About me

I am a Marie Skłodowska Curie Research Fellow working with Slobodan Žumer in the Soft Matter team of the Faculty of Physics and Mathematics at the University of Ljubljana. We want to develop a new research direction by combining knowledge from photonics and topological soft matter to find novel ways of guiding light using chiral birefringent media. The non-linear optical response of these media allows a laser beam to be self-confined and to propagate over long distances, leading to what is called spatial optical solitons. Our primary objective is to develop a complete model of optical solitons in chiral birefringent media and examine how these light solitons can be steered and controlled using topological solitons — localized and tunable perturbations of the molecular orientational field which cannot be continuously deformed into the uniform state. Our methodology is based on the theoretical and numerical modeling of the non-linear equations for the propagation of light in chiral birefringent media, combined with collaborative experiments.

PhD - Lehmann effect

You can download my PhD thesis with the following link:

PhD thesis

This thesis is focused on the Lehmann effect, an out-of-equilibrium effect which couples a temperature gradient with the rotation of the internal texture of liquid crystal droplets in coexistence with the isotropic phase.

First, we characterized the thermomechanical coupling terms of Leslie, Akopyan and Zel’dovich by measuring the rotation velocity of the molecules in two translationally invariant configura- tions with different orientations, below the cholesteric/isotropic transition.

Then, we characterized the texture of the droplets observed in the Lehmann experiment, both using optical observations and numerical simulations. More important, we showed for the first time that it is possible to observe the Lehmann effect in achiral nematic droplets, providing that the internal texture is chiral. We also used a photobleaching experiment to show that there is no visible flow in the vicinity of the droplet, which implies that the texture rotation is due to a local rotation of the molecules – not to a solid rotation of the droplet.

Finally, we proposed a theoretical model of the Lehmann effect based on the thermome- chanical coupling of Leslie, Akopyan and Zel’dovich. By applying this model to the numerically computed textures, we fitted our experimental data and found values for the thermomechanical coupling constants much bigger than those measured below the cholesteric/isotropic transition. This model is therefore incomplete.

SM1 — (-1/2) disclination line observed under crossed polarizers just below the cholesteric/isotropic temperature in a planar sliding sample of the mixture CCN-37 + 3 % CC. \(d=\) 10.6 µm and \(\Delta T=\) 40 °C. The bar represents 50 µm.

SM2 — Pair of \(\pm\) 1 disclination lines observed under crossed polarizers just below the cholesteric/isotropic temperature in a mixed sample of the mixture CCN-37 + 3 % CC. \(d=\) 10.8 µm and \(\Delta T=\) 40 °C. The bar represents 100 µm.

SM3 — Lehmann rotation of banded droplets observed in a sample of 7CB + 0.6 \% R811. The temperature gradient is oriented towards the internaut. \(d=\) 50 µm and \(\Delta T=\) 5 °C. The bar represents 50 µm.

SM4 — Lehmann rotation of cholesteric twisted bipolar droplets observed in a sample of CCN-37 + 5.9 \% CC. The temperature gradient is oriented towards the internaut. \(d=\) 50 µm and \(\Delta T=\) 1.25 °C. The bar represents 50 µm.

SM5 — Lehmann rotation of nematic twisted bipolar droplets observed in a sample of water + 28 \% SSY. The temperature gradient is oriented towards the internaut. \(d=\) 110 µm and \(\Delta T=\) 20 °C. The bar represents 10 µm.

SM6 — Fluorescence signal after a laser shot near a banded droplet of 7CB + 0.25 % R811 + 0.05 % NBD C6-ceramide. The droplet rotates at \(\omega_g=\) 0.139 rad/s when \(\Delta T=\) -10 K. The white point represents the center of the gaussian fit and the white circle represents the circle of equation \(|\vec{x}-\vec{x}_0|=\sigma/2\). The bar represents 50 µm.

