Initial Foam Height Research Articles

Purification and concentration of a rhamnolipid biosurfactant produced by Pseudomonas aeruginosa SP4 using foam fractionation

Pseudomonas aeruginosa SP4 was cultivated to produce a rhamnolipid biosurfactant from a nutrient broth with palm oil. The foam fractionation technique in batch mode was used for the recovery of the excreted biosurfactant from the free-cell culture medium. The effects of air flow rate, initial foam height, the pore size of the sintered glass disk, initial liquid volume, and operation time on the process performance were studied. The results showed that the operating conditions were optimized at an air flow rate of 30 ml/min, an initial foam height of 60 cm, a pore size of the sintered glass disk in the range of 160–250 μm (No. 0), an initial liquid volume of 25 ml, and an operation time of 4 h, providing a biosurfactant recovery of 97% and an enrichment ratio of 4. The HPLC results also indicated that the rhamnolipid was concentrated by using the foam fractionation technique.

Study of Foaming Properties and Effect of the Isomeric Distribution of Some Anionic Surfactants

AbstractUsing different reaction conditions of photosulfochlorination of n‐dodecane, two samples of anionic surfactants of sulfonate type are obtained. Their micellar behavior has been already reported and the relationship between their isomeric distribution and their chemical structures and micellar behaviors have been more thoroughly explored. In this investigation, we screened the foaming properties (foaming power and foam stability) by a standardized method very similar to the Ross–Miles foaming tests to identify which surfactants are suitable for applications requiring high foaming, or, alternatively, low foaming. The results obtained for the synthesized surfactants are compared to those obtained for an industrial sample of secondary alkanesulfonate (Hostapur 60) and to those of a commercial sample of sodium dodecylsulfate used as reference for anionic surfactants. The foam formation and foam stability of aqueous solutions of the two samples of dodecanesulfonate are compared as a function of their isomeric distribution. These compounds show good foaming power characterized in most cases by metastable or dry foams. The highest foaming power is obtained for the sample rich in primary isomers which also produces foam with a relatively high stability. For the sample rich in secondary isomers we observe under fixed conditions a comparable initial foam height but the foam stability turns out to be low. This property is interesting for applications requiring low foaming properties such as dishwashing liquid for machines. The best results are observed near and above the critical micellar concentrations and at 25 °C for both the samples.

Effect of added fragrances on the foaming properties of aqueous surfactant solutions

Foaming properties are important characteristics of surfactant solutions used for personal washing products, hair styling foam, shaving foam, etc. Fragrances are often used in these cosmetic products, but they also influence the foaming properties of aqueous surfactant solutions. In this study, we investigated the effects of added fragrances [d‐limonene (LN), α‐hexyl‐cinnamic‐aldehyde (HCA), β‐ionone (IN), benzyl acetate (BA), linalool (LL), geraniol (GL), eugenol (EL), and cis‐3‐hexenol (HL)] on the initial foam heights and foam stability of sodium dodecyl sulphate (SDS) aqueous solutions. GL and EL increase the initial foam heights of 0.1 wt% and 0.3 wt% SDS aqueous solutions. Dynamic surface tension measurement shows that these fragrances quickly lower the surface tension of SDS solutions. Hence, GL and EL increase the initial foam heights because of the fast adsorption at the air/water interface. Further, GL and EL also increase the foam stability of SDS solutions and act as foam boosters. For the application to shampoo, the addition of GL results in the largest improvement of the initial foam height and the foam stability among the fragrances investigated here.

