DERNIERES PUBLICATIONS
- Daniela Georgieva, Alain Cagna (Teclis), Dominique Langevin - France
Link between surface elasticity and foam stability
Soft Matter May, 2009 - 2063-2071.
We have measured the surface dilational elastic moduli of bubbles immersed in water
and soap bubbles in air. The short time response was obtained by submitting the bubbles
to a rapid expansion after which the surface tension evolution was monitored, using either
image analysis or pressure measurements.
It was possible with this method to measure directly the Gibbs elasticity. The longer time
response was obtained by submitting the bubbles to low frequency oscillations.
Experiments were performed with solutions of non-ionic surfactants, C12E6, C12G2, their
1:1 mixture, Pluronic F-68 and 127 and the surface elastic moduli were compared with the
stability of foams made with these surfactants.
The foams evolve with time, first by Ostwald ripening, controlled by the low frequency
elasticity, and then by bubbles coalescence, controlled by the high frequency elasticity.
Properties of aqueous foams stabilized by dodecyltrimethylammonium bromide
Available online 21 February 2009
a University College Dublin, School of Chemical and Bioprocess Engineering, Belfield, Dublin 4, Ireland
b Centre for Synthesis and Chemical Biology, SFI-Strategic Research Cluster in Solar Energy Conversion,
University College Dublin, Belfield, Dublin 4, Ireland
Foamability, foam stability and the liquid volume of aqueous foams stabilized by dodecyltrimethylammonium
bromide (C12TAB) are studied. The foams are generated with a sparging method at different gas flow rates
and surfactant concentrations. It is found that at concentrations c ≥ cmc drainage dominates foam destruction
while at c < cmc additional processes lead to a dramatic decrease in foam stability.
Qualitatively similar results are obtained with the Ross–Miles (pouring) method and the winding (shaking)
method, respectively. Increasing the gas flow rate of the sparging method at a fixed surfactant concentration,
one observes a decrease in the time required for the production of 60 ml foam, whilethe liquid volume of the
generated foam increases. On the other hand, an increase of the surfactant concentrationat a fixed gas flow
rate leads to an increase in the required foaming time with a plateau atc ≥ cmc, while the liquid volume of the
generated foam decreases. Finally, the influence of small impuritiesis also tested and it is found that small
amounts of impurities (“as received sample”) lead to asignificant increase of both the foamability and the
stability of foams stabilized by C12TAB. The obtainedresults are discussed in terms of the different processes
leading to foam destruction and a comparisonbetween the three different methods is made. Whenever possible
and feasible, the correlation betweensingle surfaces, single foam films and foams is addressed.
SOME RELATED PUBLICATIONS FOR TRACKERLittle resume for publications below
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Petroleum
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USA
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Bitumen
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France
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Chemical industry
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USA
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Polymer
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Russia
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Polymer
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China
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Food industry
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Sweden
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Protein
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Spain
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Biochemistry
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Switzerland, Sweden, Germany and Ukraine
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Tunis and France
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- Dynamic Asphaltene-Resin Exchange at the Oil Water Interface Time-Dependent WO Emulsion Stability
for AsphalteneResin model oils
Energy & Fuels 2007, 21, 1343-1349 Xiaoli.Yang, Vincent. J. Verruto and Peter. K. Kilpatrick
Abstract:
The critical electric field (CEF) technique was used to determine the time-dependent stability of water-in-oil
emulsions in which asphaltenes stabilize the film. Stabilizing films comprising purely asphaltenes were
observed to increase monotonically in stability with time. However, in the presence of resins, particularly in
mass ratios of resins to asphaltenes of 0.5−1.0, the stability of the emulsions as probed by CEF were
observed to exhibit a very sharp local maximum. Similar behavior was observed in dilatational interfacial
rheology experiments using an oscillating drop tensiometer. The dilatational modulus (ε) for the stabilizing
film, as obtained from the variation of interfacial tension with interfacial area, of an aging asphaltene/resin
model oil droplet in water exhibited a time-dependent local maximum. Values of ε were nominally lower for
asphaltene/resin model oil systems than asphaltene model oil systems, qualitatively similar to CEF trends.
