An increase in temperature typically leads to a decrease in the interfacial tension of a water/oil interface. The addition of surfactants to the system can complicate the situation significantly, i.e., the interfacial tension can increase or decrease with an increasing temperature. For most concentrations of the two studied surfactants, the cationic tetradecyl trimethyl ammonium bromide (TTAB) and the nonionic tridecyl dimethyl phosphine oxide (C13DMPO), the measured interfacial tension of the aqueous mixed surfactant solutions against hexane increases when the temperature decreases between 30 °C and 20 °C. However, with a further temperature decrease between 20 °C and 15 °C, the reverse effect has also been observed at some concentrations, i.e., a decrease of interfacial tension. Additionally, the corresponding dilational interfacial visco-elasticity shows some discrepant temperature effects, depending on the bulk concentration and oscillation frequency. The experiments have been performed with a capillary pressure tensiometer under the conditions of micro-gravity. The reason for the positive and negative interfacial tension and visco-elasticity gradients, respectively, within certain ranges of the temperature, concentration and mixing ratios, are discussed on the basis of all available parameters, such as the solubility and partitioning of the surfactants in the two liquid phases and the oscillation frequency.

Amphiphilic silk fibroin (SF) forms stable adsorption layers at the air–water interface. The range of the investigated protein concentrations can be divided into two parts according to the peculiarities of the surface layer properties. At protein concentrations from 0.0005 to 0.01 mg/mL, the dynamic surface elasticity monotonically increases with the concentration and surface age and reaches values of up to 220 mN/m. In this range, the adsorption layer compression leads to a fast increase of the surface pressure. In the second part (>0.01 mg/mL), the surface elasticity decreases again and the kinetic dependences of the film thickness and adsorbed amount change only a little. In this case, the layer compression leads only to a slight increase of the surface pressure. These two types of behavior can be attributed to the distinctions in the protein aggregation in the surface layer. Atomic force microscopy (AFM) investigations of the layers transferred from the liquid surface onto a mica surface by the Langmuir–Schaefer method show some peculiarities of the layer morphology in the intermediate concentration range (~0.02 mg/mL).

The dynamic surface properties of aqueous dispersions of α-lactalbumin (ALA) amyloid fibrils differ noticeably from the properties of the fibril dispersions of other globular proteins. As a result, the protocol of the application of ALA fibrils to form stable foams and emulsions has to be deviate from that of other protein fibrils. Unlike the fibrils of β-lactoglobulin and lysozyme, ALA fibrils can be easily purified from hydrolyzed peptides and native protein molecules. The application of the oscillating barrier method shows that the dynamic surface elasticity of ALA fibril dispersions exceeds the surface elasticity of native protein solutions at pH 2. ALA fibrils proved to be stable at this pH, but the stability breaks at higher pH levels when the fibrils start to release small peptides of high surface activity. As a result, the dynamic surface properties of ALA coincide with those of native protein solutions. The ionic strength strongly influences the adsorption kinetics of both fibril dispersions and native protein solutions but have almost no impact on the structure of the adsorption layers.

The spread layers of lysozyme (LYS) microgel particles were studied by surface dilational rheology, infrared reflection–absorption spectra, Brewster angle microscopy, atomic force microscopy, and scanning electron microscopy. It is shown that the properties of LYS microgel layers differ significantly from those of ß-lactoglobulin (BLG) microgel layers. In the latter case, the spread protein layer is mainly a monolayer, and the interactions between particles lead to the increase in the dynamic surface elasticity by up to 140 mN/m. In contrast, the dynamic elasticity of the LYS microgel layer does not exceed the values for pure protein layers. The compression isotherms also do not exhibit specific features of the layer collapse that are characteristic for the layers of BLG aggregates. LYS aggregates form trough three-dimensional clusters directly during the spreading process, and protein spherulites do not spread further along the interface. As a result, the liquid surface contains large, almost empty regions and some patches of high local concentration of the microgel particles.

The application of surface rheology and Brewster angle microscopy on mixed monolayers of DPPC and polymeric nanoparticles (cationic and anionic) showed that the sign of the particle charge affects the dynamic properties of the monolayers less than the nanoparticles’ ability to aggregate. Under almost physiological conditions, the effect of nanoparticles on the elasticity of DPPC monolayer is insignificant. However, the particles prevent the surface tension from decreasing to extremely low values. This effect could affect the functionality of pulmonary surfactants.

Although the formation of the layers of fibrillar aggregates at liquid–liquid and liquid–gas interfaces can significantly increase the stability of disperse systems, like foams and emulsions, any information on their structure and properties is rather limited. In the present work, surface properties of the adsorption layers of fibrils of intrinsically disordered β-casein are investigated. For unpurified dispersions of the fibrils of this protein, the dynamic surface elasticity proved to be close to the values for the native protein solutions. This behavior is typical for dispersions of fibrils of globular proteins. However, previously studied fibrils of another intrinsically disordered protein, κ-casein, do not demonstrate this similarity. The contribution of β-casein fibrils to the dynamic surface properties becomes noticeable only after the purification of the dispersions from impurities of high surface activity. The dynamic surface elasticity increases up to 48 mN/m after two purification cycles, i.e., to values 4 times higher than the steady-state values of native protein adsorption layers at the same protein bulk concentrations.