Mass transfer of volatile organic carbons through aqueous foams

A model is developed to study diffusive mass transfer of hydrocarbon vapor through a flexible foam blanket. The model accounts for the diffusion of hydrocarbon vapor through gas-phase and liquid lamellae, the combined gravity and capillary drainage from the plateau border, the thinning of foam lamellae caused by the forces of capillary suction, London–van der Waals attraction, and electrostatic double-layer repulsion, and foam collapse. Uniform bubble size is assumed, and hence, interbubble gas diffusion arising out of variation in bubble sizes alone is not incorporated into the model. A high-stability aqueous foam formulation that remains stable in the presence of oil (hexane) at foam–oil contact was developed using surfactants, stabilizers, and viscosifiers. Emission of hexane vapor through the foam was measured. The model predicts that the initially taller foam columns collapse faster. Their mass-transfer resistance is higher before the onset of collapse but not very different from that of the shorter foam columns at long times. If the solubility and diffusivity of the hexane gas in the foam liquid are unaffected, the foams with higher viscosities persist longer and provide greater diffusive mass-transfer resistance. Foam bubble size does not significantly impact the mass-transfer resistance of the foam column before the onset of foam collapse. However, the foams with smaller bubbles collapse earlier, and their ability to act as a mass-transfer barrier to the diffusing hydrocarbon vapor diminishes rapidly. The experimental results compared reasonably with the model for varying initial foam heights and bubble sizes.

Surfactant properties of purified polyglycerol monolaurates

AbstractA series of purified polyglycerol monolaurates (PGML), such as di‐, tri‐, tetra‐, and pentaglycerol monolaurates, were synthesized, and their surfactant properties in aqueous solutions were examined. The surfactant properties of PGML were compared with those of n‐dodecyl polyoxyethylene monoethers (C12EOn) to examine the function of the hydrophilic part of these compounds. The critical micelle concentration (CMC) values and the surface tension at CMC of PGML and C12EOn increased linearly with an increase in the number of glycerol and oxyethylene units, respectively; the slope of the increase was greater for PGML than C12EOn. The minimum surface area per molecule of PGML was smaller than that of C12EOn at the air/aqueous solution interface. The initial foam heights of the surfactants at the CMC increased with an increase in the number of glycerol or oxyethylene units, and the foam heights of PGML were consistently higher and more stable than those of C12EOn. Detergency depended on a reduction in interfacial tension. Triglycerol monolaurate showed the lowest interfacial tension and the highest detergency among all the surfactants tested. Overall, the PGML showed better performance in all the surfactant properties tested than C12EOn. It is noteworthy that the surfactant properties of PGML having few glycerol units (di‐ to tetraglycerol monolaurates) are on par with those of C12EOn having many oxyethylene units (hexa‐ and octaoxyethylene). These results suggest that PGML having a secondary hydroxyl group on every glycerol unit of the hydrophilic part could be more hydrophilic than C12EOn; this characteristic feature guaranteed the superior surfactant properties of PGML.

Relation of foam stability to solution and surface properties of gemini cationic surfactants derived from arginine

The dynamic surface tensions, under constant area and pulsating area are reported for one cationic monomeric surfactant LAM (N α-lauroyl arginine methyl ester) and three related bicationic gemini surfactants C n (LA) 2, or bis (Args), with a spacer chain of n=3, 6, or 9 methylene groups. The tension equilibrates faster the higher the concentration, even beyond the cmc, indicating a substantial micellar contribution to tension dynamics. Both LAM and the gemini surfactants form more stable foams at 25°C as the concentration increases up to about half the cmc of LAM or half the second cmc of the geminis. The geminis are about twenty times more efficient foam stabilizers than LAM. The foam stability correlates strongly with tension equilibration time. The logarithm of the time t 50 f, for the initial foam height to drop by 50%, is a linear function of t 50 γ , which is the time for the tension to drop 50% of its equilibrium change. At comparable concentrations, the gemini surfactant with the shorter spacer chain ( n=3 or 6) equilibrate faster and form more stable foams than the one with n=9.