These observed phenomena are similar to the “Vroman effect”, observed in competitive protein adsorption.
One plausible explanation is that resin-solvated asphaltenic aggregates are able to diffuse and adsorb to
the interface more quickly than larger pure asphaltenic aggregates, but then a molecular rearrangement
occurs in which resins become the primary adsorbent in the monolayer by reptation through the consolidated
asphaltene network, displacing the asphaltenes and reducing the stability and the dilatational elasticity.
- Interfacial Tension of Bitumen-Water Interfaces. Part 1 Influence of endogenous surfactants at Acidic PH
Energy Fuels, 22 (2), 790–798, 2008
Alain. Cagna, P. Chaverot, Sylvie. Glita and Francis. Rondelez
Abstract :
We have studied the time dependence of the interfacial tension between acidic aqueous solutions (pH 2)
and commercial straight-run bitumen droplets of different origins by the pendent drop method. Because of
the existence in bitumen of naturally occurring surface-active species, significant changes of the interfacial
tension are observed over timescales of several thousands of seconds. The kinetics of the decrease is
consistent with the exodiffusion of endogenous surfactants toward the bitumen−water interface and throughout
the bitumen matrix. At T = 90 °C, one observes that the interfacial tension decreases as t1/2 at short times
and as t−1/2 at long times when the interface becomes nearly saturated. Combining these two kinetic data
allows for a direct estimate of the surface concentration of these endogenous surfactants. If one makes the
assumption that they organize in a dense, close-packed monolayer, their size and concentration in bulk
bitumen can also be readily derived. At T = 140 °C, the viscosity of bitumen is 20 times lower than at 90 °C
and the short time kinetics can no longer be resolved with our experimental apparatus. This restricts the data
analysis, but we can nevertheless obtain an estimate of the size of the surfactant molecules if one makes the
reasonable hypothesis that the bulk concentration of surfactants remains unchanged between 90 and 140 °C.
Our results suggest that the surface-active species at pH 2 are asphaltene moieties of basic character. They
are probably in an aggregated form because the measured, nanometric size decreases at elevated
temperatures. Quite remarkably, they correspond to a very small fraction of the total asphaltenes contained
in bitumen, which explains why they are extremely difficult to detect analytically. To the best of our knowledge,
this is the first time that quantitative data on the endogenous surfactants are obtained in industrial bitumen.
The present results thus complete the numerous existing observations on model oil–water systems. - Interfacial rheological studies of gelatin-sodium dodecyl sulfate complexes adsorbed at the air-water interface
Langmuir 2005, 21, 617-621
Ashwin. Rao, Jongdae. Kim and Richard. R. Thomas
Abstract:
The dilational rheological behavior of gelatin molecules adsorbed at the air−water interface has been studied
as a function of sodium dodecyl sulfate (SDS) concentration for a 7 wt % gelatin−SDS solution at 40 °C. Binding
of SDS molecules to the gelatin strands disrupts the cross-linked network structure of adsorbed gelatin molecules
and results in a reduction of the surface elastic modulus of the adsorbed layer that continues until the bulk SDS
concentration reaches 1 mM. Beyond this SDS concentration, the dilational rheological properties of the adsorbed
gelatin layer are indistinguishable from those of pure SDS adsorbed layers.
- Dynamic Surface Tension and Dilational Viscoelasticity of Adsorption Layers of a Hydrophobically Modified Chitosan
Colloids and surface A-2004
Valery. G.Babak, Jacques. Desbrières and Vladimir.E.Tilhonov
Abstract: The kinetics of the adsorption at the air–water interface and the processes of the structure formation inside the
adsorption layers of the alkylated chitosan (the cationic polysoap) have been studied in function of its bulk concentration
and the ageing time of the adsorption layers. It has been shown that the dynamic surface tension γ(t) of this polysoap
aqueous solution measured by the axisymmetric rising bubble shape analysis is characterized by several stages with
different characteristic relaxation times. During induction and post-induction times the adsorption is the diffusion-controlled
process of macromolecules from the bulk of the solution to the interface. At the final stage the adsorption is characterized
by much lower rate due to the steric hindrance exerted by the yet formed adsorption layer on newly adsorbing
macromolecules.
