Correlating surface rheology with bulk rheology in foams stabilized by hemp proteins and hemp protein-pectin...

Foams are dispersions of gas in a liquid, consisting of multiple closely packed air bubbles. The bulk elasticity of foams is positively correlated with surface elasticity and can be tuned by controlling surface mechanical properties.

We studied surface rheology of air-water interfaces stabilized by hemp proteins and their complexes with pectin using small and large amplitude oscillatory shear or dilatation (i.e., SAOS/LAOS and SAOD/LAOD). These stabilizers produce air-water interfaces with a wide range of interfacial stiffness. Bulk rheology of foams formed with these stabilizers was studied using small and large amplitude oscillatory shear (SAOS and LAOS) and continuous shear rheological tests.

Albumin-pectin complexes formed the stiffest air-water interfaces and the most stable foams, followed by globulin-pectin complexes and hemp globulins, while hemp albumin formed the weakest air-water interface and thus the most unstable foams. The relationship between surface rheology (G_i' and E_d') and bulk foam rheology (G') was explored and correlations between several parameters were observed both in the linear and nonlinear viscoelastic regimes. In the latter regime, the relationship between interfacial and bulk rheological properties is rarely studied, and for many systems not known. Finally, good agreement between experimental results for the bulk shear modulus in the linear regime and the prediction of a physical model was found, showing the broad applicability of this model across a wide range of stabilizers, and across systems (i.e., air-water and oil-water based). These insights allow for a more efficient control of bulk rheological properties of foam-based materials, both at small and large deformations, by tuning the (nonlinear) 2D rheology of their air-water interfaces.