Silicone Antifoam Performance: Correlation with Spreading and Surfactant Monolayer Packing

The relationship between the spreading of antifoam oils and their performance is much discussed in the literature, but a demonstrated connection between antifoam spreading and performance has been lacking. This paper reports the performance of a poly(dimethylsiloxane) (PDMS)-based antifoam on foam produced by 12 surfactant solutions. These include single or mixed surfactant systems, including impure surfactant mixtures to model fabric washing detergents. The oil film spreading pressure, πo/w, is presented as a simple and relevant measurement of the thermodynamics of antifoam oil spreading. Antifoaming efficacy was measured as the relative reduction in the initial foam height, ΔHrel, using cylinder shake tests at a fixed antifoam dosage. ΔHrel is shown to increase with πo/w, demonstrating a strong statistical correlation between antifoam oil spreading and its performance. Antifoam effectiveness varies with surfactant concentration, surfactant type, and surfactant hydrophobe size and also with increased density of surfactant packing. Surface shear viscosity, μs, was used to quantify surfactant packing. Antifoam effectiveness decreases with increasing surface shear viscosity. This finding provides a potentially useful link between antifoam efficacy and surfactant selection based on well-established surfactant molecular packing parameters. The role of spreading of antifoam oil at the air/surfactant solution interface is investigated. Oil film spreading pressure is shown to decrease by a power law function with increasing surface shear viscosity of the surfactant film. A new fluorescence technique was used to measure the extent of PDMS spreading. Initial results suggest a correlation between the spreading distance and antifoaming performance. An antifoam mechanism is proposed that features antifoam spreading as a direct contributor to bubble film rupture and incorporates surfactant type and concentration, surfactant packing density, and antifoam oil film spreading pressure as factors contributing to antifoam efficacy.

Continuous foaming for protein recovery: part I. Recovery of beta-casein.

Foam separation is known to have potential for separation of biological molecules with a range of surface activities. A statistical study (factorial design) was carried out to establish the optimum operating conditions for the continuous foam separation of beta-casein. Maximum values of enrichment of beta-casein into the foam phase were found for low levels of initial feed protein concentration, gas flow rate, feed-flow rate, and high foam heights. Maximum values of protein recovery, were generally found at high levels of initial feed protein concentration, gas-flow rate, feed-flow rate, and low foam heights. The highest values obtained for enrichment and separation ratio were 54.7 and 181.3, respectively, with a simultaneous protein recovery of 62%; thus, illustrating the potential effectiveness of this technique. The effect of foaming on protein conformation is also important, and in this study protein structure was analyzed before and after foam separation experiments. Techniques used were: native polyacrylamide gel electrophoresis (PAGE), UV absorbance spectroscopy, circular dichroism, and fluorescence. Native PAGE showed no detectable changes in protein structure. However, absorbance scanning, fluorimetry, and circular dichroism revealed some conformational changes over a range of concentration effects.

Experimental investigation of static drainage of protein stabilized foams — Comparison with model

Experimental measurements of the transients of the foam-liquid interface for static drainage of foams stabilized by different proteins such as Bovine Serum Albumin (BSA), Human Serum Albumin (HSA) and casein were made. The foam was generated by bubbling nitrogen through protein solution. Foam drainage was found to be faster and the extent of drainage larger for smaller bubbles, larger initial foam heights, larger ionic strengths and for larger bubbling flow rates employed for foam generation. When the same nitrogen bubble flow rate was employed for the generation of foams of differnt viscosity liquids, the rate as well as the extent of drainage were found to be larger for more viscous liquids. When the initial liquid holdup profiles were maintained the same by varying the gas flow rate for foam formation inversely to the viscosity, however, the extent of drainage remained the same with the rate of drainage being inversely proportional to viscosity. Drainage rates of foam stabilized by BSA were found to be intermediate at pI of BSA. The rate and the extent of drainage were larger for globular proteins such as BSA and HSA compared to casein. Prediction of the transitions of the foam-liquid interface employing a previously developed model (Narsimhan, 1991, J. Food Eng., 14, 139) compared favorably with experiments for a characteristic bubble size. Because of the broad bubble size distribution in the foam, this characteristic bubble size was found to be different from the mean.