The structure (physical gel) formation within the adsorption layers of the alkylated chitosan via intermolecular hydrophobic
interaction or by hydrogen bonding in function of the ageing time (up to tf 5 × 104 s) has been studied with the help of the
two-dimensional dilational rheology by applying sinusoidal deformation to the bubble area within the frequency range of
w = 0.05–0.4 rad/s. One characteristic relaxation frequency rheological model of Maxwell has been applied to determine
two-dimensional “storage” E′ and “loss” E″ elasticity moduli, as well as the intrinsic elasticity module E0 and the
characteristic relaxation frequency ω0 (or the intrinsic viscosity η0 = E0ω0/2π) of the adsorption layer in function of the bulk
polymer concentration Cp. It has been shown that the parameters E0 and η0 sharply decrease with increasing Cp. This finding
is interpreted on the basis of proposed mechanism explaining the effect of the conformational state of the macro-ions inside
the adsorption layers on the Gibbs elasticity and the characteristic relaxation time.
- Aggregation behavior of block polyethers with branched structure at air/water surface
European Polymer Journal 45 (2009) 2540–2548
Houjian Gong, Guiying Xu, Hui Ding, Xiaofeng Shi and Yebang Tan
Abstract:
The block polyethers with various branch structure, such as TEPA[(PO)36(EO)100]7, TEPA[(PO)36(EO)100(PO)36]7, and
TEPA[(PO)36(EO)100(PO)56]7 were synthesized. Moreover, the aggregation behavior was investigated via the
measurements of equilibrium surface tension, dynamic surface tension, and surface dilational viscoelasticity, in order to
probe the effect of the block structure on the property of the branched block polyethers. The surface tension results
show that the efficiency and effectiveness of the block polyethers to lower surface tension increase with the increase
of the PO group numbers. The maximum surface excess concentration (Γmax) values and the minimum occupied area
per molecule at the air/water interface (Amin) values of the branched block polyethers obtained from Gibbs adsorption
equations increase and decrease with the increases of the PO group numbers, respectively. The dynamic parameters n
and t* representing the diffusion speed of the polyether molecules from bulky solution to the subsurface and from the
subsurface to the air/water surface are obtained according to the equation proposed by Rosen. The results show that the
n values firstly increase and then decrease and t* values decrease with the increase of the polyether concentrations.
The results of surface dilational viscoelasticity show that the dilational modulus of TEPA[(PO)36(EO)100(PO)56]7
is the largest among the three block copolymers at the low concentration (<1 mg L−1) but that of TEPA[(PO)36(EO)100]7
is the largest at the high concentration (>1 mg L−1).
- Adsorption of hydrophobically modified anionic starch at oppositely charged oil/water interfaces
Journal of colloid and interface science 308 (2007) 508-513
Lars.Nilsson and Björn. Bergenstahl Abstract:
In this paper we study the adsorption at cationic emulsion droplets of starch which had been hydrophobically modified
with octenyl succinic anhydride (OSA), a modification which also renders the starch anionic. Emulsions were formed with
didodecyldimethylammonium bromide (DDAB) after which the OSA-starch was added. The emulsions were separated by
centrifugation and the surface load of OSA-starch was determined through serum depletion. The results show the adsorbed
amounts can become very high, in some cases reaching approximately 40 mg/m2. The surface load correlates positively
with the surface charge density of the starch which depends on the degree of substitution, rms radius and molar mass.
Furthermore, the surface load obtained depends on the ratio between polymer surface charge density and the interface
charge density which could be varied experimentally by combining various amounts of DDAB and dioleoyl phosphatidylcholine
(DOPC) in the formation of the emulsion. The very high surface loads should correspond to very thick adsorbed layers.
Thus, OSA-starch should be appropriate for encapsulation applications provided a suitable adhesion substance is employed.
