S. D. Hong

Crystallization behaviour of poly(ether-ether-ketone)

Abstract A study has been made of the crystallization behaviour of poly(ether-ether-ketone), PEEK, under isothermal and non-isothermal conditions. A differential scanning calorimeter was used to monitor the energetics of the crystallization process from the melt and from the rubbery amorphous state. During isothermal crystallization, relative crystallinity develops with a time dependence described by the Avrami equation, with exponent n = 3. Greater absolute crystallinity develops during melt crystallization, nearly twice that which develops from the rubbery state, for comparable rates of crystallization. For non-isothermal studies, amorphous films were crystallized by heating or cooling at rates from 1°C/min to 50°C/min. A large fraction of crystallinity, from 0.45 to 0.70, develops by secondary processes. A kinetic treatment based on the Avrami equation is presented to describe the primary processes leading to non-isothermal crystallization. We have calculated activation energies of 68 kcal mol−1 for crystallization from the melt, and 52 kcal mol−1 for crystallization from the rubbery amorphous state. Results of isothermal and non-isothermal crystallization of PEEK are compared with those of poly(ethylene terephthalate).

Thermal diffusivity measurements using a pulsed dual‐beam thermal lens technique

A novel pulsed dual‐beam thermal lens technique for the determination of thermal diffusivity of liquids and solids was developed. In this technique a transient thermal lens is formed in the test specimen by using a dye laser pulse as a heating source and the thermal lens decay is monitored by means of a cw He‐Ne laser. The technique is fast and contactless and avoids some of the major difficulties of conventional methods. Thermal diffusivities for water and a polycarbonate plastic were measured and found to be in agreement with literature values. Considerable simplification and minimization of certain errors was achieved by use of a reference material.

Viscoelastic properties of entangled polymers: Ternary blends of monodisperse homopolymers

In a previous publication from this laboratory, the Rouse‐Bueche‐Zimm molecular theory of viscoelasticity has been extended by using a transient network model to apply to binary blends of monodisperse polymers with chain entanglements. The dynamics of the entanglements were modeled both by the enhanced frictional coefficients and by the additional elastic couplings. It was recognized that entanglements not only may form between chains of the same lengths (intracomponent entanglements) but also between those of different lengths (intercomponent entanglements). At a given intercomponent entanglement, the longer chain was assumed to have the frictional coefficient of the shorter chain. Similarly, for blends consisting of several monodisperse components with different molecular weights, such modifications are also required to predict their linear viscoelastic behavior. The frequency of these interactions is assumed to be proportional to the weight ratio of the respective component chains in the blend. Equatio...

A failure model for sealed nickel-cadmium batteries

A model has been developed to describe failure in electrochemical batteries. The model is based on the concept of the existence and subsequent growth of flaws which ultimately lead to battery failure. This model provides, in a natural way, for the statistical variability of lifetime data. The model as applied to the Crane data indicates that when the effects of temperature and depth of discharge are taken into account, the observed variability in lifetime data is due almost entirely to statistical variability inherent in the battery itself.

Molecular deformation and stress‐strain behavior of poly(bisphenol‐A‐diphenyl sulfone)

Stress‐optical studies have been carried out to determine the modes of molecular deformation in poly(bisphenol‐A‐diphenyl sulfone) and its relationship to stress‐strain behavior. Stress and birefringence were measured simultaneously as a function of strain at a strain rate of 0.0133 min−1 in the temperature range −179 to 150 °C. In the temperature range from 150 to −100 °C, measurements were performed using four strain rates, 0.0133 min−1, 0.133, 1.33, and 13.3 min−1 at each testing temperature. The results indicate that the processes involved in the molecular deformation appear to be invariant at temperatures below −100 °C. At higher temperatures, the statistical chain segments participate in the deformation process and the degree of participation increases with increasing temperature. The mechanism controlling the stress‐strain response is attributed to chain orientation. The stress‐strain response at temperatures below −100 °C is attributed to the temperature dependence of an internal energy contributi...

Characterization of Thermal and Optical Properties of Polymers by Thermal Lensing Technique

When a light beam passes through a material, some of the absorbed light energy may be converted into heat, generating a time dependent temperature gradient. Increase in temperature causes a change in the index of refraction. Hence, a transient thermal lens is formed in the volume element absorbing the radiation. The temperature rise is typically of the order of 10-2°C within a volume element of less than 10-3 cm3. Several physical and chemical properties of materials such as thermal diffusivity, optical absorption coefficient, multiphoton crossections quantum yield of photoprocesses etc... may be determined by monitoring the time dependence of the amplitude of the thermal lens. This technique is fast, precise and contactless.