Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F01: Broadband Dielectric Spectroscopy and its Applications in Materials ResearchInvited Live
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Sponsoring Units: DPOLY Chair: Joshua Sangoro, University of Tennessee |
Tuesday, March 16, 2021 11:30AM - 12:06PM Live |
F01.00001: Density scaling and isochronal superposition in liquids -- combining neutrons and dielectric spectroscopy Invited Speaker: Kristine Niss By using a high pressure cell designed for simultaneous dielectric spectroscopy and neutron scattering, we have studied the pressure and temperature dependent dynamics in a handful of different glass-forming liquids including van der Waals liquids, hydrogen bonding liquids and a room temperature ionic liquid. Combining dielectric spectroscopy and quasielastic neutron scattering gives access to time scales from pico- to kilosecond and make it possible to follow the relaxation dynamics in the liquid from above the melting point and all the way down to the glass transition. Moreover, the neutron scattering data give information on the boson peak and fast relaxation in the deeply supercooled liquid. The data is analysed in view of the so-called isomorph theory which predicts the existence of lines in the temperature-pressure phase diagram where dynamics is invariant both in terms of time scale and spectral shape. Put in other words: density scaling and isochronal superposition are predicted by isomorph theory. Isomorph theory is only expected to hold in liquids without directional bonds, nevertheless the predictions hold to a very large extend in all the studied liquids, particularly in the high temperature / low pressure region. |
Tuesday, March 16, 2021 12:06PM - 12:42PM Live |
F01.00002: How macromolecules penetrate narrow pores Invited Speaker: George Floudas Herein we address the question of how macromolecules penetrate narrow pores relevant in several applications. In particular, we follow the polymer dynamics in situ at the chain length scale by studying the evolution of normal modes in the type A polymer polyisoprene (PI) during imbibition in nanopores. The specific scientific question we address is, if and how, adsorption affects the imbibition kinetics of polymers. This question, despite of importance in the design of membranes/devices, has not been addressed so far. It requires precise measurements of polymer dynamics during flow. Herein we follow the details of polymer imbibition in situ by employing the nanofluidic method. The latter provides simultaneous access to (i) the kinetics of imbibition, (ii) the molecular dynamics and (iii) the viscosity experienced by the polymer during flow. Results show that polymer imbibition proceeds in two time-regimes with higher effective viscosity than in bulk. We discuss this finding with the help of a microscopic picture that considers the competition from an increasing number of chains entering the pores and a decreasing number of fluctuating chains with time. The latter provide unambiguous evidence for increasing adsorption sites during flow. In a second step we investigate the imbibition of PI blends in the same nanopores. We show that a homogeneous mixture composed of long and short PI chains phase separates on entering the pores by the different imbibition speeds of the respective chains and evaluate the dynamics at the chain length scale. |
Tuesday, March 16, 2021 12:42PM - 1:18PM Live |
F01.00003: Interfacial dynamics and mechanics of polymer nanocomposites through broadband dielectric spectroscopy and rheology Invited Speaker: Shiwang Cheng The inclusion of nanoparticles (NPs) to polymer matrices not only introduces mechanical modifiers but also brings hierarchical interactions between the polymer and NPs. The large surface area of the NPs and the strong nanoconfinement effect among NPs significantly modifies the structure and dynamics of the matrix polymer that are the key for the advanced macroscopic properties of PNCs. In this contribution, we present the recent development of broadband dielectric spectroscopy (BDS) on quantifying the dynamics of PNCs, spanning from the secondary relaxation to the chain dynamics. Special focus will be given to the dynamics of the polymers at the interface between the polymer matrix and NPs. Additionally, the recent studies of combining the BDS with rheology to unravel the desorption dynamics as well as the mechanical properties of the polymer at the interface will also be discussed. |
Tuesday, March 16, 2021 1:18PM - 1:54PM Live |
F01.00004: Applications of Linear and Nonlinear Dielectric Spectroscopy Invited Speaker: Ranko Richert Dielectric relaxation spectroscopy has provided an enormous body of information on the dynamics and structure of liquids, supercooled liquids, and glasses. Covering the range of about 20 orders of magnitude in time or frequency, very different types of materials can be studied, which translates into a large temperature window across which relaxation processes can be observed. Due to the high resolution of this technique, subtle residual mobility of molecules in glasses and very thin films can be measured. |
Tuesday, March 16, 2021 1:54PM - 2:30PM Live |
F01.00005: Molecular Dynamics of Janus Polynorbornenes: Glass transitions and Nanophase separation Invited Speaker: Andreas Schoenhals For the first time, dielectric and calorimetric investigations of an homologous series of Janus polynorbornenes with rigid main backbones and flexible -Si(OR)3 side groups, of differing length alkyl chains (R = Propyl, Butyl, Hexyl, Octyl, Decyl) is reported. Generally, this class of polymers has some potential for applications in the field of gas separation membranes. Two dielectrically active processes are observed at low temperatures, denoted as β- and α- relaxation. The former can be assigned to localized fluctuations, whilst the latter is related to the glassy dynamics of the flexible -Si(OR)3 side groups, creating a nanophase separation in both the alkyl chain rich and backbone rich domains. This is confirmed through temperature modulated DSC measurements and X-ray scattering experiments. The glass transition temperatures of the backbone rich domains, which are beyond or near to their degradation temperatures in terms of conventional DSC, are determined for the first time using Fast Scanning Calorimetry employing both fast heating and cooling rates. This is complimented with scattering experiments that show how the size of the alkyl chain rich domains increases with chain length. Alongside these results, a significant conductivity contribution was observed for all poly(tricyclononenes) with -Si(OR)3 side groups, which is interpreted in terms of a percolation model. |
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