Foamability of aqueous solutions: Role of surfactant type and concentration

B. Petkova, S. Tcholakova*, M. Chenkova, K. Golemanov, N. Denkov, D. Thorley, S. Stoyanov

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

In this paper we study the main surface characteristics which control the foamability of solutions of various surfactants. Systematic series of experiments with anionic, cationic and nonionic surfactants with different head groups and chain lengths are performed in a wide concentration range, from 0.001 mM to 100 mM. The electrolyte (NaCl) concentration is also varied from 0 up to 100 mM. For all surfactants studied, three regions in the dependence of the foamability, VA, on the logarithm of surfactant concentration, lgCS, are observed. In Region 1, VA is very low and depends weakly on CS. In Region 2, VA increases steeply with CS. In Region 3, VA reaches a plateau. To analyse these results, the dynamic and equilibrium surface tensions of the foamed solutions are measured. A key new element in our interpretation of the foaming data is that we use the surface tension measurements to determine the dependence of the main surface properties (surfactant adsorption, surface coverage and surface elasticity) on the surface age of the bubbles. In this way we interpret the results from the foaming tests by considering the properties of the dynamic adsorption layers, formed during foaming. The performed analysis reveals a large qualitative difference between the nonionic and ionic surfactants with respect to their foaming profiles. The data for the nonionic and ionic surfactants merge around two master curves when plotted as a function of the surface coverage, the surface mobility factor, or the Gibbs elasticity of the dynamic adsorption layers. This difference between the ionic and nonionic surfactants is explained with the important contribution of the electrostatic repulsion between the foam film surfaces for the ionic surfactants which stabilizes the dynamic foam films even at moderate surface coverage and at relatively high ionic strength (up to 100 mM). In contrast, the films formed from solutions of nonionic surfactants are stabilized via steric repulsion which becomes sufficiently high to prevent bubble coalescence only at rather high surface coverage (> 90%) which corresponds to related high Gibbs elasticity (> 150 mN/m) and low surface mobility of the dynamic adsorption layers. Mechanistic explanations of all observed trends are provided and some important similarities and differences with the process of emulsification are outlined.

Original languageEnglish
Article number102084
JournalAdvances in Colloid and Interface Science
Volume276
DOIs
Publication statusPublished - 1 Feb 2020

Fingerprint

Surface-Active Agents
Surface active agents
surfactants
aqueous solutions
foaming
Nonionic surfactants
Adsorption
Elasticity
adsorption
elastic properties
foams
Surface tension
Foams
interfacial tension
bubbles
Emulsification
Anionic surfactants
Cationic surfactants
Ionic strength
logarithms

Keywords

  • Dynamic surface tension
  • Foam
  • Foaminess
  • Surface modulus
  • Surfactant

Cite this

Petkova, B. ; Tcholakova, S. ; Chenkova, M. ; Golemanov, K. ; Denkov, N. ; Thorley, D. ; Stoyanov, S. / Foamability of aqueous solutions: Role of surfactant type and concentration. In: Advances in Colloid and Interface Science. 2020 ; Vol. 276.
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Foamability of aqueous solutions: Role of surfactant type and concentration. / Petkova, B.; Tcholakova, S.; Chenkova, M.; Golemanov, K.; Denkov, N.; Thorley, D.; Stoyanov, S.

In: Advances in Colloid and Interface Science, Vol. 276, 102084, 01.02.2020.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Foamability of aqueous solutions: Role of surfactant type and concentration

AU - Petkova, B.

AU - Tcholakova, S.

AU - Chenkova, M.

AU - Golemanov, K.

AU - Denkov, N.

AU - Thorley, D.

AU - Stoyanov, S.

