Using a surface force balance, we have measured the forces between bare (hydrophilic) mica surfaces, and between hydrophobized mica surfaces, in each case coated with the amphiphilic protein hydrophobin (HFBI) from Trichoderma reesei. We additionally characterized these surfaces by contact angle measurements and AFM. The results are consistent with the formation of hydrophobic surfaces exposed by HFBI adsorbed on the hydrophilic substrate, and hydrophilic surfaces exposed by HFBI adsorbed on the hydrophobic substrate. In particular, friction between HFBI surfaces on hydrophobized mica, exposing hydrophilic surfaces, is an order of magnitude lower than friction between HFBI-coated hydrophilic surfaces, which expose the hydrophobic side of the protein to the water interface. This result can be readily understood in terms of the greater hydration level of the exposed outer surfaces in the former case.
Goldian, I., Jahn, S., Laaksonen, P., Linder, M., Kampf, N., & Klein, J. (2013). Modification of interfacial forces by hydrophobin HFBI. Soft Matter, 9(44), 10627-10639. https://doi.org/10.1039/C3SM51924D