Research Interests
 Protein nucleation and crystal growth
 Nonlinear diffusion
 Theory of Nucleation
 Zeolites
 Crystallization
 Bubble Cavitation and Sonoluminescence
 Reactive flows far from equilibrium
 Structure of nonequilibrium fluids
 Granular Fluids
 Nonextensive statistical mechanics
 Fuzzy rule induction
Publications
Useful Links
American Physical Society
American Institute of Physics
Materials Research Society
Info
Cirriculum Vitae
Cirriculum Vitae (en française)
Email: jlutsko AT ulb.ac.be
Address:
Center for Nonlinear Phenomena and Complex Systems
University Libre de Bruxelles
Campus Plaine, CP 231, 1050 Bruxelles, Belgium

Solute particle near a nanopore: influence of size and surface properties on the solventmediated forces
Nanoscopic pores are used in various systems to attract nanoparticles. In general the behaviour is a result of two types of interactions: the material specific affinity and the solventmediated influence also called the depletion force. The latter is more universal but also much more complex to understand since it requires modeling both the nanoparticle and the solvent. Here, we employed classical density functional theory to determine the forces acting on a nanoparticle near a nanoscopic pore as a function of its hydrophobicity and its size. A simple capillary model is constructed to predict those depletion forces for various surface properties. For a nanoscopic pore, complexity arises from both the specific geometry and the fact that hydrophobic pores are not necessarily filled with liquid. Taking all of these effects into account and including electrostatic effects, we establish a phase diagram describing the entrance and the rejection of the nanoparticle from the pore.

This work is a product of the AMECRYS project: "Revolutionizing Downstream Processing of Monoclonal Antibodies by Continuuous TemplateAssisted Membrane Crystallization"



Solventmediated forces create effective interactions between nanoparticles and surfaces.


Step Crowding Effects Dampen the Stochasticity of Crystal Growth Kinetics
Crystals grow by laying down new layers of material which can either correspond in size to the height of one unit cell (elementary steps) or multiple unit cells (macrosteps). Surprisingly, experiments have shown that macrosteps can grow under conditions of low supersaturation and high impurity density such that elementary step growth is completely arrested. We use atomistic simulations to show that this is due to two effects: the fact that the additional layers bias fluctuations in the position of the bottom layer towards growth and by a transition, as step height increases, from a 2D to a 3D nucleation mechanism.

This article was featured in Physics News and Commentary: see the Synopsis: Growing Crystals in Macrosteps


A macrostep bridging impurities on the crystal surface


Mesoscopic Impurities Expose a NucleationLimited Regime of Crystal Growth
Nanoscale selfassembly is naturally subject to impediments at the nanoscale. The recently developed ability to follow processes at the molecular level forces us to resolve older, coarsegrained concepts in terms of their molecular mechanisms. In this Letter, we highlight one such example. We present evidence based on experimental and simulation data that one of the cornerstones of crystal growth theory, the CabreraVermilyea model of step advancement in the presence of impurities, is based on incomplete physics. We demonstrate that the piercing of an impurity fence by elementary steps is not solely determined by the GibbsThomson effect, as assumed by CabreraVermilyea. Our data show that for conditions leading up to growth cessation, step retardation is dominated by the formation of critically sized fluctuations. The growth recovery of steps is counter to what is typically assumed, not instantaneous. Our observations on mesoscopic impurities for lysozyme expose a nucleationdominated regime of growth that has not been hitherto considered, where the system alternates between zero and nearpure velocity. The time spent by the system in arrest is the nucleation induction time required for the step to amass a supercritical fluctuation that pierces the impurity fence.


AFM images showing steps breaking through array of mesoscopic impurities.


Observing classical nucleation theory at work by monitoring phase transitions with molecular precision.
It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multistep nucleation has made the inverse question relevant: does multistep nucleation always dominate singlestep pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multistep nucleation. Molecular resolution atomic force microscopy imaging of the twodimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by revalidating some of the key assumptions that have been recently questioned... Read more ... The article is open source


AFM images showing crystallinity of subcritical and supercritical clusters.



2variable extension of classical nucleation theory.
A twovariable stochastic model for diffusionlimited nucleation is developed using a formalism derived from fluctuating hydrodynamics. The model is a direct generalization of the standard Classical Nucleation Theory. The nucleation rate and pathway are calculated in the weaknoise approximation and are shown to be in good agreement with direct numerical simulations for the weaksolution/strongsolution transition in globular proteins. We find that Classical Nucleation Theory underestimates the time needed for the formation of a critical cluster by two orders of magnitude and that this discrepancy is due to the more complex dynamics of the two variable model and not, as often is assumed, a result of errors in the estimation of the free energy barrier. Read more...


Free energy surfaces as functions of radius and density of a cluster. Left: subcritical, Right: supercritical  the line shows the most likely nucleation pathway.



The physical basis of step pinning.
The growth of crystals from solution is a fundamental process of relevance to such diverse areas as Xraydiffraction structural determination
and the role of mineralization in living organisms. A key factor determining the dynamics of crystallization is the effect of impurities on step growth.
For over fifty years, all discussions of impuritystep interaction have been framed in the context of the CabreraVermilyea (CV) model for step blocking,
which has nevertheless proven difficult to validate experimentally. Here we report on extensive computer simulations which clearly falsify the CV model,
suggesting a more complex picture. While reducing to the CV result in certain limits, our approach is more widely applicable, encompassing nontrivial impuritycrystal interactions,
mobile impurities and negative growth, among others. Read the paper... view movies


Left: Snapshot of kineic Monte Carlo simulation. Right: Step velocity shown as size of circles as a function of impurity size, L, and impurity spaceing, n_{c} shown for three different supersaturations. Blue indicates positive velocity, red is negative velocity and white is statistically zero. The CV prediction for zero velocity is everything below the broken line marked CV.

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