Light scattering from solid polymers

The sorbent materials used to construct this type of sensor are widely varied (ion exchangers, adsorbent solids, polymers) and are employed as particles (larger than 30 pm in order to avoid overpressure in the flow system) or films. Most of these sensors are optical and rely on absorption, reflectance or molecular fluorescence measurements. In order to ensure that the sensing microzone is fully compatible with the detector, the sorbent material used must be as transparent as possible (photometry) or give rise to no appreciable light scatter (fluorimetry) so that the baseline (resulting from passage of the carrier) may be as low as possible. 

From among the natural carbohydrate polymers, we mention here cellulose, chitin and its deacetylated form chitosan, hyaluronic acid (hyaluronan), and heparin. Apart from cellulose, the monomer-unit sequences are not strictly regular, but the structures given below are representative. Chitosan, hyaluronic acid, and heparin are water-soluble because they carry electrically-charged functions. Since cellulose and chitin are insoluble in water, most of their radiation chemistry has been done in the solid state, as discussed below. Yields of molecular-weight reduction have usually been determined by viscosimetry and, more recently, by the laser light-scattering technique. 

Figure 3. Mass diffusion coefficient D of the polyst3T ene-toluene solutions as a function of the polymer concentration. The open symbols indicate data obtained with an optical beam-bending technique [22] and the filled S3Tnbols data obtained from light scattering. The dashed line represents Eq. (5) and the solid curve represents Eq.(7).

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