- Dilatational properties of soy globulin adsorbed films at the air–water interface from acidic solutions
Journal of Food Engineering 68 (2005) 429–437
Juan.M.Rodriguez. Patino, M.Rosario.Rodriguez. Nino, Cecilio.Carrera. Sanchez, Sara.E.Molina. Ortiz, M.Cristina. Anon
Abstract:
In this paper we present surface dilatational properties of soy globulins (β-conglycinin, glycinin, and reduced glycinin
with 10 mM of dithiothreitol (DTT)) adsorbed on the air–water interface, as a function of adsorption time. The surface
rheological parameters (surface dilatational modulus, E, its elastic and viscous components, and phase angle) were
measured as a function of protein concentration (ranging from 1 to 1 × 10−3%, wt/wt) at pH 2.0 and 5.0. We found
that the surface dilatational modulus, E, increases with time, θ. This phenomenon has been related to protein adsorption,
unfolding, and/or protein–protein interactions (at long-term adsorption). The dilatational properties of the adsorbed films
depend on the molecular structure of the protein, the pH, and on the protein concentration in the aqueous phase. Soy
globulins are adsorbed at the air–water interface with different degrees of association at different concentrations in the
bulk phase and at different aqueous phase pH.
- Adsorption of polar lipids at the water-oil interface
Langmuir 2008, 24, 5781-5786
P. Reis, R. Miller, M. Leser, H. Watzke, V. B. Fainerman and K. Holmberg
Abstract: Dietary fat has long been recognized as an essential component in nutrition. However, most of the lipids present in
food need to be converted into more bioavailable compounds. Lipases have a crucial role in converting triglycerides
into more polar lipids with increased water solubility and a tendency to form micelles. However, the surface active
molecules generated by lipolysis may have a detrimental effect on the interfacial biocatalysis. In the present work
we evaluate the interfacial properties of lipase-generated molecules during fat digestion. By using the pendant drop
technique we assessed the amphiphilic character of fatty acid salts, monoglycerides, and diglycerides as individual
surfactants and mixtures. The experimental results are fitted with a mathematical model, which assists in the
determination of the interfacial properties of the surfactants. Our results show that monoglycerides have considerably
higher interfacial activity than fatty acid salts and diglycerides. Therefore, the interface will soon be dominated by
monoglycerides. The pH dependency of the interfacial activity of fatty acids is also explored in the current work.
We believe that our results can contribute to a better understanding of the complex interfacial phenomena occurring
during fat digestion.
- Influence of clay addition on the properties of olive oil in water emulsions
Applied clay science ISSN 0169-1317 CODEN ACLSER
Nciri H., Benna-Zayani M., Stambouli M., Kbir-Ariguib N., Trabelsi-Ayadi M., Rosilio V. and Grossiord J.-I.
Abstract: The behaviour of olive oil-in-water emulsions (O/W) was studied in the presence of smectite particles. The distribution
of these particles in the emulsions and the effect of their interaction with the surfactant on the stability of the emulsions
were investigated. Whereas the variation of surfactant and/or clay content did not seem to affect the nature of the
emulsion, it had a significant influence on emulsion stability. This observation led to two main assumptions on the
distribution of clay particles within the emulsion, either exclusively in the continuous phase, or also at the oil-water
interface. In the absence of clay, the variation of surfactant concentration (from 0 to 17% (w/w)) allowed to distinguish
3 domains. In the first concentration domain (0-4.2%) emulsions stability increased with the content of surfactant.
Within the second domain (4.2-8.5% (w/w)), a slight decrease in stability was observed due to flocculation by depletion.
For surfactant concentrations equal or higher than 8.5% (3rd domain), emulsion stability increased sharply, probably
due to the development of interactions between surfactant molecules as they came closer to their gelling concentration.
The effect of clay addition to the aqueous phase (up to 10% (w/w)) on the physicochemical properties of the studied
emulsions was assessed from stability, drop size, interfacial tension, rheological and acido-basic analyses. A model
based on the location of clay particles either in the bulk or at the interface could be proposed, in which clay particles
would interact with surfactant molecules in the bulk phase, and form a mechanical barrier around the oil droplets,
thus increasing emulsion stability.
