摘要:

When thin films of polar plastic materials are subjected to d.c. potentials of 10 to 300 volts per mil they exhibit current fluctuations (with frequencies in the range of 60 to 1000 c.p.s.) which last for minutes and which even persist for a few seconds on removing the voltage. These fluctuations are about 1000 fold above the noise level of the circuit and are about 1 percent of the steady d.c. current. They eventually die out but can usually be restored by reversing the polarity. This noise is greater the more polar the nature of the polymer and the higher its moisture content. The effect seems to arise from water or impurity ions which can jump whenever a hole opens between polymer chains and is thus an activated rate process sufficiently slowed down by the highly viscous nature of the polymeric medium to be readily observable. On an oscillograph screen it is possible to see both the forward and the backward diffusion. This noise is most pronounced in Cellophane, Nylon, and copolymers of vinylidene chloride with acrylonitrile, but also appears with polystyrene stored at 86 percent relative humidity. Films of methylcellulose do not show the effect. Numerically the effect seems to arise from the random motion of groups of several hundred ions as a unit. As an extension of these ideas it is suggested and demonstrated that the moisture vapor diffusion constants for a series of polymers increase with the frequency of the loss factor maximum while the moisture vapor permeability increases with the direct current conductivity.

ISSN:0021-8979    

DOI:10.1063/1.1699688

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Emulsion‐type polymerization reactions have been accelerated by irradiation with ultrasonic energy.A magnetostriction oscillator at 15 kc gave essentially the same results as a piezoelectric oscillator at 500 kc. The rate of formation of polystyrene was doubled and higher final yields obtained using about 0.03 watt of vibrational power per cc of latex. Experiments were made to separate local heating effects from those due to vibrational energy.A thermostatted stainless steel cell was developed for irradiating butadiene emulsions under pressures up to 60 p.s.i. About ½ watt of vibrational power per cc of latex doubled the rate of reaction for GR‐S, Redox, and Redsol formulas.The ultrasonic intensity apparently must exceed a critical value before any appreciable accelerative effect is observed. Above the critical intensity, the time to reach a given yield of polymer is approximately inversely proportional to the power used.

ISSN:0021-8979    

DOI:10.1063/1.1699689

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The evidence for and against the interpretation of the ``second‐order'' transition in polymers in terms of a thermodynamic transition of the second order is reviewed and some new experimental data concerning transition in mixtures of polymers are presented. It is shown that the relaxation theory is insufficient to explain the transition, as observed by mechanical, electrical and thermal measurements. The usual objections which are raised against the assumption of a thermodynamic transition are shown to be invalid. Various molecular processes responsible for a thermodynamic transition are discussed and it is shown that the general mechanism of ``hindered'' rotation (changes in rotational configuration) is the most likely.

ISSN:0021-8979    

DOI:10.1063/1.1699690

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Cast films of polystyrene were oriented by stretching at temperatures above the softening temperature of the material and then cooled. A factorially designed experiment was carried out in which the amount of stretching, temperature of stretching, time held in the stretched state before cooling, and effect of several cycles of stretching before cooling were investigated as they affect the birefringence, the stress‐strain properties, dynamic modulus and damping, and the softening temperature of polystyrene.The values of many of the mechanical properties are more closely related to the birefringence than to the amount of hot stretching. In general, the value of the stress‐strain properties in the direction of hot stretch, the dynamic modulus, and the birefringence all increase with an increase in the amount of stretching, a decrease in temperature, an increase in rate of cooling after stretching, and a decrease in the number of times the film was stretched before finally cooling. The softening temperature is decreased in direct proportion to the birefringence. Annealed films give higher softening temperatures than films which have been stretched and then allowed to shrink before cooling.

ISSN:0021-8979    

DOI:10.1063/1.1699691

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The slope of the force‐extension curve in the Hooke's law region can be measured non‐destructively, for animal fibers, at three to fifteen minute intervals. The change of this Hookean slope with time is used to follow the course of the heterogeneous reaction between wool and a reagent.Data are presented on the interaction between concentrated neutral salt solutions and wool fibers. These results indicate that wo processes occur: (a) Relatively rapid hydration or dehydration of the fiber until equilibrium with the activity of water in the salt solution is attained; (b) Relatively slow absorption of salt ions by the fiber. Very concentrated salt solutions dehydrate the fiber so completely that absorption of salt ions is not possible. Swelling experiments and experiments involving other mechanical properties confirm these hypotheses. The interaction between wool fibers and aqueous solutions of large organic molecules follows a similar pattern.

ISSN:0021-8979    

DOI:10.1063/1.1699692

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An explicit relationship is set forth for the time‐temperature dependence of theviscoelasticphenomena in the superelastic polymers. An empirical equation that was found to represent adequately the above‐mentioned relationship over the entire multiple‐temperature curve is of the form: logtc= [C&agr;/(T−b)]+C&bgr;. Experimental verification is given for the equivalent influence of time and temperature on the creep and recovery of compounds based on Hevea, GR‐S, Neoprene GN, Butaprene, and butyl rubber. A comparison of the empirical equation with that of a theoretical reaction‐rate equation of Tobolsky and Eyring indicates a temperature dependence of the energy of activation.

ISSN:0021-8979    

DOI:10.1063/1.1699693

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The softening of a hard resin, polyvinyl chloride, by a liquid, dioctyl phthalate, is a set of processes occurring in sequence. Imbibition of the liquid is accompanied by volume reduction in the system. Dilatometer methods evaluate the amount and rate of volume decrease. The rate is temperature dependent, activation energy about 80 kcal. Solution of liquid into the resin follows with no further volume, but large dielectric change. Dielectric changes are measured on material in a cylindrical condenser, using a Schering bridge, and are rate dependent, activation energy about 110 kcal. Data are best described, assuming that segments of the polymer molecule ``react'' independently of one another.

ISSN:0021-8979    

DOI:10.1063/1.1699694

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Polyvinyl chloride resin is softened by certain liquids, called plasticizers, through a set of processes with high activation energies, 50–100 kcal. At fixed temperature, ``reaction'' rates are directly proportional to vapor pressure of the liquid. The dielectric change may be treated similarly to a chemical reaction between a solid and a vapor, and free energy of activation, &Dgr;F**, evaluated. &Dgr;F** is constant for various liquids with one resin. &Dgr;E**=&Dgr;H**+Lin this system, where &Dgr;E** is Arrhenius activation energy, &Dgr;H** energy barrier,Llatent heat of vaporization of the liquid.

ISSN:0021-8979    

DOI:10.1063/1.1699695

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The dynamic rigidities and viscosities of concentrated solutions of polyvinyl acetate in 1,2,3‐trichloropropane have been obtained from transducer and wave propagation measurements. Two polymer samples with number‐average molecular weights of 140,000 and 840,000 were studied in the lower audiofrequency range at concentrations from 3 to 40 percent and temperatures from −3 to 41°C. For each sample, when the reduced dynamic rigidityG′T0/Tcand the reduced dynamic viscosity &eegr;′/&eegr; were plotted against the reduced frequency, &ohgr;&eegr;T0/Tc, all the data superposed to give two composite dispersion functions. The distribution of Maxwellian relaxation times can be derived from the dispersion of eitherG′ or &eegr;′, and the two calculations are in reasonable agreement.

ISSN:0021-8979    

DOI:10.1063/1.1699696

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Flow and elastic properties are considered, in a qualitative manner, for the following types of materials: crystalline solids, simple liquids, glasses, and high polymers.

ISSN:0021-8979    

DOI:10.1063/1.1699697

出版商:AIP    

年代:1950

数据来源: AIP