Khr. Khristov

Direct measurement of disjoining pressure in black foam films II. Films from nonionic surfactants

Abstract Experiments are reported with foam films from two different polyoxyethylenic nonionic surfactants of relatively short and long polyoxyethylene chains. The direct measurement of the film disjoining pressure was combined with measurements of the film thickness dependence on the electrolyte concentration. The results obtained are discussed in connection with: (i) the type of black films observed, (ii) the influence of the POE chain length on the film properties, (iii) the agreement between the disjoining pressure isotherms obtained and the theoretical ones, (iv) the relationship between the charge and potential of the interacting diffuse double layers.

Thin liquid film technique — application to water–oil–water bitumen emulsion films

Abstract We describe an adaptation of the thin liquid film-pressure balance technique (TLF-PBT) for a systematic study of water/diluted-bitumen/water thin films. Recent research into the stability of water-in-oil emulsions, particularly those occurring in the oil industry, has not properly addressed the dependence of the emulsion stability on the thin films that are formed between approaching water droplets. The objective of this study is to obtain some insight into the mechanisms that stabilize the emulsion with particular attention to the relative importance of the resin, asphaltene, and solids fractions of the bitumen. Measurements of film lifetime and equivalent thickness indicated that the behavior of the film strongly depended on the type and concentration of solvent used to dilute the bitumen. Toluene-diluted-bitumen films drained continuously until a stable, uniform grey film was formed. Heptane-diluted-bitumen films formed black films covered with a scatter of small white dimples containing trapped liquid except at heptane:bitumen weight ratios of 10:1–15:1, where a network of fine white spots of unknown origin was formed. While the asphaltene and resin fractions alone provide a partially stable film, the combination of resin and asphaltene produced extremely stable films, a result that agrees well with emulsion studies by other researchers.

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

The behaviour and the life time (τp) 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 (ΔP), applied in the Plateau-Gibbs-borders of the foam. The foam stability and the course of theτp/ΔP-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.

Influence of the pressure in the Plateau-Gibbs borders on the drainage and the foam stability

SummaryThe effect of the pressure in the Plateau-Gibbs borders of the foam upon its drainage and its stability has been investigated. The principle of the method and the apparatus for applying pressure gradient in the Plateau-Gibbs borders of the foam are described. The kinetics of establishing of the capillary pressure in the Plateau-Gibbs borders of the foam in dependence of the height of the foam column, the applied pressure difference and the type of the surfactant has been studied. The obtained results are qualitatively confirmed by an investigation of the foam water content change (calculated by measurements of its specific conductivity) at the same experimental conditions. The influence of the increased drainage rate and respectively the decreased foam water content on the foam stability when a pressure gradient is applied in its Plateau-Gibbs borders is discussed. It is shown that the time for the foam destruction when a pressure gradient is applied in the foam Plateau-Gibbs borders can be used for characterising the foam stability at definite conditions.ZusammenfassungEs wurde der Einfluß des Druckes auf dessen Syneresis und Stabilität in den Plateau-Gibbsschen Kanälen eines Schaumes untersucht. Das Prinzip der Methode und die Apparatur zur Schaffung eines Druckgradienten in den Plateau-Gibbsschen Kanälen des Schaumes werden beschrieben. Es wurde die Kinetik der Änderung des Kapillardruckes in den Plateau-Gibbsschen Kanälen des Schaumes in Abhängigkeit von der Schaumsäulenhöhe, der Druck-differenz und den Typ des Schäumers untersucht. Die Ergebnisse wurden qualitativ bestätigt durch die Änderung des Wasserinhalts des Schaumes, die aus der spezifischen Leitfähigkeit (bei den selben Experimentalbedingungen gemessen) berechnet wurde. Der Einfluß des beschleunigten Syneresis, bzw. des verminderten Wasserinhaltes des Schaumes auf dessen Stabilität werden diskutiert. Es wurde gezeigt, daß man die Zeit zur Zerstörung des Schaumes durch einen Druckgradienten in den Plateau-Gibbsschen Kanälen als eine Charakteristik der Schaumstabilität bei definierten Bedingungen (gegebener Kapillardruck, gegebener Wasserinhalt) benutzen kann.

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

Abstract 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, Pcr,film while for foam destruction, we introduced a new parameter—critical capillary pressure of foam destruction, Pcr,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, Pcr,film and Pcr,foam are close by value, when over 20 kPa, there is a significant difference between them. The Pcr,film versus film size and Pcr,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 Pcr,film and Pcr,foam values. This parameter, Pcr,foam is considered of significant with respect to foam stability and could find use in industry.

Steady-state foams: Influence of the type of liquid films

Abstract Properties of “dry” steady-state foams formed from sodium lauryl sulphate (NaLS) solutions containing various amounts of electrolyte have been investigated. The results of the foamability measurements performed under dynamic steady-state conditions are described in terms of retention time (rt) values. Upper limits of NaLS concentrations, for which the measurements of steady-state foamability could be performed were found to depend strongly on the amounts of electrolyte added. Investigations of the action of α-particle showed that three types of foam film were formed in the highest layers of the foams studied. Newton black, common black and normal thin liquid films were formed in the presence of 0.5, 0.1 and 10−4M NaCl, respectively. The properties of these three types of film determined the observed behaviour of the steady-state foam formed.

New possibilities for foam investigation : creating a pressure difference in the foam liquid phase

Abstract In this review we describe some theoretical and experimental studies of the properties of polyhedral foams, and some new methods for investigating foams in which a pressure gradient is created in the Plateau-Gibbs borders in the foams. The role of the foam film type in foam stability, and in particular, in the establishment of high foam stability, is demonstrated by performing model investigations of microscopic foam films and foams.

Foam analyzer: An instrument based on the foam pressure drop technique

The foam pressure drop technique allows measurement of the characteristic properties of aqueous foams. A new fully automated instrument called the FA1 Foam Analyzer employs this technique. The reduced pressure applied to the measurement cell allows reasonably short experiments even for very stable foams. The technique determines the drainage (water content as a function of time) and lifetime of a foam at an applied reduced pressure. The lifetime as a function of applied reduced pressure depends both on the kind of surfactant stabilizing the foam and the type of liquid films (common thin, common black or Newton black) that built up the foam. We give sample experiments for various surfactant solutions.

FOAM STABILIZING PROPERTIES OF SURFACTANTS DETERMINED AT CONSTANT AND VARIABLE PRESSURE IN THE FOAM LIQUID PHASE

Abstract The foam stabilizing ability of anionic, cationic and nonionic surfactants are studied with two methods, involving constant and variable capillary pressure in the foam liquid phase: the method of determining the foam lifetime at constant pressure and the Ross-Miles test. It is reported that the most important parameters for foam stability are the capillary pressure and the type of the foam films. It is proved that the foam lifetime τp determined at constant capillary pressure is a more precise and defined characteristics of foam stability.

Determination of foam stability at constant pressure in the Plateau-Gibbs borders of the foam

The lifetime of a foam column (or of a part of the column) is a parameter widely used as a characteristic of foam stability. During the destruction process, the pressure in the upper layers of the foam changes (the height H of the foam column decreases) and the lifetime of the different layers of the foam column will be different. Therefore, the lifetime of a foam column at constant pressure in the Plateau-Gibbs borders (constant along the height of the column and with time) is a much more accurate characteristic of foam stability.