Dynamic heterogeneity in complex interfaces of soft interface-dominated materials

Abstract

Complex interfaces stabilized by proteins, polymers or nanoparticles, have a much richer dynamics than those stabilized by simple surfactants. By subjecting fluid-fluid interfaces to step extension-compression deformations, we show that in general these complex interfaces have dynamic heterogeneity in their relaxation response that is well described by a Kohlrausch-Williams-Watts function, with stretch exponent β between 0.4–0.6 for extension, and 0.6–1.0 for compression. The difference in β between expansion and compression points to an asymmetry in the dynamics. Using atomic force microscopy and simulations we prove that the dynamic heterogeneity is intimately related to interfacial structural heterogeneity and show that the dominant mode for stretched exponential relaxation is momentum transfer between bulk and interface, a mechanism which has so far largely been ignored in experimental surface rheology. We describe how its rate constant can be determined using molecular dynamics simulations. These interfaces clearly behave like disordered viscoelastic solids and need to be described substantially different from the 2d homogeneous viscoelastic fluids typically formed by simple surfactants.

The structure, viscoelasticity and charge of potato peptides adsorbed at the oil-water interface determine the physicochemical stability of fish oil-in-water emulsions

“…1S). All the slope (n) values were lower than 0.5, indicating that the exchange of peptides between the bulk water phase and the J o u r n a l P r e -p r o o f interface was not the main contribution to the observed response of the interface, and that other processes had a significant contribution, e.g., in-plane interactions at the interface (Sagis et al, 2019). The latter seemed to be particularly important for interfacial layers formed by α10, γ36, γ38 and γ40 as a result of their much lower slope value when compared with caseinate, α12, β22, γ1, γ75 and γ76 peptides (Fig.…”

Polymer Conformations, Entanglements and Dynamics in Ionic Nanocomposites: A Molecular Dynamics Study

“…We further complement this statement by additionally investigating the NP and chain center-of-mass mobility, see discussions at the end of this section. To quantify the chain's orientational relaxation for dispersed liquid-like systems, we fit the numerical results of C ee (t) to the Kohlrausch-William-Watts stretched exponential function (dash-dotted line in Figure 6b), which is also suitable for describing the relaxation process in soft disordered heterogeneous systems [79,80]. It is given by:…”

The Importance of Interfacial Tension in Emulsification: Connecting Scaling Relations Used in Large Scale Preparation with Microfluidic Measurement Methods

“…Bubbles have dimpling instabilities that are more prominent than in droplets, which facilitates film rupture [106,107]. Last but not least, β-lactoglobulin may have a higher affinity for oil than for air, which may lead to a higher interfacial protein concentration with a more compact and protective structure at the oil-water interface [108][109][110][111][112]. To distinguish between these effects, more observations are needed, and that is possible combining high speed imaging and microfluidic observations.…”