Joint Virtual Workshop on
Soft Matter Physics and Self-Assembly
and
Panel Discussion on the Life of a PhD Candidate
April 13
th2021, 9:00–13:00
Experimental Soft Matter Physics Group, University of Luxembourg
Physics of Living Matter Group, University of Luxembourg
Soft Matter and Liquid Crystals Group, University of Stuttgart
Theoretical Soft Matter and Biophysics Group, University of Magdeburg
Program
About the panel discussion
Our four panelists, young enough to have their Ph.D. life in fresh memory, yet old enough to have
experience of searching for jobs beyond Ph.D. and of supervising Ph.D. candidates, will start the
discussion by bringing up some issues that they believe are worth discussing, from the best aspects
of Ph.D. life to the most stressful moments of a Ph.D. candidate or a young post-doc. Topics can
range from the recruitment of Ph.D. candidates, via the research challenges of a Ph.D. project,
difficulties in English, culture shock, mismatch in expectations, to the benefits and/or concerns of
“Ph.D. afterlife”, i.e., the stage that begins with a successful Ph.D. defense. These are just some
examples; all issues are welcome for discussion. For all the topics, the role of the supervisor and the
interplay between candidate and supervisor, as well as between PhD. candidates, and between Ph.D.
candidates and post-docs, will be central themes.
We hope that the panelists’ initial analysis will kick off a lively discussion, and all participants are
welcome to bring up topics for discussion, and/or comment on what has been said, via the chat. The
host of the workshop, Jan Lagerwall, will act as a moderator. Our hope is to be able to summarize
the discussion at the end with a list of ‘best practices’ and perhaps highlight issues that may not
always get the attention they deserve.
8:50–9:00
Jan Lagerwall
Welcome address.
9:00–9:35
Johanna Bruckner Lyotropic Liquid Crystals as Direct Templates for
Highly Defined Nanostructured Materials.
9:35–10:10
Irvine Ong
Toward an interdisciplinary approach for creating
novel functionalized interfaces and bioassays.
10:10–10:20
Break
10:20–10:55
Kirsten Harth
Drop Impact on Hot Plates:
Contact, Rupture and the Leidenfrost Transition.
10:55–11:30
Yong Geng
Selective Reflectors from Self-Assembled
Cellulose Nanocrystals Confined in shell geometry.
11:30–11:40
Break
11:40–12:00
Panelist thoughts on Ph.D. education.
Lyotropic Liquid Crystals as Direct Templates for
Highly Defined Nanostructured Materials
Johanna R. Bruckner
[email protected]
Institute of Physical Chemistry, University of Stuttgart,
Pfaffenwaldring 55, 70569 Stuttgart, Germany
Lyotropic liquid crystals spontaneously self-assemble when mixing surfactants with water. Depending on the composition, various structures such as 1D lamellar, 2D hexagonal, 3D cubic or helical phases form in which the structural parameters are well defined over the whole macroscopic sample volume. If we add a polymer precursor to the aqueous phase and polymerize it, we can transfer these filigree structures into solid materials. Afterwards, we remove the surfactant by calcination or solvent extraction and obtain a highly ordered mesoporous material, which may be used for applications such as energy storage and conversion, adsorption and separation, production of nanoparticles or nanowires and heterogeneous catalysis.
Compared to similar materials prepared by a conventional preparation process from diluted surfactant solutions, we find that our materials exhibit two very intriguing structural differences: 1) they consist of well-defined monodomains with spatial extensions of at least several hundreds of nanometers and 2) they possess a much narrower distribution of the pore diameters, which follows a Gaussian. To obtain an in-depth understanding of the templating process, we monitored the structural changes throughout the process and found that an intermediary formed liquid crystal phase is crucial for its success. We showed that there is a direct and quantifiable correlation between the structural parameters of the lyotropic liquid crystalline parent system and the produced mesoporous material, which enables a predictive synthesis of new materials from known liquid crystal systems. Furthermore, we explore the possibility of tailoring the structures with the help of additives and investigate the use of cellulose nanocrystals as chiral templates.
Toward an Interdisciplinary Approach for Creating
Novel Functionalized Interfaces and Bioassays
Irvine Ong
[email protected]
University of Luxembourg, Department of Physics & Materials Science
Functional interfaces are intriguing, both fundamentally and for their potential applications. During this talk, I will illustrate the richness of functional interfaces by highlighting the inherent interdisciplinarity of this field of research, with specific examples from my ongoing research.