SM7 — Same as SM6 with a droplet more distorted rotating at \(\omega_g=\) 0.036 rad/s when \(\Delta T=\) -10 °C. Mixture of 7CB + 0.25 % R811 + 0.05 % NBD C6-ceramide. The bar represents 50 µm.

SM8 — Fluorescence signal after a laser shot (left) and images in transmission between crossed polarizers under white light illumination (right) of a cholesteric twisted bipolar droplet. The black circle represents the outer contour of the droplets. The tilted black line gives the orientation of the bipole. The white point and circle have the same meaning as in SM6 and SM7. Mixture of CCN-37 + 5.9 % CC + 0.05 % NBD C6-ceramide, \(\Delta T=\) 2.5 °C. The bar represents 10 µm.

Master 2 - Rheology of

cornstarch suspensions

Rheology correspond to the study of the flow of matter. The simplest case of study is the shear experiment, where you submit a flowing sample to a shear flow by imposing either a force or a velocity on one of the two plates delimiting the sample (schema on the left). We can then define the strain rate \(\dot\gamma\) as the plate velocity \(v\) divided by the thickness \(d\), the stress \(\sigma\) as the place force \(F\) divided by the plate surface \(S\), and the viscosity \(\eta\) as the proportionality factor between the stress and the strain rate:

When the viscosity of a material is independant of the strain rate or the stress, this material is called newtonian (e.g. water). On the other hand, many materials exhibit a dependance of the viscosity with the strain rate ; these materials are called complex fluids. Suspensions (particles suspended in a fluid) are a perfect exemple of a complex fluid. For low packing fraction of particles, the suspension stays newtonian if the carrier-fluid is newtonian, but with an increase of viscosity due to the hydrodynamic interactions between particles. For high packing fraction, the friction and electrostatic interactions becomes relevant, and interesting dependance between the viscosity and the the strain rate appears. One of these behaviours, called shear-thickening, is the increase of viscosity with the strain rate, which can lead to spectacular effects: for example, one can run across a pool filled with a suspension of cornstarch in water

During my internship, I studied two types of suspensions: supensions of cornstarch in water (repulsive interaction between particles) and suspensions of cornstarch in oil (attractive interaction between particles). The repulsive suspensions are found to be shear-thickening, and a comparison with a recent theoretical model for shear-thickening suspensions is proposed. The attractive suspensions display an interesting dynamic behaviour in Large Amplitude Oscillatory Shear (LAOS) experiment, which is interpreted in terms of shear-reversal and structures forming in the compression direction.

Shear Thickening in Dense Suspensions

Report Abstract

Unsteady flow and particle migration in dense, non-Brownian suspensions

M. Hermes, B. M. Guy, W. C. K. Poon, G. Poy, M. E. Cates, M. Wyart, Journal of Rheology, 60, 905–916 (2016)

DOI Article Abstract/Bibtex

We present experimental results on dense corn-starch suspensions as examples of non-Brownian, nearly hard particles that undergo continuous and discontinuous shear thickening (DST) at intermediate and high densities, respectively. Our results offer strong support for recent theories involving a stress-dependent effective contact friction among particles. We show, however, that in the DST regime, where theory might lead one to expect steady-state shear bands oriented layerwise along the vorticity axis, the real flow is unsteady. To explain this, we argue that steady-state banding is generically ruled out by the requirement that, for hard non-Brownian particles, the solvent pressure and the normal-normal component of the particle stress must balance separately across the interface between bands. (Otherwise, there is an unbalanced migration flux.) However, long-lived transient shear bands remain possible.

