Total internal reflection , polymer

Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

A. Itaya, T. Yamada, K. Tokuda, and H. Masuhara, Interfacial characteristics of poly(methyl methacrylate) film Aggregation of pyrene and micropolarity revealed by time-resolved total internal reflection fluorescence spectroscopy, Polym. J. 22, 697-704 (1990). 

What is even more relevant to the present subject is that a thin dielectric layer of polymer can be situated between two media without grossly distorting the optical nature of the interface, i.e. total internal reflection would occur as if no polymer layer is present even if its refractive index is unmatched to both media. Such a layer will, however, affect the intensity of the evanescent wave and particularly its depth of penetration. ... 

Chronis, N., Lee, L.R, Total internal reflection-based biochip utilizing a polymer-filled cavity with a micromirror sidewall. Labchip 2004, 4, 125-130. 

Because of total internal reflection only a fraction (l/2n where n 1.8 is the index of refraction of the polymer) is emitted through the substrate [170]. That fraction of the emitted radiation that is waveguided is partially lost as a result of residual self-absorption in the polymer and, more importantly, as a result of losses in the metal cathode and the semitransparent anode. As a result, the external quantum efficiencies are smaller than the internal quantum efficiencies. 

As discussed later, in Section 3.4, this technique is particularly well adapted to coupling to optical fibres, so a probe that can be immersed in a polymer reaction stream may be fabricated to enable spectra to be collected in real time. The principles of total internal reflection and its application in fibre-optics are discussed in more detail in Section 3.4.1. 

Another ammonia sensor speciHcally designed for use in bioliquids is based on the evanescent wave technique and can be applied to the vapor-phase determination of ammonia above blood and serum [136]. It utilizes the ninhydrin reaction occurring in the polymer coating of the fiber, and the resulting color change is monitored by total internal reflection. The probe is applicable to clinical determinations normally carried out in the vapor phase, but works irreversibly. A linear relationship exists between absorbance and ammonia concentration in the clinically useful range of 0-4.0 pg mL. Comparison with the reference method showed a correlation coefficient of 0.92. 

Figure 16.1 Fiber optics essentials, (a) Total internal reflection principle (b) optical fiber embedded in a carbon fiber-reinforced polymer (CFRP) composite [2] (c) single-mode and multi-mode fibers [3].

This relationship ensures that the critical angle of incidence of the interface is not exceeded and that total internal reflection occurs (Levi, 1980). Typical values of NA for fused SiOj fibers with polymer cladding are in the range of 0.36-0.40. The typical values of = 14° used to insert the beam of the biomedical laser into the fiber is much smaller than those values ( 21-23°) corresponding to typical NA values. The maximum value of the propagation angle a typically used in biomedical laser systems is i 4.8°. 

Surface characterization by spectroscopic techniques yields information on the functional groups and elemental composition on the surface of polymeric biomaterials. The most common spectroscopic tools used for biomedical polymers are X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), and Fourier transform infrared spectroscopy (FTIR) (diffuse reflectance and attenuated total internal reflectance modes). Each of these techniques is discussed in the succeeding text. 

The process of formation of the epoxy polymer in bulk was studied using IR spectroscopy, and on the boundary with the KRS-5 element was studied by the method of disturbed total internal reflection [20]. In 24 h the degree of conversion of the epoxy groups was 28% in bulk and was zero at the boundary. In 8 h of heating the conversion level was 70% both for bulk and at the bormdary. Formation of a surfactant... 

In many cases precision methods allowed detection of the thin layer of adhesive on the substrate surface [37—39]. For example, using disturbed total internal reflection it was shown [40] that when polyethylene was peeled off the quartz a thin layer of the polymer remained on the latter. The remnants of the polyethylene are completely washed off the quartz by xylene, which is proof of the absence of interaction between the quartz and the polyethylene. Such disintegration of adhesive-bonded joints is determined both by the adhesion interaction between the polymer and the substrate and by differences between the behavior of the polymer when in thin layers on the substrate and when in the free state [85—89]. 

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