Optical studies of rubbers

Perhaps the major weakness of all these theories is that they are too much concerned with getting the right answer and too little concerned with what actually happens at the interface. This is brought out most clearly by Schallamach s recent paper in which he described an optical study of the contact between a rubber hemispherical slider and a transparent perspex flat. He shows that adhesion between the surfaces causes buckling of the rubber and generates waves of detachment" which traverse the contact area at a high speed from front to rear. The energy dissipation process must be very different from that proposed in most of the past theories. These waves of detachment are observed with hard, as well as with soft rubbers (Courtel ), but whether they always occur and under what conditions is not yet established. Evidently we need a new look, literally, at the problem. 

Since the tack and green strength of these rubbers may depend on their ability to undergo strain induced crystallization, this behavior was studied and compared with that shown by NR. Information on the strain induced crystallization behavior of these experimental rubbers was obtained from x-ray diffraction measurements and from rheo-optical studies. 

Study of the morphological features of EEC indicate precipitation in the course of the epoxy resin cm"e of particles of the discrete phase of the rubber, the dispersion of which in the epoxy polymer matrix has a considerable effect on the mechanical properties of the latter. If the rubber particles are large enough, they can be detected by optical microscopy, but the most important results are obtained by electron microscopy. 

Walters and Keyte [102] first observed dispersed particles in blends of rubber pol)m[iers by phase contrast optical microscopy. Marsh et al [103] studied elastomer blends by both optical phase contrast and TEM. Electron microscopy was applied to study blends of natural rubber, st)n-ene-butadiene rubber (SBR), a s-polybuta-diene (PB) and chlorobutyl rubber [104]. It became obvious that both hardening of the... 

Molau and Keskkula [351] were among the first to study the mechanism of particle formation in rubber containing polymers. They showed that phase separation occurs between the rubber and a vinyl polymer during the polymerization of solutions of rubber in vinyl monomers which is followed by formation of an oil-in-oil emulsion. During phase inversion of the emulsion, rubber solution droplets are formed which change into solid rubber particles in the final polymer. Structural investigations by phase contrast optical microscopy, shown in this chapter (Section 5.3), reveal dispersed particle size and distribution. Ugelstad and Mork [352] reported on new diffusion methods for the preparation of emulsions and polymer dispersions where the size and distribution of the latex particles were monitored by very simple optical, SEM and TEM methods. A microemulsion polymerization has been reported for the first time [353] with... 

The conventional spectrometer with a dispersive prism or grating has been largely superseded by the Fourier transform (FTIR) technique. This uses a moving mirror in an interferometer to produce an optical transform of the infrared signal. Numerical Fourier analysis gives the relation of intensity and frequency, that is, the IR spectrum. FTIR can be used to analyze gases, liquids and solids with minimal preparation in short times. FTIR has been applied to the study of many systems, including adsorption on polymer surfaces, chemical modification and irradiation of polymers and oxidation of rubbers [36]. The application of infrared spectroscopy to the study of polymers has been reviewed by Bower and Maddams [35]. 

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