Paul Dommersnes | Norwegian University of Science and Technology (original) (raw)

Papers by Paul Dommersnes

Physical Review E, 2002

We study the interplay between entropy and topological constraints for a polymer chain in which s... more We study the interplay between entropy and topological constraints for a polymer chain in which sliding rings ͑slip links͒ enforce pair contacts between monomers. These slip links divide a closed ring polymer into a number of subloops which can exchange length among each other. In the ideal chain limit, we find the joint probability density function for the sizes of segments within such a slip-linked polymer chain ͑paraknot͒. A particular segment is tight ͑small in size͒ or loose ͑of the order of the overall size of the paraknot͒ depending on both the number of slip links it incorporates and its competition with other segments. When self-avoiding interactions are included, scaling arguments can be used to predict the statistics of segment sizes for certain paraknot configurations.

The European Physical Journal E - Soft Matter, 2003

We investigate the effects of topological constraints (entanglements) on two dimensional polymer ... more We investigate the effects of topological constraints (entanglements) on two dimensional polymer loops in the dense phase, and at the collapse transition (Θ point). Previous studies have shown that in the dilute phase the entangled region becomes tight, and is thus localised on a small portion of the polymer. We find that the entropic force favouring tightness is considerably weaker in dense polymers. While the simple figure-eight structure, created by a single crossing in the polymer loop, localises weakly, the trefoil knot and all other prime knots are loosely spread out over the entire chain. In both the dense and Θ conditions, the uncontracted knot configuration is the most likely shape within a scaling analysis. By contrast, a strongly localised figure-eight is the most likely shape for dilute prime knots. Our findings are compared to recent simulations.

Physical Review Letters, 2006

We report a cylindrical-peristaltic shape transformation in axons exposed to a controlled osmotic... more We report a cylindrical-peristaltic shape transformation in axons exposed to a controlled osmotic perturbation. The peristaltic shape relaxes and the axon recovers its original geometry within minutes. We show that the shape instability depends critically on swelling rate and that volume and membrane area regulation are responsible for the shape relaxation. We propose that volume regulation occurs via leakage of ions driven by elastic pressure, and analyse the peristaltic shape dynamics taking into account the internal structure of the axon. The results obtained provide a framework for understanding peristaltic shape dynamics in nerve fibers occurring in vivo.

The European Physical Journal E, 2008

Starting from a high surface free-energy state, lipid nanotube networks are capable to selforgani... more Starting from a high surface free-energy state, lipid nanotube networks are capable to selforganize into tree-like structures with particular geometrical features. In this work we analyze the process of self-organization in such networks, and report a strong similarity to the Euclidian Steiner Tree Problem (ESTP). ESTP is a well-known NP-hard optimization problem of finding a network connecting a given set of terminal points on a plane, allowing addition of auxiliary points, with the overall objective to minimize the total network length. The present study shows that aggregate lipid structures self-organize into geometries that correspond to locally optimal solutions to such problems. PACS. 87.16.D-Membranes, bilayers, and vesicles -47.61.-k Micro-and nano-scale flow phenomena

Nano Letters, 2008

We report the controlled release of immobilized cholesteryl-tetraethyleneglycol-DNA (chol-DNA) fr... more We report the controlled release of immobilized cholesteryl-tetraethyleneglycol-DNA (chol-DNA) from micropatterned SU-8 surfaces by a spreading lipid film. The release of chol-DNA is rapid and on the order of the spreading rate of the lipid film beta = 1-3 microm2/s ( approximately 10(5) molecules of DNA per second). The lipid film serves as a poor solvent for the DNA adduct, which upon contact redistributes into the aqueous phase. Thus, the release of DNA is accompanied by a change in surface hydrophobicity. The method can be used for creating arbitrary concentration profiles of DNA in solution over time or to dynamically change surface properties on demand in, for example, micro- and nanofluidic devices. Examples of DNA release from spiral, comb, meander, and triangular as well as from nanoscale SU-8 lanes are shown.

