Martin Luther University Halle-Wittenberg

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Institut für Physik - NMR

phone: +49 (0) 345 55 28551

Betty-Heimann-Str. 7
06120 Halle (Saale)

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P3S Webinar Archive

Below is a list of past events, including titles and abstracts. Recorded talks, pdf files of the presentations as well as Q+A are posted in the P3S Webinar Archive cloud folder .

Thursday, June 11, 2020, 4 pm CEST

Prof. Dr. Enrique D. Gomez

Dept. of Chemical Engineering, Penn State University, University Park, PA, USA

Local Chain Alignment Via Nematic Ordering Reduces Chain Entanglement in Conjugated Polymers

Abstract:
Conjugated polymers provide an opportunity to examine the role of  entanglement in melts of semiflexible polymers.  Given that liquid  crystallinity is ubiquitous in this class of materials, we examined the  role of nematic order on entanglement in a few model systems. The onset  of local chain alignment reduces entanglement, resulting in an order of  magnitude increase in the entanglement length.

Dr. Ryan C. Nieuwendaal

Materials Science and Engineering Division, NIST, Gaithersburg, MD, USA

An examination of OPV interfacial structures from REDOR NMR data and analysis

Abstract:
Structures in mixed amorphous phases control important OPV properties such fill factor and donor/acceptor interfacial area. Unfortunately, these regions are both difficult to measure because of their fine size scales and irregular packing patterns, and difficult to predict because there are numerous parameters that control the kinetics and thermodynamics of BHJ film formation. In this talk, I will give highlights of 13C-2H REDOR solid-state NMR measurements on a P3HT-PCBM BHJ film, and show that when paired with molecular dynamics simulations, important interfacial characteristics can be unveiled. Although, the structures that result from pairing solid-state NMR and MD simulations are not unique, we show that the donor/acceptor interfacial characteristics can be well-defined, which will be important for future work in predicting structures in mixed amorphous phases in general.

Thursday, June 25, 2020, 4 pm CEST

Prof. Dr. Michael R. Hansen / Steffen Böckmann

Institut für Physikalische Chemie, Universität Münster, Germany

How Molecular Packing and Conformation Translates into Function in π-Conjugated Polymers Revealed by Solid-State NMR

Abstract:
Polymers with extended π-conjugation may serve as organic semiconductors in various electron devices. Their function is established via solution processing, which results in active materials that are semi crystalline with no pronounced long-range ordering. This prevents the direct access to details about molecular organization, conformation, and packing from a conventional approach. Here, two examples will be given where small molecular changes lead to subtle changes in the performance of the respective π-conjugated polymers. The changes in performance are elucidated using a combination of experimental techniques, where the decisive molecular insights are provided from a multinuclear approach via one- and two-dimensional 1H, and 19F solid-state NMR experiments.

Prof. Dr. Yu Zhu

Dept. of Polymer Science, U Akron, OH, USA

Molecular Packing of π-Conjugated Molecules through Fused Hydrogen Bond-mediated Self-assembly

Abstract:
The molecular arrangement is pivot for charge transport in organic materials. Understanding the interplay between intermolecular interactions and crystal structure and being able to control it are essential to achieving the desired molecular packing, crystal structure and alignment/interconnection of the crystalline grains, enabling the control of charge transfer in organic materials. In this presentation, a fused hydrogen bond-mediated self-assembly was demonstrated to control the molecular packing of conjugated molecules. When hydrogen bonding sites are fused with the π-plane of the conjugated molecules, the orientations of hydrogen bonding and π-plane are directly related. Therefore, the directional characteristic of hydrogen bonding will guide the formation of π-π stacking in a specific direction, leading to the enhancement of charge transport.

