Experiment 56 Measuring Refractive Index

Note At the conclusion of the experimental work with refractive index, maintain the logbook for the equipment used, recording the date, your name(s), the experiment name and number (the parts you performed), and calibration information, if applicable. 

If the refractometer uses a temperature-controlled water bath, ensure that the temperature is set properly and the pumps are circulating the temperature-controlled water through the sampling platform of the refractometer. 

Carefully clean the prism with lint-free lens paper. 

Place a drop of the liquid on the lower prism and carefully lower the upper prism. 

Look through the eyepiece and turn the compensator knob until the colored indistinct boundary between the light and dark fields becomes a sharp line. 

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The response of the experiment is the measured refractive index difference, which can be readily seen on the computer screen and also recorded by the chart recorder during operation. The descriptions of the experiments are as follows. 

Hie polarizability a(-o) a)) is involved in several linear optical experiments including refractive index measurements. Equation (93) shows that the solute molecule experiences a local field which is larger than the macroscopic field by the cavity field factor/ " and by the reaction field factor For typical media the magnitude of the product is of the order of 1.3-1.4. In the case of... 

Five shock experiments for SiCh glass were performed at pressures of 17.8, 21.8, 26.3, 32.0, and 43.4 GPa. The measured refractive index, n, and density, p, are shown in Fig. 3.9. X-ray diffraction data were measured with Mo-Ka radiation. Raman spectra in the range 115-1200 and 400-1400 cm-1 were measured for each sample [26,32,70]. 

The next step in this study is to test this control algorithm on the actual laboratory reactor. The major difficulty is the direct measurement of the state variables in the reactor (T, M, I, W). Proposed strategy is to measure total mols of polymer (T) with visible light absorption and monomer concentration (M) with IR absorption. Initiator concentration (I) can be monitored by titrating the n-butyl lithium with water and detecting the resultant butane gas in a thermal conductivity cell. Finally W can be obtained by refractive index measurements in conjuction with the other three measurements. Preliminary experiments indicate that this strategy will result in fast and accurate measurements of the state vector x. 

The advantages of SPR experiments are that only small amounts of sample are required,72 often hundreds of microliters of solutions with nanomolar to micromolar concentration of reactants and the substrate attached to the surface can oftentimes be reused after washing in buffer. The fact that changes in the refractive index values are measured avoids the need to use absorption or fluorescence markers to follow the binding kinetics. 

From the kinetic point of view SPR experiments have the advantage that both the association and dissociation processes can be measured from the two phases in one sensogram. However, it is possible for artifacts to arise from refractive index mismatch during the buffer change and, for this reason, in general the initial parts of the association and dissociation phases are excluded from the kinetic analysis.73 When multiexponential decays are observed it is important to distinguish between kinetics related to the chemistry and potential artifacts, such as conformational changes of the bound reactant or effects due to mass transport limitations.73,75 The upper limit of detectable association rate constants has been estimated to be on the order of... 

The cell is fitted with windows, and the concentration of polymer along its length is determined by optical methods which are based on measurements of refractive index of absorption solvents to be used for ultracentrifugation experiments must be chosen for difference from the polymer in both density and refractive index. An effort be made to avoid mixed solvents. Low solvent viscosity is also desirable. 

In the equation s is the measured dielectric constant and e0 the permittivity of the vacuum, M is the molar mass and p the molecular density, while Aa and A (po2) are the isotope effects on the polarizability and the square of the permanent dipole moment respectively. Unfortunately, because the isotope effects under discussion are small, and high precision in measurements of bulk phase polarization is difficult to achieve, this approach has fallen into disfavor and now is only rarely used. Polarizability isotope effects, Aa, are better determined by measuring the frequency dependence of the refractive index (see below), and isotope effects on permanent dipole moments with spectroscopic experiments. 

A quantitative measure of interaction between polymer and monomer in solution can be expressed by a value of preferential solvation. Preferential solvation can be calculated from the measurements of refractive index increments in dialysis experiments. This experiment can be illustrated as in Figure 3.1. 

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