@article{hermes_unsteady_2016,
	title = {Unsteady flow and particle migration in dense, non-Brownian suspensions},
	volume = {60},
	issn = {0148-6055, 1520-8516},
	doi = {10.1122/1.4953814},
	number = {5},
	journal = {Journal of Rheology},
	author = {Hermes, Michiel and Guy, Ben M. and Poon, Wilson C. K. and Poy, Guilhem and Cates, Michael E. and Wyart, Matthieu},
	year = {2016},
	pages = {905--916},
}

Master 1 - Stability

of relativistic jets

Astrophysical jets correspond to well-calibrated flows of matter and energy whose source can be a galactic object (for example a microquasar, i.e. a binary system with one compact object and an accretion disk) or an extra-galactic object (for example an active galactic nuclei, i.e. a compact region at the center of a glaxy with a high luminosity). These jets can propagate over considerable distances (up to millions of light-year), which raises the following question: how can we explain the remarkable stability of these jets? This question is relevant, because many magnetohydrodynamic effects (such as the Kelvin-Helmholtz instability) can destabilize the jet.

During my internship, I studied theoretically the mechanisms of stability and instability for a simple model of jet, the beam model. Using the linearized equations of the magnetohydrodynamics for a jet, I computed the dispersion relation of the perturbation of a relativistic and compressible jet, and solved this relation under special limit cases. I showed that there is instable modes at all frequencies when there is no magnetic field, and that the effect of a magnetic field is to shift the most unstable modes to lower frequencies.

Stabilité des jets ultrarelativistes

Report Abstract

Bachelor - Rotational

viscosity measurement

Liquid crystals are products which possess a mesophase, i.e. a phase intermediate between a solid and a liquid. The most simple mesophase is the nematic phase, with no positional order and an orientational order. The latter allows us to define the director \({\bf n}\) as the mean direction of the molecules on a mesoscopic volume. Similarly to an isotropic fluid, where a shear is associated with a viscous stress, a rotation of the molecules without flow in a nematic phase is associated with a bulk viscous torque: \[ {\bf\Gamma}_{vb} = \gamma_1 {\bf n} \times \frac{\partial{\bf n}}{\partial t}, \] where \(\gamma_1\) is called the bulk rotational viscosity. When the nematic phase is confined within two parallel plates treated with a sliding planar anchoring (the molecules are parallel to the plates and can freely rotate on the plate surface), we can similaryly describe the rotational friction on the surface with a surface viscous torque: \[ {\bf\Gamma}_{vs} = \gamma_s {\bf n} \times \frac{\partial{\bf n}}{\partial t}, \] where \(\gamma_s\) is called the surface rotational viscosity.

If a rotating magnetic field \({\bf B}\) is applied parallel to the plates, the director will also rotates at the same angular velocity \(\omega\), but will make a small angle \(\alpha\) with \({\bf B}\) due to the dissipation by \(\gamma_1\) and \(\gamma_s\). By measuring this delay angle for different \(\omega\) and \(B\), it is possible to measure both \(\gamma_1\) and \(\gamma_s\). During my internship, I interfaced with Labview the experimental setup designed by Patrick Oswald to apply the rotating magnetic field, and systematically measured the bulk and surface rotational viscosities of a typical liquid crystal in function of the temperature.

Experimental relationship between surface and bulk rotational viscosities in nematic liquid crystals

P. Oswald, G. Poy, F. Vittoz, V. Popa-Nita, Liquid Crystals, 40, 734–744 (2013)

DOI Article Abstract/Bibtex

Systematic measurements of the surface viscosity \(\gamma_s\) of several nematic liquid crystals in contact with a polymercaptan layer show that the latter scales like the bulk rotational viscosity \(\gamma_1\). This result is interpreted in the framework of a ‘delocalized model’ for the surface viscosity.

@article{oswald_experimental_2013,
	title = {Experimental relationship between surface and bulk rotational viscosities in nematic liquid crystals},
	volume = {40},
	issn = {0267-8292, 1366-5855},
	doi = {10.1080/02678292.2013.783936},
	number = {6},
	journal = {Liquid Crystals},
	author = {Oswald, Patrick and Poy, Guilhem and Vittoz, Franck and Popa-Nita, Vlad},
	year = {2013},
	pages = {734--744},
}

Peer-reviewed articles

Dislocations dynamics during the nonlinear creep of a homeotropic sample of smectic-A liquid crystal

P. Oswald, G. Poy, The European Physical Journal E, 41, 73 (2018)

DOI Article Abstract/Bibtex

New creep experiments under sinusoidal compression/dilation deformation of a homeotropic sample of smectic-A liquid crystal (8CB) show that its response is nonlinear at very small amplitude of deformation. This behavior is explained by taking into account the crossing between the edge dislocations that climb parallel to the layers and the screw dislocations joining the two surfaces limiting the sample. The activation energy of the crossing process and the density of the screw dislocations as a function of the sample thickness are estimated experimentally.

