Rotational Dynamics of a Probe in Rubbery Polymers Characterized by Time‐Resolved Fluorescence Anisotropy Measurement

Abstract

The rotational relaxation time (τrot) of a fluorescent molecule, coumarin 153 (C153), dispersed in different rubbery polymers is characterized by time‐resolved fluorescence anisotropy measurement, and an attempt is made to quantitatively combine it with the segmental relaxation time (τseg) of the corresponding matrix polymer obtained by dielectric relaxation spectroscopy. This study here demonstrates that τseg extrapolated to higher temperatures using the Vogel–Fulcher–Tammann law can be superimposed on τrot, resulting in a single curve. This behavior is common for polymers with different glass transition temperatures such as polyisoprene and acrylonitrile/butadiene copolymer, implying that the rotational dynamics of C153 is a useful tool for the characterization of polymer dynamics.

Dynamics Gradient of Polymer Chains near a Solid Interface

“…TRFA is effective for characterizing the segmental dynamics of polymers in a short time range from a few to tens of nanoseconds. 51 Thus, combining TRFA with DRS enables us to gain access to the segmental dynamics of adsorbed chains in a long time range. 51 In TRFA measurements, a small amount of fluorescent probes is dispersed into a polymer matrix and the fluorescence anisotropy, which is related to the polymer dynamics, is tracked as a function of time.…”

“…51 Thus, combining TRFA with DRS enables us to gain access to the segmental dynamics of adsorbed chains in a long time range. 51 In TRFA measurements, a small amount of fluorescent probes is dispersed into a polymer matrix and the fluorescence anisotropy, which is related to the polymer dynamics, is tracked as a function of time. When exciting laser pulses were guided into a sample from the solid side at an incident angle (θ) smaller and larger than the critical angle (θ c ) related to the total reflection, respectively, they crossed the bulk region and totally reflected at the interface, as schematically illustrated in the inset of Figure 1a.…”

“…A brief description of the fitting procedure is provided in the SI, and more details can be found in our previous report. 51 Panels (a) and (b) of Figure 1 show τ values for PI and NBR as a function of temperature both in the bulk and in the interfacial regions, respectively. The temperature on the abscissa was subtracted by the T g b for each polymer.…”

“…It was previously confirmed that both TRFA and DRS data for bulk polymers could be well superimposed on the temperature versus relaxation time relationship. 51 Extending this knowledge to the interfacial data obtained by TRFA and DRS, the temperature-dependence of the relaxation time can be broadened. Interfacial chains exhibited a slower relaxation time than the bulk one by approximately 2 orders as the temperature approached the T g b .…”

“…As a fluorescent probe, coumarin 153 (C153) was purchased from Sigma-Aldrich Co. LLC and used as received. Precipitated SiO 2 nanoparticles (Nipsil AQ, Nippon Silica, Japan), with an average diameter of 18 nm, were also provided by Bridgestone Corp. For TRFA, thin films of PI and NBR containing a small amount of C153 were prepared from tetrahydrofuran solutions by a solvent-casting method onto a LiNbO 3 prism coated with a 7 nm thick SiO 2 layer beforehand . For DRS, neat polymers and polymer matrices filled with different fractions of SiO 2 nanoparticles were used.…”