Effect of interfacial viscoelasticity on the bulk linear viscoelastic moduli of globular protein solutions

The role of interfacial rheology on the bulk linear viscoelastic moduli of low concentration bovine albumin solutions is probed. Previously reported soft gel properties of these systems were attributed to either protein aggregation or organization within the bulk. Instead, these behaviors are shown to be attributable to the measurement error caused by interfacial rheology due to adsorption of bovine serum albumin to the air and water interface. Even at low bulk concentrations, fast interfacial adsorption results in erroneous measurements. When these effects are removed, the solutions are viscous dominated with a dynamic viscosity slightly larger than water.

Figure 1

Linear viscoelastic moduli of bovine serum albumin solutions: (□) $G^{\prime }$ and (○) $G^{″}$. (a) Amplitude sweep at 1 rad/s. (b) Frequency sweep at 0.01 strain. Dashed lines represent minimum resolution of moduli.

Figure 2

Interfacial linear viscoelastic moduli of bovine serum albumin solutions. (■) $G_s^{\prime }$ after 6 h of aging; ($•$) $G_s^{″}$ after 6 h of aging; (□) $G_s^{\prime }$ after 1 h of aging; (○) $G_s^{″}$ after 1 h of aging. (a) Amplitude sweep at 1 rad/s. (b) Frequency sweep at 0.01 strain. Dashed lines represent minimum resolution of moduli.

Figure 3

Linear viscoelastic moduli of bovine serum albumin solutions, (□) $G^{\prime }$ and (○) $G^{″}$ and of bovine albumin solutions with SDS added to the interface, (■) $G^{\prime }$ and ($•$) $G^{″}$. (a) Amplitude sweep at 1 rad/s. (b) Frequency sweep at 0.01 strain. Dashed lines represent minimum resolution of moduli.