Adsorption of sodium dodecyl sulfate and sodium dodecyl benzenesulfonate on poly(vinyl chloride) latexes

Deciphering the role of premicellar and micellar concentrations of sodium dodecyl benzenesulfonate surfactant in insulin fibrillation at pH 2.0

Amyloid fibril formation by proteins and their deposition in cells and tissues are associated with several amyloid-based disorders. Understanding the mechanism of amyloid fibril formation is thus of the utmost importance for the designing ligands that could prevent or inhibit the fibrillation process and help to treat of such disorders. We describe the stimulatory effect of sodium dodecyl benzenesulfonate (SDBS) on insulin amyloid fibrillation at pH 2.0 and the characterization of SDBS-induced insulin aggregation using spectroscopy and microscopy. We found that SDBS induced amyloid-like aggregates of insulin at sub-micellar (0.1-1.2 mM), but not post-micellar (≥2.0 mM) concentrations. The amyloid fibrillation of insulin induced by SDBS was kinetically rapid and escaped the lag phase. Far-UV CD findings suggested that the α-helical content of insulin transformed into cross-β structure and mixed α and β structures when incubated with sub-micellar and post-micellar SDBS concentrations, respectively. The overall results indicated that low, but not high SDBS concentrations induce amyloid-like insulin aggregates and fibrils.

Governing Influence of Thermodynamic and Chemical Equilibria on the Interfacial Properties in Complex Fluids

We propose a comprehensive analysis and a quasi-analytical mathematical formalism to predict the surface tension and contact angles of complex surfactant-infused nanocolloids. The model rests on the foundations of the interaction potentials for the interfacial adsorption-desorption dynamics in complex multicomponent colloids. Surfactant-infused nanoparticle-laden interface problems are difficult to deal with because of the many-body interactions and interfaces involved at the meso-nanoscales. The model is based on the governing role of thermodynamic and chemical equilibrium parameters in modulating the interfacial energies. The influence of parameters such as the presence of surfactants, nanoparticles, and surfactant-capped nanoparticles on interfacial dynamics is revealed by the analysis. Solely based on the knowledge of interfacial properties of independent surfactant solutions and nanocolloids, the same can be deduced for complex surfactant-based nanocolloids through the proposed approach. The model accurately predicts the equilibrium surface tension and contact angle of complex nanocolloids available in the existing literature and present experimental findings.

Simulation of Vertical Surfactant Distributions in Drying Latex Films

Following our previous contribution ( Gromer, A. et al. Langmuir 2015 , 31 , 10983 - 10994 ) presenting a new simulation tool devoted to particle distributions in drying latex films, this Article describes the prediction of surfactant concentration profiles in the vertical direction during the complete film formation process. The simulation is inspired by cellular automata and equations by Routh and co-workers. It includes effects that were not considered before: surfactant convection by water and surfactant desorption upon particle deformation. It is based on five parameters describing the nature of the polymer/surfactant system and on film formation conditions. In particular, the viscoelastic properties of the polymer were taken into account through the λ̅ parameter introduced by Routh and Russel. Results show the importance of convection by water and the influence of the particular deformation mechanism on the final surfactant distribution. Excesses or depletions can be predicted either on the surface or on the substrate sides, in qualitative agreement with the numerous existing experimental studies. The complex interplay between parameters governing surfactant distributions makes the results unpredictable without the help of such a simulation tool. Therefore, it should be of interest to both industrial and academic scientists.

Adsorption and desorption behavior of ionic and nonionic surfactants on polymer surfaces

We report combined experimental and computational studies aiming to elucidate the adsorption properties of ionic and nonionic surfactants on hydrophobic polymer surface such as poly(styrene). To represent these two types of surfactants, we choose sodium dodecyl sulfate and poly(ethylene glycol)-poly(ethylene) block copolymers, both commonly utilized in emulsion polymerization. By applying quartz crystal microbalance with dissipation monitoring we find that the non-ionic surfactants are desorbed from the poly(styrene) surface slower, and at low surfactant concentrations they adsorb with stronger energy, than the ionic surfactant. If fact, from molecular dynamics simulations we obtain that the effective attractive force of these nonionic surfactants to the surface increases with the decrease of their concentration, whereas, the ionic surfactant exhibits mildly the opposite trend. We argue that the difference in this contrasting behavior stems from the physico-chemical properties of the head group. Ionic surfactants characterized by small and strongly hydrophilic head groups form an ordered self-assembled structure at the interface whereas, non-ionic surfactants with long and weakly hydrophilic head groups, which are also characterized by low persistence lengths, generate a disordered layer. Consequently, upon an increase in concentration, the layer formed by the nonionic surfactants prevents the aprotic poly(ethylene glycol) head groups to satisfy all their hydrogen bonds capabilities. As a response, water molecules intrude this surfactant layer and partially compensate for the missing interactions, however, at the expense of their ability to form hydrogen bonds as in bulk. This loss of hydrogen bonds, either of the head groups or of the intruding water molecules, is the reason the nonionic surfactants weaken their effective attraction to the interface with the increase in concentration.

Contact angles of surfactant solutions on heterogeneous surfaces

Exploration of new model for contact angle of surfactant solutions on smooth/rough heterogeneous surfaces, allowing adsorption at all interfaces.

Tristearin bilayers: structure of the aqueous interface and stability in the presence of surfactants

Molecular dynamics simulations predict that sodium dodecylbenzene sulphonate surfactant molecules embed themselves in a tristearin bilayer, packing commensurate with the hexagonally packed lattice formed by the acyl tails of tristearin.

Surfactant kinetics and their importance in nucleation events in (mini)emulsion polymerization revealed by quartz crystal microbalance with dissipation monitoring

Surfactants are vital components of almost all heterogeneous polymerizations for maintaining colloidal stability, but they also play an important role in the kinetics and mechanism of particle nucleation. Despite many decades of research, the knowledge of adsorption-desorption surfactant kinetics and their application in (mini)emulsion polymerization is largely based on qualitative arguments. In this paper we show that the use of a quartz crystal microbalance with dissipation monitoring can provide quantitative information on both the adsorption equilibrium of ionic and nonionic surfactants, and also the kinetics of adsorption/desorption, that can be applied to the understanding of nucleation processes in (mini)emulsion polymerization. We show that surfactant dynamics and nucleation phenomena in (mini)emulsion polymerization are not dominated by diffusion phenomena linked to molecular size of surfactant as previously thought but rather are driven by the large differences in the rate of surfactant adsorption and desorption at the polymer-water interface. Finally, we show the application of this knowledge to explain the differences between nucleation processes for ionic and nonionic surfactants in emulsion polymerization.

Chitosan-based aerogels with high adsorption performance

New natural polymer-based aerogels, cross-linked chitosan aerogels, were prepared by the sol-gel route with glutaradehyde, glyoxal, and formaldehyde as cross-linkers. The alcogels were dried by supercritical carbon dioxide (CO2) fluid extraction. The resulting materials were characterized using scanning electron microscopy (SEM), nitrogen adsorption/desorption analysis, and Fourier transform infrared (FT-IR) spectroscopy. Furthermore, the adsorption of the anionic surfactant sodium dodecylbenzene-sulfonate (SDBS) from aqueous solution by the materials was investigated. The aerogels exhibit high adsorption capability, can remove SDBS from acidic aqueous solutions, and have potential applications in controlling SDBS pollution.