Lawrence E. Nielsen

Models for the Permeability of Filled Polymer Systems

Abstract A theory has been developed which predicts the minimum permeability that can be expected for a polymer filled with platelike particles. Models are also developed for the permeability of liquids through filled polymers when the liquid adsorbs or collects at the filler-polymer interface. Some of the cases discussed include different types of dispersions, orientation of filler particles, and the effects of filler aggregation. Permeability, especially of liquids, is extremely complex, and many different types of behavior can be expected.

Generalized Equation for the Elastic Moduli of Composite Materials

A generalized equation is proposed for the relative elastic moduli of composite materials. By the introduction of a generalized Einstein coefficient and a function which considers the maximum volumetric peaking fraction of the filler phase, the moduli of many types of composite systems can be calculated.

Mechanical Properties of Particulate-Filled Systems

The theory of the elastic moduli of filled systems is reviewed from the interests of the experimental scientist rather than that of the theoretician. From the many theories and equations to be found in the literature, only those which fit closest to what is considered to be the best experimental data are selected for dis cussion. The effects of filler concentration, size, shape, and agglomeration are reviewed as well as the effects of interfacial adhesion. Based largely on experimental experience rather than theory, the general behavior of the stress-strain and dynamic mechanical properties of filled systems are summarized. Theoret ical equations are presented which cover the wide variations found in experimental determinations of thermal coefficients of expansion. To give some perspective to the scientist interested in all types of composite materials, a comparison is made between the modulus of an isotropic composite filled with spherical par ticles and the moduli of anisotropic composite containing uni axially oriented fibers.

Morphology and the Elastic Modulus of Block Polymers and Polyblends

SummaryThe theory of the elastic moduli of composite materials in which an inversion of the phases can occur is reviewed. The morphology of the system and the packing fraction of the dispersed phase are important in determining the moduli. The applicability of the theoretical equations is illustrated for four systems of block polymers and polyblends. In three of the systems, phase inversion occurs. Agreement between theory and experiment is good, and where the morphology of the composites is known, the moduliagree with the values expected for that morphology.ZusammenfassungDie Elastizitätsmodul-Theorie der zusammengesetzten Stoffe, in welchen eine Phaseninversion vorkommen kann, wird untersucht. Die Systemmorphologie und die Packungsfraktion der dispersen Phase sind für die Modulbestimmung wichtig. Die Anwendbarkeit der theoretischen Gleichungen ist für vier Systeme von Blockpolymeren und Polygemischen veranschaulicht. Eine Phaseninversion kommt in drei von den Systemen vor. Die Theorie und Praxis sind in einer guten Übereinstimmung, und da, wo die Morphologie der zusammengesetzten Stoffe bekannt ist, stimmen die Moduli mit den für die Morphologie erwarteten Werten überein.

Coalescence of liquid drops at oil-water interfaces

Abstract Measurements were made of the length of time single drops can exist at an oil-water interface before coalescence takes place with a bulk phase of the same composition as the drop. The effect of stabilizing agents soluble in either the oil or water phases was investigated. Factors investigated included: ( 1 ) temperature; ( 2 ) size of drops and curvature of O-W interfaces; ( 3 ) O/W vs. W/O drops; ( 4 ) kind of oil; ( 5 ) mutual solubility of oil and water phases; ( 6 ) type of stabilizing agent, its concentration, pH, interfacial viscosity, and rigidity. The stability of drops decreases as the temperature is raised; the temperature dependence depends upon both the type of oil and the stabilizing agent. Oil drops are generally more stable than water drops when the stabilizing agent is water-soluble; the opposite is true for oil-soluble stabilizers. Oil-water phases which are mutually saturated with each other form more stable drops than unsaturated systems. The lifetime of drops depends roughly upon the cube root of the concentration of stabilizing agent in general. Stabilizers which produce a large viscosity or rigidity at the O-W interface also give stable drops; however, some good stabilizers show no interfacial viscosity or rigidity. Polyelectrolytes such as polymethacrylic acid and carboxymethyl cellulose stabilize drops better as acids than as salts; this behavior correlates with the interfacial viscosity behavior but not with the bulk solution viscosity. Simple mechanical models of drop coalescence can explain only some of the observed results. Many of the data may be understood in terms of the generalizations: ( 1 ) any factor which disturbs the O-W interface on a molecular scale decreases the stability of drops; ( 2 ) many stabilizers are most effective when they are on the verge of precipitation.

A Recording Torsion Pendulum for the Measurement of the Dynamic Mechanical Properties of Plastics and Rubbers

A recording instrument for measuring the dynamic shear modulus and mechanical damping of plastic and rubber‐like materials using the principle of the torsion pendulum has been constructed. The mechanical oscillations are converted into electrical potentials for recording by a torque measuring device which is actuated by a differential transformer. The apparatus is capable of measuring the modulus and damping of materials over an extremely wide range.

Characterization of Network Structure of Epoxy Resins by Dynamic Mechanical and Liquid Swelling Tests

Abstract A combination of dynamic mechanical and swelling properties has been used to elucidate the structure of epoxy resin systems as a function of time and temperature of cure, concentration of flexibilizer, and curing agent concentration. The dynamic properties of the resin in the rubbery region were used to determine the molecular weights between cross-links. The poor network structure formed with epoxies is shown by the dynamic and swelling tests. The existence of heterogeneity or two phases has been found in the epoxy resin system under certain polymerization conditions. Broad damping peaks may not be due to chemical heterogeneity but may be the result of the curing reaction continuing during the tests.

Mechanical and Electrical Properties of Plasticized Vinyl Chloride Compositions

The temperature dependence of the dynamic mechanical and a.c. electrical properties of a given polyvinyl chloride plasticizer composition can be characterized by two quantities: (a) the transition temperature which is defined as the temperature of maximum dissipation factor and (b) the half‐widths of the loss factor‐temperature curve. A simple relationship exists between the transition temperature determined mechanically or electrically and the volume fraction of a compatible plasticizer. The modification of this relationship for non‐compatible plasticizer has been indicated. The half‐width is a function of the volume fraction of the plasticizer, although this relationship is not as simple as the one obtained for the transition temperature. A simple correlation exists between the electrical and mechanical half‐width. The compliance measured in tensile creep has been found to be a function of the applied load and the compliance‐load relationship varies depending on the region in which the material finds it...

Effect of Crystallinity on the Dynamic Mechanical Properties of Polyethylenes

Six polyethylenes which differed widely in the degree of crystallinity were studied. The crystallinity was determined from density measurements. Both the density and the dynamic mechanical measurements were made over the temperature range from 25°C to above the melting point of the material.The dynamic shear modulus drops rapidly as the melting point is approached. The mechanical damping goes through a maximum near 60°C and then through a minimum just below the melting point. It is possible to predict the density of any of the polyethylenes at any temperature below the melting point from the value of the shear modulus at the same temperature. The more crystalline materials have the higher shear moduli and the higher melting points.

Mechanical Properties of Oriented Polystyrene Film

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...