Soft condensed matter scientist – CNRS research director

I am a soft condensed matter theorist interested in understanding self-assembly, phase behavior and dynamical aspects of a variety of soft matter systems, with a focus on colloidal systems and lyotropic liquid crystals. Most systems I study are subject of ongoing experimental research and/or have a strong technological relevance. Examples include condensed phases of filamentous virus, motile bacteria, cellulose nanocrystals, clays, living polymers, colloid-polymer mixtures, and nematic colloids.

Research interests

  • Self-assembly and dynamics of liquid crystals and polymers
  • Phase behavior of colloidal systems and colloid-polymer mixtures
  • Emergent behavior of active matter

Education

  • 2004: PhD Physical Chemistry, Utrecht University, The Netherlands
  • 2018: Habilitation à diriger des recherches (HDR), Université Paris-Saclay, France

Latest:

Contact information

Laboratoire de Physique des Solides – UMR 8502
Université Paris-Saclay & CNRS
Bâtiment 510
91405 Orsay Cedex, France

Office:  S118 (south wing, 1st floor)

Email: rik (dot) wensink (at) cnrs (dot) fr

Skype: rik.wensink

Google scholar

Career background

senior CNRS researcher (DR), Laboratoire de Physique des Solides, Orsay, France

2012: I joined the theory group of the Laboratoire de Physique des Solides (LPS) as a CNRS researcher to nucleate the current Soft Matter Theory unit.      

“Akademischer Rat”, Düsseldorf University, Germany

2010 – 2011: I rejoined the Theoretical Physics group as a postdoctoral fellow to collaborate with Hartmut Löwen on computer simulation of emergent behavior in active matter.

Ramsay Fellow, Imperial College London, UK

2008 – 2009: I joined the Chemical Engineering group as a Ramsay scholar to develop thermodynamic theory of chiral liquid crystals in collaboration with George Jackson.        

Humboldt Fellow, Düsseldorf University, Germany

2005 – 2007: I joined the Theoretical Physics group headed by Hartmut Löwen as a Humboldt postdoctoral fellow to study a variety of topics related to driven and complex colloidal liquid crystals using numerical modelling.

PhD, Utrecht University, The Netherlands

2000 – 2004: During my PhD project I worked on a theoretical study of the phase behavior of mixed-shape colloidal liquid crystals at the van ‘t Hoff Laboratory under the supervision of Henk Lekkerkerker and Gert Jan Vroege.

Directed soft matter: nanoparticle-based liquid crystals

Our research is devoted to unravelling the microscopic principles that underpin self-assembly, phase behavior and dynamical aspects of a variety of soft matter systems. Our interest goes to systems that are subject of ongoing experimental research and/or have a strong technological relevance. Examples include filamentous virus, motile bacteria, cellulose nanocrystals, clays, living polymers, colloid-polymer mixtures, and nematic colloids.

The common thread characterizing these systems is that different sources of entropy – related to orientations, steric avoidance, mixing, polymer-backbone flexibility or depletion – conspire with weak enthalpic forces emerging from chirality, surface anchoring or living polymerization and active transport to generate a rich variety of self-assembled structures and phase behaviors with well-defined and facile reconfigurability.

Key manifestations of such complexity are spontaneous handedness inversions in chiral fluids, multiphase coexistence in colloid-polymer mixtures, empty lamellar fluids of non-convex colloids, self-sustained turbulence in bacterial flow, low symmetry fluidity in nematic colloids, or tunable photonics of lamellar clays.

As part of an international research consortium funded by the European Innovation Council in 2022 we have begun modelling complex mixtures of rod-shaped cellulose nanocrystals with adsorbing, actuable co-polymers for use as 3D printable biomimetic muscles.

Our approach to understanding soft matter is to start from coarse-grained, particle-based models that mimic the (orientation-dependent) interaction between the constituent nanoparticles. Subsequently, we invoke common tools from classical statistical mechanics such as variational and scaling theory, density functional methods and computer simulation to address collective properties such as phase behavior, diffusive dynamics and response to external stimuli.

