Implications of interfacial characteristics of food foaming agents in foam formulations

The manufacture of food dispersions (emulsions and foams) with specific quality attributes depends on the selection of the most appropriate raw materials and processing conditions. These dispersions being thermodynamically unstable require the use of emulsifiers (proteins, lipids, phospholipids, surfactants etc.). Emulsifiers typically coexist in the interfacial layer with specific functions in the processing and properties of the final product. The optimum use of emulsifiers depends on our knowledge of their interfacial physico-chemical characteristics - such as surface activity, amount adsorbed, structure, thickness, topography, ability to desorb (stability), lateral mobility, interactions between adsorbed molecules, ability to change conformation, interfacial rheological properties, etc. -, the kinetics of film formation and other associated physico-chemical properties at fluid interfaces. These monolayers constitute well defined systems for the analysis of food colloids at the micro- and nano-scale level, with several advantages for fundamental studies. In the present review we are concerned with the analysis of physico-chemical properties of emulsifier films at fluid interfaces in relation to foaming. Information about the above properties would be very helpful in the prediction of optimised formulations for food foams. We concluded that at surface pressures lower than that of monolayer saturation the foaming capacity is low, or even zero. A close relationship was observed between foaming capacity and the rate of diffusion of the foaming agent to the air-water interface. However, the foam stability correlates with the properties of the film at long-term adsorption.     

Effect of double-layer repulsion on foam film drainage

This paper presents an experimental validation of new theoretical development for foam film drainage, which focuses on the role of surface forces. The drainage of microscopic foam films (with radii smaller than 100 μm) from aqueous solutions of 10⁻⁶ to 10⁻⁴ mol/L sodium dodecyl sulphate (SDS) was studied by means of an improved Scheludko micro-interferometric technique which consisted of a conventional Scheludko cell, a high-speed camera system, and the software for digital analysis Optimas used for the digitisation of the interferometric images to obtain the monochromatic light intensity. The experimental technique allowed fast processing of the interferometric data for determining the transient film thickness with high accuracy. The zeta-potential of the air–water interface was determined from the electrophoretic mobility of micro-bubbles in SDS solutions of the same concentrations. Advanced predictions for the electrical double-layer repulsion at either constant surface potential or constant surface charge were employed. Significant discrepancy between the theoretical prediction and the experimental data was obtained. The analysis showed that the adsorption layer, which is located on the film surfaces, is far away from equilibrium, while the theory assumes condition close to equilibrium. In this term the interaction between the film surfaces is affected by the dynamics of the adsorption layers during the film drainage.     

Influence of polymers on dust-related foam properties of sodium dodecyl benzene sulfonate with Foamscan

Foamability, liquid holdup, and foam appearance are key factors that determine dust control efficiencies. As the foam production method of the FoamScan instrument is similar to foaming device used for dust control, and its measurement means can satisfy the requirements of precise measuring, the FoamScan technology is adopted to explore the influence of xanthan gum (XG) and partial hydrolytic polyacrylamide (HPAM) on dust-related foam properties of sodium dodecyl benzene sulfonate (SDBS). It was found that with the increase of the polymer mass fraction, the liquid volume in the foam gradually increased. Additionally, the foaming time t₂₀₀ of the foaming agent decreased at first, then remained almost constant for both polymers, which indicated that the foamability and liquid holdup were enhanced by the addition of polymers into SDBS. In addition, the efficiencies of XG are higher than that of HPAM. The image analysis using the CSA software revealed that the mean radius formed by XG was smaller than that by HPAM and the number of bubbles was larger with XG than with HPAM. Thus, the XG foam has more area to contact with dust and could control dust better. The highly branched molecular structure and hydrogen bonds formed by XG played important roles in dust-related foam properties.     

Protein foam application for enhanced oil recovery

Protein foam was explored as a foaming agent for enhanced oil recovery application in this study. The influence of salinity and oil presence on bulk stability and foamability of the egg white protein (EWP) foam was investigated. The results were compared with those of the classical surfactant sodium dodecyl sulfate (SDS) foam. The results showed that the EWP foam is more stable than the SDS foam in the presence of oil and different salts. Although, the SDS foam has more foamability than the EWP foam, however, at low to moderate salinities (1–3 wt% NaCl), both foam systems showed improvement in foamability. At a NaCl concentration of 4.0 wt% and above, foamability of the SDS foam started to decrease drastically while the foamability of the EWP foam remained the same. The presence of oil has a destabilizing effect on both foams but the EWP foam was less affected in comparison to the SDS foam. Moreover, increasing the aromatic hydrocarbon compound percentage in the added oil decreased the foamability and stability of the SDS foam more than EWP foams. This study suggests that the protein foam could be used as an alternative foaming agent for enhanced oil recovery application due to its high stability compared to the conventional foams.     

