摘要:

The assumption of additive properties was applied to a series of eight crosslinked epoxy/amine polymers. The thermodynamic properties of the four independent structural components of these polymers were determined from experimental measurements on the polymers. This approach was applied to: density, thermal expansion, bulk modulus, and heat capacity. Using the component values, polymer properties were then calculated with the result that the predictions agree on the average with the measurements to within the accuracy of the measurements.

ISSN:0021-8979    

DOI:10.1063/1.327460

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Transcrystalline films of the &agr; polymorph of poly(vinylidene fluoride) have been prepared. X‐ray diffraction shows that such films have a high degree of crystallographic orientation normal to the surface. The orientation shows that thebaxis of the &agr; phase unit cell is the principal crystal‐growth direction. As is well established for other systems, it was found that the formation and growth of a transcrystalline layer requires relatively dense surface nucleation combined with sparse nucleation in the interior of the film. Experimental variables which favor the formation of surface nuclei include high polymer molecular weight, a mold surface which acts as a nucleating agent (such as Teflon), and a temperature gradient through the film during crystallization. Films exhibiting virtually no nucleation in the interior could be prepared from very pure PVF2synthesized in our lab, while samples prepared from biaxially oriented films showed very dense internal nucleation. Annealing at high melt temperatures drastically decreased the internal nucleation in these films. An explanation to account for the behavior is proposed.

ISSN:0021-8979    

DOI:10.1063/1.327461

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Investigations of the piezoelectric response of biaxially oriented poly(vinylidene fluoride) films subjected to a series of static positive and negative poling fields produces a hysteresis curve ford31ande31showing the ferroelectric character of phase IV. Examination of changes in the crystalline regions, using differential scanning calorimetry and x‐ray methods, of films cycled (statically) through large positive and negative poling fields provides insight into the switching mechanisms of both phase I and phase IV. The experimental results show a cyclic broadening and narrowing of the endothermic melting peaks as the film polarization is switched. Cyclic changes in the intensities of the phase I (110) (200) and phase II (or phase IV) (100), (020), and (110) reflections are also observed.

ISSN:0021-8979    

DOI:10.1063/1.327462

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

At the present time, only poled, drawn poly (vinylidene fluoride) (PVF2) films give evidence of sufficiently high piezoelectric response to be useful in device applications, and for this reason the great majority of research has centered around this polymer. As in the case of PVF2, many odd nylons crystallize in a polar space group with a large net dipole moment in the unit cell. On the basis of the understanding now reached of the properties of poled PVF2films, it would appear that the odd nylons have the potential to make films with high piezoelectric activity. Piezoelectricity and pyroelectricity in nylon 11 films have been studied previously. The piezoelectric strain constants found were larger than most polymers, but still two orders of magnitude less than the corresponding activity found in poled oriented PVF2(d31∼20 pC/N). Studies carried out in this laboratory have shown that by appropriate variation of poling conditions and sample microstructure, relatively large piezoelectric constants can be obtained for nylon 11 films (d31∼3 pC/N). The dependence of the piezoelectric strain constantd31on poling temperature, poling field, and crystal structure will be discussed.

ISSN:0021-8979    

DOI:10.1063/1.327283

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Brillouin‐frequency shifts have been obtained for atactic polystyrene at pressures up to 2 kbars and temperatures up to 180 °C. The temperature and pressure dependencies of the data have been analyzed. The resulting values ofTghave been found to increase with pressure towards a limit. The temperature dependence of the Brillouin frequencies in the amorphous solid have been separated into a temperature coefficient at constant volume and a volume effect. We comment on the equilibrium entropy theory of Gibbs and DiMarzio using specific volume data from the literature.

