Dielectric and Fluorescent Probes To Investigate Glass Transition, Melt, and Crystallization in Polyolefins

Abstract

Investigation of glass transition dynamics in polyolefins by broadband dielectric spectroscopy (DRS) is facilitated by the addition of a novel dielectric probe, (4,4′-(N,N-dibutylamino)-(E)-nitrostilbene (DBANS), which introduces dipoles and made the polymers dielectrically active. For probe concentrations between 0.1% and 1.0% the dielectric strength ∆ associated with the dynamic glass transition increases proportionally to the probe concentration. This result indicates that the probe exhibits no intramolecular relaxations, and the probe rotational diffusion effectively senses the "microviscosity" of the probe environment on the length scale of the segmental dynamics. Temperature-dependent fluorescence spectroscopy on doped polymers shows no changes in fluorescence wavelength around the glass transition temperature. Crystallization and melting of the polyolefin matrix results in an increase or decrease of the probe concentration in the amorphous phase, which was clearly detected by real-time fluorescence because the probe emission is sensitive to the probe content, particularly at higher probe concentrations.

Threshold Temperature Sensors with Tunable Properties

“…Some examples of these stimuli include heat, [1][2][3][4][5][6][7][8][9] deformation, [10][11][12][13][14][15][16][17][18][19][20] chemicals, [21][22][23] light, [24][25][26] and others, [27,28] which make the sensors useful for a wide range of technologies. [29,30] We recently reported on a new class of polymers with built-in optical deformation [31][32][33][34][35] and threshold temperature [33,34,36] sensors.…”

Glass transition andα-relaxation dynamics of thin films of labeled polystyrene

“…As for the use of guest dipoles to enhance the dielectric response of a weak polar material, there are several reports in the literature [27,28,29,30,31,32,33]. Thus, it has been previously established that the incorporation of guest dipoles into a non-polar polymer is a useful method to enhance its dielectric strength.…”

Monitoring the cold crystallization of poly(3-hydroxy butyrate) via dielectric spectroscopy

“…Dielectric spectroscopy has widely been applied to monitor the kinetics of both cold and melt crystallization polar [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and non-polar [15] polymer systems. In isothermal cold crystallization experiments, i.e., annealing an amorphous sample above its glass transition temperature, T g , the changes occurring to the amorphous phase are analyzed in terms of reduction of the amorphous volume fraction (by following the drop in the dielectric strength of the structural relaxation process, De a ) and changes of the segmental mobility (in terms of shift of mean relaxation time of the a-relaxation, s a ); in an isothermal melt crystallization, i.e., holding a polymer melt at a temperature below the melting point, T m , the solidification of the liquid sample is monitored by studying the changes in the dielectric constant at higher (dipole relaxation) or lower frequencies (charge carriers relaxation).…”