SOME RELATED PUBLICATIONS FOR FOAMSCANLittle resume for publications below
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Food industry
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Switzerland
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Protein
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Switzerland
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Search
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France
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Protein
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France
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Emulsion
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Belgium
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Ireland
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Japan
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Protein
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Bulgaria
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Sweden
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- Hydrocolloids from coffee physicochemical and functional properties of an arabinogalactan–protein fraction
from green beans
Food Hydrocolloids 19(2005)1005-1015 R.J. Redgwell, C. Schmitt, M. Beaulieu, D. Curti
Abstract: The arabinogalactan–protein (AGP) fraction of green coffee beans accounts for 15% of the dry bean. A procedure was
developed to solubilise most of the AGP content of the beans so that its properties as a hydrocolloid could be
investigated. An AGP fraction was partially purified from green arabica coffee beans, its rheological properties
characterised and compared to those of some commercially important hydrocolloids, particularly acacia gum. The
coffee AGP fraction dissolved readily in water to give colourless clear solutions. The polymer was a polyelectrolyte
with a high molecular weight (Mw 3.78×106), characterised by a narrow polydispersity index (Mw/Mn 1.3). The intrinsic
viscosity was close to that of acacia gum ([η]=0.23 dL g−1), but a 1 wt% solution of coffee AGP was three times more
viscous than acacia gum at the same concentration. Coffee AGP showed Newtonian flow for concentrations below 6 wt%,
but above this concentration the flow behaviour entered a shear-thinning regime. The coffee AGP fraction possessed
interesting foaming properties providing that the biopolymer concentration was high enough to initially stabilize the
interface that is created. The high molecular weight of coffee AGP combined with its globular structure conferred upon
it a high ability to retain water within a foam thin film. However, the structure of the interfacial film was less effective
than that of acacia gum to entrap efficiently the gas into the foam. In summary, coffee AGP shows some interesting
rheological features which suggest that coffee beans could be used as an alternative source of the class of surface-active
polymers which find many commercial applications.
- Automatic analysis of 2D foam sequences: Application to the characterization of aqueous proteins foams stability
Image and vision computing (2008)
S. Rami-shojaei, C. Vachier, C. Schmitt
Abstract:
Aqueous foams occur in several industrial applications including food production. One of the challenging issues in foams
study is to evaluate the air bubbles stability. This problem is addressed in the present work using sequences of 2D
macroscopic images of aqueous foams carried out in a glass column. Despite commercial softwares that are currently used in microscopy, the automatic analysis of foam sequences is still an
unsolved problem. It can be related to two fundamental problems in the field of image analysis: the granulometric
analysis and the automatic tracking of objects in image sequences. Rather than an adaptation of existing granulometric
or tracking methods, the proposed foam analyzer consists in a new algorithm based on a double tracking of the foam
bubbles: a scale-space tracking, where the scale parameter is the size, and a temporal tracking. It ensures a complete
description of any bubble through the time and the detection of any bubbles interaction so that the foam’s structure is
finally entirely and very precisely described.The proposed foam analyzer has been validated by comparing the characteristics
computed by the automatic method to those that can be predicted via the foams physical properties.
- Surface rheology and foaming properties of sodium oleate and C12(EO)6 aqueous solutions
Journal of Colloid and Interface Science 268(2003)221-229
D. Beneventi, Robert J. Pugh, B. Carré, A. Gandini
Abstract:
The dynamic surface tension (DST) and the surface viscoelastic modulus of sodium oleate aqueous solutions at
different concentrations were measured using an image analysis tensiometer based on the oscillating bubble
technique. The diffusion coefficient of oleate moieties was calculated from DST measurements and the surface
viscoelastic modulus using the Langmuir-Szyszkowski and the diffusion-controlled adsorption models. The viscoelastic
moduli obtained from model calculations were compared with the corresponding experimental values. The diffusion
coefficient of C(12)(EO)(6) in water and the parameters of the Langmuir-Szyszkowski adsorption isotherm were taken
from the literature and used to calculate the surface viscoelastic modulus of its aqueous solutions at different concentrations.
