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Titolo:
ADSORPTION OF CATIONIC SURFACTANTS ON A HYDROPHILIC SILICA SURFACE ATLOW SURFACE COVERAGES - EFFECTS OF THE SURFACTANT ALKYL CHAIN AND EXCHANGEABLE SODIUM-CATIONS AT THE SILICA SURFACE
Autore:
ZAJAC J; TROMPETTE JL; PARTYKA S;
Indirizzi:
UNIV MONTPELLIER 2,LAB AGREGATS MOL & MAT INORGAN,PL E BATAILLON F-34095 MONTPELLIER 05 FRANCE UNIV MONTPELLIER 2,LAB AGREGATS MOL & MAT INORGAN F-34095 MONTPELLIER05 FRANCE
Titolo Testata:
Langmuir
fascicolo: 5, volume: 12, anno: 1996,
pagine: 1357 - 1367
SICI:
0743-7463(1996)12:5<1357:AOCSOA>2.0.ZU;2-D
Fonte:
ISI
Lingua:
ENG
Soggetto:
VARIABLE-CHARGE SURFACES; IONIC SURFACTANTS; WATER INTERFACE; ADSORBED LAYER; MECHANISM; HETEROGENEITY; FORCES; MODEL; MICA; SIZE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
46
Recensione:
Indirizzi per estratti:
Citazione:
J. Zajac et al., "ADSORPTION OF CATIONIC SURFACTANTS ON A HYDROPHILIC SILICA SURFACE ATLOW SURFACE COVERAGES - EFFECTS OF THE SURFACTANT ALKYL CHAIN AND EXCHANGEABLE SODIUM-CATIONS AT THE SILICA SURFACE", Langmuir, 12(5), 1996, pp. 1357-1367

Abstract

The influence of the alkyl chain length and the concentration of exchangeable sodium cations at the solid/water interface on the energeticsof cationic surfactant adsorption on a hydrophilic silica surface at free pH has been studied. Adsorption isotherms, electrophoretic mobilities of the silica particles, and differential molar enthalpies of displacement for benzyldimethyldodecylammonium bromide (BDDAB) on the original silica sample (SilNa) at different ionic strengths (pure deionized water and 0.1 M NaBr solution) were compared, as well as those on awashed silica sample (SilH). The stability of silica suspensions,as characterized by the changes in turbidity, was analyzed with the intention of shedding light on the possible orientation of the adsorbed surfactant ions. Adsorption of BDDAB was also compared with that of benzyldimethyloctylammonium bromide (BDOAB) on SilNa. Individual surfactant adsorption occurs by ion pairing or cation exchange mechanisms, depending on the purity of silica sample and composition of the bulk phase. A significant endothermic contribution to the total enthalpy of displacement upon individual surfactant adsorption derives from desorption of the very structured interfacial water due to the specific adsorptionof a hydrophobic surfactant moiety. In the presence of sodium cationsat the silica surface,this endothermic contribution dominates over others because the enthalpy of adsorption for surfactant ionic heads andthe enthalpy of desorption for sodium cations cancel each other out to a great extent. For moderate interfacial concentrations of sodium, the overall enthalpy change is endothermic in a certain adsorption interval, whereas for high concentrations it is always exothermic. Individual surfactant adsorption at free pH causes the pH of the equilibrium bulk solution to decrease, indicating an increase in the surface charge of silica.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 05/04/20 alle ore 03:55:59