Experimental Soft Matter Physics

New book on Liquid Crystals with Nano and Micro Inclusions

Finally, it's out! After a long process, sometimes with unexpected turns, the book edited by Giusy Scalia and Jan Lagerwall on nano and micro inclusions in liquid crystals, is now published, printed and available for purchase. "Liquid Crystals with Nano and Microparticles" is published by World Scientific (Singapore) and you can read all about it (and order it, on paper or as an e-book) here. Featuring the world leaders of this broad field and covering a diverse range of aspects, it ended up filling two volumes. The content is as follows (chapter authors in parentheses):

Volume 1:
1. Introduction (G Scalia and J P F Lagerwall)
I. Fundamentals:
2. A Phenomenological Introduction to Liquid Crystals and Colloids (J P F Lagerwall)
Nanoparticle Dispersions: A Colloid and Polymer Solution Perspective (P van der Schoot)
Nematic Liquid Crystals Doped with Nanoparticles: Phase Behavior and Dielectric Properties (M A Osipov and M V Gorkunov)
II: Methods for Studying Liquid Crystals and Their Inclusions:
Conventional and Nonlinear Optical Microscopy of Liquid Crystal Colloids (T Lee and I I Smalyukh)
X-Ray Scattering (G Ungar, Z Chen and X Zeng)
Raman Spectroscopy (H F Gleeson)
Manipulation of Inclusions with Optical Tweezers (M Skarabot)
Atomic Force Microscopy on Liquid Crystals (C Bahr and B Schulz)
III. Micron Scale Inclusions in Liquid Crystals:
Solid Microparticles in Nematic Liquid Crystals (Igor Muševič)
Inclusions in Freely Suspended Smectic Films (R Stannarius and K Harth)
Liquid Crystal-Enabled Electrophoresis and Electro-Osmosis (O D Lavrentovich)

Volume 2:
IV. Nanoparticles in Liquid Crystals:
Nanoparticles in Discotic Liquid Crystals (S Kumar)
Metallic and Semiconducting Nanoparticles in LCs (A Sharma, M Urbanski, T Moria, H-S Kitzerow and T Hegmann)
Inorganic Nanotubes and Nanorods in Liquid Crystals (I Drevenšek-Olenik)
Liquid Crystals from Mesogens Containing Gold Nanoparticles (W Lewandowski and E Gorecka)
Carbon Nanotubes in Thermotropic Low Molar Mass Liquid Crystals (S Schymura, J Park, I Dierking and G Scalia)
Carbon Nanotubes Dispersed in Liquid Crystal Elastomers (Y Yang and Y Ji)
Ferromagnetic and Ferroelectric Nanoparticles in Liquid Crystals (Y Reznikov, A Glushchenko and Y Garbovskiy)
Nanoparticle Guests in Lyotropic Liquid Crystals (S Dölle, J H Park, S Schymura, Hyeran Jo, G Scalia and J P F Lagerwall)
Control of Nanoparticle Self-Assemblies Using Distorted Liquid Crystals (E Lacaze and D Coursault)
Nanoparticles and Networks Created Within Liquid Crystals (S-W Kang and S Kundu)

Liquid Crystals Formed by Nanoparticle Suspensions:
Nematic Phase Formation in Suspensions of Carbon Nanotubes (C Zakri and Ph Poulin)
Nematic Phase Formation in Suspensions of Graphene Oxide (N Fresneau and S Campidelli)
Electro-Optical Switching of Liquid Crystals of Graphene Oxide (J Song)
Liquid Crystalline Phases in Suspensions of Pigments in Non-Polar Solvent (S Klein, R Richardson and A Eremin)
Cholesteric Liquid Crystal Formation in Suspensions of Cellulose Nanocrystals (C Honorato-Rios, J Bruckner, C Schütz, S Wagner, Z Tosheva, L Bergström and J P F Lagerwall)

Hakam Agha joins the team

We have the great pleasure of welcoming Dr. Hakam Agha into the ESMP team. He will be working as a post-doc with us and with the LC Nano group of Giusy Scalia for at least six months, hopefully more. He got his Ph.D. in physics from the University of Strasbourg and was most recently working as post-doc with Christian Bahr and Stefan Herminghaus at the Max Planck Institute for Dynamics and Self-Organization in Göttingen. You can contact Hakam via e-mail here.


