DOI: 10.1073/pnas.2003225117
论文题名: Amorphous polymer dynamics and free volume element size distributions from ultrafast IR spectroscopy
作者: Hoffman D.J. ; Fica-Contreras S.M. ; Fayer M.D.
刊名: Proceedings of the National Academy of Sciences of the United States of America
ISSN: 0027-8424
出版年: 2020
卷: 117, 期: 25 起始页码: 13949
结束页码: 13958
语种: 英语
英文关键词: Dynamics
; Free volume
; Polymers
; Stark effect
; Ultrafast IR spectroscopy
Scopus关键词: cyanic acid derivative
; methacrylic acid derivative
; phenyl selenocyanic acid
; poly(methylmethacrylic acid)
; unclassified drug
; absorption spectroscopy
; analytic method
; anisotropy
; Article
; controlled study
; density functional theory
; electric field
; Fourier transform infrared spectroscopy
; free volume element size
; hydrogen bond
; molecular size
; priority journal
; probability
; room temperature
; vibration
; vibrational frequency
英文摘要: A method for measuring the size and size probability distribution of free volume regions in polymeric materials using ultrafast infrared (IR) polarization-selective pump-probe experiments is presented. Measurements of the ultrafast dynamics of a vibrational probe (the CN stretch of phenyl selenocyanate) in poly(methyl methacrylate) show that the probe dynamics are highly confined. The degree of confinement was found to be both time-dependent and dependent on the vibrational frequency of the probe molecule. The experiments demonstrate that different vibrational frequencies correspond to distinct subensembles of probe molecules that have different dynamic properties determined by their local structural environments. By combining the degree of dynamical confinement with the molecular size of the probe molecule, the free volume element size probability distribution was determined and found to be in good agreement with the best established experimental measure of free volume. The relative probability of a free volume element size is determined by the amplitude of the nitrile absorption spectrum at the frequency of the measurement. The inhomogeneous broadening of the spectrum was linked to the vibrational Stark effect, which permits site selectivity. The observed dynamics at each frequency were then associated with a different size free volume element and distinct local electric field. The multiple timescales observed in the pump-probe experiments were connected to local structural fluctuations of the free volume elements. © 2020 National Academy of Sciences. All rights reserved. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/163457
Appears in Collections: 气候变化与战略
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作者单位: Hoffman, D.J., Department of Chemistry, Stanford University, Stanford, CA 94305, United States; Fica-Contreras, S.M., Department of Chemistry, Stanford University, Stanford, CA 94305, United States; Fayer, M.D., Department of Chemistry, Stanford University, Stanford, CA 94305, United States
Recommended Citation:
Hoffman D.J.,Fica-Contreras S.M.,Fayer M.D.. Amorphous polymer dynamics and free volume element size distributions from ultrafast IR spectroscopy[J]. Proceedings of the National Academy of Sciences of the United States of America,2020-01-01,117(25)