Some topics of current interest are:

Chirality in liquid crystals

Chirality is generally the absence of symmetry and plays a key role in biological matter and, more specifically, in liquid crystals (LCs). The mechanisms underpinning the helical organization of the nematic director and its handedness are, however, rather unclear even in simple systems. We design simple coarse-grained LC models that enable us to address fundamental questions such as ‘‘How does the helicity propagate from the macromolecular to the supramolecular scale?’’ and ‘‘What are the fundamental physical aspects that control their left- or right-handed symmetry?’

Hybrid molecular-colloidal liquid crystals

Colloidal rods or discs immersed in low-molecular weight liquid crystalline host medium experience much more intricate interactions than in the case of simple isotropic media. Elastic distortions of the molecular director field induced by the presence of colloidal particles result in defect-mediated elastic colloidal interactions, which emerge to minimize the free energy cost of the colloidal inclusions. Along with emerging colloid-colloid interaction these surface-anchoring effects may stabilize colloidal nematic fluids with, for instance, orthorhombic and monoclinic point group symmetries. Together with the experimental group of Ivan Smalyukh we explore the rich behavior of these new classes of liquid crystals using simple theoretical concepts.

Self-assembly of directed living polymers

Self-assembly through reversible polymerization plays a key role in numerous processes in both passive and living soft matter. Microtubules, actin, and other filaments found in the cell cytoplasm are composed of dynamically organizing molecular units forming highly interconnected structures that provide essential mechanical functions to the cell. Rigid filaments may hierachically self-organize into liquid crystals (LCs). We theoretically study LC order of living polymer in complex environments due to, for instance, the presence of polymerization inhibitors and non-adsorbing colloidal discs that act as a “orientational” templates.

Size-polydisperse colloids

Polydispersity is ubiquitous in colloidal and polymeric sys-tems given that their constituents are hardly ever fully identical but exhibit a continuous spread in size, shape, or charge. A disparity in microscopic interactions can have a considerable impact on the phase stability as well as on the mechanical properties of colloidal and nanoscale materials via aggregation, packing, and percolation processes. We are interested in understanding the role of size dispersity in driving multiphase coexistence, in particular, nematic-nematic demixing as well as its impact on mesocale chirality.

Depletion effects in colloidal self-assembly

Depletion effects arise when large colloids are mixed with small non-adsorbing species (such as simple polymers) that induce an effective attraction between the colloids. These attractions are entirely of entropic nature and are tunable through the size and concentration of the depletants. The effect lead to rich myriad of phase behaviors and self-assemblies that we study using free-volume theory and density functional theory.

Active matter

Active matter relates to systems that are intrinsically out-of thermal equilibrium and are composed of molecular, colloidal or granular units capable of taking up energy from their immediate surroundings and engage in active processes such as replication or locomotion. Prominent examples include swimming bacteria or algae, self-propelled colloids and driven granulates. Using computer simulation we address complex emergent behavior of these systems such as bioturbulence, swarming and anomalous long-time diffusion.

Peer reviewed publications

[Google scholar][Publons]

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Conference proceedings and other publications

  1. Differently shaped hard body colloids in confinement: From passive to active particles
    H. H. Wensink, H. Löwen, M. Marechal, A. Härtel, R. Wittkowski, U. Zimmermann, A. Kaiser and A. M. Menzel,
    Eur. Phys. J. Special Topics 222, 3023 (2013)
  2. Driven colloidal mixtures and colloidal liquid crystals
    H. Löwen, H. H. Wensink and M. Rex
    AIP Conf. Proc. 982, 284 (2008)

Physics of Active Matter

Master 2: Systèmes Biologiques et Concepts Physiques – Université Paris-Saclay (2014 – 2024)

This course provides an overview of experimental, theoretical and simulation work on active matter involving microswimmers, active colloids, driven granulates and living liquid crystals. The course is divided into the following lectures:

  • Lecture 1: Physics of microswimmers and active Brownian particles
  • Lecture 2: Particulate active matter: emergent states and motility-induced phase separation
  • Lecture 3: Dry flocks; symmetry breaking and density fluctuations
  • Lecture 4: Wet flocks; nematic instabilities, bioturbulence, and viscosity

For more info please contact: Luis Gómez Nava

Soft Matter Theory @ LPS

Current members:

Alumni:

Collaborations (past and present)

Job opportunities

If you are interested in joining our group please drop me an email at:

rik (dot) wensink (at) cnrs (dot) fr