Effect of pH on the interfacial viscoelasticity and stability of the silk fibroin at the oil/water interface

• Interfacial rheology of silk fibroin at O/W interface with pH effect was discussed.
• Effect of pH on the stability of silk fibroin emulsions was investigated.
• At pH4, silk fibroin forms compact conformation and adsorbs quickly at the interface.
• At pH4, silk fiborin emulsions exhibit low emulsion stability and large droplet size.

Effect of pH on the interfacial viscoelasticity of silk fibroin at both nonpolar dodecane/water interface and polar butyl butyrate/water interface was investigated, and the emulsions stabilized by silk fibroin with different pH and different oil phases were also prepared to check the interfacial stability and emulsification effectiveness of silk fibroin. The silk fibroin can adsorb to the oil/water interface, reduce the interfacial tension efficiently and exhibit good emulsifier effects. At pH 4 with respect to isoelectric point, the silk fibroin molecules aggregate more easily, form more compact conformation and have less chances to interact with neighboring molecules, which results in faster molecular adsorption at the interface but lower modulus of interfacial layers. Moreover, the interfacial layers formed by silk fibroin at pH 4 are relatively rigid, rupture more easily and are more likely to allow droplet coalescence upon small emulsion disturbance, and the corresponding emulsions exhibit lower emulsion stability and larger emulsion droplet size.

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