Book reviewPhysics of non-crystalline solids: edited by J. A. Prins. 667 pages, diagrams, illus. 6 × 9 in. New York, John Wiley & Sons, Interscience, 1965. Price, $27.50

The field of mesophases is subdivided into six different phases: liquid crystals, plastic crystals, condis crystals and the corresponding LC, PC, and CD glasses. Liquid and plastic crystals are the traditional phases with positional and orientational disorder, respectively. Condis crystals are conformationally disordered. On hand of tables of thermodynamic transition parameters of small and large molecules it is shown that the orientational order in liquid crystals is only a few per cent of the total possible, while the positional order in plastic crystals is virtually complete. Condis crystals have a wide variety of different degrees of conformational disorder. The glass transitions of all mesophases are similar in type. Macromolecules in the liquid crystalline state produce high orientation on deformation. Plastic crystals consist always of small molecules. Condis crystals may under proper conditions anneal to extended chain crystals.

Thermotropic mesophases and mesophase transitions of linear, flexible macromolecules

Two experimental techniques are described for the determination of the change of specific volume of polymers with temperature and aging time, which allow measurements between − 160 °C and + 200 °C. Four technical amorphous polymers, PS, PVC, PMMA and PC have been investigated. Volume-temperature curves under constant rate of cooling are presented and interpreted with respect to relaxation processes known from other physical investigations. The rate dependence of dilatometric glass transition temperatures is compared with the time dependence of rheometric glass transition temperatures from shear creep data. Volume relaxation data at constant aging temperature are presented. Aging is found to proceed until very low temperatures in the glassy state for e.g. PMMA.

Thermal contraction and volume relaxation of amorphous polymers

It is pointed out that research efforts are at present being directed in two areas, one comprising experimental studies of this phenomenon in various glassy polymer systems and the other involving the development of a quantitative theory capable of satisfactorily predicting aging behavior for a variety of polymer materials under different conditions. Recent work in both these areas is surveyed. The basic principles of nonequilibrium behavior are outlined, with emphasis placed on changes in material properties with annealing below the glass transition temperature. Free volume theory and thermodynamic theory are discussed.

https://apps.dtic.mil/sti/pdfs/ADA096682.pdf

An overview of the nonequilibrium behavior of polymer glasses

The dielectric loss in a rigid‐molecular glass (toluene–pyridine) and in poly(propylene oxide) has been measured from 50 to 2×105 Hz during the course of isothermal annealing at several temperatures. The decrease in the loss on annealing is predominantly due to a decrease in the number of molecules participating in the secondary relaxation. Measurements of the loss at different temperatures, but a fixed frequency, indicate a similar effect of annealing. Explanations for the secondary or β relaxations in amorphous polymers in terms of the motion of the side group attached to the main chain seem inconsistent with the observed temperature dependence of the amplitude of secondary relaxation. Several implications for our concepts of small scale molecular motions in glasses arising from these results are considered. It is suggested that the discrepancy between the relaxation rates determined from the loss spectrum at a constant temperature and from the loss‐temperature plots at a constant frequency arises from a rapid increase in the amplitude of secondary relaxation with temperature.

Effect of annealing on the secondary relaxations in glasses

The dynamic mechanical properties of glassy polymers, such as atactic polystyrene and poly(ethylene terephthalate), have been followed as a function of the excess enthalpy during isothermal annealing at selected temperatures below their respective glass transition temperatures. For glassy polymers prepared from crystallizable as well as noncrystallizable polymers, the changes in modulus parallel the extent of enthalpy relaxation that occurs during the annealing period as a result of the nonequilibrium nature of the glassy state, i.e., the modulus increases with time and approaches a limiting value that increases with decreasing temperature. These results suggest that the observed changes in the dynamic mechanical moduli are associated with changes in the excess thermodynamic properties of the polymeric glasses, and not with structure formation other than the normal liquidlike packing of the chain segments. Thus the physical properties for corresponding equilibrium glassy states can be determined ...

The effect of excess thermodynamic properties versus structure formation on the physical properties of glassy polymers

To gain further understanding regarding the modes of molecular motion which contribute to the ductility and toughness of glassy polymers, and the factors that influence such molecular mobility, a study has been undertaken of the effect of the amount of excess volume in glassy poly(ethylene terephthalate) on the mode of failure observed in tensile tests and on the associated level of molecular motion. The results of tensile stress-strain studies on films annealed at temperatures below the glass transition temperature indicate that there is a relationship between the mode of failure and the level of excess volume trapped in the glassy polymer. From dynamic mechanical loss studies of the annealed films, however, it is evident that the modes of motion associated with the major subsidiary dynamic mechanical absorption, i.e., the γ-relaxation process, are relatively unaffected by the loss of free volume caused by the densification of the glassy polymer on annealing. Further, these studies suggest that ...

The effect of excess volume on molecular mobility and on the mode of failure of glassy poly(ethylene terephthalate)

In an attempt to formulate a general picture of the influence of diluents on the physical properties of polymers without invoking specific molecular characteristics of the diluents, a systematic study has been undertaken of the mobility of both the polymer and the diluent in polymer‐diluent systems, and of the resulting effects on the physical properties of these systems. In dynamic mechanical and dielectric loss studies of polymer‐diluent systems, the influence of the mobility of the diluent on the background loss as well as on the loss associated with subsidiary relaxation transitions has been followed as a function of temperature and correlated with the temperature dependence of the modulus, over temperature ranges which include the low‐temperature γ and β transitions. The temperature ranges of plasticization and antiplasticization have been established for bisphenol A polycarbonate and atactic polystyrene plasticized with various phthalates and chlorinated biphenyls and terphenyls, which were selected to have a wide range of glass transition temperatures and plasticizing efficiencies.

S. E. B. Petrie

Papers

The effect of excess thermodynamic properties versus structure formation on the physical properties of glassy polymers

The effect of excess volume on molecular mobility and on the mode of failure of glassy poly(ethylene terephthalate)

Influence of diluent mobility on the plasticization of polymers