Thursday, July 9, 2020, 4 pm CEST

Prof. Dr. Karen I. Winey

Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia

Self-Assembly of Segmented Polyolefin Ionomers:  New Morphologies and Ion Conductivity

Abstract:
Controlling the self-assembled nanoscale ionic aggregates in single-ion conducting polymers is a crucial step toward exceptional transport properties. We report a series of precisely-segmented polyethylene-like ionomers containing sulfonate groups (PES) with Li+, Na+, Cs+, or NBu4+ counterions synthesized from step-growth polymerization. At room temperature, the PES ionomers with 23 or 48 methylene units are semicrystalline with well-defined nanoscale ionic layers with spacings influenced by the spacer length and cation. In situ X-ray scattering measurements reveal that the layered ionic aggregates in PES23Li, PES23Na, and PES23Cs transform, upon melting the PE segments, into the Ia3 ̅d gyroid morphology. The gyroidal ionic aggregates in PES23Li and PES23Na further evolve into hexagonal symmetry as the temperature increases. These order-to-order transitions in ionic aggregate morphologies were also confirmed by oscillatory shear rheology. The ion transport behavior of these PES23 polymers is strongly dependent on the ionic aggregate morphologies. Specifically, the 3D interconnected gyroid morphology of PES23Li exhibits higher ionic conductivity than the isotropic layered or hexagonal morphologies. This innovative and versatile molecular design of ionomers leads to unprecedented percolated gyroidal ionic aggregate morphologies that provide a continuous pathway for improved ion transport.

Prof. Dr. Yefeng Yao

Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai

Suppressing crystallinity of semicrystalline polymer electrolyte by exploiting the ion concentration difference between the phase structures

Abstract:
Solid-state polymer electrolytes (SPEs) have attracted a lot of research interests for their promising applications in all-solid-state rechargeable batteries. Comparing with the ceramic electrolytes, the virtues of semi-crystalline SPEs lie on the superior elasticity and plasticity which are very crucial for the material processibility and recycle stability of the batteries. At the present time the practical application of SPE on the battery industry is limited by the low conductivity of SPE. Reducing the crystallinity has been approved to be an effective approach to improve the conductivity of SPE. In this work, we will present a novel and general way to reduce crystallinity of SPE by exploiting the ion concentration difference between the different phase structures in SPEs. We will show that we are able to prepare a complete amorphous PEO/Li+ SPE. Similarly, by controlling ion concentration difference between the different phase structures we could also prepare the PEO/Li+ crystals containing high content of defects. In such crystals, the segmental mobility is 2 orders higher than that of the normal PEO/Li+ crystals. Varied NMR techniques were performed to understand the structure and dynamics in the samples. The implications of this work on developing high conductive SPE are discussed afterwards.

Thursday, July 23, 2020, 4 pm CEST

Prof. Dr. Monika Schönhoff

Institute of Physical Chemistry, University of Münster, Germany

Electrophoretic NMR to determine ion mobilities and correlated ion transport in poly- and oligo-ethyleneoxide- based electrolytes

Abstract:

Ion transport in electrolyte materials, e.g. for Li ion batteries, is often influenced by the strong ion correlations in concentrated electrolytes. Commonly employed multinuclear (e.g. 1H, 7Li, 19F) Pulsed-Field-Gradient (PFG)-NMR diffusion is not sufficient to identify the conductivity contributions of specific ion species, since the electrophoretic mobility µ has to be known. Electrophoretic NMR (eNMR) allows to directly measure the electrophoretic mobility of ions with NMR-active nuclei. The lecture focusses on its application to polymeric and oligomeric (glyme) electrolyte systems. Drift velocities of ions and even of uncharged molecular components in the electric field can be identified and lead to conclusions on Li+ coordination and the role of anticorrelations of different ion species.

Prof. Dr. Bryan Vogt

Dept. of Chemical Engineering, Penn State University, University Park, PA, USA

Are ionomers ideal polymers for 3D printing via material extrusion?

Abstract:
3D printing has been used to address some medical supply shortages  during the COVID-19 pandemic with thermoplastics being used to craft  components for face shields, ventilators and various other personal  protective equipment and medical  supplies worldwide. Obtaining desired fit (shape accuracy) and function  (properties) for 3D printed plastics can be challenging. Here, I will  illustrate how ionomers can be readily 3D printed and how these printed  ionomers can produce new functionality and  significant improvements in properties. Some of the limitations of  material extrusion-based can be readily addressed with ionomers due to  their structure and dynamics.

