Microscopic dynamics of the glass transition investigated by time-resolved fluorescence measurements of doped chromophores

Abstract

The microscopic dynamics of several monomeric and polymeric glass-forming materials has been investigated by time-resolved fluorescence measurements of doped malachite green molecules in a wide temperature region. For monomers, 1-propanol, propylene glycol, and glycerol, and a polymer without side chains, polybutadiene, the temperature dependence of nonradiative decay time of doped malachite green molecules behaves in a similar way through the glass-transition region. Besides a kink around the calorimetric glasstransition temperature T g , another crossover at a critical temperature T c about 30-50 K above T g has been clearly observed. This experimental finding is in agreement with the prediction of the mode-coupling theory that a dynamical transition exists well above T g . On the other hand, for the complex polymers with side chains, poly͑vinyl acetate͒, poly͑methyl acrylate͒, and poly͑ethyl methacrylate͒, the crossover at T g is less pronounced than those for the monomers and the polymer without side chains. Moreover, although we could not distinguish any singularities above T g for these complex polymers, we observed another kink below T g , which may be attributed to the side-chain motions. ͓S0163-1829͑97͒02333-3͔

Probing the cooperative dynamics varying the side-chain length of poly(alkyl acrylate)s: ESR experiments

“…that also were found to work in other ESR studies by us [14][15][16][17], and also with other kinds of probe spectroscopy [11].…”

“…For all the investigated samples, the crossover between the two regimes takes place at a temperature C T located in the range 1.15-1.25T g (see table 5) that well agrees with the critical temperature range of the mode coupling theory [30], and with related recent experimental studies [7] in polymers. In this temperature interval, crossovers between different dynamic regimes in glass-formers are also a current finding of various spectroscopies [5,6,11,12]. The above result on PAAs intrigues and proposes the ESR as a major spectroscopy to investigate the crossover dynamics.…”

“…This represents one of the reasons of the appeal exerted by molecular probe spectroscopy, as its recent application in the framework of dielectric spectroscopy also testifies [10]. With time resolved fluorescence measurements of doped malachite green molecules dissolved in different glass formers [11] and with positron annihilation lifetime spectroscopy studies [12] dynamic anomalies were enlightened in the range 1.15-1.4T g .…”

Micromorphology and Relaxation Processes of Low Density Polyethylene Probed by Fluorescence Spectroscopys

“…The temperature dependence of the luminescence of several guests or labels in polymers is a complex process and different approaches have been employed [10][11][12][13][14][15][16][17][18][19][20][21][22]. It was demonstrated that phosphorescence emission of several probes sorbed in different polymers were able to detect the…”

“…Additional focuses were introduced in studies of the temperature dependence of the luminescence properties of fluorescent condensed aromatic hydrocarbons, because they allowed the determination of the polymer relaxation processes [10][11][12][13][14][15][16][17][18][19][20][21][22]. Luminescent polymers necessary for these studies may be produced by several methods: copolymerization of luminescent monomers, sorption of luminescent guests in a polymer host and chemical modification of pre-formed polymer attaching luminescent groups [11,12,[16][17][18][19][20][23][24][25].…”