Study on liquid-liquid transition of chlorinated butyl rubber by positron annihilation lifetime spectroscopy

Abstract

The existence of liquid-liquid transition (Tll) above the glass transition (Tg) in amorphous polymers remains a controversial topic. In this letter, positron annihilation lifetime spectroscopy was used to detect Tll in cured and uncured chlorinated butyl rubber. It is found that the temperature spectra of orthopositronium lifetime and free-volume fraction of both samples clearly demonstrate two inflection points around −70 and −10°C, corresponding to Tg and Tll, respectively, while the orthopositronium intensity decreases at the transition regions, which may imply molecular cooperativity. Moreover, two equations should be adopted to describe the development of free-volume fraction after Tg.

Positron annihilation response and broadband dielectric spectroscopy: Propylene carbonate

“…While the above considerations show that a quantitative description of dielectric and, at least, a qualitative account for PALS data is possible within the TOP model, one has to state that this approach relates to the structural relaxation and does not explain the observation of at least two distinct regions in the increasing part of s 3 ðTÞ separated by T L b1 , as observed in some glass-formers [10][11][12][13]17]. In section 4.1, based on a comparison with temperaturedependent dielectric loss data at x % 1=s 3 , we have argued that the anomaly at T L b1 could be related to the transition from a-relaxation to EW dominated behavior.…”

“…Moreover, at T L b2 , s 3 is often close to the mean relaxation time of the primary a process, s a ðT L b2 Þ, as obtained from a standard peak analysis [10,13,16,17]. Often, a slighter change of slope at T L b1 , closer to the glass transition temperature T PALS g is observed [7][8][9][10][11][12][13] as was sometimes quantified by the best linear fitting [10][11][12][13]. Similarly as for T L b2 , it is found that T L b1 is related to the temperature T a (À6), at which the mean a -relaxation time from DS s a ðT L b1 Þ reaches a value of 10 À6 ± 1 s [10,13].…”

“…obtained over a wide temperature range from 15 up to 300 K. As usually observed for many small molecular and polymer glassformers [6][7][8][9][10], the s 3 À T plot of PC exhibits a nearly sigmoidal shape with a well-defined plateau region at high temperatures. The two most pronounced changes of slope are situated at around $160 and $200 K. A phenomenological analysis of the s 3 À T dependence for rapidly cooled PC using the best linear regression fitting [10][11][12][13] suggests the presence of three temperature regions of distinct thermal behavior as indicated by dashed lines in Fig. 1 …”

“…A phenomenological model-free analysis of these s 3 À T plots in a series of small molecular and polymeric glass-formers revealed the existence of several characteristic PALS temperatures marked according to a unified notation [10] as, T PALS g ; T L b1 and T L b2 ¼ T r [7], the two latter being located at T L b1 $ 1:2-1:4 T PALS g [10][11][12][13] or T L b2 $ 1:4-1:7 T PALS g [7-10,13], respectively. Evidently, the full utilization of the PALS method for the characterization of any disordered system requires understanding of the physical significance of these PALS temperatures as completely as possible.…”

Positron annihilation response and broadband dielectric spectroscopy: Poly(propylene glycol)

“…Phenomenological analysis revealed the existence of several characteristic PALS temperatures in the liquid state marked according to a unified notation [9] as T PALS g , T L b1 and T L b2 ¼ T r [7] = T e [8], the two latter being located at T L b1 $ 1.2-1.4 T PALS g [9][10][11] or T L b2 $ 1.4-1.7 T PALS g [7][8][9], respectively. Evidently, the full utilization of PALS method for the structuraldynamic characterization of any disordered system requires understanding of the physical significance of these PALS temperatures.…”