@article{oswald_dislocations_2018,
  title={Dislocations dynamics during the nonlinear creep of a homeotropic sample of smectic-A liquid crystal},
  author={Oswald, P and Poy, G},
  journal={The European Physical Journal E},
  doi = {10.1140/epje/i2018-11684-9},
  volume={41},
  number={6},
  pages={73},
  year={2018},
}

On the existence of the thermomechanical terms of Akopyan and Zel’dovich in cholesteric liquid crystals

G. Poy, P. Oswald, Liquid Crystals (2018)

DOI Article Abstract/Bibtex

We revisit a theoretical paper of Akopyan and Zel’dovich about the thermomechanical coupling terms in nematic liquid crystals. We show that the expressions of these terms given by these authors must be corrected to satisfy the Onsager reciprocity relations, a point already stressed by Pleiner and Brand in 1987. We then extend this calculation to the cholesteric phase and show that there are no additional terms in the uniaxial approximation of this phase. Finally, we give the correspondence between the Akopyan and Zel’dovich terms and those calculated by Pleiner and Brand in 1996 by making a different choice for the forces and the fluxes in the theory.

@article{poy_existence_2018,
  title={On the existence of the thermomechanical terms of Akopyan and Zel’dovich in cholesteric liquid crystals},
  author={Poy, G and Oswald, P},
  journal={Liquid Crystals},
  doi = {10.1080/02678292.2018.1446552},
  year={2018},
}

Role of anchoring energy on the texture of cholesteric droplets: Finite-element simulations and experiments

G. Poy, F. Bunel, P. Oswald, Physical Review E, 96 (2017)

DOI Article Abstract/Bibtex

We present a numerical method to compute defect-free textures inside cholesteric domains of arbitrary shape. This method has two interesting properties, namely a robust and fast quadratic convergence to a local minimum of the Frank free energy, thanks to a trust region strategy. We apply this algorithm to study the texture of cholesteric droplets in coexistence with their isotropic liquid in two cases: when the anchoring is planar and when it is tilted. In the first case, we show how to determine the anchoring energy at the cholesteric-isotropic interface from a study of the optical properties of droplets of different sizes oriented with an electric field. This method is applied to the case of the liquid crystal CCN-37. In the second case, we come back to the issue of the textural transition as a function of the droplet radius between the double-twist droplets and the banded droplets, observed for instance in cyanobiphenyl liquid crystals. We show that, even if this transition is dominated by the saddle-splay Gauss constant \(K_4\), as was recently recognized by Yoshioka et al. [Soft Matter 12, 2400 (2016)], the anchoring energy does also play an important role that cannot be neglected.

@article{poy_role_2017,
	title = {Role of anchoring energy on the texture of cholesteric droplets: {Finite}-element simulations and experiments},
	volume = {96},
	issn = {2470-0045, 2470-0053},
	doi = {10.1103/PhysRevE.96.012705},
	number = {1},
	journal = {Physical Review E},
	author = {Poy, Guilhem and Bunel, Felix and Oswald, Patrick},
	year = {2017},
}

Fréedericksz transition under electric and rotating magnetic field: application to nematics with negative dielectric and magnetic anisotropies

