Stress optical sensitivity

Transparent plastic parts are examined for stress-optical sensitivity by using a relatively simple setup, as shown in Figure 6-5. The object to be examined is placed in... 

Figure 6-5. Setup for examination of stress-optical sensitivity. (Reprinted with permission of McGraw-Hill Company.)...

Figure 6-7. Light box for stress-optical sensitivity examination.

Stress optical sensitivity The ability of some materials to exhibit double refraction of light when placed under stress is referred to as stress-optical sensitivity. 

Define a locally anisotropic property as a property whose value is highly sensitive to whether each atom or bond is in the chain backbone or in a side group. By contrast, while the value of a globally anisotropic property may be very sensitive to the overall orientation of the polymer chains, it is somewhat less sensitive to the precise location of any given atom or bond in the structure. For example, the refractive index is a globally anisotropic property. The stress-optic coefficient, whose value depends both on the refractive index and on the difference in the polarizability of a polymer chain segment parallel and perpendicular to the chain, is a locally... 

The stress-induced birefringence is used to characterize striae five different quality levels are distinguished depending on the optical path difference caused by the striae. The path difference is measured with white light and given in nm. The standard quality may have striae causing a maximum optical path difference of less than 60 nm. For applications with very strict striae requirements the stress optical method is not sensitive enough in these cases... 

This is a very important feature of XRDI. While some optical techniques can reveal surface stresses, the sensitivity of X-rays is much higher. X-rays can reveal subsurface stresses, and the technique can be made quantitative. 

As stressed in the introduction, the main difficulty ofthe voltaic cell method of investigating systems is its lack of molecular specificity. Therefore, complementary information should be obtained by using techniques sensitive to the polar ordering and arrangement of molecules in a surface or interfacial layer, such as optical, spectroscopic, and scanning tunneling microscope methods. " ... 

In this chapter, the motivations to adopt MLR systems for optical e-beam, x-ray, and ion-beam lithographic systems will be given, followed by a survey of published MLR systems. Specific practical considerations such as planarization, pinhole and additive defects, interfacial layer, etch residue, film stress, interference effects, spectral transmission, inspection and resist stripping will be discussed. The MLR systems will be compared in terms of resolution, aspect ratio, sensitivity, process complexity and cost. 

Optical measurements often have a greater sensitivity compared with mechanical measurements. Semidilute polymers, for example, may not be sufficiently viscous to permit reliable transient stress measurements or steady state normal stress measurements. Chow and coworkers [113] used two-color flow birefringence to study semidilute solutions of the semirigid biopolymer, collagen, and used the results to test the Doi and Edwards model discussed in section 7.1.6.4. That work concluded that the model could successfully account for the observed birefringence and orientation angles if modifications to the model proposed by Marrucci and Grizzuti [114] that account for polydispersity, were used. 

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