Contact angles of protein black foam films under dynamic and equilibrium conditions

Abstract

Abstract:The contact angles of protein Newton black foam films from ALG (alpha-lactalbumin), BLG (beta-lactoglobulin) and BSA (bovine serum albumin) are measured here within. The measurements are carried out under dynamic and equilibrium conditions. For all proteins, a strong hystheresis effect of the contact angle is observed under dynamic conditions. An attempt is made to explain these results by the slow adsorption and desorption kinetics of the protein bilayers and by the dynamic structure and the rheology of the protein network forming the bubble walls. In addition, we propose a modification of the experimental device reported previously for contact angle measurements of large flat films in equilibrium. The advantages of this method are discussed in detail. Some shortcomings (precision, reproducibility) of this preliminary variant of the device in this initial stage of its application, do not allow one to draw reliable conclusions about the interactions of these films. Some improvements of the measurement quality are proposed.

Self-Assembled Bilayers from the Protein HFBII Hydrophobin: Nature of the Adhesion Energy

“…Because the surfaces of the protein black films adhere to each other, there is contact angle hysteresis, so that the advancing angle (at a shrinking contact line and detaching film surfaces), θ adv , can be considerably greater than the equilibrium one. The following maximum values of the advancing angles have been reported for different systems: θ adv = 1.4° for BSA, θ adv = 1.8° for human serum albumin, and θ adv ≈ 7° for α-lactalbumin . The greatest value of the advancing angle was detected for β-casein black films in the presence of bridging Ca 2+ ions: θ adv ≈ 90° at a rate of contact line shrinking ≤ 10 μm/s …”

“…The formation of black films, which represent protein bilayers, has been observed many times, but never with such large contact angles. For example, the maximum equilibrium contact angles of protein black films reported in the literature are θ = 0.9° in the case of bovine serum albumin (BSA) + 0.15 M NaCl, θ = 1.7° for α-chymotrypsin + 0.1 mM NaCl, and 2.7° for α-lactalbumin …”