P. Oswald, G. Poy, F. Vittoz, Liquid Crystals, 1–8 (2017)

DOI Article Abstract/Bibtex

We study the action of a rotating magnetic field on the Fréedericksz instability under electric field of a homeotropic nematic sample sandwiched between two parallel electrodes. The liquid crystal (LC) is of negative dielectric and magnetic anisotropies and the magnetic field is parallel to the electrodes used to apply the electric field. We show that the sample destabilises above a critical voltage \(V_c\) that depends on the magnetic field \(B\) and its angular rotation velocity \(\omega\). The relation \(V_c(B,\omega\) is calculated analytically in the synchronous regime, where the director rotates at the same angular velocity as the magnetic field. These predictions are compared to the experiment performed with the LC CCN-37. From this experiment, the values of the bend constant \(K_3\), of the rotational viscosity \(\gamma_1\) and of the magnetic anisotropy \(\chi_a\) are deduced.

@article{oswald_freedericksz_2017,
	title = {Fréedericksz transition under electric and rotating magnetic field: application to nematics with negative dielectric and magnetic anisotropies},
	issn = {0267-8292, 1366-5855},
	doi = {10.1080/02678292.2016.1272722},
	journal = {Liquid Crystals},
	author = {Oswald, P. and Poy, G. and Vittoz, F.},
	year = {2017},
	pages = {1--8},
}

Lehmann rotation of twisted bipolar cholesteric droplets: role of Leslie, Akopyan and Zel’dovich thermomechanical coupling terms of nematodynamics

P. Oswald, G. Poy, A. Dequidt, Liquid Crystals, 1–20 (2016)

DOI Article Abstract/Bibtex

We show that the Leslie and texture-dependent Akopyan and Zel’dovich thermomechanical coupling terms of nematodynamics cannot explain the thermal Lehmann rotation of the twisted bipolar droplets observed in the coexistence region between a cholesteric phase and the isotropic liquid. On the other hand, these terms are pertinent below the transition temperature and can be determined by measuring the director rotation velocity in two different molecular configurations. In addition, a complete characterisation of the liquid crystal used (CCN-37) is also given.

@article{oswald_lehmann_2016,
	title = {Lehmann rotation of twisted bipolar cholesteric droplets: role of {Leslie}, {Akopyan} and {Zel}’dovich thermomechanical coupling terms of nematodynamics},
	issn = {0267-8292, 1366-5855},
	doi = {10.1080/02678292.2016.1255363},
	journal = {Liquid Crystals},
	author = {Oswald, P. and Poy, G. and Dequidt, A.},
	year = {2016},
	pages = {1--20},
}

Unsteady flow and particle migration in dense, non-Brownian suspensions

M. Hermes, B. M. Guy, W. C. K. Poon, G. Poy, M. E. Cates, M. Wyart, Journal of Rheology, 60, 905–916 (2016)

DOI Article Abstract/Bibtex

@article{hermes_unsteady_2016,
	title = {Unsteady flow and particle migration in dense, non-Brownian suspensions},
	volume = {60},
	issn = {0148-6055, 1520-8516},
	doi = {10.1122/1.4953814},
	number = {5},
	journal = {Journal of Rheology},
	author = {Hermes, Michiel and Guy, Ben M. and Poon, Wilson C. K. and Poy, Guilhem and Cates, Michael E. and Wyart, Matthieu},
	year = {2016},
	pages = {905--916},
}

Generalized drift velocity of a cholesteric texture in a temperature gradient

A. Dequidt, G. Poy, P. Oswald, Soft Matter, 12, 7529–7538 (2016)

DOI Article Abstract/Bibtex

We propose a general method to calculate the drift velocity of cholesteric textures subjected to a temperature gradient when the backflow effects are negligible. The textures may be Translationally Invariant Configurations (TICs) or localized structures such as cholesteric droplets or cholesteric fingers. For the TICs and for the droplets, the drift is rotational while for the fingers, the drift is translational. We show that for the TICs, the drift is only due to the thermomechanical coupling terms of Leslie (classical term) and of Akopyan and Zel’dovich (which are additional texture-dependent terms). For the localized structures, we show that another mechanism involving the temperature variations of the elastic constants and the existence of a transverse temperature gradient can lead to a drift which adds to the one due the classical thermomechanical effects.

