In this study, the foamability of pure solutions of alkyltrimethylammonium bromides (C n TAB with n = 8, 12, and 16) of various concentrations and their mixtures with n-octanol was studied. It was found from the results that n-octanol behaved as a foamability enhancer, depending on the C n TAB solution concentration. A similar foam height was obtained in C n TAB/octanol systems compared to pure C n TAB solutions with a greatly reduced amount of cationic surfactants. This synergistic effect between C n TAB and n-octanol was quite significant, and it could be observed for systems where the C n TAB concentration differed even by two orders of magnitude. Such behavior was observed only below some characteristic concentration of C n TAB, called a critical synergistic concentration (CSC), above which the synergistic effect was either no longer visible or significantly reduced. Moreover, it was found that the presence of n-octanol affected only the solution foamability without significant changes in the stability of the foams. A possible origin of this effect was analyzed and discussed on the basis of the magnitude of the surface elasticity forces induced in the foam films during the foam generation period and while operating during foam decay.

Cationic alkyltrimethylammonium bromides (C n TAB, with n = 8, 12, 16, 18) and their mixtures with n -octanol as a nonionic surfactant were chosen as a model system to study the synergistic effect on foamability (two-phase system) and floatability (three-phase system) of quartz in the presence of binary mixtures of ionic/nonionic surfactants. The foam height of one-component solutions and binary mixtures and floatability of quartz particles were characterized as a function of the surfactant concentration and the number of carbons ( n ) in the alkyl chain of C n TAB. The experimental results of foamability and floatability measurements in one-component and mixed solutions revealed the synergistic effect, causing a significant enhancement in the foam height and recovery of quartz. In the presence of n -octanol, the height of foam increased remarkably for all C n TAB solutions studied, and this effect, whose magnitude depended on the C n TAB hydrophobic tail length, could not be justified by a simple increase in total surfactant concentration. A similar picture was obtained in the case of flotation response. The mechanism of synergistic effect observed in mixed C n TAB/ n -octanol solutions was proposed. The discussion was supported by molecular dynamics simulations, and the probable mechanism responsible for synergism was discussed. In addition, an analysis allowing accurate determination of the concentration regimes, where the synergistic effect can be expected, was given. It was shown that for the two-phase system, the n -octanol molecule preadsorption at the liquid/gas interface causes an increase in C n TAB adsorption coverage over the level expected from its equilibrium value in the one-component solution. In the case of the three-phase system, the synergistic effect was related to the ionic surfactants serving as an anchor layer for n -octanol, which, in water/ n -octanol solution (one-component system), do not adsorb on the surface of quartz.

This paper presents a simple method for determination of synergism in binary surfactant mixtures. A homologous series of cationic alkyltrimethylammonium bromides (CnTAB, with n = 8, 12, 16, 18) mixed with three non-ionic surfactants (n-octanol, methyl isobutyl carbinol, tri(propylene glycol) butyl ether) was chosen as a model system. In addition to the cationic-non-ionic system, the mixture of anionic-non-ionic surfactants (sodium dodecyl sulphate and tri(propylene glycol) butyl ether) was investigated. The foam behavior of one-component solutions and binary mixtures was characterized as a function of surfactant concentration, number of carbons (n) in alkyl chain of CnTAB as well as type of surfactant. It was shown that synergism in foamability could be produced by the ionic-non-ionic systems, and the concentration below the synergism occurs, called the critical synergistic concentration (CSC), that can be easily predicted based on the surface tension data on individual components.

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It is well known that carbon nanotube (CNT) oxidation (usually with concentrated HNO3) is a major step before the electrophoretic deposition (EPD). However, the recent discovery of the “onion effect” proves that multiwalled carbon nanotubes are not only oxidized, but a simultaneous unsheathing process occurs. We present the first report concerning the influence of unsheathing on the properties of the thus-formed CNT surface layer. In our study we examine how the process of gradual oxidation/unsheathing of a series of multiwalled carbon nanotubes (MWCNTs) influences the morphology of the surface formed via EPD. Taking a series of well-characterized and gradually oxidized/unsheathing Nanocyl™ MWCNTs and performing EPD on a carbon fiber surface, we analyzed the morphology and wettability of the CNT surfaces. Our results show that the water contact angle could be gradually changed in a wide range (125–163°) and the major property determining its value was the diameter of aggregates formed before the deposition process in the solvent. Based on the obtained results we determined the parameters having a crucial influence on the morphology of created layers. Our results shed new light on the deposition mechanism and enable the preparation of surfaces with steerable roughness and wettability.