chaired by Saskia Lindhoud/ Tibor Kudernac
Annealing of polyelectrolyte multilayers for membrane applications
Dennis Reurink (MST)
Tumbling of arbitrarily shaped Brownian rigid bodies in shear flow
Durai Palanisamy (MSM)
Delayed coalescence of surfactant droplets
Maxime Costalonga (POF)
Design and binding properties of biomimetic lipid bilayers
Mark Verheijden (MNF)
Annealing of polyelectrolyte multilayers for membrane applications, Dennis Reurink (MST)
First research on annealing of polyelectrolyte multilayer based membranes. A system suitable for membrane applications is the polyelectrolyte system of PDADMAC (poly diallyldimethylammonium chloride) and PSS (polystyrene sulfonate) because of the chemical stability of the system.
When forming these layers, however, PDADMAC overcompensates due to its relatively high mobility. This overcompensation provides a net positive charge inside the multilayer, leading to swelling and a less compact structure. A method to counteract this swelling phenomenon was provided in literature and is based on annealing the as-made PEM with a high salt concentration, resulting in removal of excess PDADMAC by additional adsorption of PSS.
Hollow fibre membranes were used as substrate in this project, in which the influence of annealing PDADMAC-PSS PEM-based membranes on its performance was investigated. From this study could be concluded that salt annealing allows for control of membrane charge and counteracts positive charge built up in the layer.
Tumbling of arbitrarily shaped Brownian rigid bodies in shear flow, Durai Palanisamy (MSM)
Rigid multi-bead models are regularly used to calculate the mobility matrix of arbitrarily shaped bodies with hydrodynamic self-interaction, e.g. in the HYDRO++ package. This approach is typically limited to translational, rotational and translational-rotational coupling terms, and therefore cannot be applied to bodies in a shear flow. We have extended the formalism to include coupling between the rate-of-strain and the translational and rotational motions, yielding a 11x11 matrix describing the full hydrodynamic mobility tensor of the rigid body. In combination with a recently developed rotational Brownian dynamics scheme, this enables direct simulation of arbitrarily shaped rigid bodies in linear flow fields. As an example, we discuss the surprisingly complex motions of helices in shear flow, ranging from stable orbits to chaotic motions. We also calculate the stresses acting on the body, and thereby the intrinsic viscosity of a dilute suspension of these particles.
Delayed coalescence of surfactant droplets, Maxime Costalonga (POF)
Understanding sessile drop coalescence is of prime importance to optimise industrial processes such as inkjet printing. When two drops of the same liquid meet, they merge into one drop in order to minimize their surface. However, the coalescence is hindered, or even prevented completely, when the two drops have different surface tensions. A temporary state of non-coalescence arises, during which the drops move on their substrate, only connected by a thin neck between the droplets. Here we study the transition from coalescence to non-coalescence for surfactant solutions of varying concentration. It is found that shifting the surfactant concentrations while keeping the same surface tension difference between the drops, changes the duration of the non-coalescence state. This reveals that the merging process is not solely governed by the surface properties, but also involves surfactant exchange with the bulk liquid.
Design and binding properties of biomimetic lipid bilayers, Mark Verheijden (MNF)
Here we present a material surface modification method to dynamically interact with biological vectors ranging from small molecules, to viruses, and finally to cells. The surface modification consists of a supported lipid bilayer (SLB). The SLB is not only a convenient surface functionalization method (ease of preparation, controlled functionalization, nonfouling), it also is a well-known cell membrane mimic. These qualities have been used here for 1) probing the effect of receptor affinity on cell behaviour using bioactive lipidated peptides 2) studying interaction characteristics of a virus model and 3) the design of a vesicle-based system that targets not only based on the type of receptor but also on the density of receptors (i.e. superselectivity). In all these examples, multivalency and the dynamic character of these interactions play a central role. Read-out is performed with surface sensitive techniques (QCM-D, ellipsometry, fluorescence microscopy and flow cytometry) on the one hand, and cell behaviour (live cell imaging and staining of fixed cells) on the other hand.