摘要:

Results indicating the extent to which flow in a miscible polymer blend can displace the phase separation temperature are reported. Data were obtained on the system, polystyrene/poly (vinyl methyl ether), in the temperature ranges where it undergoes exsolution upon heating. The theoretical framework for the observed flow‐induced miscibility is described.

ISSN:0021-8979    

DOI:10.1063/1.331833

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The concept of molecular strain energy is defined. The temperature, crystallinity, molecular strain, and free volume dependence of the nonequilibrium glassy state in PVC is analyzed. Quenched PVC samples were (1) cycled between room temperature and 112 °C and (2) annealed belowTgfollowed by cycling to 112 °C. The measured spectra were subjected to digital subtraction and Fourier self‐deconvolution routines to extract the amorphous‐state results from competing effects. It was seen that heating a quenched glass to 112 °C produced a discontinuity &Dgr;&xgr;″ in the slope of the 1100 cm−1skeletal frequency versus temperature curve atTg. The value of &Dgr;&xgr;″ was essentially zero in all slow cooling experiments and after annealing belowTg. A small shift in frequency, &Dgr;&ngr;isowas observed during isothermal annealing. Theoretical considerations indicate that &Dgr;&xgr;″ and &Dgr;&ngr;isohave both intra‐ and intermolecular contributions. It is believed that this observational technique might be used to monitor physical aging in the nonequilibrium glassy state of polymers.

ISSN:0021-8979    

DOI:10.1063/1.331759

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Normal mode calculations have been done on planar zigzag chains Cn(n=22 to 82), terminated or connected by various fold structures and subjected to force and mass perturbations, to determine how the longitudinal acoustic mode (LAM) is influenced by such defects. We find that in general LAM‐like displacements are distributed over a frequency range (depending on the stem length), with a total intensity smaller than that for the unperturbed case. Only when the fold comprises ∼3% or less of the mass of the stem does it behave like a point mass perturbation. These results show that the perturbed elastic rod model has limited validity and that caution is necessary in attributing the shape of a LAM band entirely to a distribution of stem lengths.

ISSN:0021-8979    

DOI:10.1063/1.331834

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A Monte Carlo simulation of polymer crystal growth from the melt is presented. This two‐dimensional model approximates growth by laying down crystal stems one at a time. The Monte Carlo simulation of various geometric models of the crystal surface yields Regime I and Regime II growth similar to that predicted by Lauritzen and Frank. The analytical expression of Frank is shown to be accurate. A recent prediction by Hoffman of a low temperature region (Regime III) with properties similar to Regime I has been verified. Regime III is lattice dependent. Specifically the solid‐on‐solid model commonly used to model monatomic systems yields Regime III but is not space filling. The hexagonal lattice yields correctly formed crystals but does not show Regime III as long as we require that the crystals grow on one plane. On the hexagonal lattice, if we allow growth on more than one growth plane, we obtain both space filling crystals and Regime III growth. There are no regimes of growth other than the three discussed here.

ISSN:0021-8979    

DOI:10.1063/1.331835

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Electron diffraction patterns have been obtained from the macromonomer and crosspolymerized crystals of poly(1, 8‐nonadiyne). Thin (∼150 A˚) crystals of the macromonomer, grown from a chloroform solution, were used for obtaining electron diffraction intensity data. Crosspolymerization resulted from subsequent exposure of these crystals to Co60&ggr; radiation. Twenty‐four reflections for the crosspolymerized sample and 18 for the macromonomer were obtained. Refinement of the structures was accomplished using these data. The unit cells of both the macromonomer and the crosspolymerized material were monoclinic and the space groupsP21andP21/n, respectively.

ISSN:0021-8979    

DOI:10.1063/1.331836

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Composite samples of graphite fibers in both an epoxy matrix and a polyimide matrix have been prepared with different fiber arrangements and irradiated with 0.5‐MeV electrons up to 104Mrad. Interlaminar shear strengths decreases significantly with radiation dosage while little change was observed in the flexural strengths and moduli. The results indicate that radiation causes significant degradation at the interface but not much change in the fiber or matrix.

ISSN:0021-8979    

DOI:10.1063/1.331837

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Kinematic measurements of Fatigue Crack Propagation (FCP) in thick compact tension polypropylene specimens shows that the rate of FCP does not increase monotonically as predicted by conventional laws of fracture mechanics. Specifically, crack deceleration occurs with increasing crack length. Microscopic examination indicates that crazes (damage) disseminate around and ahead of the main crack, thus controlling its rate of propagation. Accounting for damage dissemination, in terms of the crack layer theory, shows that the rate of FCP is controlled by the shape of the active zone and by its size, in addition to the crack length. Abrupt changes in the first two parameters are directly related to the observed crack deceleration.

ISSN:0021-8979    

DOI:10.1063/1.331838

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Up to now, the growth rate of a craze has been considered either constant or inversely proportional to time. By taking into consideration the effect of the surrounding population of crazes, it is found that the craze growth rate is affected by the local effective stress acting in the vicinity of the craze. Measured data of craze length as a function of time are found to be greatly affected by local interactions.

ISSN:0021-8979    

DOI:10.1063/1.331813

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The role of chain scission in the mechanical degradation of polyethylene has been examined using Fourier transform infrared spectroscopy to measure changes in molecular end group concentrations. The increase in chain scission concentration during cyclic fatigue of ultrahigh molecular weight polyethylenes has been investigated by this technique. The concentration of chain scissions at macroscopic failure was independent of the peak stress and time to failure in the fatigue experiment, but dependent on fatigue test frequency and molecular weight.

ISSN:0021-8979    

DOI:10.1063/1.331814

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Composites oftrans‐polyacetylene (t‐(CH)x) and low density polyethylene (LDPE) have been studied by Electron Nuclear Double Resonance (ENDOR), Electron Nuclear Nuclear Triple Resonance (TRIPLE), and Electron Spin Echo (ESE) spectroscopies. The results are compared with analogous studies conducted on puret‐(CH)xfilms and on samples containing mixtures ofcis/transisomers. ENDOR measurements indicate that the paramagnetic electron in all materials studied resides in a pure &pgr; molecular orbital. The measured spin densities at carbon of ‖0.06 and ‖0.02‖ for two inequivalent13C nuclei along the polyene backbone imply that the defect spin density is spread over a polyene segment length on the order of 70 A˚. The absolute magnitude of the spin densities, +0.06 and −0.02, obtained by TRIPLE indicate the existence of electron Coulomb correlation effects. Detailed analysis of ENDOR spectra places strict limits on the allowable soliton diffusion coefficient. ENDOR, ESE phase memory (TM), and ESE spin‐lattice (T1e) relaxation times are observed to be a function oft‐(CH)xconcentration in the host material. The importance of other dynamic processes such as electron Heisenberg spin exchange, electron dipolar interactions, and nuclear spin diffusion, are considered as mechanisms for obtaining the observed spectral responses. The analysis indicates the need for caution in interpreting electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) data in terms of models which consider the only active dynamic process to be soliton diffusion.

ISSN:0021-8979    

DOI:10.1063/1.331815

出版商:AIP    

年代:1983

数据来源: AIP