First, I will describe how combining the molecular responses of liquid crystals towards surfaces’ chemical compositions with the specificity of peptides can provide a feasible and generic approach towards biosensor development. Going beyond solid interfaces, I will introduce design and synthesis concepts of functional surfactants that bestow specificity to fluid interfaces, thereby creating selective fluid interfaces to modulate specific transport of small molecules across immiscible fluid phases. I will conclude by showcasing how these concepts are key to uncovering active microbial interactions at dynamic interfaces, and in tailoring the phase transition dynamics of passive liquid crystals within strict microfluidic constraints.
Fundamental phenomena and applications of functional interfaces. 1–4 (Image on “Molecular Orientation” courtesy of Prof. Anupam SENGUPTA).
1. Ong, L. H. & Yang, K. L. Surfactant-Driven Assembly of Poly(ethylenimine)-Coated Microparticles at the Liquid Crystal/Water Interface. J. Phys. Chem. B 120, 825–833 (2016).
2. Ong, I. L. H. & Yang, K.-L. Recent developments in protease activity assays and sensors. Analyst 142, 1867–1881 (2017).
3. Ong, I. L. H. & Amstad, E. Selectively Permeable Double Emulsions. Small 15, 1–12 (2019).
4. Sharma, A., Ong, I. L. H., Sengupta A. Time Dependent Lyotropic Chromonic Textures in Microfluidic Confinement. Crystals 11, 35 (2021).
Drop Impact on Hot Plates:
Contact, Rupture and the Leidenfrost Transition
Kirsten Harth
[email protected]
Institut für Physik, Otto-von-Guericke Universität Magdeburg, Germany
Everyone who poured water into a hot pan has experienced the manifold boiling behaviours of drops impacting on a hot plate, a problem which is of high relevance in many technical applications. When the drop is gently deposited, and the surface temperature is sufficiently high, it hovers on a vapour layer (Leidenfrost effect). For impacting drops, this critical temperature for a contact-less rebound is substantially increased, and much harder to determine. In fact, determining contact times between drops and smooth substrates from side view imaging is impossible for most temperatures above the boiling point—the vapor layer is too thin, and the dynamics too fast to be followed.
We combine High-Speed Total Internal Reflection and synchrotron X-Ray measurements to reliably determine contact times and the Leidenfrost temperature for drops impacting on smooth hot surfaces. Standard side-view X-ray data provide information about the height evolution of bubbles and vapor layers on the scale of tens of micrometers, while FTIR allows to probe the wetting and sub-micron height-scale structures. With increasing plate temperature, we find localized bubble formation and coalescence, oscillatory wetting with repeatedly collapsing central vapor domes, finally only localized and delayed contacts causing oscillations of the liquid-vapour interface. In the Leidenfrost regime, the initial vapour layers grow calmly, until capillary waves emerge under retracting drops.
Beyond the focus on wetting and vapour layer characteristics, we study the time until lift-off of our drops from the heated substrates. A local minimum in lift-off times, smaller than expected from theory, correlates with spontaneous lamella rupture and the morphology of the contact.
Selective Reflectors from Self-Assembled
Cellulose Nanocrystals Confined in shell geometry
Yong Geng
[email protected]
University of Luxembourg, Department of Physics & Materials Science
Fabricating of well defined self-assembled structures from drying a suspension or a solution is an attractive and powerful concept for advanced materials design, but it is challenging due to the complex combination of physical phenomena in the dynamic process. These include, e.g., flows, phase transitions, phase separation, kinetic arrest and volume shrinkage. Additionally, the self-assembly process continuously responds to the changing conditions up to the point of kinetic arrest. Here we confine a cholesteric liquid crystalline suspension of cellulose nanocrystals (CNCs) into a shell shape, by which a well defined single domain structure is obtained after relaxation, with the cholesteric helix axis uniformly in the radial direction. Due to the shrinkage during drying around an incompressible inner core liquid, the shell ruptures, leaving behind a punctured solid spherical shell with well ordered self-assembled structure. As the helix period shrinks to values giving rise to a visible optical band-gap, the shells become wavelength- and polarization-selective retroreflectors that are biocompatible. Our study provides a new strategy to fabricate functional particles through controlled self-assembly from anisotropic colloids or polymers without collapse, with a different drying mechanism compared to flat films or droplet geometries. This opens a window for new applications of bioderived materials like cellulose.