Thursday, September 3, 2020, 4 pm CEST

Dr. Cedric Lorthioir

Laboratoire de Chimie de la Matière Condensée de Paris, Sorbonne Université, Paris

Topology and dynamical processes in polymer-based gels: An insight  from solid-state NMR

Abstract:
Continuous research efforts have been dedicated over the last decade to  design gel architectures with improved, and also tunable, mechanical  behaviors. The modeling of such properties is a non-trivial issue since  it involves both structural and dynamical descriptions related to  various length and time scales. Gel topology is one of the key  structural information that cannot be easily determined experimentally  while solid-state NMR appears as a well-suited and powerful approach to  probe both elastically active chains and defects. The gel mechanical  behavior is also influenced by dynamical processes occurring at  different length / time scales: the (global) chain dynamics on the one  hand, and the (more local) segmental motions on the other hand. Again,  solid-state NMR may provide an excellent opportunity to investigate  these motions, thus allowing correlations with the mechanical properties  to be determined. These features will be exampled and discussed through  two kinds of physical gels: hybrid (clay-based) hydrogels and ionic  organogels.

Prof. Dr. Costantino Creton

Laboratory of Soft Matter Science and Engineering, ESPCI Paris Tech

Polymer gels with permanent and dynamic bonds:  relationship between dynamics and large strain behavior and fracture.

Abstract:
In recent years there has a lot of interest in improving the resistance to fracture of hydrogels by modifying their network topology. One such toughening strategy has been to combine a population of permanent chemical crosslinks with a population of physical reconfigurable crosslinks. While the effect of dynamic crosslinks on linear rheology has been well studied, the large strain behavior and in particular the fracture behavior of the gels remains more complex and involves not only the dynamics but the change in network topology as bonds break. We will present some recent results and discuss some open questions on connecting molecular structure and fracture of gels.

Thursday, September 17, 2020, 4 pm CEST

Prof. Dr. Alexei Sokolov

U Tennessee, Knoxville

Designing Polymer Nanocomposites: Critical Role of the Interfacial Layer

Abstract:
In this talk we overview recent studies on structure and dynamics of the interfacial layer in various polymer nanocomposites (PNCs). We employ broad array of experimental techniques and MD-simulations that provide detailed characterization of the interfacial layer. These studies revealed a gradient in the interfacial layer dynamics, but no “glassy” or “dead“  layer. The thickness of the interfacial layer increases upon cooling to Tg, and depends strongly on polymer rigidity, increasing from ~2nm in flexible polymers to ~5 nm in more rigid ones. We discuss a possible connection of the interfacial layer thickness to the dynamic heterogeneity length scale. We emphasize usually overlooked dynamic property of the interfacial layer – strong suppression of the amplitude of structural relaxation on time scale of segmental dynamics. At the end, we present a general picture how microscopic parameters control the interfacial layer, and how by tuning the interfacial layer we can tune macroscopic properties of polymer nanocomposites.  

Prof. Dr. Linda Reven

McGill U, Montreal

Liquid Crystal Polymer Nanocomposites

Abstract:
Inorganic nanoparticles and polymers are being combined  with liquid crystals to both understand the effect of these additives on  liquid crystal properties and to create new hybrid materials.This  lecture will give an overview of our past and current studies, focusing  on the role of the polymer chain flexibility in producing stable  dispersions versus controlled phase separations.

Thursday, October 1, 2020, 4 pm CEST

Prof. Dr. Nitash Balsara

Chemical and Biomolecular Engineering, UC Berkely

Ion transport in polymer electrolytes for lithium batteries and electrophoretic NMR

Abstract:
I will discuss some of the fundamental factors that limit ion transport in polymers.  In all electrolytes, the current generated at steady state is governed by the applied potential.  This relationship, which one might call a modified Ohm’s Law, depends on Stefan-Maxwell diffusion coefficients.  We find that these diffusion coefficients in many electrolytes are negative over a substantial salt concentration range.  The relationship between Stefan-Maxwell diffusion coefficients and ion velocities measured by electrophoretic NMR will be discussed.  