Hydration force due to the reduced screening of the electrostatic repulsion in few-nanometer-thick films

Experiments with foam films from solutions of 1 mM SDS + 100 mM electrolyte (LiCl, NaCl and CsCl) were carried out by a thin-film-pressure balance. The measured dependences of disjoining pressure versus film thickness exhibit a steep increase when the thickness of the film's water core becomes smaller than 3.7 nm. This behavior can be interpreted as a manifestation of the hydration force. We unsuccessfully tried to interpret the data with different available theoretical models. Eventually, we found that a relatively simple model of “reduced screening” can fit the data. Such reduced screening of the electric field could exist only in a narrow range of film thicknesses, which practically coincides with the region where the hydration repulsion is acting. This model and its experimental verification are described in the article.     

竹纤维改性聚丙烯超临界CO2发泡性能的研究

为了提高竹纤维的分散性,借鉴打浆造纸法制备得到了已表面处理的竹纤维和聚丙烯纤维的复合材料,并在扫描电镜下对复合材料样品的断面进行了表征.结果表明,打浆造纸法这种工艺很好地解决了竹纤维在聚丙烯中的分散,得到了竹纤维分布均匀的竹纤维/聚丙烯复合材料;并以竹纤维含量为25％的复合材料作为超临界CO2发泡的研究对象,根据异相成...     

Adsorption layer properties and foam film drainage of aqueous solutions of tetraethyleneglycol monododecyl ether

The aim of the present study is to clarify how the surfactant adsorption layer properties are related to the course of the drainage parameters of microscopic foam films in the special case of aqueous solutions of the non-ionic amphiphile tetraethyleneglycol monododecyl ether (C₁₂E₄), containing premicellar nanostructures. The scope of the research covers adsorption dynamics, construction of equilibrium adsorption isotherms, studies on surface rheology of the interfacial layers and microscopic foam film drainage kinetics. It is established that in the premicellar concentration domain considerable irregularities of the adsorption layer properties are observed: two plateau regions are registered in the experimental surface tension isotherm along with unusual changes of the surface rheological characteristics. The systematic investigation of the drainage of microscopic foam films obtained from these solutions show that the dependencies of basic kinetic parameters of the films on the amphiphile concentration run in synchrony with the changes in the adsorption layer properties. This fact is related to the presence of smaller surfactant aggregates (premicelles). They are presumed to be organized as Platonic bodies. The premicelles play also a significant role in the kinetic stability of the films. The importance of this research is in providing better insight into the initial stages of self-assembling phenomena and into the factors determining the adsorption layer properties and the drainage behaviour of thin liquid films.     

Determination of Traces Of Bismuth in Water with Polyurethane Foak Thin-Layer Spectrophotometry

Abstract

A method for the spectrophotometric determination of bismuth is described. The method is based on using polyether polyurethane foam sorbent as a favourable matrix. Sorption of the bismuth iodide complex into the foam thin layer contributed into substantial improvement of the measured absorbance value of the coloured species. In this way quite satisfactory results were achieved, the average recovery amounts to 105.25%.     

Role of alkaline cations and water content on geomaterial foams: Monitoring during formation

The synthesis of an in situ inorganic foam based on alkaline polysialate was achieved at a slightly elevated temperature by alkaline activation of raw minerals and industrial waste based on a geopolymer synthesis process. To understand the formation of the foam, the differences induced by the variations in the alkaline element (sodium or potassium) and water content were investigated throughout XRD, in situ FTIR-ATR, volume expansion and thermal analysis coupled with mass spectrometry. The amount of water is the determining parameter for volume expansion but does not interfere with the structure formation of foams. The comparison between geopolymers and foams has elucidated the formation of at least two amorphous networks in the case of sodium foam and three in the particular case of potassium as the alkaline element.     

Effect of gamma-irradiation on the foaming behavior of ethylene-co-octene polymers

Ethylene-co-octene polymers containing different branching levels were irradiated in air and under vacuum at 25, 50 and 100 kGy. Gel fraction measurements, thermal analysis and rheology were used to assess the effect of the treatment on polymer structure modifications. The copolymer with 24 wt% octene was shown to be more sensitive to gamma rays and degradation was observed in some cases. Cross-linking in the amorphous phase also occurred as a consequence of irradiation and affected the foaming behavior of these materials.