(a) Suspensions of CNCs in water with increasing concentration from left to right, triggering phase separation from isotropic to cholesteric phase. (b) Fingerprint texture from a cholesteric CNCs suspension. (c) Microfluidic shell production. (d) Cholesteric CNC suspension shell with single domain structure after hours of relaxation. (e) SEM image of dried shell. (a), (b) and (d) are obtained between crossed polarizers, (d) with a lambda plate inserted.
Johanna Bruckner studied chemistry at the University of Stuttgart and worked on
her PhD thesis in the group of Prof. Frank Giesselmann, in which she found a first example of a lyotropic SmC*-analog. After finishing her PhD in 2015, she did an eight months post-doc in the group of Prof. Jan Lagerwall at the University of Luxembourg, studying the properties of cellulose nanocrystals in non-aqueous solvents. She then worked at the Robert Bosch GmbH, developing assembly and interconnection technologies, before she came back to academia in 2018 to join the cooperative research center 1333 at the University of Stuttgart. Johanna Bruckner won several prizes and scholarships, among others from the International Liquid Crystal Society and the state of Baden-Württemberg. Her research interests are lyotropic liquid crystals, functional materials and nature-inspired design.
Irvine Ong completed his B.Eng and PhD in Chemical & Biomolecular
Engineering at Nanyang Technological University (NTU, Singapore) and National University of Singapore (NUS), respectively. In his PhD under the supervision of Prof. Kun-Lin YANG, he developed bio-functionalized surfaces that were applied within liquid crystals- (LCs)-based systems for biosensing and fundamental studies. After his PhD, he worked in an NUS-based start-up company, where he scaled-up emulsion production platforms for pharmaceutical and cosmetic applications. In 2018, he moved to École Polytechnique Fédérale de Lausanne (EPFL, Switzerland) as a Postdoctoral Researcher under the supervision of Prof. Esther AMSTAD, where he designed and synthesized functional surfactants for the selective transport of small molecules in-and-out of core-shell emulsion structures (or double emulsions). In 2019, he moved to the Physics of Living Matter Group in University of Luxembourg for his 2nd Postdoctoral position, under the supervision of Prof. Anupam SENGUPTA, to develop an interdisciplinary approach to the study the behaviour of microbial populations, which are complex active fluids, in the vicinity
of particulate matter (e.g., microplastics), alongside understanding the complementary response of complex passive fluids (e.g., LCs) to geometric interfaces. In 2020, he received a Marie Skłodowska-Curie Actions-Individual Fellowship (MSCA-IF) to continue his research in Sengupta Lab on microbe-microplastic interactions in the context of the ocean ecology.
Kirsten Harth is a researcher at the Institute for Physics at the Otto-von-Guericke
University Magdeburg in Germany. Her research interests span from fluid mechanics including drop impact on complex substrates, the influence of complex surface properties on drop and bubble relaxation and dynamics of an-(isotropic) fluid membranes, over pattern formation and dynamics in liquid crystals to granular matter. Her research is mostly experimental, with involvement in several experiments performed in micro-gravity, but also includes numerical modeling of bubble shape relaxation and flow in quasi two-dimensional membranes. She received her Diplomas in Physics and Mathematics, as well as a Doctorate in Physics from the Otto-von-Guericke University Magdeburg, and spent almost 3 years in the Physics of Fluids Group of D. Lohse at the Max Planck Center and
University of Twente, with major interest in the dynamics of impacting drops. In 2019, she returned to Magdeburg to pursue her own project on Drop Impact on Soft (Adaptive) Substrates of the Priority Programme 2171 funded by the German Research Foundation.
Yong Geng studied physics from 2001 to 2009 for Bachelor and Master degrees in
China, followed by a PhD (2010-2013) in materials science from the New University of Lisbon, Portugal, in the group of Prof. Maria Helena Godinho. After a short post-doc in the Godinho group he moved to Magdeburg, Germany, for a one-year post-doc in Prof. Ralf Stannarius’s group, working with Alexey Eremin. Dr. Geng is currently a senior post-doc in the Experimental Soft Matter Physics (ESMP) group of Prof. Jan Lagerwall at the University of Luxembourg, which he first joined in 2015, staying until September 2017. After a 1.5-year interruption working as Assistant Professor in China, he rejoined the ESMP group. His research interests cover structures of nematic and chiral nematic liquid crystal in different geometries, optical properties of cholesteric liquid crystals, and liquid crystalline networks.
