Optical properties, foams

A complete knowledge of the cell structure of a particular polymer would require the size, shape, and location of each cell. Because this is impractical, approximations are employed. Cell size has been characterized by measurements of cell diameter [25] and of average cell volume [26,27]. Mechanical, optical, and thermal foam properties depend on cell size. 

Cell si has been characterized by measurements of the cell diameter in one or more of the three mutually perpendicular directions (143) and as a measurement of average cell volume (144,145). Mechanical, optical, and thermal properties of a foam are all dependent upon the cell size. 

The physical properties of the synthetic glycosyl derivatives of l-asparagine, L-serine, and L-threonine are reported in Tables I-V. Derivatives characterized otherwise, but without m.p. and optical rotation, have also been included. Whenever more than one reference is given, the physical constants are taken from the references printed in bold letters. The abbreviations used in the m.p. column are as follows foam., foaming dec., decomposing and soft., softening. 

Experimental Materials. All the data to be presented for these illustrations was obtained from a series of polyurethane foam samples. It is not relevant for this presentation to go into too much detail regarding the exact nature of the samples. It is merely sufficient to state they were from six different formulations, prepared and physically tested for us at an industrial laboratory. After which, our laboratory compiled extensive morphological datu on these materials. The major variable in the composition of this series of foam saaqples is the aaK>unt of water added to the stoichiometric mixture. The reaction of the isocyanate with water is critical in determining the final physical properties of the bulk sample) properties that correlate with the characteristic cellular morphology. The concentration of the tin catalyst was an additional variable in the formulation, the effect of which was to influence the polymerization reaction rate. Representative data from portions of this study will illustrate our experiences of incorporating a computer with the operation of the optical microscope. 

Polyolefins are well adapted to the mono-material concept talc-filled polypropylene and LFRT for structural parts, foamed polyethylene and polypropylene for damping, polypropy-lene/EPDM alloys or copolymers for skins. Some other functions need incompatible polymers with specific characteristics such as optical properties. Without claiming to be exhaustive, the other thermoplastic materials are ... 

Finally, for practical reasons it is useful to classify polymeric materials according to where and how they are employed. A common subdivision is that into structural polymers and functional polymers. Structural polymers are characterized by - and are used because of - their good mechanical, thermal, and chemical properties. Hence, they are primarily used as construction materials in addition to or in place of metals, ceramics, or wood in applications like plastics, fibers, films, elastomers, foams, paints, and adhesives. Functional polymers, in contrast, have completely different property profiles, for example, special electrical, optical, or biological properties. They can assume specific chemical or physical functions in devices for microelectronic, biomedical applications, analytics, synthesis, cosmetics, or hygiene. 

This property can be used to separate highly volatile and low-viscous mineral oils from oil-water dispersions.To demonstrate this,a dispersion of 20 ml of ligroin or petroleum ether in 200 ml of water is prepared in a 400 ml beaker with a fast-running mixer.Then approx. 5 g of crushed urea/formaldehyde foam are added. After 5 min the solution is filtered through a folded filter.The aqueous filtrates are optically free from dispersed hydrocarbons. In the same way a crude oil/water dispersion can be separated. 

The extinction of the luminous flux passing through a foam layer occurs as a result of light scattering (in the processes of reflection, refraction, interference and diffraction from the foam elements) and light absorption by the solution. In a polyhedral foam there are three structural elements, clearly distinct by optical properties films, Plateau borders and vertexes. The optical properties of single foam films have been widely studied (see Section 2.1.3) but these of the foam as a disperse systems are poorly considered. 

Special cells have been constructed for the study of the optical properties of foams [75], They allow a simultaneous determination of the foam optical density, the pressure in Plateau borders and the electrical conductivity of the foam. Furthermore, the foam produced by these cells is homogeneous with respect to all structural parameters (border radius and bubble size). The homogeneity of the foam formed is achieve by glass filters which provide foam drying and control on the formation of air spaces. 

Fig. 8.2. A cel) for the study of optical and electrical properties of a foam I - glass cuvette 2 - sintered...

The optical properties of single foam films have been extensively studied, but those of the foam as disperse system are poorly considered. It has been concluded that the extinction of luminous flux where I is the intensity of the light... 

Below, in Sections 5.2 and 5.3, we consider effects related to the surface tension of surfactant solution and capillarity. In Section 5.4 we present a review of the surface forces due to intermo-lecular interactions. In Section 5.5 we describe the hydrodynamic interparticle forces originating from the effects of bulk and surface viscosity and related to surfactant diffusion. Section 5.6 is devoted to the kinetics of coagulation in dispersions. Section 5.7 regards foams containing oil drops and solid particulates in relation to the antifoaming mechanisms and the exhaustion of antifoams. Finally, Sections 5.8 and 5.9 address the electrokinetic and optical properties of dispersions. 

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