Relationship of structure to properties of surfactants. 16. Linear decyldiphenylether sulfonates

The properties of some well‐characterized sodium linear decyldiphenylether (C10DPE)sulfonates have been studied. Among the properties investigated are dynamic and equilibrium surface tension, critical micelle concentration (CMC), area per molecule at the aqueous solution/air interface, wetting time by the Draves technique, foaming by the Ross‐Miles method, solubilization, and hydrotropy. The decyldiphenylether moiety appears to be equivalent to a terminally substituted straight alkyl chain of 16 carbon atoms. The trialkyl‐ and dialkyl‐mono‐sulfonates have solubilities of < 0.01 g/dm3 in water, but are readily soluble in hexane. The didecyldiphenyl ether disulfonate (DADS) has a very low CMC value (1.0 × 10−5 mol dm−3) in aqueous 0.1 N Na+ solution (NaCl), characteristic of surfactants with two hydrophilic and two hydrophobic groups. It also has a much larger area per molecule at the aqueous solution/air interface than the monodecyldiphenyl‐ether monosulfonate (MAMS) and a much higher surface tension at the CMC. MAMS has a much lower surface tension at a surface age of 1 second (γ1s) than either DADS or the monodecyldiphenylether disulfonate (MADS). In agreement with γ1s and γeq values, wetting times increase in the order: MAMS < DADS < MADS and initial foam heights decrease in the order: MAMS > DADS > MADS. Solubilization for three water‐insoluble surfactants decreases in the order: DADS > MAMS > MADS, while hydrotropy is most pronounced with the disulfonates.

Relationship between fundamental interfacial properties and foaming in linear and branched sulfate, ethoxysulfate, and ethoxylate surfactants

The effect of hydrocarbon chain branching on the foaming performance of a variety of sulfate, ethoxysulfate, and ethoxylate surfactants was determined by the Ross—Miles test. Data from static and dynamic surface tension experiments were used to obtain a structure—property—performance correlation. Initial foam heights correlated with π (CMC), the effectiveness of surface tension reduction, while foam instability correlated with R 1 2 , the rate of surface tension reduction at the air—water interface. Hydrocarbon chain branching resulted in increased π (CMC) and R 1 2 . Consequently, surfactants wherein the hydrocarbon chain is branched exhibited high initial foam heights and low foam stability.

Relationship of structure to properties of surfactants. 15 Isomeric sulfated polyoxyethylenated Guerbet alcohols

AbstractThe properties at 25°C in aqueous 0.1M NaCl at the aqueous solution/air, aqueous solution/hexadecane, and aqueous solution/hydrophobic solid interfaces of two isomeric Guerbet alcohol‐derived surfactants C8H17CH(C6H13)CH2(OC2H4)5SO4Na, one in which the octyl and hexyl groups are both linear (L isomer), the other in which they are both highly branched (B isomer), have been investigated and compared in some cases with commercial sodium linear dodecylbenzene‐sulfonate (LAS). The cmc value increases, the pC20 value decreases, and the ΔGoad value becomes less negative in the order: L isomer—B isomer—LAS. The minimum area/molecule at the aqueous solution/air interface increases in the order: LAS≪L isomer<B isomer.The L isomer is slightly more hydrophobic than the B isomer, and both are considerably more surface‐active than LAS. The greater steric inhibition to micellization in the B isomer results in the lowest minimum surface tension. Both isomers have similar minimum interfacial tension values against hexadecane. Unusually small minimum area/molecule values for the two isomers at the aqueous solution/hydrophobic solid interface may indicate multilayer adsorption there. Both isomers are more efficient at reducing the contact angle than LAS. Mixtures of the B isomer with the corresponding unsulfated Guerbet alcohol show only weak interaction between the two. No synergism in surface (or interfacial) tension reduction efficiency or micelle formation exists at either the aqueous solution/air or aqueous solution interface but the mixture does show synergism in surface (or interfacial) tension reduction effectiveness, yielding a surface tension value of 28.2 dynes/cm, and an interfacial tension value of 0.1 dyne/cm against hexadecane. Draves wetting times increase in the order: B isomer<LAS<L isomer, and Ross‐Miles initial foam heights decrease in the order B isomer ≈LAS>L isomer.

