title: Stabilizing and destabilizing protein surfactant-based foams in the presence of a chemical surfactant: Effect of adsorption kinetics.
abstract: Stimuli-responsive protein surfactants promise alternative foaming materials that can be made from renewable sources. However, the cost of protein surfactants is still higher than their chemical counterparts. In order to reduce the required amount of protein surfactant for foaming, we investigated the foaming and adsorption properties of the protein surfactant, DAMP4, with addition of low concentrations of the chemical surfactant sodium dodecylsulfate (SDS). The results show that the small addition of SDS can enhance foaming functions of DAMP4 at a lowered protein concentration. Dynamic surface tension measurements suggest that there is a synergy between DAMP4 and SDS which enhances adsorption kinetics of DAMP4 at the initial stage of adsorption (first 60s), which in turn stabilizes protein foams. Further interfacial properties were revealed by X-ray reflectometry measurements, showing that there is a re-arrangement of adsorbed protein-surfactant layer over a long period of 1h. Importantly, the foaming switchability of DAMP4 by metal ions is not affected by the presence of SDS, and foams can be switched off by the addition of zinc ions at permissive pH. This work provides fundamental knowledge to guide formulation using a mixture of protein and chemical surfactants towards a high performance of foaming at a low cost.
authors.affiliation: Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Huazhen
authors.initials: H
authors.lastname: Li
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia.
authors.forename: Anton P
authors.initials: AP
authors.lastname: Le Brun
authors.affiliation: Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Dominic
authors.initials: D
authors.lastname: Agyei
authors.affiliation: Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Wei
authors.initials: W
authors.lastname: Shen
authors.affiliation: The University of Queensland, Australian Institute for Bioengineering and Nanotechnology, St. Lucia, QLD 4072, Australia.
authors.forename: Anton P J
authors.initials: AP
authors.lastname: Middelberg
authors.affiliation: Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia. Electronic address: lizhong.he@monash.edu.
authors.forename: Lizhong
authors.initials: L
authors.lastname: He
mesh_terms: D000327:Adsorption; D007700:Kinetics; D010316:Particle Size; D055550:Protein Stability; D011506:Proteins / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D011506:Proteins; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate
keywords: Adsorption kinetics; Dynamic surface tension; Foaming; Protein DAMP4; X-ray reflectometry