Dirk Jan Mulder visits the ESMP group

We have the pleasure of hosting Dirk Jan Mulder, Ph.D. candidate in the group of Prof. Albert Schenning, Technical University of Eindhoven, during November. Dirk Jan is working on microfluidic liquid crystal elastomer shell production together with Rao and Kevin (see action pictures from the yellow lab), and also on porous shell production together with JungHyun.

New paper on polymer-stablized liquid crystal shells in Advanced Materials

Congratulations to JungHyun and Benjamin for their new Adv. Mater. paper "Taming Liquid Crystal Self-Assembly: The Multifaceted Response of Nematic and Smectic Shells to Polymerization" on polymer-stabilization of nematic and smectic liquid crystal shells, and the sometimes unexpected consequences for the liquid crystal self-assembly. By polymerizing a small fraction of the reactive mesogen RM257 in shells of 8CB or its homologues, certain defect configurations can be locked in place, the exact result depending sensitively on the mixture composition and the temperature at which polymerization is carried out. Surprisingly, when polymerizing close to a phase boundary, a transition into the adjacent phase can be induced. The new phase can be more or less ordered, depending on the starting situation. The lifetime of the shells is dramatically enhanced, as is the temperature stability. By tuning the conditions, the self-assembled structure can be made fully permanent, being visible even upon heating to the isotropic phase of the non-polymerized component, or it can be retained in a latent state, allowing macroscopic loss of order on heating to the isotropic phase yet with a memory of the chosen defect configuration when cooling down. Apart from proposing explanations for the various observations we discuss possibilities to apply the polymer-stabilized shells, for instance in advanced materials generation or in sensing.

Here you can find the full paper (don't forget to check out the rich supporting information, including many spectactular movies), and here is a layman's abstract for the paper.

New paper on quantitative optical characterization of CNC films

We have a new article out in the journal Cellulose, describing the results from a collaboration with Sweden and Slovenia. The article, entitled "Correlation between structural properties and iridescent colors of cellulose nanocrystalline films", describes an optical and electron microscopy study of dried films of cellulose nanocrystals (CNC), prepared with or without circular shear flow. This is a follow-up study of our previous study on the influence of shear flow when drying CNC samples to make iridescent films, and the new component is a quantitative spectrophotometric study as a function of location in the films, together with a high-resolution electron microscopy characterization of the fractured films. It turns out that the reflection spectra are surprisingly similar between the two types of films, but the film cross section is very different. Whereas films dried with shear flow have a clearly periodic helical structure throughout the film, the ones dried without shear flow are disordered near the air interface. Because there is still a sufficiently thick internal regime, close to the bottom substrate, that is helical, the reflection spectra are similar, but the structural difference at the film top can have a strong effect on birefringence. The reflection spectra are much broader than what is expected for a cholesteric liquid crystal with well-defined pitch, indicating a variation in pitch within the film, which may be related to the polydispersity of CNC samples.

Read the article on the Cellulose website.