Synergism in binary mixtures of surfactants. 7. Synergism in foaming and its relation to other types of synergism

AbstractThe relationship between synergism in Ross‐Miles foaming and the existence of other types of synergism in binary mixtures of surfactants has been investigated. All studies were conducted in solutions of constant ionic strength (0.1 M NaCl) at 25 and/or 60 C. Six anionic‐zwitterionic or anionic‐nonionic mixtures and a sodium dodecylbenzenesulfonate (LAS)‐soap mixture, all consisting of commercial surfactants, were studied. Synergism in foaming effectiveness, measured by initial foam heights, appears to be related to synergism in surface tension (γ) reduction effectiveness, but not to synergism in γ reduction efficiency or in mixed micelle formation. The LAS‐soap system showed negative synergism in foaming effectiveness, correlated with negative synergism in γ reduction effectiveness, the conditions for which are defined. There appears to be no correlation between synergism in foaming efficiency and synergism in either γ reduction efficiency or mixed micelle formation. There also appears to be no unambiguous relationship between foam stability, measured by the ratio of the 5‐minute to the initial foam height, and the average area per surfactant molecule at the aqueous solution/air interface.

Factors affecting initial foam height in the Ross‐Miles foam test

AbstractA study has been made of the relationship between initial foam height, H, as measured by the Ross‐Miles test, and such factors as surfactant concentration, critical micelle concentration (CMC) of the solute, surface tension (γ) of the solution, surface area (A) of the foam, and the work involved in the production of the foam surface. The initial foam was remarkably constant in character for the systems studied and there was a linear relationship between H and A. For five of the six solutes used, the work of producing the foam surface fell within a narrow range at concentrations in the neighborhood of the CMC, indicating an inverse relationship between A and γ. For these solutes, H≈(1000/γ)−3.6. The maximum in H occurred in the neighborhood of the CMC.

Molecular weight distribution of nonionic surfactants. III. Foam, wetting, detergency, emulsification and solubility properties of normal distribution and homogeneous p,t‐octylphenoxyethoxyethanols

AbstractThe effect of mol wt distribution on the foaming, wetting, detergency, emulsification and solubility properties of p,t‐octylphenoxyethoxy‐ethanols (OPE's) has been studied by comparing normal distribution and homogeneous compounds: Ross‐Miles foam studies indicate that, although homogeneous OPE7‐10 are higher in initial foam height than normal distribution OPE7‐10, their foam stability is poorer. Hard surface and textile wetting were studied by contact angle determinations and the Draves' skein test, respectively. An exact correlation exists between hard surface wetting by solutions of OPE's of a Teflon surface and surface tension lowering. Normal distribution OPE's are, in general, better hard surface wetting agents than the corresponding homogeneous compounds. In textile wetting, normal distribution OPE5‐10 are approximately equivalent in performance and by implication are probably equivalent in wetting performance to the corresponding homogeneous compounds. Hard surface detergency studies show that normal distribution OPE's are generally slightly superior in detersive power to homogeneous OPE's at corresponding ethylene oxide chain lengths. OPE10 is the best hard surface detergent of the OPE series, there being no distinguishable difference in performance between homogeneous and normal distribution OPE10. Emulsification studies on the system, water‐isooctane, show that only normal distribution OPE5 is capable of forming stable o/w emulsions. Both homogeneous and normal distribution OPE3 and OPE4 form stable w/o (invert) emulsions. Solubility studies in isooctane and Ultrasene show that homogeneous OPE4 is soluble at lower temp than the corresponding normal distribution compound. Studies of aqueous OPE solutions at temp above their cloud points show that solubility of both homogeneous and normal distribution materials is of the same order of magnitude as their critical micelle concn and that homogeneous OPE4 is more soluble than normal distribution OPE4.