摘要:

One result of recent interest in Gru¨neisen constants, &ggr; = −dln&ngr;/dlnV, of polymers is a considerable spread of reported &ggr;'s for solids like polyethylene. From elasticity data (bulk modulus or sound velocities for example) one finds &ggr; ≈ 6 for linear polymer solids. Values of &ggr; from thermal data are much lower than 6 because the relationship usually employed, &ggr; = &agr;B V/CV, is not valid for polyatomic solids. Measurements of the shifts in lattice frequencies with volume strains are the most direct way of measuring &ggr;. However, the results for pressure‐induced strains differ from those for temperature‐induced strains, and both differ from the results from elasticity data. In this paper we consider vibrations in a simple anharmonic well and show how the apparent shifts in vibrational frequency with pressure and temperature can be derived from changes in force constants.

ISSN:0021-8979    

DOI:10.1063/1.1661948

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The mechanical relaxation time in a glassy polymer depends on the magnitude of strain. The stress relaxation modulus of a styrene acrylonitrile and polybutadiene composite system (ABS) was measured at strains ranging from 0.005 to 0.10. The relaxation time was observed to shorten by up to four orders of magnitude. In addition, there was observed a decrease in the elastic contribution to the modulus. These two aspects of nonlinear viscoelasticity are interpreted in terms of the excess enthalpy associated with dilatation under strain, a crucial factor for ductile behavior and the formation of crazes. Up to 0.9 cal/g of the excess enthalpy associated with the stress‐induced dilatation is obtained from the differential scanning calorimetry study.

ISSN:0021-8979    

DOI:10.1063/1.1661949

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Specimens of regenerated cellulose films (cellophane) have been subjected to a pretreatment followed by microbial degradation. Pretreatments included mechanical deformation, acid hydrolysis, and alkaline degradation, and the subsequent fungal deterioration process was monitored by x‐ray diffraction, infrared spectroscopy, and tensile property tests. Longitudinal prestraining of films, which produces small surface cracks, caused accelerated weakening due to action of cellulase enzymes; transverse prestraining of films, which produces internal reorganization but no surface cracks did not lead to any significant change in degradation rate. Nonenzymatic hydrolysis appeared to cause recrystallization of cellulose chain segments cleaved in disordered regions, and subsequent fungal degradation was found to remove these recrystallized regions preferentially.

ISSN:0021-8979    

DOI:10.1063/1.1661950

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Data are presented to show that when linear polyethylene is quenched from room temperature to temperatures below 273 K, it exhibits a volume decrease for times long compared with that required to establish temperature equilibrium. The time, temperature, and density dependence of this decrease is shown to be consistent with a relaxation occurring in the amorphous portion (lamella boundary layers) of the samples. The data can be superposed and the shift factors follow the WLF formalism. Analysis by this method yields aTgof 231 ± 9 K but the uncertainties preclude any correlation with specific volume over the range 1.01–1.05 cm3g−1. The data indicate the absence of any comparably strong time dependence of the volume near 150 K. This method of detecting a glass transition in partially crystalline polymers is relatively freer of subjective judgment than most.

ISSN:0021-8979    

DOI:10.1063/1.1661951

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The mechanical behavior of glassy PC was investigated as a function of strain and temperature by stress relaxation measurements and by dynamic mechanical measurements. For stress relaxation, the stress decay, measured by an Instron tensile tester, linearized vs logarithmic time from 1 sec to up to 16 h. From these data a plot of the relaxation time vs strain was obtained showing that the relaxation time decreased with increased strain. To separate the effect of the elastic and viscous components,E′andE″were investigated by the Rheovibron. At a constant strain level,E′showed a slight increase with time whileE″decreased considerably. With stepwise increase in strain,E′showed a slight decrease whileE″increased considerably. Furthermore, the dynamic mechanical spectra showed that the peak did not shift with strain, but intensified and broadened considerably. The stress relaxation can be related to the Rheovibron data.

ISSN:0021-8979    

DOI:10.1063/1.1661952

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Small‐angle x‐ray scattering (SAXS) from amorphous polycarbonate (PC) exhibits a sharp rise in intensity at ultrasmall angles (2&thgr; <0.08° for CuK&agr;radiation). At much higher angles, SAXS is superimposed on a diffuse halo centered at an angle corresponding to a spacing of[inverted lazy s]10 Å. Since doping the PC with small amounts of I2results in a reversible decrease in SAXS intensity, SAXS is not due to voids but is probably attributable to the ``nodule'' structure observed in PC with electron microscopic techniques. The invariant,∫0∞&thgr;2I(&thgr;)d&thgr;and lim[&thgr;4I(&thgr;)] as &thgr; → ∞, are used to compute a specific surface of 150 m2/cm3based on the assumption of 0.5 volume fraction of spherical nodules. The ``range of inhomogeneity'' of the nodules is then found to be 130 Å. From absolute intensity measurements the minimum relative density fluctuation between the nodules and their surroundings is 1.6%; an upper limit of 1.8% is found for fcc close packing of nodules. This result demonstrates that the model of Yeh, which assumes crystalline density for the nodules and predicts a relative density fluctuation of 21% is much too extreme.

ISSN:0021-8979    

DOI:10.1063/1.1661953

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The long slender crystals of polyoxymethylene that grew in irradiated trioxane crystals all grew toward the negative end of the trioxane crystal. The observed direction of growth was consistent with the assumption that the ion at the growing end of the polyoxymethylene chain was a cation. Certain morphological features such as facets and direction of taper of these polyoxymethylene crystals indicated the direction in which the crystals grew. Incidental observations of polyoxymethylene precursor crystals, electret domains in trioxane, and the effects of electron irradiation on polyoxymethylene crystals were made.

ISSN:0021-8979    

DOI:10.1063/1.1661954

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The formation of the dense surface skin of asymmetric reverse osmosis membranes is analyzed in terms of a composite process involving solvent diffusion and polymer relaxation. The analysis indicates that films with minimum skin thickness result from (i) rapid polymer relaxation; (ii) strongly concentration‐dependent solvent diffusion coefficients. The numerical results are discussed in terms of experimental variables. It indicates great difficulty in producing asymmetric films with extremely thin surface skins. The implications of this finding are discussed. Experimental NMR self‐diffusion studies of acetone in cellulose acetate are reported.

ISSN:0021-8979    

DOI:10.1063/1.1661955

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Phase transformations involving growth and impingement of randomly centered and oriented rods, fixed in number and cross section, have been studied using computer modeling techniques. As expected, the Avrami equation does not adequately describe the process. Deviations of up to 15% from the Avrami predictions are frequently encountered. The biggest deviations are in the Avrami constantK, which contains the rate constants, rather than in the time exponentn, which reflects growth and nucleation modes.

ISSN:0021-8979    

DOI:10.1063/1.1661956

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The sorption of benzene vapor by a biaxially oriented polystyrene film was studied in the temperature range 30–70°C. A comparison of the sorption isotherms for the oriented and the unoriented materials allowed the calculation of the enthalpy and entropy of orientation. The enthalpy of orientation is about − 1 to − 1.4 cal/g and the entropy change is about − 2.6 to − 4.3 cal/g. It was also concluded that the clustering tendency for benzene molecules was greater in the oriented specimen.

ISSN:0021-8979    

DOI:10.1063/1.1661957

出版商:AIP    

年代:1973

数据来源: AIP