Prof. Dr. Lou Madsen

Dept. of Chemistry, Virginia Tech, Blacksburg

Tracking motions in soft materials by NMR diffusometry: Discoveries and dangers

Abstract:
Our group combines NMR  transport measurements that are species-specific and length/time-scale  specific with structural and dynamical information to build  comprehensive models for the behaviors of soft materials.   I will touch on transport phenomena in polymer-based systems that  include nanometer-scale confinement in separations membranes, and drug  and chain partitioning in micelles.  I will also describe a few of the  classic (and yet still ubiquitous) pitfalls in the  interpretation of NMR diffusion data.

Thursday, October 15, 2020, 4 pm CEST

Dr. Whitney Loo

(Chemical and Biomolecular Engineering, UC Berkely)
(U Chicago)

Polymer dynamics in block copolymer electrolytes detected by neutron spin echo spectroscopy

Abstract:
We investigated the effect of salt concentration on the  polymer dynamics of a nanostructured block copolymer electrolyte on the  0.1-100 ns time-scale using the Rouse and reptation tube model. In this  talk, I will demonstrate how quantifying chain motion in the presence of  ions is essential for predicting the behavior of  polymer-electrolyte-based batteries operating at large currents.

Prof. Dr. Michael Vogel

Dept. of Physics, Solid-State Physics, Technische Universität Darmstadt

NMR studies of rotational and translational diffusion in polymer electrolytes and ionic liquids

Abstract:
In my talk, I will combine manifold NMR methods to study rotational dynamics and translational diffusion in polymer electrolytes and ionic liquids in broad ranges of time and length scales. In particular, I will discuss to which extent nanoscopic concentration fluctuations in these mixtures affect the relation of local and diffusive dynamics for the individual constituents and, thus, the transport mechanisms.

Thursday, October 29, 2020, 3 pm CET

Prof. Dr. Mitsushiro Shibayama

Institute for Solid State Physics, University of Tokyo

DLS Studies of Speckle-free gels and Crowed Microgels

Abstract:
Dynamic light scattering (DLS) is a powerful tool for investigations of the dynamics of complex fluid systems. Here, we report DLS studies of polymer gels and microgels, which are non-ergodic and characterized by strong speckles in light scattering originating from frozen-concentration fluctuations in the gel. It has been believed that the appearance of speckles is inherent for polymer gels. Recently, however, we developed speckle-free gels which do not show any change in both static and dynamic scattering while they undergo rheological sol-gel transition. The strategy for the preparation of speckle-free gels will be discussed. The second topic is a DLS study of microgels in a wide concentration range from dilute to concentrated across a jamming transition, achieved by using tens-nanometer sized microgels which do not scatter light. Universal/specific features of time-intensity correlation functions in complex fluid systems will be discussed.

Dr. Todd M. Alam

Dept. of Organic Material Sciences, Sandia Nat'l Laboratories, Albuquerque

Exploring High Resolution Magic Angle Spinning (HRMAS) NMR Diffusometry in Swollen Polymers and Gels

Abstract:
In this presentation I will describe our efforts in combining high resolution magic angle spinning (HRMAS) NMR spectroscopy and pulse field gradient (PFG) NMR diffusometry techniques to measure mixtures in swollen polymer materials. Magnetic susceptibility differences for liquids absorbed in heterogenous materials are significant, but MAS efficiently suppresses these differences resulting in dramatic improvements of the NMR spectral resolution, thereby allowing the use of PFG NMR diffusion experiments to probe multiple chemical environments simultaneously. I will discuss a few examples of successes in 1H HRMAS NMR diffusometry, as well as some caveats.

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