ISSN:
1435-1536
Schlagwort(e):
Polyelectrolytes
;
co-polyelectrolytes
;
surface potential
;
acid-base indicators
;
dyes
;
neutral red
;
safranine-T
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
,
Maschinenbau
Notizen:
Abstract The surface potential, ψ in mV, was determined for the following polyelectrolytes and co-polyelectrolytes in aqueous solution: sodium poly(styrene sulfonate); sodium poly(vinyl sulfonate); poly(vinyl alcohol-co-55% sodium vinyl sulfate); poly(methylmethacrylate-co-40% sodium styrene sulfonate); poly (methylmethacrylate-co-60% sodium styrene sulfonate); poly(styrene-co-56% styrene sulfonate); and poly(styrene-co-80% styrene sulfonate). For comparison, the surface potentials of aqueous sodium dodecyl sulfate and sodium dodecylbenzene sulfonate micelles were also determined. The dyes neutral red and safranine-T were used as indicators. ThepKa of the former was calculated from the Henderson-Hasselbach equation, using UV-VIS spectroscopy to determine the concentration of protonated ground state as a function of pH. The surface potential of the aggregates was culculated from the equation: $$pKa_{\text{i}} = pKa_0 - {{F\Psi } \mathord{\left/ {\vphantom {{F\Psi } {2.3RT}}} \right. \kern-\nulldelimiterspace} {2.3RT}}$$ wherepKa i andpKa o refer to the indicatorpKa in the presence of charged and nonionic interfaces, respectively, and the other terms have their usual meaning. The protonation kinetics of the triplet state of safranine-T (measured from the decay of its transient absorption at 830 nm) was used to determine hydronium ion concentrations at aggregate interfaces, and the corresponding surface potentials were calculated from: $$a_{{\text{Hi}}} = a_{{\text{Haq}}} \times \exp \left( {{{ - F\Psi } \mathord{\left/ {\vphantom {{ - F\Psi } {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right)$$ wherea Hi anda Haq refer to the hydronium ion activity at the aggregate interface, and in bulk water, respectively. Surface potentials determined by both techniques were in excellent agreement. Values of ψ were found to depend on the structure of the polyelectrolyte, sodium poly(styrene sulfonate) versus sodium poly(vinyl sulfonate) and, for the same type of co-polyelectrolyte, on the percentage of charged monomer.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00652471
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