NO Nick Jaensson

Bio: NO Nick Jaensson is an academic researcher from Eindhoven University of Technology. The author has contributed to research in topics: Viscoelasticity & Newtonian fluid. The author has an hindex of 10, co-authored 24 publications receiving 298 citations. Previous affiliations of NO Nick Jaensson include ETH Zurich.

Tensiometry and rheology of complex interfaces

Abstract: Complex fluid-fluid interfaces play an important role in a variety of application domains, from emulsion and foam stability, to thin films in biomedical applications, to coating flow phenomena. The current work reviews progress made in particular for interfaces where rheological stresses, peculiar to the interface, play an important role. The developments made in the area of constitutive modeling are briefly reviewed to clarify which material functions can be measured. For shear rheometry, progress in analyzing the flow field in the measurement device has been key, combined with advances in control over surface concentration and microstructural evaluation. For dilation/compressional rheometry much work has been done on separating changes in the surface tension from the extra rheological stresses. Finally, we discuss how “simple complex flows”, such as thin film and drainage flows, offer a first step up in complexity and seem to present a good benchmark problem for testing constitutive equations and the interplay between transport phenomena, interfacial rheology and the changes in state variables.

Microscale Marangoni Surfers

Abstract: We apply laser light to induce the asymmetric heating of Janus colloids adsorbed at water-oil interfaces and realize active micrometric "Marangoni surfers." The coupling of temperature and surfactant concentration gradients generates Marangoni stresses leading to self-propulsion. Particle velocities span 4 orders of magnitude, from microns/s to cm/s, depending on laser power and surfactant concentration. Experiments are rationalized by finite elements simulations, defining different propulsion regimes relative to the magnitude of the thermal and solutal Marangoni stress components.

Thin Liquid Films: where Hydrodynamics, Capillarity, Surface Stresses, and Intermolecular Forces meet

Abstract: Thin liquid films arise in many technological applications and biological phenomena. They also present a fascinating object of study, because of a rich interplay between capillarity, hydrodynamics, interfacial transport phenomena and interfacial rheology, as well as the effects of interaction forces when films thin down to molecular thicknesses. Recent advances in experimental techniques have given further insights in the variety of physical phenomena, which can occur. These techniques are briefly reviewed. How these techniques can be utilised is illustrated by recent studies addressing the effect of interfacial rheological stresses on drainage, the interplay between capillarity and hydrodynamics during film retraction, and the solutocapillary stabilisation of films. Finally, we briefly discuss the challenges of conducting drainage measurements at high and varied capillary numbers and how these could be overcome by the combined use of experiments and simulations.

Direct numerical simulation of particle alignment in viscoelastic fluids

Abstract: Rigid particles suspended in viscoelastic fluids under shear can align in string-like structures in the flow direction. Although this phenomenon was first reported almost four decades ago by Michele et al. [J. Michele, R. Patzold, R. Donis, Alignment and aggregation effects in suspensions of spheres in non-Newtonian media, Rheologica Acta 16 (1977) 317–321.], the exact mechanism of particle alignment is not completely understood. Initially, it was believed that normal stress differences are responsible for the alignment of particles, but recent experimental work by van Loon et al. [S. Van Loon, J. Fransaer, C. Clasen, J. Vermant, String formation in sheared suspensions in rheologically complex media: The essential role of shear thinning, Journal of Rheology 58(1) (2014) 237–254.] showed particle alignment in a shear-thinning fluid without significant normal stress differences. To unravel the phenomenon of particle alignment, we present for the first time 3D direct numerical simulations of the alignment of two and three rigid, non-Brownian particles in a viscoelastic shear flow, with the shear rate denoted by γ ˙ . The equations are solved on moving, boundary-fitted meshes, which are locally refined to accurately describe the polymer stresses around and in between the particles. A small minimal gap size between the particles is introduced. The Giesekus model, with a relaxation time λ, is used for the viscoelastic fluid, and the effect of the Weissenberg number Wi = λ γ ˙ , shear thinning parameter α and ratio between the solvent viscosity and zero-shear viscosity β is investigated. The numerical method allows for the detailed investigation of particles interacting in viscoelastic flows. Alignment of two and three particles is observed in the simulations. Morphology plots were created for various values of α, β and Wi. Alignment is mainly governed by the value of the elasticity parameter S, defined as half of the ratio between the first normal stress difference and shear stress of the suspending fluid. Alignment appears to occur above a critical value of S, which decreases with increasing α, thus shear thinning promotes alignment. Furthermore, three particles align at lower S than two particles. Finally, simulations were performed in a shear-thinning Carreau fluid, where we never observed alignment of the particles. These results lead us to the conclusion that the presence of normal stress differences is essential for particle alignment to occur, although it is strongly promoted by shear thinning.

