A study of the deep structure of the energy landscape of glassy polystyrene: the exponential distribution of the energy barriers revealed by high-field electron spin resonance spectroscopy

Abstract

The reorientation of one small paramagnetic molecule ( spin probe ) in glassy polystyrene ( PS ) is studied by high-field Electron Spin Resonance spectroscopy at two different Larmor frequencies ( 190 and 285 GHz ). The exponential distribution of the energy-barriers for the rotational motion of the spin probe is unambigously evidenced at both 240 K and 270 K. The same shape for the distribution of the energybarriers of PS was evidenced by the master curves provided by previous mechanical and light scattering studies. The breadth of the energy-barriers distribution of the spin probe is in the range of the estimates of the breadth of the PS energy-barriers distribution. The evidence that the deep structure of the energy landscape of PS exhibits the exponential shape of the energy-barriers distribution agrees with results from extreme-value statistics and the trap model by Bouchaud and coworkers .

Electron Paramagnetic Resonance

“…Buchenau confirmed that conclusion by comparing results from several techniques covering a wide time window from 1Hz up to about 100GHz [18]. The same result has been reached by HF-EPR [10,11,19].…”

“…The shape of the energy-barriers distribution g(E) in glasses has been extensively investigated via experiments [8,10,11,16,17,[19][20][21][22][23][24], theories [25][26][27][28][29] and simulations [30]. Basically, two different distributions are usually recovered, the gaussian distribution [8,16,20,21,24,25,30,31] and the exponential distribution [8,10,11,17,19,22,[26][27][28][29].…”

“…Basically, two different distributions are usually recovered, the gaussian distribution [8,16,20,21,24,25,30,31] and the exponential distribution [8,10,11,17,19,22,[26][27][28][29].…”

“…In particular, during the last few years continuous-wave ( CW ) and pulsed HF-EPR techniques were developed involving large polarizing magnetic fields, e.g. B 0 ∼ = 3T corresponding to Larmor frequencies about 95GHz ( W band ), [37,38] or even larger frequencies [19,39,40]. HF-EPR is widely used in polymer science [10,11,19,[41][42][43][44].…”

“…B 0 ∼ = 3T corresponding to Larmor frequencies about 95GHz ( W band ), [37,38] or even larger frequencies [19,39,40]. HF-EPR is widely used in polymer science [10,11,19,[41][42][43][44]. One major feature is the remarkable orientation resolution [44] due to increased magnitude of the anisotropic Zeeman interaction leading to a wider distribution of resonance frequencies [45].…”