Instrument for measurement of interfacial structure-property relationships with decoupled interfacial shear and dilatational flow: "Quadrotrough".

Understanding the interfacial structure-property relationship of complex fluid-fluid interfaces is increasingly important for guiding the formulation of systems with targeted interfacial properties, such as those found in multiphase complex fluids, biological systems, biopharmaceuticals formulations, and many consumer products. Mixed interfacial flow fields, typical of classical Langmuir trough experiments, introduce a complex interfacial flow history that complicates the study of interfacial properties of complex fluid interfaces. In this article, we describe the design, implementation, and validation of a new instrument capable of independent application of controlled interfacial dilation and shear kinematics on fluid interfaces. Combining the Quadrotrough with both in situ Brewster angle microscopy and neutron reflectometry provides detailed structural measurements of the interface at the mesoscale and nanoscale in relationship to interfacial material properties under controlled interfacial deformation histories.

Competitive Surface Activity of Monoclonal Antibodies and Nonionic Surfactants at the Air-Water Interface Determined by Interfacial Rheology and Neutron Reflectometry.

Interfacial stresses can destabilize therapeutic formulations containing monoclonal antibodies (mAbs), which is proposed to be a result of adsorption and aggregation at the air-water interface. To increase protein stability, pharmaceutical industries add surfactants, such as Polysorbate 20 (PS20), into protein formulations to minimize mAb adsorption at the interface but rarely quantify this process. We determine that mAb adsorption in surfactant-free solutions creates a monolayer with significant viscoelasticity, which can influence measurements of bulk mAb solution viscosity. In contrast, PS20 absorption leads to an interface with negligible interfacial viscosity that protects the air-water interface from mAb adsorption. These studies were performed through a combined study of surface tensiometry, interfacial rheology, capillary viscometry, and neutron reflectometry to determine the surface activity of a model surfactant, PS20, and mAb system, which can be useful for the successful formulation developments of biotherapeutics.