摘要:

A theoretical relationship has been obtained between viscosity and the PVT properties of a glass‐forming liquid. First an equation of state is determined for the liquid by using a hole model of the liquid state. This equation of state is then combined in a unique way with the Cohen‐Turnbull theory of self‐diffusion and an important result from Brownian motion theory to obtain what is essentially an equation of state for viscosity. The principal results of the theory are as follow: (i) The change in the thermal expansion coefficient &Dgr;&agr; that occurs at the glass transition temperatureTgcan be predicted from the WLFC2constant (T∞≡Tg−C2),Tg&Dgr;&agr; = 2(T∞/Tg) × [exp (1 + 2T∞/Tg)−1]−1. Except for the polyakylmethacrylates, good agreement is obtained between observed and theoretical &Dgr;&agr; values for many polymers. (ii) A theoretical upper bound forTg&Dgr;&agr; has been found and is equal to 0.159. To within the experimental uncertainties in measured &Dgr;&agr; values, there are no known violations of this bound. (iii) The hole energyEhrequired to form a hole in a glass‐forming liquid is equal to 2RT∞. (iv) A glass‐forming liquid tends to an isofree volume state atT∞. The calculated hole fraction equalse−3= 0.0498. (v) A correlation has been found between the hole energy and a viscosity parameter. This correlation is sensitive to the chemical structure of a polymer chain backbone. (vi) Both WLF constants,C1andC2, can be predicted from the observed &Dgr;&agr; and viscosity‐temperature behavior. Excellent agreement has been obtained for polyvinyl acetate and a nonpolymeric glass‐forming liquid, tri‐&agr;‐naphtyhl benzene. (vii) Even though the theory is a free‐volume theory, the temperature derivative of the viscosity at constant volume is nonzero when we identifyT∞with the second‐order phase transition temperature of the Gibbs‐DiMarzio theory.

ISSN:0021-8979    

DOI:10.1063/1.1663037

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A previous theory of thickening has been extended to encompass the possible dependence of cooperative chain transport on lamella thickness and crystallinity changes during annealing. These have marked effects on the thickening rate leading to changes in slope and departures from straight‐line behavior of the plots of lamella thickness versus the logarithm of time. The resulting curves bear a resemblance to many exprimental ones in the literature. Also brought out by the analysis is the important fact that the volumes of the coherently thickening domains are not known from experiment.

ISSN:0021-8979    

DOI:10.1063/1.1663038

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Holographic interferometry has been used to determine the differential stress concentration at the tip of a craze as a function of over‐all strain. The differential stress concentration factor &dgr;K&sgr;yyis unity at low strains. Upon further strain increase, &dgr;K&sgr;yyincreases, passing through two maxima before it finally decreases again to approximately a value of unity before fracture. In addition, the differential craze opening displacements of, and stress increments borne by, various regions along the craze have been determined as a function of strain. It is found that the craze opens unevenly, with the base of the craze opening at lower applied stresses than the craze tip. As a result, the differential stress concentration in the craze at a point well behind the craze tip can be greater than that at the craze tip. The strain dependence of &dgr;K&sgr;yyis in qualitative agreement with that expected, given the nonlinear stress‐strain curve of similar crazes measured by Kambour and Kopp. A detailed explanation of the stress concentration and the uneven craze opening requires consideration of the structural differences between craze fibers in the base and tip of the craze as well as the possibility of structure differences along individual fibers in the craze.

ISSN:0021-8979    

DOI:10.1063/1.1663039

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A two‐site model for a relaxation process has been used in conjunction with the results of illustrative potential‐energy calculations on a model system to examine the effects of isolated methyl branches on the chain packing and mechanical relaxations of a linear hydrocarbon host crystal. The results indicate that a branched molecule can be accommodated in an array of linear chains in two different modes of packing and that each mode has two orientations. For one of the modes, the two orientations have nearly equal energies. Upon mechanical deformation of the array, this mode gives rise to a relaxation. The relative strengths are evaluated for different deformations, some of which yield values of the order of those observed experimentally. This relaxation is much weaker for unbranched chains in the planar zigzag conformation.