The foaming properties of both C(12)(EO)(6) and sodium oleate solutions, viz., the foam conductance and the water
volume fraction in the foam, were measured using a commercial Foamscan device. Foaming experiments with
C(12)(EO)(6) and sodium oleate solutions were carried out either under static conditions; i.e., the foam conductance
and the water volume fraction were measured as a function of time after the generation of a fixed volume of foam,
or under dynamic conditions; i.e., the foam conductance and the water volume fraction were measured during foam
formation. The variations in the foam permeability as a function of surfactant concentration were related to the
viscoelastic properties of the air/water interface and to the presence of micelles in the foam films. With foams in which
the water volume fraction was higher than 0.05, the foam electrical conduction could be described using a simple
parallel resistor model and their conductance measurements were related to the foam water volume fraction.
The results related to water drainage under static conditions were used to interpret water drainage under dynamic conditions.
Preliminary conjectures on the influence of foam permeability and water volume fraction on the yield of the flotation deinking
process were drawn from these results.
- b-Lactoglobulin aggregates in foam films: Correlation between foam films and foaming properties
Journal of Colloid and Interface Science 336 (2009) 750–755
B. Rullier, M.A.V. Axelos, D. Langevin, B. Novales
Abstract :
Single foam films made from aqueous protein solutions containing aggregates have been studied using a thin film
balance apparatus. When the solutions are free from non-aggregated proteins, the films are either fluid or gelified,
depending on the aggregate size. When non-aggregated proteins are present, they adsorb at the film surfaces, acting
as anchors for the aggregates, and ultimately leading to stable foam films if the amount of non-aggregated proteins
is sufficient. In all cases, gel-like films are more stable than fluid films and there is a good correlation between
foam and film stability.
- Effect of proteose-peptone addition on some physico-chemical characteristics of recombined dairy creams
International Dairy Journal 17 (2007) 889–895
C. Vanderghem, S. Danthine, C. Blecker, C. Deroanne
Abstract:
The effect of the addition of the total proteose-peptone (TPP) fraction on some physico-chemical properties of
recombined cream was studied. Oil-in-water emulsions, 30% or 20% (w/w) fat, were prepared using only the dairy
components buttermilk, milkfat and TPP. The effect of different concentrations of TPP on droplet size, creaming stability,
flow behaviour, viscosity and whippability of
recombined creams was tested. Of the different creams, those containing 2% (w/w) or more TPP were more viscous,
showed different flow behaviour, and had improved stability and whippability compared with the other creams. The
modifications in physico-chemical properties appeared to be driven by changes in particle size distribution caused by
droplet aggregation. The percentage of fat also influenced the properties of the final product. It may therefore be
possible to obtain desirable modifications in ecombined cream using only dairy ingredients.
- Properties of aqueous foams stabilized by dodecyltrimethylammonium bromide
Journal of Colloid and Interface Science 333 (2009) 619–627
E. Carey, C. Stubenrauch
Abstract: Foamability, foam stability and the liquid volume of aqueous foams stabilized by odecyltrimethylam-monium bromide
(C12TAB) are studied. The foams are generated with a sparging method at different gas flow rates and surfactant
concentrations. It is found that at concentrations c _ cmc drainage dominates foam destruction while at c < cmc additional
processes lead to a dramatic decrease in foam stability. Qualitatively similar results are obtained with the Ross–Miles
(pouring) method and the winding (shaking) method, respectively. Increasing the gas flow rate of the sparging method
at a fixed surfactant concentration, one observes a decrease in the time required for the production of 60 ml foam, while
the liquid volume of the generated foam increases. On the other hand, an increase of the surfactant concentration at a
fixed gas flow rate leads to an increase in the required foaming time with a plateau at c _ cmc, while the liquid volume
of the generated foam decreases. Finally, the influence of small impurities is also tested and it is found that small amounts
of impurities (“as received sample”) lead to a significant increase of both the foamability and the stability of foams
stabilized by C12TAB.
The obtained results are discussed in terms of the different processes leading to foam destruction and a comparison
between the three different methods is made. Whenever possible and feasible, the correlation between single surfaces,
single foam films and foams is addressed.
