Influence of the type of foam films and the type of surfactant on foam stability

The behaviour and the life time ( _p) of different types of foam films (thin liquid films, for which DLVO-theory is valid; common black films, Newton black films) have been studied as a function of external pressure (P), applied in the Plateau-Gibbs-borders of the foam. The foam stability and the course of thep/P-dependence are determined mainly by the type of the foam films. A criterion for estimation of foam stability is proposed on the base of the obtained experimental results.     

Effect of environmental humidity on static foam stability

The quality of foaming products (such as beer and shampoo) and the performance of industrial processes that harness foam (such as the froth flotation of minerals or the foam fractionation of proteins) depend upon foam stability. In this study, experiments are performed to study the effect of environmental humidity on the collapse of static foams. The dependency of the rate at which a foam collapses upon humidity is demonstrated, and we propose a hypothesis for bubble bursting due to Marangoni instability induced by nonuniform evaporation to help explain the dependency. This hypothesis is supported by direct experimental observations of the bursting process of isolated bubbles by high speed video recording and the thinning of isolated foam films under different values of humidity and temperature by microinterferometric methods.     

Effect of lidocaine on ovalbumin and egg albumin foam stability

Foam fractionation is a simple separation process that can remove and concentrate hydrophobic molecules such as proteins, surfactants, and organic wastes from an aqueous solution. Bovine serum albumin and ovalbumin have been widely used as model proteins due to their strong foaming potential and low price. Here, we study the effect of lidocaine on albumin foam, since drugs like lidocaine are known to bind with albumin. We observed that lidocaine not only enhances the amount of foam produced but also the stability of that foam as well. The foam stability was evaluated as the decay rate constant of the foam, determined from a change in height (or volume) of the foam over a given time period.     

The effect of external reflux on the foam fractionation of proteins

Applied Biochemistry and Biotechnology - Foam fractionation of proteins is especially advantageous in treating dilute solutions where other separation methods run into economical limitations....     

Film junction effect on foam drainage

Foam drainage is modelled by the flow of liquid through Plateau borders (PBs) that are the liquid channels resulting from the merging of three liquid films separating the gas bubbles. Available models generally neglect the influence of these films. Yet, within drainage conditions, experimental observations indicate a strong coupling of these films with the channels. We consider the influence of films on foam drainage through their effect on the cross-section geometry of the channels. More precisely, we assume that the Plateau border cross-section is enclosed by three circular arcs that are not always tangent but instead exhibit a non-zero contact angle θ as it has been observed experimentally. The liquid flow through the channels is studied using numerical simulations whose parameters are θ and the Boussinesq number, Bo, that reflects the surface shear viscosity of the interface. We show that, for values of Bo relevant for foam drainage conditions, a slight increase of θ results in a strong decrease of the average liquid velocity.     

Relating foam lamella stability and surface dilational rheology

The surface dilational elasticity module E of a soluble cationic surfactant at the air-water interface is measured in a frequency range of 1-500 Hz. The data are then correlated with the lifetime of a foam lamella formed with the same surfactant solution. The surface rheological measurement have been performed with an improved design of the oscillating bubble technique that measures precisely the real and imaginary part of the complex dilational module E. The imaginary part captures a dissipative process which is interpreted as an intrinsic surface dilational viscosity kappa. The cationic surfactant 1-dodecyl-4-dimethylaminopyridinium bromide shows a transition between a surface elastic to a viscoelastic behavior with an increase of the bulk concentration. The transition corresponds to a striking increase in the lifetime of the foam lamella. The lamella lifetime of the viscoelastic system exceeds the one of an elastic system by 2 orders of magnitude while the absolute value of the E module remains comparable. The results suggest that surface dilational viscosity kappa is crucial for the ability of a surfactant system to form a stable foam. A simple picture that explains this observation is discussed.     

The effect of clay on foaming and mechanical properties of glass foam insulating material

In the current study, the main composition was prepared using soda-lime glass with dolomite [CaMg(CO₃)₂] as a foaming agent. The clay powder was added to the main composition in different ratios, and then, the mixtures were shaped by one-axial pressing. Differential thermal analysis (DTA) was used for the determination of crystallization temperatures, and the samples were heated according to the DTA results. Furthermore, heating microscopy was employed for studying the high-temperature behaviours of the mixtures. The samples were characterized using scanning electron microscopy, X-ray diffraction analysis, and comprehensive strength testing. Porosity and bulk density were measured to assess the foaming capability of the mixtures. The results showed that clay addition has a positive role on the mechanical properties of glass foam.     