New paper in Langmuir on CNC dispersion in non-aqueous polar solvents

Congratulations to Johanna and co-authors for the publication in Langmuir of the article "Enhancing Self-Assembly in Cellulose Nanocrystal Suspensions Using High-Permittivity Solvents". The team studied dispersion of Cellulose Nanocrystals (CNC) and the associated liquid crystal formation in water and in non-aqueous but polar solvents. Johanna developed a new method for exchanging the solvent of CNC suspensions from the water used during synthesis to formamide, N-methylformamide (NMF) and N,N-dimethylformamide (DMF), without inducing aggregation of the nanorods. She found striking differences between the solvents concerning the liquid crystal formation. The four solvents span a large range of dielectric permittivity, a parameter that turns out to be of key importance. The cholesteric helical superstructure develops much faster in high-permittivity NMF than in water and the pitch depends much less on CNC concentration than when water is the solvent. In low-permittivity DMF the first trace of liquid crystal formation coincides with kinetic arrest of the whole sample, preventing any helix formation since an equilibrium liquid crystal phase never develops. We propose that this is due to aligned aggregation of the CNC nanorods. The experimental results are corroborated by computer simulations done in Tanja Schilling's group, which furthermore indicate that the nematic order parameter goes up for high-permittivity solvents.

If you have an institutional subscription to Langmuir, you can download the article here. If you do not, you can try the following link: http://pubsdc3.acs.org/articlesonrequest/AOR-uVuBGBqpFzkXHmtihG36 . The first 50 to try this link can download the article for free, regardless of subscription.

We regret that the published Acknowledgments section unfortunately did not mention that Rick Dannert is a member of the Laboratory for the Physics of Advanced Materials of the University of Luxembourg and that this group kindly made their equipment (AFM, rheometer and refractometer) available for some of the experiments described in the paper. We deeply apologize for having forgotten this information in the published paper. Here we would like to express our deep gratitude for the support from the Laboratory for the Physics of Advanced Materials.

New paper on gas sensing with liquid crystal core microfibers

Congrats to Catherine and Anshul, whose paper on non-electronic toluene vapor sensing using electrospun PVP fibers filled with nematic 5CB liquid crystal is now available (Open Access) from the Liquid Crystals website. In the article they demonstrate that there are two types of response to toluene vapor exposure, one slow and one fast. The slow one corresponds to a toluene diffusion-induced clearing transition, whereas the fast one is connected to a change in liquid crystal director field configuration, but the 5CB remains in the nematic phase. This fast response is seen across the mat within a fraction of a second, even several centimeters away from the exposure point, indicating that the detection threshold is very low. They also show that the responses of uniformly cylindrical fibers and beaded fibers are quite different, the latter allowing detection by the naked eye, without polarizers. Download the paper (no subscription needed) here.

Domenico Alj visits the ESMP group

Domenico Alj, Ph.D. candidate at the University of Calabria, visits the ESMP group for one month to work on alignment of cholesteric phases of cellulose nanocrystal suspensions. The visit is within the framework of the COST network IC1208.

IRES visitors 2016

We are glad to welcome Vianna Chan, Michelle Park and Laura Saunders to our group! They constitute the fourth round of visitors within the NSF-funded IRES (International Research Experience for Students) project led by our collaborator Prof. Antal Jakli at Kent State University, Kent (OH), USA. Michelle (left), Laura (middle) and Vianna (right) will be working with electrospinning and electrospray of fibers/beads with liquid crystal core.

Yong's cholesteric microshells study published in Scientific Reports


Congrats to Yong on the publication of his cholesteric microshells study in the journal Scientific Reports (Nature Publishing Group)! Together with JungHyun he succeeded in preparing shells from different cholesteric liquid crystal mixtures, giving selective reflection in different color ranges. He has developed a new method to rapidly remove defects by annealing through osmosis, and then he polymerizes a fraction of the mixture that is sufficient to make the shells robust under considerable mechanical deformation. With the help of our collaborators Romano Rupp (University of Vienna) and Irena Drevensek-Olenik (University of Ljubljana) we analyze the complex optics of the photonic cross communication between the shells, finding that the communication is active even between shells with different reflection colors, opening up new communication channels (picture). Finally, our collaborator at the Interdisciplinary Center for Security and Trust (SnT) at the University of Luxembourg, Dr. Gabriele Lenzini, provides a thorough and critical discussion on how the patterns generated by the shells may be used in secure authentication. The paper is Open Access, so please download and read it at http://www.nature.com/articles/srep26840 (and make sure to check the nice movies in the Supporting Information!).