- Interfacial properties and foam stability effect of novel gemini-type surfactants in aqueous solutions
Journal of Colloid and Interface Science 291(2005)236-243
Durga P. Acharya, José M. Gutiérrez, Kenji Aramaki, Ken-ichi Aratani,and Hironobu Kunieda
Abstract: Static and dynamic surface tension and interfacial rheological behavior of a novel anionic gemini-type surfactant without
a spacer group, sodium 2,3-didodecyl-1,2,3,4-butane tetracarboxylate (GS), were investigated. Very low values for critical
micelle concentration (8.9 × 10−5 M) as well as equilibrium surface tension (22.7 mNm−1) were observed for the aqueous
solutions. Dynamic surface tension (DST) is very slow and less sensitive to the surfactant concentration
than the conventional monomeric surfactant, suggesting the presence of a significant adsorption barrier for GS owing to
a complicated molecular structure. Presence of a small concentration of GS in sodium dodecyl sulfate (SDS) solution shows
a synergistic effect to form mixed micelles and lowers the cmc considerably. This synergism between GS and SDS and slow
exchange of GS between bulk and interface create a rigid air–liquid interface of the SDS–GS solution, which is reflected in
a higher elasticity value for the interface of the SDS–GS solution than for the SDS solution. It has been found that the
presence of a small concentration of GS in SDS solution increases the foam stability noticeably. lthough the stability of
the wet foam is correlated with the film elasticity, the stability of dry foam cannot
be explained in terms of film elasticity alone.
- Physico-chemical factors controlling the foamability and foam stability of milk proteins: Sodium caseinate and
whey protein concentrates
MARINOVA Krastanka G.; BASHEVA Elka S. ; NENOVA Boriana ; TEMELSKA Mila ; MIRAREFI Amir Y. ; CAMPBELL Bruce and
IVANOV Ivan B. Food hydrocolloids ISSN 0268-005X CODEN FOHYES
Abstract: We explored the foaming behavior of the two main types of milk proteins: flexible caseins and globular whey proteins.
Direct foam comparison was complemented with measurements in model experiments such as thin foam films, dynamic
surface tension, and protein adsorption. Foaming was studied as a function of pH (from below to above isoelectric point, pI)
and range of ionic strengths. Maximum foamability was observed near pl = 4.2 for WPC in contrast to sodium caseinate
which had minimum foaming near pI = 4.6. Good foamability behavior correlated well with an increased adsorption, faster
dynamic surface tension decrease and increased film lifetime. Differences in the stability of the foams and foam were
explained with the different molecular structure and different aggregation behavior of the two protein types. Far from its
isoelectric pI, casein adsorption layers are denser and thicker thus ensuring better stabilization. Added electrolyte increased
further the adsorption and the repulsion between the surfaces (probably by steric and/or osmotic mechanism). In contrast
the globular molecules of WPC probably could not compact well to ensure the necessary films and foams stabilization far
from pI, even after electrolyte addition.
- Experimental techniques for studying the structure of foams and froths
R.J. Pugh
Colloid and Interface Science 114 – 115 (2005) 239 – 251
Abstract: Several techniques are described in this review to study the structure and the stability of froths and foams. Image
analysis proved useful for detecting structure changes in 2-D foams and has enabled the drainage process and the
gradients in bubble size distribution to be determined. However, studies on 3-D foams require more complex techniques
such as Mutiple-Light Scattering Methods, Microphones and Optical Tomography. Under dynamic foaming conditions,
the Foam Scan Column enables the water content of foams to be determined by conductivity analysis. It is clear that the
same factors, which play a role in foam stability (film thickness, elasticity, etc.) also have a decisive influence on the
stability of isolated froth or foam films. Therefore, the experimental thin film balance (developed by the Bulgarian
Researchers) to study thinning of microfilms formed by a concave liquid drop suspended in a short vertical capillary
tube has proved useful. Direct measurement of the thickness of the aqueous microfilm is determined by a micro-
reflectance method and can give fundamental information on drainage and thin film stability.
It is also important to consider the influence of the mineral particles on the stability of the froth and it have been
shown that particles of well defined size and hydrophobicity can be introduced into the thin film enabling stabilization/
destabilization mechanisms to be proposed. It has also been shown that the dynamic and static stability can be
increased by a reduction in particle size and an increase in particle concentration.
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