Critical capillary pressure for destruction of single foam films and foam: effect of foam film size

Foams and single foam films stabilised by ionic and amphiphile polymer surfactants are studied with foam pressure drop technique (FPDT) and thin liquid film-pressure balance technique (TLF-PBT). A pressure is reached at which the single foam films rupture and the foams destruct very fast (avalanche-like). For film rupture we named this pressure—critical capillary pressure of film rupture, P_cr,film while for foam destruction, we introduced a new parameter—critical capillary pressure of foam destruction, P_cr,foam. The surfactant kind and foam film type (common thin, common black and Newton black) affect the values of both parameters. When below 20 kPa, P_cr,film and P_cr,foam are close by value, when over 20 kPa, there is a significant difference between them. The P_cr,film versus film size and P_cr,foam versus foam dispersity dependences, indicate that the film size and foam dispersity strongly affects the critical capillary pressure values. Film size distribution histograms reveal that a foam always contains films that are of a larger than the most probable size. They rupture at lower pressures, does initiating the destruction of the whole foam, which can be an explanation why higher than 20 kPa there is a difference between P_cr,film and P_cr,foam values. This parameter, P_cr,foam is considered of significant with respect to foam stability and could find use in industry.     

Studies on foam stability by the actions of hydrophobically modified polyacrylamides

Hydrophobically modified polyacrylamide (HMPAM), as a foam stabilizer, was prepared with a cationic surfomer, acrylamide and acrylic acid by free-radical polymerization in aqueous solution. The actions of HMPAM on foam stability have been investigated with the Waring blender method. The results showed the foam containing HMPAM was stabler than that contained polyacrylamide. Moreover, a linear relationship between the logarithm of the half decay time and polymer concentration was observed, and the slope reflects the polymer ability to stabilize the foam.     

The effect ofpH on thermal stability of globular proteins

In this study we try to re-analyze thepH dependence of thermal stability of small globular proteins. From the thermodynamic point of view a long series of calorimetric and spectroscopic investigations has shown that the decreased stability in very acidic conditions can be ascribed to entropic effects. The same conclusion is reached, from a microscopic point of view, by assuming that a binding of protons on equal and noninteracting sites takes place as a consequence of unfolding process. By linking the conformational unfolding equilibrium to the proton binding equilibrium, a model is developed that is able to describe the dependence on thepH of the thermal denaturation processes of small globular protiens. The application of the model to hen lysozyme and T4 lysozyme correctly accounts for the experimental results.     

The effect of trimethylamine N-oxide on RNase a stability

The thermal stability of bovine pancreatic ribonuclease (RNase A) has been investigated in the presence of trimethylamine N-oxide (TMAO), a naturally occurring osmolyte, by means of differential scanning calorimetry (DSC) and circular dichroism (CD) measurements at neutral and acid pH conditions. It is well known that compatible osmolytes such as TMAO are effective in stabilizing protein structure and counteracting the denaturing the effect of urea and guanidinium hydrochloride (GuHCl). Calorimetric results show that TMAO stabilizes RNase A at pH 7.0 and does not stabilize the protein at pH 4.0. RNase A thermal denaturation in the presence of TMAO is a reversible two-state N ⇆ D process. We also show that TMAO counteracts the urea and GuHCl denaturing effect at neutral pH, whereas the counteracting ability is lost at acid pH.     

A 3D-impedimetric immunosensor based on foam Ni for detection of sulfate-reducing bacteria

A 3D-immunosensor based on simple and efficient trapping platform (foam Ni) combining with adsorption of gold nanoparticles and specific recognition of biological/chemical molecular has been reported for detection of sulfate-reducing bacteria (SRB) using electrochemical impedance spectroscopy (EIS). The impedance spectra were also used to characterize the successful construct and stepwise modification of the impedimetric immunosensors. This results show that a linear relationship between electron-transfer resistance (R_ct) values and the logarithm of the SRB concentrations was obtained for the SRB concentration range of 2.1 × 10¹–2.1 × 10⁷ cfu/ml. Additionally, the fabricated immunosensor shows a high selectivity against other bacteria.     

