Operating windows for oscillatory interfacial shear rheology

Abstract

Interfacial rheology becomes important when surface active species such as surfactants, particles, or proteins are present in sufficient quantities at liquid-liquid interfaces and interact between them. Interfacial rheometry measurements are challenging for various reasons. The mechanical response of the thin interface is often weaker compared to that of bulk materials and so one is often measuring close to the lower force and torque limits of rheometers, hence signal-to-noise ratios merit closer attention. In addition, the role of both instrument and sample inertia is more important for interfacial rheometry compared to bulk rheometry. Effects of misalignment and imperfections of the measurement geometries lead to effects of surface and line tension. Finally, peculiar for interfacial rheometry is the need to deconvolute the contributions of flow and deformation in the surrounding phases from that at the interface. Whereas some of these aspects have received attention in previous works, a clear and unambiguous view on the operating limits of interfacial rheometers has been missing. In the present work, we investigate the different experimental challenges and develop a generic methodology, which provides a clear definition of the operating limits of various interfacial rheometers including the interfacial needle shear rheometer, the double wall ring, and the bicone geometries. We validate this methodology by investigating the limitations defined intrinsically by the instrument as well as the ones emerging from the properties of the interface of interest for an interface composed of fatty alcohols which represents a challenging test case. The results provide cautionary examples and clear guidelines for anyone measuring interfacial rheology with these direct rheological techniques.

The role of lipids in determining the air-water interfacial properties of wheat, rye, and oat dough liquor constituents

“…Because of the slow adsorption of constituents at the A-W interface in defatted wheat DL, Bq numbers were not calculated for the initial modulus of the complex surface shear viscosity (|η s *|), but with the magnitude of the |η s *| value measured 25 min after positioning the ring at the A-W interface. As Bq numbers were lower than 100, the components of |η s *| were corrected using an iterative solver to take into account the coupling of the flow in the subphase with the A-W interface (Renggli, Alicke, Ewoldt, & Vermant, 2020). This was essential to obtain the exact deformation profile and shear rates at the A-W interface.…”

“…In the present case, wheat, rye, and oat DLs powders were dissolved at 1.50 mg protein/mL to obtain sufficiently low bulk viscosities. Moreover, as wheat, rye, and oat DLs at 1.50 mg protein/mL had different bulk viscosities (Janssen et al, 2020), the contribution of the bulk phase viscosity was subtracted from that of the A-W interfacial film by means of an iterative solver (see section 2.2.4.3) (Renggli et al, 2020).…”

The Exo-Polysaccharide Component of Extracellular Matrix is Essential for the Viscoelastic Properties of Bacillus subtilis Biofilms

“…For intermediate the material response contains both bulk, given by phases 1 and 2, and biofilm contributions to the interfacial flow [ 33 ] (see also the method description ahead). Defining the lower measurable limits, , of interfacial rheological techniques is not a trivial matter and depends, among others, on the measuring geometry, measurement instrument, and so on, as highlighted in [ 34 , 35 , 36 ]. In this work, we use , as previously used in similar studies in terms of experimental setup and materials [ 33 , 37 ].…”

Interfacial Properties of β-Lactoglobulin at the Oil/Water Interface: Influence of Starch Conversion Products with Varying Dextrose Equivalents

“…Thus, this number will not be discussed in detail. More details about operating windows for oscillatory interfacial shear rheology can be found in other publications [39,40].…”