Computational interfacial rheology

Abstract: Fluid-fluid interfaces, laden with polymers, particles or other surface-active moieties, often show a rheologically complex response to deformations, in particular when strong lateral interactions are present between these moieties. The response of the interface can then no longer be described by an isotropic surface tension alone. These “structured” soft-matter interfaces are found in many industrial applications, ranging from foods, cosmetics and pharmaceuticals, to oil recovery. Also many biomedical applications involve such interfaces, including those involving lung surfactants and biofilms. In order to understand, design and optimize processes in which structured interfaces are present, flow predictions of how such multiphase systems deform are of the utmost importance, which is the goal of “computational interfacial rheology”, the main topic of this review. We start by rigorously establishing the stress boundary condition used in the computation of multi-phase flows, and show how this changes when the interface is rheologically complex. Then, constitutive models for the extra stress in interfaces, ranging from 2D generalized Newtonian to hyperelastic and viscoelastic, are reviewed extensively, including common pitfalls when applying these models. This is followed by an overview of different approaches to measure interfacial rheological properties, and a discussion of advanced numerical implementations for deforming interfaces. We conclude with an outlook for this relatively young and exciting field.

Interfacial tension of alkane + water systems

Abstract: Interfacial tension was measured for hexane + water, heptane + water, octane + water, nonane + water, decane + water, undecane + water, and dodecane + water, using the emergent drop experimental technique with a numerical method based on a fourth degree spline interpolation of the drop profile. The experimental equipment used to generate the drop consists of a cell with a stainless steel body and two Pyrex windows. The inner cell was previously filled with water. A surgical needle (at the bottom of the cell) was used to introduce the organic phase into the cell (forming the emergent drop). Water was used to keep the temperature constant inside the cell (between 10 °C and 60 °C). The cell was illuminated from the back using a fiber optic lamp and a diffuser. A video camera (with a 60 mm microlens and an extension ring) was located at the front window. The emergent drop image was captured and sent to the video recording system. The cell and the optical components were placed on an optical table with vibration isolation legs. A new correlation was found to predict interfacial tension (γ) as a function of temperature (t) and the number of carbon atoms (n) with a deviation of less than 0.05% from experimental values.

Surfactant dynamics: hidden variables controlling fluid flows

Abstract: Surfactants - molecules and particles that preferentially adsorb to fluid interfaces - play a ubiquitous role in the fluids of industry, of nature, and of life. Since most surfactants cannot be seen directly, their behavior must be inferred from their impact on observed flows, like the buoyant rise of a bubble, or the thickness of a coating film. In so doing, however, a difficulty arises: physically distinct surfactant processes can affect measurable flows in qualitatively identical ways, raising the specter of confusion or even misinterpretation. This Perspective describes, in one coherent piece, both the equilibrium properties and dynamic processes of surfactants, to better enable the fluid mechanics community to understand, interpret, and design surfactant/fluid systems. Specifically, §2 treats the equilibrium thermodynamics of surfactants at interfaces, including surface pressure, isotherms of soluble and insoluble surfactants, and surface dilatational moduli (Gibbs and Marangoni). §3 describes surfactant dynamics in fluid systems, including surfactant transport and interfacial stress boundary conditions, the competition between surface diffusion, advection, and adsorption/desorption, Marangoni stresses and flows, and surface excess rheology. §4 discusses paradigmatic problems from fluid mechanics that are impacted by surfactants, including translating drops and bubbles, surfactant adsorption to clean and oscillating interfaces; capillary wave damping, thin film dynamics, foam drainage, and the dynamics of particles and probes at surfactant-laden interfaces. Finally, §5 discusses the additional richness and complexity that frequently arise in 'real' surfactants, including phase transitions, phase coexistence, and polycrystalline phases within surfactant monolayers, and their impact on non-Newtonian surface rheology.

Laser-based additively manufactured polymers: a review on processes and mechanical models

Abstract: Additive manufacturing (AM) is a broad definition of various techniques to produce layer-by-layer objects made of different materials. In this paper, a comprehensive review of laser-based technologies for polymers, including powder bed fusion processes [e.g. selective laser sintering (SLS)] and vat photopolymerisation [e.g. stereolithography (SLA)], is presented, where both the techniques employ a laser source to either melt or cure a raw polymeric material. The aim of the review is twofold: (1) to present the principal theoretical models adopted in the literature to simulate the complex physical phenomena involved in the transformation of the raw material into AM objects and (2) to discuss the influence of process parameters on the physical final properties of the printed objects and in turn on their mechanical performance. The models being presented simulate: the thermal problem along with the thermally activated bonding through sintering of the polymeric powder in SLS; the binding induced by the curing mechanisms of light-induced polymerisation of the liquid material in SLA. Key physical variables in AM objects, such as porosity and degree of cure in SLS and SLA respectively, are discussed in relation to the manufacturing process parameters, as well as to the mechanical resistance and deformability of the objects themselves.

Tuning the Conductivity of Nanocomposites through Nanoparticle Migration and Interface Crossing in Immiscible Polymer Blends: A Review on Fundamental Understanding

Abstract: Copyright: 2018 Wiley Online Library. Due to copyright restrictions, the attached PDF file only contains the preprint version of the published article. For access to the published version, please consult the publisher's website. The definitive version of the work is published in Macromolecular Materials and Engineering, vol 0(0), pp 9336- 9347