Nano Letters, 2007

We introduce a novel technique for the controlled spreading and mixing of lipid monolayers from m... more We introduce a novel technique for the controlled spreading and mixing of lipid monolayers from multilamellar precursors on surfaces covered by the hydrophobic epoxy resin SU-8. The lipid spreads as a monolayer as a result of the high surface tension between SU-8 and the aqueous environment. A micropatterned device with SU-8 lanes, injection pads, and mixing regions, surrounded by hydrophilic Au, was constructed to allow handling of lipid films and to achieve their mixing at controlled stoichiometry. Our findings offer a new approach to dynamic surface functionalization and decoration as well as surface-based catalysis and self-assembly.

Computer Physics Communications, Aug 1, 2002

Several small globular proteins exhibit a simple two-state folding process (sharp transition). Th... more Several small globular proteins exhibit a simple two-state folding process (sharp transition). The rather short folding times of proteins (fast folders) indicate that folding is guided through some sequence of contact bindings. We discuss the possibility for reconciling a two-state folding event with a sequential folding process, i.e. a folding pathway in a schematic model of protein folding. We show that both single and multiple folding pathways can lead to an apparent two-state folding from a thermodynamic point of view. We also discuss water interactions in protein folding, leading to cold and warm destabilization of the protein.

Inclusions embedded in fluctuating fluid membranes have been shown to experi- ence membrane media... more Inclusions embedded in fluctuating fluid membranes have been shown to experi- ence membrane mediated forces decaying as 1=R4. Modeling the inclusions as local constraints on the membrane curvature tensor, we show that the presence of external torques (mechanical or eld-induced) strongly enhances and increases the range of the interactions. Repulsive mean-eld contributions and attractive fluctuation (Casimir) contributions of range 1=R2 or longer are found, which may combine to yield equilibrium distances.

$Research paper thumbnail of Electrohydrodynamic controlled assembly and fracturing of thin colloidal particle films confined at drop interfaces$

The European Physical Journal Special Topics, 2014

Particles can adsorb strongly at liquid interfaces due to capillary forces, which in practice can... more Particles can adsorb strongly at liquid interfaces due to capillary forces, which in practice can confine the particles to the interface. Here we investigate the electrohydrodynamic flow driven packing and deformation of colloidal particle layers confined at the surface of liquid drops. The electrohydrodynamic flow has a stagnation point at the drop equator, leading to assembly of particles in a ribbon shaped film. The flow is entirely controlled by the electric field, and we demonstrate that AC fields can be used to induce hydrodynamic "shaking" of the colloidal particle film. We find that the mechanical properties of the film is highly dependent on the particles: monodisperse polystyrene beads form packed granular monolayers which "liquefies" upon shaking, whereas clay mineral particles form cohesive films that fracture upon shaking. The results are expected to be relevant for understanding the mechanics and rheology of particle stabilized emulsions. a

Nature Communications, 2014

Janus and patchy particles have designed heterogeneous surfaces that consist of two or several pa... more Janus and patchy particles have designed heterogeneous surfaces that consist of two or several patches with different materials properties. These particles are emerging as building blocks for a new class of soft matter and functional materials. Here we introduce a route for forming heterogeneous capsules by producing highly ordered jammed colloidal shells of various shapes with domains of controlled size and composition. These structures combine the functionalities offered by Janus or patchy particles, and those given by permeable shells such as colloidosomes. The simple assembly route involves the synergetic action of electro-hydrodynamic flow and electro-coalescence. We demonstrate that the method is robust and straightforwardly extendable to production of multi-patchy capsules. This forms a starting point for producing patchy colloidosomes with domains of anisotropic chemical surface properties, permeability or mixed liquid-solid phase domains, which could be exploited to produce functional emulsions, light and hollow supra-colloidosome structures, or scaffolds.

The response of rotational alignment of lithium fluorohectorite (Li-Fh) to an external electric f... more The response of rotational alignment of lithium fluorohectorite (Li-Fh) to an external electric field has been studied by employing image analysis. Large aggregates consisting of many single clay particles were prepared using a sedimentation technique in order to control both their shapes and sizes. Such aggregates have a layered structure which was confirmed by wide-angle X-ray scattering (WAXS) studies. Measuring the electric-field-induced alignment of these particles we obtained a data collapse by plotting ln(i) versus t/E 2 , where i is the rotational angle, t is time and E is the electric field strength. Se estudia la respuesta de la alineación rotacional de la fluorohectorita de litio (Li-Fh) debido a un campo eléctrico externo mediante análisis de imágenes. Se prepararon grandes agregados consistentes en muchas partículas individuales de arcilla usando una técnica de sedimentación, con el objetivo de controlar tanto sus formas como sus tamaños. Tales agregados poseen una estr...

