analysis further verifies the presence of both polyelectrolytes at the interface. With this approach, emulsions can be stabilized for several weeks; moreover, using the sensitivity of the complex to changes in pH, we are able to reversibly break and make the emulsions on demand.
Binding of alkylpyridinium chloride surfactants to sodium polystyrene sulfonate
Ishiguro, M. ; Koopal, L.K. - \ 2009
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 347 (2009)1-3. - ISSN 0927-7757 - p. 69 - 75.
streaming current detector - monte-carlo simulations - variable-charge surfaces - metal-oxide surfaces - field lattice model - ionic surfactants - cationic surfactants - anionic surfactants - humic substances - opposite charge
Binding of cationic surfactants to anionic polymers is well studied. However, the surfactant binding characteristics at very low concentration near the start of binding and at high concentration, where charge compensation may Occur. are less well known. Therefore, the binding characteristics of hexadecylpyridinium chloride (C16PC), dodecyl-pyridinium chloride (C12PC) and decyl-pyridinium chloride (C10PC) to sodium polystyrene sulfonate (SPSS) are investigated over a wide concentration range. The equilibrium surfactant concentration is measured with a surfactant-selective membrane electrode. The electrode shows good performance for the three surfactants, also in presence of SPSS. The observed critical micelle concentrations (CMCs) of the surfactants as a function of the ionic strength agree well with literature values and the CIVIC is not significantly affected by the presence of SPSS. For each surfactant, binding isotherms are obtained from depletion studies at three different NaCl concentrations. For C16PC and C12PC the binding isotherms at different NaCl concentration have a common intersection point (CIP) at relatively high surfactant concentration. For C10PC the experimental accuracy is too small to observe a CIP. The CIP closely corresponds with the bound amount at the iso-electric point (IEP) of the surfactant-SPSS complex. At the IEP/CIP the charge of SPSS is compensated by bound surfactant ions. In region between the CIP and the CMC the polyelectrolyte charge is overcompensated by surfactant ions. Similar behavior has been found before with the same surfactants and humic acid as polyelectrolyte. At very low surfactant concentrations the C10P+ ions bind on isolated sites along the SPSS chain, the C12P+ ions form some dimers and the C16P+ ions form. already at the lowest concentration that could be measured, aggregates. At somewhat higher concentrations also C10PC and C12PC start to form small aggregates along the SPSS chain. The concentration at which this occurs is the critical aggregation concentration (CAC). Similarly as the CMC the CAC is a function of the surfactant chain length and the ionic strength. The size of the small aggregates increases with increasing chain length, but hardly depends on the ionic strength. With increasing surfactant concentration the formation of the aggregates along the SPSS chain continues. Electrode calibration at very low concentrations C16PC and C12PC can be improved when the SPSS-surfactant complex is used to buffer the solutions.
Monte Carlo simulations of flexible polyanions complexing with whey proteins at their isoelectric point
Vries, R.J. de - \ 2004
Journal of Chemical Physics 120 (2004)7. - ISSN 0021-9606 - p. 3475 - 3481.
polyelectrolyte-macroion complexation - continuous capillary-electrophoresis - heterogeneously charged surfaces - bovine serum-albumin - light-scattering - chain flexibility - opposite charge - adsorption - polymer - binding
The complexation of globular proteins with flexible polyelectrolytes with homogeneous, oppositely charged spheres was discussed using Monte Carlo simulations. The proteins were considered at their respective isoelectric points. A coarse-grained model of the protein shape was also considered in order to take into account the protein excluded volume. A simple statistical analysis of the surface charge density was found sufficient for identifying potential polyelectrolyte binding regions. The protein-only approach identified only possible regions of polyelectrolyte binding, and did not account for any of the polyelectrolyte properties tha influenced binding.