Camila's article on cholesteric-isotropic phase transitions in cellulose nanocrystal suspensions published

Congratulations to Camila on her first scientific article since she joined our group: "Equilibrium Liquid Crystal Phase Diagrams and Detection of Kinetic Arrest in Cellulose Nanocrystal Suspensions" by Camila Honorato Rios, Anja Kuhnhold, Johanna Bruckner, Rick Dannert, Tanja Schilling, and Jan P.F. Lagerwall, is now published (open access) in Frontiers in Materials, section Biomaterials. In the article, we study the phase diagram and helical pitch behavior in the cholesteric phase of aqueous suspensions of cellulose nanocrystal (CNC) nanorods, as a function of mass fraction, surface charge and concentration of added inorganic salt. The study is a combined experimental and computer simulation thrust, where our group's experimental data are complemented by simulation results by Anja Kuhnold, in the group of Prof. Tanja Schilling. An unexpected—and very interesting—observation is that the nature of the cholesteric-isotropic phase transition appears to change with ionic strength of the solvent. While it is strongly first order, as expected for lyotropic liquid crystals of hard-rod colloids, at low ionic strength, the barrier between isotropic and cholesteric phase appears to decrease upon salt addition, such that the isotropic phase becomes increasingly turbid as the ionic strength is increased. This is what is illustrated in the image, the concentration written at the top of each vial referring to the added salt; the CNC mass fraction is the same in all vials. The phenomenon reminds of the strong light scattering typical of critical fluctuations, normally seen only in the vicinity of a second order phase transition. You can read and download the paper, without subscription (Frontiers of Materials is an open access journal), by clicking on this link.

Johanna moves on to a career in industry

We wish Dr. Johanna Bruckner best of luck for the next stage of her career, which will be at Bosch in Stuttgart, Germany. During her post-doc with us from August 2015 until the end of March 2016 she has done fantastic work on suspensions of cellulose nanocrystals in non-aqueous solvents (publications are on their way...) and she has been a wonderful group member. We will all miss her very much, but we are happy that she will surely meet exciting new challenges at her next work place.

Martin's article on the effect of gold nanoparticle doping on the dielectric properties of nematics on-line

Congratulations to Martin for the publication in J. Mater. Chem. C of his new paper on nematic liquid crystals doped with gold nanoparticles, entitled "Nanoparticles dispersed in liquid crystals: Impact on conductivity, low-frequency relaxation and electro-optical performance". The paper deals specifically with the effect of the nanoparticles on the dielectric and conductive behavior of the composite, finding that the doping has negligible effect on the permittivity as such, but it comes with an ionic contamination that leads to electrode polarization build-up and increased low-frequency conductivity. This means that the low-frequency electrooptic response is also negatively affected by the doping. Read the paper here.

Johanna gets best poster prize at the German-British liquid crystal conference

Congratulations to Johanna Bruckner, who was awarded the German Liquid Crystal Society's best poster award at the joint conference of the British and German liquid crystal societies, in Edinburgh, UK, 21-23rd of March 2016. The poster, entitled "Solvent effects on chiral nematic self‐assembly of cellulose nanocrystals" (co-authors Camila Honorator-Rios and Jan Lagerwall), describes the behavior of cellulose nanocrystal suspensions in non-aqueous but polar solvents, as well as a new method of exchanging the solvent without inducing aggregation of the rods. A publication is on the way...

JungHyun and Jan represent FSTC in THE advertisement

In an advertisement for the Faculty of Science, Technology and Communication (FSTC) of the University of Luxembourg in the last issue of the journal Times Higher Education, JungHyun and Jan are featured as representatives.

Anshul Sharma joins the ESMP team

The Experimental Soft Matter Physics group is now strengthened by a chemist, Dr. Anshul Sharma who recently defended her Ph.D. at Kent State University, under the supervision of Torsten and Elda Hegmann. She will work within the ERC project INTERACT on liquid crystal elastomers, in actuators produced by microfluidics and electrospinning. Welcome!!