Free Volume Element Sizes and Dynamics in Polystyrene and Poly(methyl methacrylate) Measured with Ultrafast Infrared Spectroscopy

• DOI: 10.1021/jacs.0c13397
• Publication Date: 2021-02-25T20:32:43Z
• Authors: Sebastian M. Fica...; David J. Hoffman; Junkun Pan; Chungwen Liang; Michael D. Fayer
• Keywords: Polystyrene; Poly(N-isopropylacrylamide)

The size, size distribution, dynamics, and electrostatic properties of free volume elements (FVEs) in polystyrene (PS) poly(methyl methacrylate) (PMMA) were investigated using the Restricted Orientation Anisotropy Method (ROAM), an ultrafast infrared spectroscopic technique. restricted orientational dynamics a vibrational probe embedded polymer matrix provides detailed information on FVE sizes their probability distribution. probe's vary as function its frequency within inhomogeneously broadened absorption spectrum. By characterizing degree restriction at different frequencies, radii distribution determined. PS has larger FVEs broader than PMMA. average PMMA are 3.4 3.0 Å, respectively. radius shows that is non-Gaussian, with tail to radii, whereas PMMA, closer Gaussian. structural previously unavailable through other techniques, occur ∼150 ps time scale both polymers. involve shape fluctuations which, average, conserve size. associated corresponding electric field strengths first-order Stark effect CN stretch probe, phenyl selenocyanate (PhSeCN). displayed unique measured for each strength. contrast, showed that, while correspond relatively weak fields, smallest map onto broad strong fields.