Specific effects of Ca2+ ions and molecular structure of β-lactoglobulin interfacial layers that drive macroscopic foam stability

Braunschweig B, Schulze-Zachau F, Nagel E, Engelhardt K, Stoyanov S, Gochev G, Khristov K, Mileva E, Exerowa D, Miller R, Peukert W (2016)

Publication Language: English

Publication Status: Published

Publication Type: Journal article, Original article

Publication year: 2016

Journal

Publisher: Royal Society of Chemistry

Book Volume: 12

Pages Range: 5995-6004

Journal Issue: 27

DOI: 10.1039/c6sm00636a

Abstract

β-Lactoglobulin (BLG) adsorption layers at air–water interfaces were studied in situ with vibrational sum-frequency generation (SFG), tensiometry, surface dilatational rheology and ellipsometry as a function of bulk Ca²⁺ concentration. The relation between the interfacial molecular structure of adsorbed BLG and the interactions with the supporting electrolyte is additionally addressed on higher length scales along the foam hierarchy – from the ubiquitous air–water interface through thin foam films to macroscopic foam. For concentrations <1 mM, a strong decrease in SFG intensity from O–H stretching bands and a slight increase in layer thickness and surface pressure are observed. A further increase in Ca²⁺ concentrations above 1 mM causes an apparent change in the polarity of aromatic C–H stretching vibrations from interfacial BLG which we associate to a charge reversal at the interface. Foam film measurements show formation of common black films at Ca²⁺ concentrations above 1 mM due to considerable decrease of the stabilizing electrostatic disjoining pressure. These observations also correlate with a minimum in macroscopic foam stability. For concentrations >30 mM Ca²⁺, micrographs of foam films show clear signatures of aggregates which tend to increase the stability of foam films. Here, the interfacial layers have a higher surface dilatational elasticity. In fact, macroscopic foams formed from BLG dilutions with high Ca²⁺ concentrations where aggregates and interfacial layers with higher elasticity are found, showed the highest stability with much smaller bubble sizes.

Authors with CRIS profile

Involved external institutions

Max-Planck-Institut für Kolloid- und Grenzflächenforschung / Max Planck Institute of Colloids and Interfaces Germany (DE) Bulgarian Academy of Sciences (BAS) / Българска академия на науките Bulgaria (BG)

How to cite

APA:

Braunschweig, B., Schulze-Zachau, F., Nagel, E., Engelhardt, K., Stoyanov, S., Gochev, G.,... Peukert, W. (2016). Specific effects of Ca2+ ions and molecular structure of β-lactoglobulin interfacial layers that drive macroscopic foam stability. Soft Matter, 12(27), 5995-6004. https://dx.doi.org/10.1039/c6sm00636a

MLA:

Braunschweig, Björn, et al. "Specific effects of Ca2+ ions and molecular structure of β-lactoglobulin interfacial layers that drive macroscopic foam stability." Soft Matter 12.27 (2016): 5995-6004.

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