RESUMO
The Langmuir surface balance technique has been used to study the interfacial behavior of six structurally different poly(oxyethylene) (POE)-based polymer surfactants at the air-water interface. On a pure water subphase the surfactants have collapse surface pressures dependent on the POE chain length. The surfactant monolayers collapse at well-determined surface pressures, and the lower POE chain-length surfactants collapse at higher pressures than those with high POE content. This difference vanishes as increasing amounts of salt are added to the subphase. The PiA-isotherms are smooth, which is normal for polymeric surfactants. A closer analysis of the isotherms reveals characteristic behavior that can be attributed to structural differences. Similarities in thermodynamic behavior suggest that the molecular orientation is the same despite the structural differences. A new expression for the compressibility factor is developed to explain the relationship between this parameter and surface pressure for polymeric monolayers. Copyright 1999 Academic Press.
RESUMO
Time dependent interfacial tensions between CCl4, butyl acrylate (BA), and methyl methacrylate (MMA) and water have been measured, using nine different aryl and alkyl poly(oxyethylene) surfactants with between 10 and 40 OE-groups. The effect of adding BA/MMA and BA/MMA/acrylic acid (AA) polymers to the monomer systems has also been evaluated. In all systems the interfacial tension, after a very fast initial drop, decreases slowly due to dissolution of the surfactant inside the oil. The magnitude of this decrease is dependent on the hydrophilicity of the surfactant and the oil. The equilibrium values, when plotted against the HLB of the surfactants show a minimum that shifts toward higher HLB as the oil's polarity increases. BA and CCl4 show similar behavior, but with MMA as a more polar oil. Added polymer generally lowers the time dependent decrease because of decreased surfactant solubility in monomer/polymer mixtures. The BA/MMA copolymer also generally increases the interfacial tension both with and without surfactants, but the increase is less with surfactants around the surface tension minimum. A BA/MMA/AA terpolymer neutralizes or even reverses the increasing effect in the BA/polymer system because of this polymer's more hydrophilic nature. Copyright 1999 Academic Press.
RESUMO
The pendant drop/sessile drop instrument developed by our group and based on video image analysis has been enhanced to measure oscillating drops and bubbles at a rate up to 25 pictures per second. Data analysis has been developed to analyze the results from sinusoidal oscillations in terms of dilatational surface elasticity and viscosity. The polymers ethylhydroxyethyl cellulose (EHEC) and two different poly(oxyethylene)-poly(oxypropylene) ABA block copolymers (PE6200 and PE6800) have been investigated at the air-water interface regarding rate of adsorption and surface dilatational properties. The polymers give surface pressures in the region 20-30 mN m-1, the surface elastic moduli are between 4 and 30 mN m-1, and the viscous moduli are generally low, from 0 to 6 mN m-1. The elastic moduli increase with increasing frequency, but both the slope and the concentration dependency vary. For the most water-insoluble polymer, EHEC, the modulus increases with polymer concentration, the relatively hydrophobic polymer PE6200 shows the opposite behavior, and the most water-soluble polymer, PE6800, shows a maximum in the equilibrium elasticity. These observations can be explained by the changes in the molecular orientation in the surface layer as reflected in pi vs A isotherms. The PE6200 polymer also shows a higher viscous modulus, which may be explained by diffusional transport between surface and bulk. Copyright 1998 Academic Press.
