Defoaming effect of calcium soap

Aqueous and Oil Foams Stabilized by Surfactant Crystals: New Concepts and Perspectives

Surfactant crystals can stabilize liquid foams. The crystals are adsorbed at bubble surfaces, slowing down coarsening and coalescence. Excess crystals in the liquid channels between bubbles arrest drainage, leading to ultrastable foams. The melting of crystals upon raising the temperature allows thermoresponsive foams to be designed. In the case of oil foams, the stabilization by crystals received substantial renewed interest in the last 5 years due to their potential applications, particularly in the food industry. For aqueous foams, several reports exist on foams stabilized by crystals. However, these two kinds of liquid foams possess similarities in terms of stabilization mechanisms and the design of surfactant crystal systems. This field will certainly grow in the coming years, and it will contribute to the engineering of new soft materials not only for food but also for cosmetics, pharmaceuticals, and biomedical applications.

Foams Stabilized by Surfactant Precipitates: Criteria for Ultrastability

Foams are ultrastable when all the aging processes arrest. We make such foams by precipitating sodium dodecyl sulfate with potassium chloride during the foaming process. The precipitate crystals adsorb onto the bubble surfaces to arrest coarsening and stop drainage by blocking in the interstices around the bubbles. However, if the concentration of SDS is too high, the foams are no longer ultrastable. The transition is sudden and corresponds to the point at which significant dodecyl sulfate remains in solution. The presence of the noncrystallized surfactant allows the foam to coarsen leading to the eventual disappearance of the foams, even if the crystals in the continuous phase can still block drainage. The transition occurs as the concentration of nonsolubilized KCl becomes higher than the concentration of SDS, giving us a linear stability boundary. The system offers an interesting alternative to other types of particles because the surfactant crystals break and reform as the temperature is cycled, which makes for reusable solutions and stimulable foams.

Mechanistic understanding of the modes of action of foam control agents

In this paper we present briefly our current understanding of the modes of action of foam control agents (often termed "defoamers" or "antifoams"). After summarizing the background knowledge, reviewed in previous articles, the focus of the presentation is shifted to the antifoam studies from the last decade. The new experimental results, obtained by various research groups, are reviewed briefly to reveal the main mechanisms of antifoam action and the related key factors, governing the efficiency of the foam control agents. The role of the entry, spreading and bridging coefficients, of the entry barrier of the antifoam entities, and of the dynamics of surfactant adsorption is specifically discussed.

Antifoaming effect of chemical compounds in manure biogas reactors

A precise and efficient antifoaming control strategy in bioprocesses is a challenging task as foaming is a very complex phenomenon. Nevertheless, foam control is necessary, as foam is a major operational problem in biogas reactors. In the present study, the effect of 14 chemical compounds on foam reduction was evaluated at concentration of 0.05%, 0.1% and 0.5% v/v(sample), in raw and digested manure. Moreover, two antifoam injection methods were compared for foam reduction efficiency. Natural oils (rapeseed and sunflower oil), fatty acids (oleic, octanoic and derivative of natural fatty acids), siloxanes (polydimethylsiloxane) and ester (tributylphosphate) were found to be the most efficient compounds to suppress foam. The efficiency of antifoamers was dependant on their physicochemical properties and greatly correlated to their chemical characteristics for dissolving foam. The antifoamers were more efficient in reducing foam when added directly into the liquid phase rather than added in the headspace of the reactor.

Study of the microcharacter of ultrastable aqueous foam stabilized by a kind of flexible connecting bipolar-headed surfactant with existence of magnesium ion

In this paper, ultrastable aqueous foam stabilized by a kind of flexible connecting bipolar-headed surfactant alkyl polyoxyethylene sulfate (AE3S) with coexisting Mg(2+) was reported. Detailed molecular behaviors of AE3S in foam film with coexisting divalent cationic Ca(2+) or Mg(2+) were investigated by molecular dynamic simulation, comparing with the traditional surfactant sodium dodecyl sulfate (SDS), to find out how the microcharacter and array behavior of molecules in the foam film determined by molecular interaction effect the foam stability. It was found that the ultrastable foam film obtained by the cooperation of magnesium ions and AE3S was driven from two aspects: one is the favorable arrangement of surfactant molecules, and the other is the increase of capacity of foam films for resolutely holding water molecules deduced by a dipolar pair formed by the flexible connecting head groups of AE3S and hydrated Mg(2+) via intermolecular coactions, both related to the presence of magnesium ions. Foam lamella stability measurement and foam decay method were both used to evaluate the stability of foam. Fourier transform infrared (FT-IR) was used to detect the composition variation of foam film in the drainage process; the vibration peak of OH for water molecule shifted from the 3390 cm(-1) (being assigned to the bulk water integrated by hydrogen bonds) to 3685 cm(-1) (being assigned to the vibration of isolated water molecules) for the ultrastable foam film after complete drainage, which agreed very well with the molecular simulation results.

Foam in the aquatic environment

Foams are ubiquitous in the environment, commonly seen as discoloured patches on streams, rivers, lakes and sea water. They often are assumed to be anthropogenic in origin as they are aesthetically unpleasant, yet they frequently appear in pristine environments indicating a natural origin. In contrast to "hidden" chemical pollution, e.g. heavy metals, pesticides etc. the visibility of foam alarms the public. To derive more information on foam in freshwaters and marine ecosystems, a literature review was performed. Alongside with some basic considerations on the formation of foam, on methods to measure foam formation and on the legal aspects of foam on surface waters, the ecological importance of foam in the aquatic environment is discussed in this paper.

Foaming properties of a peptide designed to form stimuli-responsive interfacial films

We have designed an amphipathic peptide, AM1, that can self-assemble at the air-water interface to form an interfacial ensemble capable of switching between a mechanically strong cohesive film state and a mobile detergent state in response to changes in the solution conditions. The mechanical properties of the AM1 ensemble in the cohesive film state are qualitatively equivalent to the protein β-LG, while in the mobile detergent state they are equivalent to the low molecular weight surfactant, SDS. In this work the foaming properties of AM1 are compared to those of β-LG and SDS at the same weight concentration and it is found that AM1 adsorbs rapidly to the interface, initially forming a dense foam like that formed by SDS and superior to β-LG. In addition, under solution conditions where interfacially adsorbed AM1 forms a cohesive film state the foam stability is high, comparable to β-LG. However when the interfacially adsorbed AM1 forms a foam under detergent-state conditions, the foam stability is poor. We have achieved control of foam stability through the design of a peptide that exhibits stimuli-responsive changes in the extent of intermolecular interactions between peptide molecules adsorbed at the air-water interface. These results illustrate the exciting potential of peptide surfactants to form a new class of stimuli-responsive foaming agents.