@article{dequidt_generalized_2016,
	title = {Generalized drift velocity of a cholesteric texture in a temperature gradient},
	volume = {12},
	issn = {1744-683X, 1744-6848},
	doi = {10.1039/C6SM01359G},
	number = {36},
	journal = {Soft Matter},
	author = {Dequidt, Alain and Poy, Guilhem and Oswald, Patrick},
	year = {2016},
	pages = {7529--7538},
}

Continuous Rotation of Achiral Nematic Liquid Crystal Droplets Driven by Heat Flux

J. Ignés-Mullol, G. Poy, P. Oswald, Physical Review Letters, 117, 057801 (2016)

DOI Article Abstract/Bibtex

Suspended droplets of cholesteric (chiral nematic) liquid crystals spontaneously rotate in the presence of a heat flux due to a temperature gradient, a phenomenon known as the Lehmann effect. So far, it is not clear whether this effect is due to the chirality of the phase and the molecules or only to the chirality of the director field. Here, we report the continuous rotation in a temperature gradient of nematic droplets of a lyotropic chromonic liquid crystal featuring a twisted bipolar configuration. The achiral nature of the molecular components leads to a random handedness of the spontaneous twist, resulting in the coexistence of droplets rotating in the two senses, with speeds proportional to the temperature gradient and inversely proportional to the droplet radius. This result shows that a macroscopic twist of the director field is sufficient to induce a rotation of the droplets, and that the phase and the molecules do not need to be chiral. This suggests that one can also explain the Lehmann rotation in cholesteric liquid crystals without introducing the Leslie thermomechanical coupling—only present in chiral mesophases. An explanation based on the Akopyan and Zeldovich theory of thermomechanical effects in nematics is proposed and discussed.

@article{ignes-mullol_continuous_2016,
	title = {Continuous Rotation of Achiral Nematic Liquid Crystal Droplets Driven by Heat Flux},
	volume = {117},
	issn = {0031-9007, 1079-7114},
	doi = {10.1103/PhysRevLett.117.057801},
	number = {5},
	journal = {Physical Review Letters},
	author = {Ignés-Mullol, Jordi and Poy, Guilhem and Oswald, Patrick},
	year = {2016},
	pages = {057801},
}

Do Lehmann cholesteric droplets subjected to a temperature gradient rotate as rigid bodies?

G. Poy, P. Oswald, Soft Matter, 12, 2604–2611 (2016)

DOI Article Abstract/Bibtex

We performed a Fluorescence Recovery After Photobleaching (FRAP) experiment during the Lehmann rotation of cholesteric droplets in thermodynamic coexistence with the isotropic liquid and subjected to a temperature gradient. By creating and tracking bleached spots near the surface of banded droplets (in which the cholesteric helix is perpendicular to the gradient) and concentric circle droplets oriented by an electric field (in which the helix is parallel to the gradient), we found that neither type of droplet rotates as a solid. This result shows that the texture rotation is mainly due to the local director rotation.

@article{poy_lehmann_2016,
	title = {Do Lehmann cholesteric droplets subjected to a temperature gradient rotate as rigid bodies?},
	volume = {12},
	issn = {1744-683X, 1744-6848},
	doi = {10.1039/C5SM02906F},
	number = {9},
	journal = {Soft Matter},
	author = {Poy, Guilhem and Oswald, Patrick},
	year = {2016},
	pages = {2604--2611},
}

Droplet relaxation in Hele-Shaw geometry: Application to the measurement of the nematic-isotropic surface tension

P. Oswald, G. Poy, Physical Review E, 92, 062512 (2015)

DOI Article Abstract/Bibtex

Shape measurements after the coalescence of isotropic droplets embedded in a thin sample of a homeotropic nematic phase provides a tool to measure the nematic-isotropic surface tension. In addition, this experiment allows us to check the scaling laws recently given by Brun et al. [P.-T. Brun, M. Nagel, and F. Gallaire, Phys. Rev. E 88, 043009 (2013)] to explain the relaxation of ellipsoidal droplets in a Hele-Shaw cell.