ISSN:0021-8979    

DOI:10.1063/1.1663040

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Characteristic vapor‐grown tungsten whiskers on tungsten substrates were studied by means of a field emission and a transmission electron microscope. The whisker growth was found to be induced by high‐field vacuum discharges caused by tungsten oxide vapors. By transmission electron microscopy of a typical specimen, evidence was obtained that the whisker growth can be accounted for by the screw‐dislocation mechanism of crystal growth.

ISSN:0021-8979    

DOI:10.1063/1.1663041

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The nucleus growth rate in the initial stages of thin‐film formation has been discussed on the basis of the collision theory of a two‐dimensional gas and the diffusion theory of surface adatoms. It has been shown that, in the formulation of the area of the capture zone, the former theory is suitable for small nuclei (&rgr; < 0.27) and the latter for large nuclei (&rgr; > 0.27), &rgr; being the ratio of the nucleus radius to one half of the mean diffusion distance of single adatoms. The foregoing theoretical considerations were examined by the deposition experiment of bismuth films onto mica substrates. It has been found that the calculated deposition time, required for obtaining amount of deposits, agrees well with the observed one.

ISSN:0021-8979    

DOI:10.1063/1.1663042

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An approximate nonlinear theory is developed to describe finite‐amplitude wave propagation parallel to the alternating layers of a laminated composite with elastic‐plastic constituents. Model construction is based upon an asymptotic method in which dominant signal wavelengths are assumed large compared to typical composite microdimensions. The final equations evolve as a one‐dimensional binary mixture theory.

ISSN:0021-8979    

DOI:10.1063/1.1663043

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An approximate nonlinear theory is developed to describe waveguide‐type propagation in unidirectional fibrous composites. The model, which is an extension of a previously developed laminate formulation, explicitly considers the effects of thermodynamics, finite deformations, and nonlinear (elastic‐plastic) constitutive behavior. The theory contains microstructure and yields information on stress, deformation, and internal energy within individual components. The resulting equations assume the form of a one‐dimensional binary mixture theory. Transient wave propagation solutions are obtained numerically, and are compared with essentially exact data from a well‐known two‐dimensional finite difference code in an effort to extract information concerning accuracy and computational economy of the mixture model.

ISSN:0021-8979    

DOI:10.1063/1.1663044

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The annealing characteristics of 50‐keV (2–3) × 1011/cm211B+‐implantedp‐channel MOS transistors were investigated from 300 to 900°C. Below 500°C, the number of activated atomsNIIdecreased rapidly with decreasing anneal temperature and theC‐Vcharacteristics showed gradual distortions. This was presumably due to surface states induced by the ion implantation. Above 500°C,NIIincreased only slightly with increasing anneal temperature and the slope of theC‐Vcharacteristics in the transition region was larger than that of the unimplanted sample. Corresponding to the above features, the gain term increased near 500°C to a value about 30% larger than that of the unimplanted sample, while the breakdown voltage decreased below 500°C. Equivalent noise voltage decreased abruptly from 500 to 600°C. However, at lower drain current levels, the generation‐recombination noise spectrum did not disappear, even after a 900°C anneal. In addition, reverse‐annealing‐like phenomena were observed in the equivalent noise voltage between 350 and 450°C. The results of surface recombination velocity measurements were consistent qualitatively with the results of equivalent noise‐voltage measurements. Furthermore, device stability was confirmed by positive and negative bias‐temperature treatments (250°C, 1 h,Eox= ± 6.7 × 105V/cm) for devices annealed above 450°C.

ISSN:0021-8979    

DOI:10.1063/1.1663045

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The stress relaxation behavior of single‐crystal MgO, single‐crystal CaF2, and polycrystalline AgCl has been examined to assess if the assumption of constancy of structure during relaxation is valid. It is shown that structural change occurs in all three materials, being severe at small plastic strains in the case of MgO and CaF2. In polycrystalline AgCl, the structural change is due to recovery and increases with increasing plastic strain.

ISSN:0021-8979    

DOI:10.1063/1.1663046

出版商:AIP    

年代:1974

数据来源: AIP