Effects of Aggregate Charge and Subphase Ionic Strength on the Properties of Spread Polyelectrolyte/Surfactant Films at the Air/Water Interface under Static and Dynamic Conditions

Abstract

We demonstrate the ability to tune the formation of extended structures in films of poly(sodium styrenesulfonate)/dodecyltrimethylammonium bromide at the air/water interface through control over the charge/structure of aggregates as well as the ionic strength of the subphase. Our methodology to prepare loaded polyelectrolyte/surfactant films from self-assembled liquid crystalline aggregates exploits their fast dissociation and Marangoni spreading of material upon contact with an aqueous subphase. This process is proposed as a potential new route to prepare cheap biocompatible films for transfer applications. We show that films spread on water from swollen aggregates of low/negative charge have 1:1 charge binding and can be compressed only to a monolayer, beyond which material is lost to the bulk. For films spread on water from compact aggregates of positive charge, however, extended structures of the two components are created upon spreading or upon compression of the film beyond a monolayer. The application of ellipsometry, Brewster angle microscopy, and neutron reflectometry as well as measurements of surface pressure isotherms allow us to reason that formation of extended structures is activated by aggregates embedded in the film. The situation upon spreading on 0.1 M NaCl is different as there is a high concentration of small ions that stabilize loops of the polyelectrolyte upon film compression, yet extended structures of both components are only transient. Analogy of the controlled formation of extended structures in fluid monolayers is made to reservoir dynamics in lung surfactant. The work opens up the possibility to control such film dynamics in related systems through the rational design of particles in the future.

Two Different Scenarios for the Equilibration of Polycation—Anionic Solutions at Water–Vapor Interfaces

“…In this case, the absence of surface tension fluctuation or significant differences in the results obtained using different tensiometers suggests the existence of dissociation and spreading of the kinetically trapped aggregates upon adsorption at the interface. Thus, the equilibration of the interface after the adsorption of the kinetically trapped aggregates occurs because of its dissociation, which is followed by the spreading of the complexes across the interface as a result of Marangoni flow associated with the lateral heterogeneity of the interface [38,42,50,59]. The differences in the adsorption mechanisms of PDADMAC-SLES and PDADMAC-SLMT complexes at the water-vapor interface may be explained on the bases of the molecular structures of the surfactant and the possibility to establish a cohesion interaction with the surrounding media.…”

“…The induction time in the adsorption of PDADMAC-SLES is explained considering that the equilibration of the interface proceeds following a two-step mechanism, as occurs for protein adsorption at fluid interfaces [61]. Firstly, polymer-surfactant complexes attach to the water-vapor interface as kinetically trapped aggregates until the surface excess overcomes a threshold value, after which point the adsorbed complexes undergo a dissociation and spreading process, which is responsible for the surface pressure increase [41,59]. It is worth mentioning that the decrease of the induction time with the increase of surfactant concentration results from the faster saturation of the interface, i.e., the shortening of the time needed to overcome the surface excess threshold, which leads The analysis of the adsorption kinetics show clearly that the increase of the surfactant concentration leads to the faster increase of the surface pressure, due to the higher hydrophobicity of the formed complexes.…”

Adsorption of Denaturated Lysozyme at the Air–Water Interface: Structure and Morphology

“…Both angles of polarization for the laser beam and analyser were set to zero, and in this way background subtraction was not needed. 43 The images were recorded at an incident angle of 53.1° (the Brewster angle of the air-water interface) for the measurement without added denaturant and 53.9° for the measurement in 5 M urea solution as a result of the refractive index difference. 44 Constant gamma correction was applied to the images to enhance uniformly the appearance of the interfacial morphologies.…”

Contrast variation of micelles composed of Ca2+ and block copolymers of two negatively charged polyelectrolytes

“…Polyelectrolytes and their interactions with oppositely charged species such as ions, [1] surfactants [2][3][4], or charged surfaces [5] are essential to understand and control a variety of industrial processes. These include waste water treatment, [6] modification of the rheological behavior of concrete through superplasticizers [7,8], or the properties of consumer goods such as shampoo [9].…”