ISSN:0021-8979    

DOI:10.1063/1.327463

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The solvent‐casting process preferentially aligns polymeric chains in the plane of the film. This paper proposes that the mechanism responsible for this behavior is the competition between the relaxation times of the concentrating solution and the time scales associated with the physical collapse of the film. The orientation of molecules has been determined as a function of the coating conditions (film thickness, polymer molecular weight, plasticizer content, casting solvent, and substrate temperature) by measuring the optical anisotropy of the coating with a single‐prism film coupler. This orientation is shown to reflect both the stresses supported by the entanglement network and the alignment of localized segments and to be a function of the difference between the casting temperature and theTgof the film.

ISSN:0021-8979    

DOI:10.1063/1.327464

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

High‐impact polystyrene (HIPS) has been processed into a specific microstructure which exhibited the hard‐elastic behavior previously restricted to crystalline polymers. Unidirectionally stacked profuse crazes formed in uniaxially elongated HIPS resembled the row nucleated structures of stacked lamellar aggregates bridged by extended fibrils. Films in this form possessed repeated high recovery from large extension without rupture. Stress‐strain and stress‐relaxation tests, performed in air and in a variety of liquids, and thermoelastic experiments indicated that this material has similar characteristics to those of hard‐elastic crystalline polymers. Our results confirmed that the recovery process of elastic HIPS, like crystalline systems, is composed of an instantaneous component and a time‐dependent healing mechanism. The first was found to be energetic in nature and the second conformational (entropic). A mechanism, based on the reversible extensive formation of fresh surface of the craze (or interlamellar) fibrils giving rise to the elastic restorative force, is proposed. Stress‐induced sorption and release of liquid, a newly discovered property, is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.327421

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A mechanism for the poling of &agr;‐phase poly(vinylidene fluoride) into its polar form is studied in which a 180° twist or kink is propagated along a chain. Results are obtained by analytical approximation and by computer experiment for the field and temperature dependence of the poling time. Intrachain and interchain potentials used in this calculation are obtained by conformational analysis. The results are compared with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.327422

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Epitaxially polymerized (SN)xon various substrates has been studied by Fourier‐transform infrared spectroscopy (FT‐ir). Those substrates include Pt‐shadowed KI, AgCl, NaCl, KCl, KI, KBr, RbI, and NaI. All samples of the polymer contained significant amounts of chemical defects, mostly as NH and S=O groups. The spectral variation observed with (SN)xpolymerized on various substrates appeared to be due to differences in its degradation by water. There are at least two distinct degradation mechanisms. One is the degradation by water incorporated into the S2N2crystals prior to the polymerization, and the other is the attack of moisture on the polymer. The nature of the chemical defects were studied by deuterium exchange and degradation by H2 18O as well as H2 16O. The band at 1400 cm−1was assigned to the NH group while two bands at 1220 and 1090 cm−1were assigned to S=O groups with different chemical environments. The band at 1220 cm−1is related to a structure produced during the early stages of degradation in the preparative vacuum chamber, but the band at 1090 cm−1is thought to arise from a structure formed at a later stage of degradation after sample preparation by atmospheric water.

ISSN:0021-8979    

DOI:10.1063/1.327431

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Disulfur dinitride was epitaxially crystallized from the vapor phase on freshly cleaved (100) faces of monovalent alkali halide single crystals. Subsequently, the dimer was polymerized in the solid state, while still on the substrates. This epitaxial polymerization leads to highly oriented crystalline polythiazyl [(SN)x] which shows no evidence of the usual fibrullar morphology. Fibrils of (SN)xhave been produced by epitaxial polymerization of a second layer of dimer on a previously polymerized layer. Three new structures of polythiazyl have been observed from crystals grown on NaCl, KBr, and KI. The structures differ significantly from the usual &agr; phase of (SN)x. Because of such large differences in the polymer chain spacing in these forms when compared to the normal form, a new polymerization mode and direction may be involved. The diagnosis of the true effect of water on (SN)xusing Fourier‐transform infrared spectroscopy (FT‐ir) aided in discovering why structural studies from samples exposed to water are impossible.

ISSN:0021-8979    

DOI:10.1063/1.327432

出版商:AIP    

年代:1980

数据来源: AIP