Polymer−Surfactant Interaction As Revealed by the Time Dependence of Surface Tension. The EHEC/SDS/Water System

Abstract

Adsorption properties at an air/water interface and interaction between a nonionic polymer ethyl-(hydroxyethyl) cellulose (EHEC) and sodium dodecyl sulfate (SDS) were studied by pendant drop tensiometry, enhanced by video-image digitization and computerized data handling. Three studies were performed over the concentration range 0-19 mM SDS with fixed concentrations of EHEC: 0.2% w/w, 12 ppm, and 2 ppm. Particular emphasis was placed on the investigation of the dynamics of surface tension in the presence and absence of SDS. This study demonstrates that the onset of complex (cluster) formation can be identified by surface-tension measurements even when a very hydrophobic polymer such as EHEC is part of the complex. Considerable synergism in surface activity is observed in the EHEC-SDS mixtures. Below the critical aggregation concentration (cac), the degree of surface-tension reduction was found to depend on the bulk concentration of surfactant molecules, as well as the number of polymer segments in actual contact with the surface at the time of measurement. At and above cac an extraordinary acceleration of polymer adsorption was observed following the addition of SDS. Considerable evidence regarding the presence of a polymer/surfactant complex at the air/water interface is discussed in the paper. The dynamics of surface tension, at and above cac, are explained in terms of the observations that charged clusters are bound along the polymer chain and cause an appreciable change of the polymer conformation. In agreement with the results, polyelectrolytic properties of the EHEC/DScomplex cause the complex to become firmly adsorbed to the air/water interface. The adsorption kinetics strongly suggested a progressive ordering of the polymer/surfactant aggregates within the monolayer, based on observations of the surface film after aging (17 h). The findings can be of practical use in applications where quick wetting and absorption are required, e.g., in injected, spread, or inhaled drug formulations. LA960976I

Physicochemical characterization of chitosan derivatives

“…A similar behaviour in relation to the polymer concentration influence has been found by different researchers (Fainerman et al, 2006;Nahringbauer, 1997). Being more specific, for chitosan aqueous solutions and chitosan sulphate, a decrease in the surface tension value is produced when the polymer concentration increases until reaching a constant value of this property.…”

“…Supplementary Figure S4 shows an example of the supposed behaviour at a gas-liquid interface of this kind of systems (Nahringbauer, 1997). Taking into account this behaviour, the conformational changes in the polymer chains produce modifications in the surface tension throughout the time.…”

“…Also, the surface tension is an interesting attribute to analyse when polymer *Corresponding author. Email: josemanuel.navaza@usc.es aqueous solutions are used, since this kind of liquid systems commonly show a dynamic behaviour (Nahringbauer, 1995(Nahringbauer, , 1997.…”

Auto-associação do dodecilsulfato de sódio (SDS) com o polímero hidrofobicamente modificado etil(hidroxietil) celulose (EHEC)

“…[1][2][3][4][5][6][7][8] A associação é vista como sendo um fenômeno induzido pelo polímero e inicia em concentrações menores do que quando na sua ausência e o resultado é a formação de complexos termodinamicamente estáveis, com propriedades físico-químicas diferentes daquelas observadas em soluções micelares. [9][10][11][12][13] Alguns questionamentos são feitos com relação à natureza da estabilidade da interação entre o surfactante e o polímero. A mais "popular" interpretação refere-se ao caráter hidrofóbico, tanto do surfactante como de seções da cadeia polimérica.…”

“…Quando a associação é entre moléculas forma em solução uma rede "mais rígida" que aumenta com o aumento da concentração de EHEC. Este último fato justifica o aumento da viscosidade em baixas concentrações de SDS; 19,21 (ii) adição de SDS -a interação inicia numa concentração de agregação crítica (cac), comprovada pelas alterações em propriedades já analisadas como diminuição da viscosidade, 1,19,[21][22][23] condutividade elétrica 2,6,19,23 e tensão superficial 9,24,25 . Acima da cac a tendência é dos agregados micelares no complexo estabelecerem-se nas regiões mais hidrofóbicas, com o aumento da concentração de EHEC.…”