Polystyrene refractive index

As mentioned earlier, unmodified polystyrene first found application where rigidity and low cost were important prerequisites. Other useful properties were the transparency and high refractive index, freedom from taste, odour and toxicity, good electrical insulation characteristics, low water absorption and comparatively easy processability. Carefully designed and well-made articles from polystyrene were often found to be perfectly suitable for the end-use intended. On the other hand the extensive use of the polymers in badly designed and badly made products which broke only too easily caused a reaction away from the homopolymer. This resulted, first of all, in the development of the high-impact polystyrene and today this is more important than the unmodified polymer (60% of Western European market). 

In order to calculate particle size distributions in the adsorption regime and also to determine the relative effects of wavelength on the extinction cross section and imaginary refractive index of the particles, a series of turbidity meas irements were made on the polystyrene standards using a variable wavelength UV detector. More detailed discussions are presented elsewhere (23) > shown here is a brief summary of some of the major results and conclusions. 

Figure 11. Imaginary part of complex refractive index for polystyrene...

Published refractive index data for the mobile phase, polystyrene, polyacrylonitrile, and the two monomers were used to calculate refractive index detector calibrations for the two homopolymers. The published data were used to determine relationship between refractive index increments of monomer and corresponding homopolymer. Chromatographic refractometer calibrations for the two homopelymers were then calculated from experimentally measured calibration data for the two monomers. 

Molecular weights were measured by gel permeation chromatography on a Perkin-Elmer Series 10 Liquid Chromatograph using tetrahydro-furan as solvent and refractive index as the detection mode. Standards were polystyrene, and reported molecular weights for the poly-siloxanes do not include a correction. 

Gel permeation chromatography was performed in tetrahydrofuran using a Waters pump system and a Model 410 differential refractive index detector for the eluant. Five Ultrastyragel columns with nominal porosities ranging from 500 to 105 angstroms were used for all the samples and the polystyrene standards. 

GPC analyses were performed with a Waters Model 244 chromatograph using Microstyragel columns. Both differential refractive index and UV (254 nm) detectors were used. THF was the eluant with a flow rate of 2 ml min-1. A benzene internal standard was employed to correct for flow variations and for normalization of the integrated peak areas. The column set was calibrated using nearly monodispersed polystyrene standards and all molecular data are reported as polystyrene-equivalent molecular weights. 

Table 3. Molecular weight M of a monodisperse polystyrene fraction in solvents of different refractive index no role of refractive index correction factor74)...

In Eq. (88), dn0/dl expresses how the refractive index % of the binary solvent alone varies with its composition expressed as volume fraction 4>y of liquid-1. Clearly, if liquids 1 and 3 are iso-refractive or nearly so, then M = M2, that is, a LS experiment will yield the true molecular weight irrespective of the composition of the mixed solvent. This situation is exemplified133) by the system polystyrene -ethyl-acetate (l)-ethanol (3) for which the molecular weight in mixed solvents of different 0i is the same as that obtained in pure ethylacetate (Fig. 40). The values of dn /d0j for the mixed solvents are only of the very small order of ca. 0.01, whilst the values of dn/dc for the polymer solutions are large (ca. 0.22 ml/g). 

The gratings can also be made in situ by holographic irradiation as was demonstrated for low molecular stilbenes in a polystyrene matrix [197]. Here, the spatial modulation of gain dominates over the refractive index modulation in its contribution to optical feedback. The principles of holographic irradiation will be described in Section VIII, which discusses photosensitive materials. 

Flow patterns of hydrodynamic systems like the compendial dissolution apparatus may be qualitatively characterized by means of dilute dye injection (e.g., methylene blue) or by techniques using particulate materials such as aluminum powders or polystyrene particles. Flow patterns may be also visualized by taking advantage of density or pH differences within the fluid stream. The Schlieren method, for instance, is based on refraction index measurement. Hot wire anemo-metry is an appropriate method to quantitatively characterize flow rates. The flow rate is proportional to the cooling rate of a thin hot wire presented to the stream. Using laser Doppler... 

In general, measuring beads requires less laser power than measuring cells because of their higher index of refraction (n 1.5 for polystyrene beads vs. n 1.37 for cells).15 The optical force imparted to a particle scales with the difference in index of refraction between the particle and the fluidic medium.16 For bead measurements, we typically operate at a laser power of 2.5 W, whereas for cell measurements the laser is operated at 10 W to obtain similar displacements. These relative power levels are in line with the comparative refractive index differences between the two different particle types and water. 

Gel permeation chromatograms were generated from a Waters Associates, Inc. GPC equipped with a refractive index detector. The following operating conditions were employed mobile phase, THF flow rate 1 ml/min., columns ICP, 10, 500, 100 A . Sample concentrations were prepared at 0.2% (w/w) a 100 microliter aliquot was used for molecular weight analysis. Standard polystyrene samples (Polymer Laboratories, Inc.) were used to create a calibration curve. 

Figure 8. Gel filtration of ethylated (/ -0-4)-(/ -/ )-DHP 16. Solid line Ethylated (/ -0-4)-(/ -/ )-DHP 16 after removal of low molecular weight fractions. The column was calibrated with (/ -0-4)-(/ -/ ) lignin substructure model trimer 6 (molecular weight 642) /3-0-4 lignin model dimer 1 (molecular weight 348) and polystyrenes of molecular weight 9000, 4000 (void), 2200 (indicated by A). Column Sephadex LH-20, 1.1 x 48 cm. Eluent DMF, 13.5-14.4 ml/hr. Detector Refractive index detector RI-2 (Japan Analytical Industry Co., Ltd.).

In one example, the colloidal structure, is made by sedimentation of polystyrene beads, giving voids in the range 120-1000 mn, and the voids are filled with TiO generated from titanium tetrapropoxide. The polystyrene bead lattice is then removed by calcining to give an iridescent material, but not with a full photonic band gap. In this case one of the controlling factors is the refractive index of the matrix, which needs to be greater than 2.8. 

Calibration of these single-particle counters is usually carried out using monodisperse polystyrene latex or polyvinyl latex spheres, which are available in sizes from 0.1 to 3 /im and have a refractive index of 1.6 alternatively, aerosols with lower refractive indices may be generated from liquids such as dioctyl phthalate (m = 1.49). Whitby and Willeke (1979) discuss the... 

---