Suppression of segmental chain dynamics on a particle's surface in well-dispersed polymer nanocomposites

Kim, J.*; Thompson, B. R.*; Tominaga, Taiki*; Osawa, Takahito; Egami, Takeshi*; Frster, S.*; Ohl, M.*; Senses, E.*; Faraone, A.*; Wagner, N. J.*

ACS Macro Letters (Internet), 13(6), p.720 - 725, 2024/06

https://doi.org/10.1021/acsmacrolett.4c00168

The Rouse dynamics of polymer chains in model nanocomposite PolyEthylene Oxide (PEO)/Silica NanoParticles (NPs) was investigated using QuasiElastic Neutron Scattering (QENS). The apparent Rouse rate of the polymer chains decreases as the particle loading increases. However, there is no evidence of an immobile segment population on the probed time scale of tens of ps. The slowing down of the dynamics is interpreted in terms of modified Rouse models for the chains in the NP inter-phase region. Thus, two chain populations, one bulk like and the other characterized by a suppression of Rouse modes, are identified. The spatial extent of the interphase region is estimated to be about twice the adsorbed layer thickness, or about 2 nm. These findings provide a detailed description of the suppression of the chain dynamics on the surface of NPs. These results are relevant insights on surface effects and confinement and provide a foundation for the understanding of the rheological properties of Polymer NanoComposites (PNCs) with well-dispersed NPs.

Relationship between viscosity and acyl tail dynamics in lipid bilayers

Nagao, Michihiro*; Kelley, E. G.*; Faraone, A.*; Saito, Makina*; Yoda, Yoshitaka*; Kurokuzu, Masayuki*; Takata, Shinichi; Seto, Makoto*; Butler, P. D.*

Physical Review Letters, 127(7), p.078102_1 - 078102_7, 2021/08

https://doi.org/10.1103/PhysRevLett.127.078102

Neutron spin-echo studies of the structural relaxation of network liquid ZnCl at the structure factor primary peak and prepeak

Luo, P.*; Zhai, Y.*; Leao, J. B.*; Kofu, Maiko; Nakajima, Kenji; Faraone, A.*; Zhang, Y.*

Journal of Physical Chemistry Letters (Internet), 12(1), p.392 - 398, 2021/01

https://doi.org/10.1021/acs.jpclett.0c03146

Using neutron spin-echo spectroscopy, we studied the microscopic structural relaxation of a prototypical network ionic liquid ZnCl at the structure factor primary peak and prepeak. The results show that the relaxation at the primary peak is faster than the prepeak and that the activation energy is % higher. A stretched exponential relaxation is observed even at temperatures well-above the melting point . Surprisingly, the stretching exponent shows a rapid increase upon cooling, especially at the primary peak, where it changes from a stretched exponential to a simple exponential on approaching the . These results suggest that the appearance of glassy dynamics typical of the supercooled state even in the equilibrium liquid state of ZnCl as well as the difference of activation energy at the two investigated length scales are related to the formation of a network structure on cooling.

Spatial scale dependence of diffusion process in glass-forming liquids

Kofu, Maiko; Faraone, A.*; Tyagi, M.*; Nagao, Michihiro*; Yamamuro, Osamu*

no journal, , 

The self-diffusion of molecules in a liquid is basically governed by Fick's law. It is known that the self-part of the van Hove correlation function is written as the Gaussian function with respect to and decays exponentially with time (Debye relaxation). In the case, the relaxation time obeys the relation . In glass-forming materials, however, the relaxation process is often described by the non-Debye KWW function, . A natural question arises as to whether the relation is valid for the non- Debye diffusion process. To address this issue, we have investigated in detail the -dependence of the relaxation times for two different types of liquid, a molecular liquid (3-methylpentane) and an ionic liquid (C4mimTFSI). The measurements were done using neutron spin echo, backscattering and chopper spectrometers at NIST. Two crossover points were clearly found. The first crossover can be due to coupling with structural relaxation and the second one is Gaussian to non-Gaussian transition. This is the first clear experimental evidence for the two crossover.

Dynamics of atomic hydrogen in bulk and nanocrystalline palladium

Kofu, Maiko; Hashimoto, Naoki*; Akiba, Hiroshi*; Kobayashi, Hirokazu*; Kitagawa, Hiroshi*; Tyagi, M.*; Faraone, A.*; Copley, J.*; Lohstorh, W.*; Iida, Kazuki*; et al.

no journal, , 

no abstracts in English