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Temperature-ramping measurement of dye reorientation to probe molecular motion in polymer glasses
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Chemical structures of the three chromophores used in this study: 4,4-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene-3-dodecanoic acid (Bodipy C12), N,N -Bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarbox-imide (BTBP), and N,N -Dipentyl-3,4,9,10-perylenedicarboximide (DPPC). The double-sided arrow indicates the direction of the transition dipole moments of these dyes. (b) Chemical structures of the three polymers used in this study: polystyrene (PS), poly(4-tert-butyl styrene) (PtBS), poly(2-vinyl pyridine) (P2VP).

Image of FIG. 2.
FIG. 2.

Schematic of instrumental apparatus: P, Polarizer; BS, beam splitter; S, shutter; ND, neutral density filter; λ/2 (λ/4), half-(quarter-) wave retardation plate; DM, dichroic mirror; H, pinhole; PBS, polarizing beam splitter; FC, fiber coupling; APD, avalanche photodiode; V, valve.

Image of FIG. 3.
FIG. 3.

Wide field illumination image of bleached pattern used to measure reorientation of dye molecules; the hole in the TEM grid is tilted in the micrograph. Photobleached regions appear dark because less fluorescence originates from these regions. Numbers indicate measurement sequence: (1) z scan; (2) x scan; (3) y scan; (4) intensity measurement of bleached region (20 × 20 μm); (5) intensity measurement of unbleached region.

Image of FIG. 4.
FIG. 4.

Temperature-ramping anisotropy measurement of BTBP reorientation in PS. (a) Fluorescence intensity data from unbleached region (open symbols, sequence 5 from Fig. 3) and bleached region (closed symbols, sequence 4 from Fig. 3). (b) Anisotropy as a function of temperature, calculated from intensity data of panel (a) using Eq. (3).

Image of FIG. 5.
FIG. 5.

Temperature-ramped anisotropy measurements of BTBP reorientation in (a) PS and (b) PtBS, with different sample and measurement positions. Inset figures show (a) where the sample was placed along the z-axis and (b) where the measurement was performed relative to the TEM grid. Based upon these results, the sample temperature is known to within 1 K.

Image of FIG. 6.
FIG. 6.

(a) Bleach depth as a function of temperature for DPPC in PS in oxygen gas and under oxygen-free conditions. (b) Anisotropy decays for bleaching conditions described in panel (a).

Image of FIG. 7.
FIG. 7.

(a) Temperature profiles of single step (S) and multistep temperature-ramping anisotropy experiments on BTBP in PS. The numbered sequence defines the multistep temperature program: 340 K→ 378 K → 345 K → 390 K →345 K. (b) Anisotropy decays for BTBP in PS with the temperature programs indicated above.

Image of FIG. 8.
FIG. 8.

Anisotropy decays for BTBP in three polymers (points) acquired by increasing temperature at 2 K/min. The sample thicknesses were 3–5 μm. Ramping rate was 2 K/min. The solid lines indicate DSC data for these polymers acquired while heating at 10 K/min rate and analyzed as described in the text.

Image of FIG. 9.
FIG. 9.

Anisotropy decays for BTBP in freestanding PtBS thin films with thicknesses down to 22 nm. The temperature where the normalized anisotropy drops to the value of 0.5 is denoted as T 0.5.

Image of FIG. 10.
FIG. 10.

Anisotropy decays of different dyes in bulk polystyrene films. The vertical straight line indicates the glass transition temperature measured by DSC.

Image of FIG. 11.
FIG. 11.

Ramping rate dependence of the anisotropy decay for BTBP in PS. The vertical straight line indicates the glass transition temperature measured by DSC at 10 K/min.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Temperature-ramping measurement of dye reorientation to probe molecular motion in polymer glasses