The study of the stability of aqueous three-phase fire-resistant foam in typical liquidus hydrocarbons

The utilization of solid particles in aqueous foam has a great potential in improving fire fighting efficiency. In this study, aqueous foam supported by micro fly-ash (FA) was prepared and its stability in a specific type of oil was characterized. Firstly, different amount of FA was added to study the influence of FA concentration on foamability. It showed that within a specific extent, foam expansion ratio increased with the increasing of FA concentration. And compared with conventional foams, oil resistance of FA stabilized foams, which was investigated by analyzing drainage rate and evolution process with a self-made apparatus, was remarkably improved when FA concentration exceed 4.8wt.%. Secondly, SiO₂ and Al₂O₃ particles with different median sizes were used to study the effect of particle size on stability. However, the smaller hydrophilic particles didn’t behave better as expected. Moreover, the foam stability in three hydrocarbons was evaluated in the same way. The results indicated that the short chain hydrocarbons had much stronger detrimental effect to both two-phase foam and three-phase foam. But overall, the three-phase foam stabilized by FA exhibited much better oil resistance, so it can be used as a promising material for pool fire extinguishing and prevention.GRAPHICAL ABSTRACT     

Assessing the stability of assembled filamentous phage coat protein P8

Assembly of viral protein coats is crucial to the protection of internal genetic cargo and is necessary for proper infection. Understanding the conditions for maintaining these supramolecular assemblies is of value for engineering-effective virus-based materials and related technologies. In this study, we examine the stability of the filamentous bacteriophage, fd-tet, in a variety of solvent and temperature conditions. On the basis of these results, we advise amenable reaction environments for modification of fd-tet. In particular, assessment of the temperature stability indicates that practical use of these viruses as reaction substrates is best performed at moderate temperatures, since loss in infectivity was found to occur within only 1-h incubation over 37°C. In addition, these findings reveal additional loss of infectivity after exposure to conditions near pH 4.5 which may be attributable to changes in the effective charge of the p8 major coat protein.     

The effect of surfactants on the stability of polarographic streaming

The frequencies of several vibrational bands of pyridine, pyrazine, p-nitroso dimethylaniline and cyanide adsorbed on a silver electrode have been investigated as a function of the electrode potential using in situ Raman spectroscopy. The frequencies of all the bands investigated were found to decrease linearly with cathodic potential. This observation is independent of the adsorbate and the anions of the supporting electrolyte. Several models explaining this effect are discussed.     

The effect of nucleating agent on radiation stability of polypropylene

The radiation stability of polypropylene (PP) with and without nucleating agent (NA) is compared in relation to radiation sterilization of medical devices. In both cases high-and-low-molecular weight PP, the addition of NA increased the transparency and peak crystallization temperature of the PP. On the other hand, in poly(propylene-co-6%ethylene) copolymer, the addition of NA did not improve the transparency but crystallization occurred at higher temperature. Thus, adding NA to PP and copolymer give the advantage of shorter moulding time in the production of medical devices. It is found that both PP and copolymer with NA are less stable during irradiation and during storage after irradiation than without NA, this being the case especially for the lower molecular weight PP. The higher transparency and peak crystallization temperature in the PP and CP with NA were found to be due to smaller spherulites. As the effect of irradiation on polymer, addition of NA induce reduction of radiation stability of polymer owing to the change in morphology.     

Protein adsorption at the electrified air-water interface: implications on foam stability

The surface chemistry of ions, water molecules, and proteins as well as their ability to form stable networks in foams can influence and control macroscopic properties such as taste and texture of dairy products considerably. Despite the significant relevance of protein adsorption at liquid interfaces, a molecular level understanding on the arrangement of proteins at interfaces and their interactions has been elusive. Therefore, we have addressed the adsorption of the model protein bovine serum albumin (BSA) at the air-water interface with vibrational sum-frequency generation (SFG) and ellipsometry. SFG provides specific information on the composition and average orientation of molecules at interfaces, while complementary information on the thickness of the adsorbed layer can be obtained with ellipsometry. Adsorption of charged BSA proteins at the water surface leads to an electrified interface, pH dependent charging, and electric field-induced polar ordering of interfacial H(2)O and BSA. Varying the bulk pH of protein solutions changes the intensities of the protein related vibrational bands substantially, while dramatic changes in vibrational bands of interfacial H(2)O are simultaneously observed. These observations have allowed us to determine the isoelectric point of BSA directly at the electrolyte-air interface for the first time. BSA covered air-water interfaces with a pH near the isoelectric point form an amorphous network of possibly agglomerated BSA proteins. Finally, we provide a direct correlation of the molecular structure of BSA interfaces with foam stability and new information on the link between microscopic properties of BSA at water surfaces and macroscopic properties such as the stability of protein foams.     

Simulation of foaming ability, multiplicity, and foam stability of shampoo

Equations for a foam height, multiplicity, and foam stability of shampoo were suggested. Model deriving was based on an assumption that foams was monodispersed systems consisting from cells of gas in the form of pentagonal dodecahedra with liquid films created by two adsorption monolayers of surfactant monomers.