Applicability of the free volume concept on relaxation phenomena in the glass transition range

1966 ◽  
Vol 5 (4) ◽  
pp. 262-269 ◽  
Author(s):  
A. J. Kovacs
Keyword(s):  
Glass Transition ◽  
Free Volume ◽  
Relaxation Phenomena ◽  
Transition Range ◽  
Glass Transition Range

Applicability of Free Volume Concept to Relaxation Phenomena in the Glass Transition Range

1968 ◽  
Vol 41 (3) ◽  
pp. 555-563
Author(s):  
A. J. Kovacs
Keyword(s):  
Glass Transition ◽  
Free Volume ◽  
Excess Entropy ◽  
Heat Content ◽  
Configurational Entropy ◽  
Wide Distribution ◽  
Dielectric Constants ◽  
Experimental Point ◽  
Transition Range ◽  
Glass Transition Range

Abstract Except for discrepancies mentioned with respect to pressure investigations, which need future clarification, we can conclude in a general way, as follows. As far as only average parameters of macroscopic specimens are considered (complex moduli, or dielectric constants, volume or heat content etc...), the free volume concept can relate variations of molecular mobility to changes of an average free volume in a semiquantitative way. This average free volume can no longer fully characterize the wide variety of molecular motions involved in the kinetics of redistribution of holes in the liquid during recovery experiments. These kinetic processes involve a wide distribution of retardation times, which may be associated with local distribution of holes, or with that of cooperating groups of molecules, or molecular segments. On the other hand, free volume is not necessarily the fundamental molecular parameter which controls rate of configurational changes, characterized by variation of entropy of the liquid. Even if this is the case, most of the above discussion may be applied to any other average excess parameter, as far as the Doolittle equation is formally adopted, in which f/b is expressed in terms of the new parameter, rather than that of free volume. However, since relaxational free volume, as determined from the WLF equation, and independently measured volume changes are often in close agreement, this means that variations of excess entropy, or those of configurational free energy, and changes in volume are closely related. This conclusion is in agreement with that of Eisenberg and Saito, who found that the Gibbs—Dimarzio theory, based on configurational entropy, is practically equivalent with the free-volume approach. Thus, the free volume concept remains still a valuable tool for unifying different kinds of rate processes from both a theoretical and an experimental point of view, especially in the glass transition range.

scholarly journals Competition between Structural Relaxation and Crystallization in the Glass Transition Range of Random Copolymers

Polymers ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1778
Author(s):  
Jürgen E. K. Schawe ◽  
Claus Wrana
Keyword(s):  
Glass Transition ◽  
Structural Relaxation ◽  
Random Sequence ◽  
High Sensitivity ◽  
Random Copolymers ◽  
High Time Resolution ◽  
Scanning Calorimetry ◽  
Transition Range ◽  
Glass Transition Range ◽  
And Control

Structural relaxation in polymers occurs at temperatures in the glass transition range and below. At these temperatures, crystallization is controlled by diffusion and nucleation. A sequential occurrence of structural relaxation, nucleation, and crystallization was observed for several homopolymers during annealing in the range of the glass transition. It is known from the literature that all of these processes are strongly influenced by geometrical confinements. The focus of our work is copolymers, in which the confinements are caused by the random sequence of monomer units in the polymer chain. We characterize the influence of these confinements on structure formation and relaxation in the vicinity of the glass transition. The measurements were performed with a hydrogenated nitrile-butadiene copolymer (HNBR). The kinetics of the structural relaxation and the crystallization was measured using fast differential scanning calorimetry (FDSC). This technique was selected because of the high sensitivity, the fast cooling rates, and the high time resolution. Crystallization in HNBR causes a segregation of non-crystallizable segments in the macromolecule. This yields a reduction in mobility in the vicinity of the formed crystals and as a consequence an increased amount of so-called “rigid amorphous fraction” (RAF). The RAF can be interpreted as self-assembled confinements, which limit and control the crystallization. An analysis of the crystallization and the relaxation shows that the kinetic of both is identical. This means that the Kohlrausch exponent of relaxation and the Avrami exponent of crystallization are identical. Therefore, the crystallization is not controlled by nucleation but by diffusion and is terminated by the formation of RAF.

.alpha.-Relaxation in the Glass Transition Range of Amorphous Polymers. 1. Temperature Behavior across the Glass transition

1995 ◽  
Vol 28 (5) ◽  
pp. 1516-1527 ◽  
Author(s):  
A. Alegria ◽  
E. Guerrica-Echevarria ◽  
L. Goitiandia ◽  
I. Telleria ◽  
J. Colmenero
Keyword(s):  
Glass Transition ◽  
Amorphous Polymers ◽  
Temperature Behavior ◽  
Transition Range ◽  
Glass Transition Range
Sign in / Sign up

Export Citation Format

Share Document