We demonstrate experimentally the possibility for promoting uniaxial orientational order in initi... more We demonstrate experimentally the possibility for promoting uniaxial orientational order in initially isotropic, soft solid dispersions of the synthetic clays Na-fluorohectorite and Laponite RD. We observe that strong orientational order can emerge from initially isotropic states when the samples are subjected to a slow concentration increase through evaporation of the dispersion water. During evaporation, there is a gradient in the order which, if evaporation is halted, slowly relaxes towards a uniform order throughout the samples. It is evident that the development of orientational order is not counterindicated by the viscoelastic nature of the samples, and that although the translational and likely also rotational diffusion of the particles is restricted in the soft solid state, the orientational degree of freedom can undergo a transition from a collectively random to an ordered state.

ABSTRACT Proteins have interesting thermodynamic features. One of the more surprising is the cold... more ABSTRACT Proteins have interesting thermodynamic features. One of the more surprising is the cold unfolding transition. At high temperature,the proteins unfold due to thermal rattling. As the temperature is lowered, they undergo a phase transition and fold. But, if the temperature is further decreased, they may undergo a second transition and revert to the unfolded state, thus melting as the temperature is lowered. We present a model that demonstrates the mechanism resposible for this strange behavior based on hydrophobicity. We also use the model to investigate other thermodynamical observations on small globular protein.

Physical Review E, 2008

We employ nuclear magnetic resonance imaging to study water penetration in cylindrical blocks of ... more We employ nuclear magnetic resonance imaging to study water penetration in cylindrical blocks of unsized paper prepared under different molding pressures. From the measured kinetics of the imbibition profiles, we determine the dependence of the effective transport diffusivity upon degree of saturation of the pores by the penetrating fluid. In general, the transport process is found to be non-Fickian and we discuss different methods of data analysis adapted to this situation. The effective transport diffusivity vividly captures the presence of a precursor front, consisting of fluid in partially filled pores, with a much higher effective diffusivity than that of fluid in largely saturated pores.

Physical Review E, 2010

Although Casimir forces are inseparable from their fluctuations, little is known about these fluc... more Although Casimir forces are inseparable from their fluctuations, little is known about these fluctuations in soft matter systems. We use the membrane stress tensor to study the fluctuations of the membrane-mediated Casimir-like force. This method enables us to recover the Casimir force between two inclusions and to calculate its variance. We show that the Casimir force is dominated by its fluctuations. Furthermore, when the distance d between the inclusions is decreased from infinity, the variance of the Casimir force decreases as −1/d 2 . This distance dependence shares a common physical origin with the Casimir force itself.

Nature Communications, 2013

Adsorption and assembly of colloidal particles at the surface of liquid droplets are at the base ... more Adsorption and assembly of colloidal particles at the surface of liquid droplets are at the base of particle-stabilized emulsions and templating. Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces, including electric-fieldassisted convective assembly of jammed colloidal 'ribbons', electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface. In addition, we demonstrate the size control of 'pupil'-like openings in colloidal shells. We anticipate that electric field manipulation of colloids in leaky dielectrics can lead to new routes of colloidosome assembly and design for 'smart armoured' droplets.

Europhysics Letters (EPL), 1997

Europhysics Letters (EPL), 1999

The European Physical Journal B, 1999

ABSTRACT We study the hydrodynamic properties of polymers and more generally self-similar structu... more ABSTRACT We study the hydrodynamic properties of polymers and more generally self-similar structures using a new recursion model. The hydrodynamic interaction between monomers is modeled by the standard Green's function of Stokes flow in which an ultrametric distance is substituted for the usual Euclidean distance. This leads to a model where the long-range hydrodynamic interactions and the long-range correlations of the polymer conformation can both be accounted for and yet allow for analytical solutions. We explore the asymptotic as well as the finite size corrections to the scaling behavior with this model. In order to compare the results of the present scheme with more conventional techniques a generalized version of the existing mean field results by Kirkwood and Riseman for the hydrodynamic drag is introduced.