@article{oswald_droplet_2015,
	title = {Droplet relaxation in Hele-Shaw geometry: Application to the measurement of the nematic-isotropic surface tension},
	volume = {92},
	issn = {1539-3755, 1550-2376},
	doi = {10.1103/PhysRevE.92.062512},
	number = {6},
	journal = {Physical Review E},
	author = {Oswald, Patrick and Poy, Guilhem},
	year = {2015},
	pages = {062512},
}

Lehmann rotation of cholesteric droplets: Role of the sample thickness and of the concentration of chiral molecules

P. Oswald, G. Poy, Physical Review E, 91, 032502 (2015)

DOI Article Abstract/Bibtex

We study the role of the sample thickness \(d\) and of the concentration \(C\) of chiral molecules during the Lehmann rotation of cholesteric droplets of radius \(R\) subjected to a temperature gradient \(\vec{G}\). Two configurations are studied depending on how the helix is oriented with respect to \(\vec{G}\). The first result is that, at fixed \(C\) and \(R\), the rotation velocity \(\omega\) increases with \(d\) when the helix is parallel to \(\vec{G}\), whereas it is independent of \(d\) when the helix is perpendicular to \(\vec{G}\). The second result is that, for a given \(C\), \(\omega_0=\lim_{R\rightarrow0}\omega(R)\) is the same for the two types of droplets independently of \(d\). This suggests that the, as yet unknown, physical mechanism responsible for the droplet rotation is the same in the two types of droplets. The third result is that the Lehmann coefficient \(\bar\nu\) defined from the Leslie-like relation \(\omega_0=−\bar\nu G/\gamma_1\) (with \(\gamma_1\) the rotational viscosity) is proportional to the equilibrium twist \(q\). Last, but not least, the ratio \(\bar R=\bar\nu/q\) depends on the liquid crystal chosen but is independent of the chiral molecule used to dope the liquid crystal.

@article{oswald_lehmann_2015,
	title = {Lehmann rotation of cholesteric droplets: Role of the sample thickness and of the concentration of chiral molecules},
	volume = {91},
	issn = {1539-3755, 1550-2376},
	doi = {10.1103/PhysRevE.91.032502},
	number = {3},
	journal = {Physical Review E},
	author = {Oswald, Patrick and Poy, Guilhem},
	year = {2015},
	pages = {032502},
}

Experimental relationship between surface and bulk rotational viscosities in nematic liquid crystals

P. Oswald, G. Poy, F. Vittoz, V. Popa-Nita, Liquid Crystals, 40, 734–744 (2013)

DOI Article Abstract/Bibtex

@article{oswald_experimental_2013,
	title = {Experimental relationship between surface and bulk rotational viscosities in nematic liquid crystals},
	volume = {40},
	issn = {0267-8292, 1366-5855},
	doi = {10.1080/02678292.2013.783936},
	number = {6},
	journal = {Liquid Crystals},
	author = {Oswald, Patrick and Poy, Guilhem and Vittoz, Franck and Popa-Nita, Vlad},
	year = {2013},
	pages = {734--744},
}

Conferences (talks & posters)

Email:	guilhem.poy@fmf.uni-lj.si
Address:	Faculty of Mathematics and Physics Jadranska 19 1000 Ljubljana, Slovenia

About me

Academic Curriculum

Marie Curie Fellow

Postdoctoral researcher

PhD Student

Research intern

Master 2 in Physics

Research intern

Master 1 in Physics

Research intern

Bachelor in Physics

"Classes Preparatoires" in Science

Scientific high school diploma

PhD - Lehmann effect

Master 2 - Rheology of

cornstarch suspensions

Master 1 - Stability

of relativistic jets

Bachelor - Rotational

viscosity measurement

Peer-reviewed articles

Conferences (talks & posters)

Master 1 - Signal processing

License 3 - Lab Work

Professional