PY - 2020/2/1

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N2 - In this paper we study the main surface characteristics which control the foamability of solutions of various surfactants. Systematic series of experiments with anionic, cationic and nonionic surfactants with different head groups and chain lengths are performed in a wide concentration range, from 0.001 mM to 100 mM. The electrolyte (NaCl) concentration is also varied from 0 up to 100 mM. For all surfactants studied, three regions in the dependence of the foamability, VA, on the logarithm of surfactant concentration, lgCS, are observed. In Region 1, VA is very low and depends weakly on CS. In Region 2, VA increases steeply with CS. In Region 3, VA reaches a plateau. To analyse these results, the dynamic and equilibrium surface tensions of the foamed solutions are measured. A key new element in our interpretation of the foaming data is that we use the surface tension measurements to determine the dependence of the main surface properties (surfactant adsorption, surface coverage and surface elasticity) on the surface age of the bubbles. In this way we interpret the results from the foaming tests by considering the properties of the dynamic adsorption layers, formed during foaming. The performed analysis reveals a large qualitative difference between the nonionic and ionic surfactants with respect to their foaming profiles. The data for the nonionic and ionic surfactants merge around two master curves when plotted as a function of the surface coverage, the surface mobility factor, or the Gibbs elasticity of the dynamic adsorption layers. This difference between the ionic and nonionic surfactants is explained with the important contribution of the electrostatic repulsion between the foam film surfaces for the ionic surfactants which stabilizes the dynamic foam films even at moderate surface coverage and at relatively high ionic strength (up to 100 mM). In contrast, the films formed from solutions of nonionic surfactants are stabilized via steric repulsion which becomes sufficiently high to prevent bubble coalescence only at rather high surface coverage (> 90%) which corresponds to related high Gibbs elasticity (> 150 mN/m) and low surface mobility of the dynamic adsorption layers. Mechanistic explanations of all observed trends are provided and some important similarities and differences with the process of emulsification are outlined.

AB - In this paper we study the main surface characteristics which control the foamability of solutions of various surfactants. Systematic series of experiments with anionic, cationic and nonionic surfactants with different head groups and chain lengths are performed in a wide concentration range, from 0.001 mM to 100 mM. The electrolyte (NaCl) concentration is also varied from 0 up to 100 mM. For all surfactants studied, three regions in the dependence of the foamability, VA, on the logarithm of surfactant concentration, lgCS, are observed. In Region 1, VA is very low and depends weakly on CS. In Region 2, VA increases steeply with CS. In Region 3, VA reaches a plateau. To analyse these results, the dynamic and equilibrium surface tensions of the foamed solutions are measured. A key new element in our interpretation of the foaming data is that we use the surface tension measurements to determine the dependence of the main surface properties (surfactant adsorption, surface coverage and surface elasticity) on the surface age of the bubbles. In this way we interpret the results from the foaming tests by considering the properties of the dynamic adsorption layers, formed during foaming. The performed analysis reveals a large qualitative difference between the nonionic and ionic surfactants with respect to their foaming profiles. The data for the nonionic and ionic surfactants merge around two master curves when plotted as a function of the surface coverage, the surface mobility factor, or the Gibbs elasticity of the dynamic adsorption layers. This difference between the ionic and nonionic surfactants is explained with the important contribution of the electrostatic repulsion between the foam film surfaces for the ionic surfactants which stabilizes the dynamic foam films even at moderate surface coverage and at relatively high ionic strength (up to 100 mM). In contrast, the films formed from solutions of nonionic surfactants are stabilized via steric repulsion which becomes sufficiently high to prevent bubble coalescence only at rather high surface coverage (> 90%) which corresponds to related high Gibbs elasticity (> 150 mN/m) and low surface mobility of the dynamic adsorption layers. Mechanistic explanations of all observed trends are provided and some important similarities and differences with the process of emulsification are outlined.

KW - Dynamic surface tension

KW - Foam

KW - Foaminess

KW - Surface modulus

KW - Surfactant

U2 - 10.1016/j.cis.2019.102084

DO - 10.1016/j.cis.2019.102084

M3 - Article

VL - 276

JO - Advances in Colloid and Interface Science

JF - Advances in Colloid and Interface Science

SN - 0001-8686

M1 - 102084

ER -

Petkova B, Tcholakova S, Chenkova M, Golemanov K, Denkov N, Thorley D et al. Foamability of aqueous solutions: Role of surfactant type and concentration. Advances in Colloid and Interface Science. 2020 Feb 1;276. 102084. https://doi.org/10.1016/j.cis.2019.102084