Reaction, absorption deflection

These products are produced by the reaction of partially hydrolyzed PVAc with aldehydes. The acetal rings on these random amorphous polymer chains restrict flexibility and increase the heat deflection temperature to a value higher than that of PVAc. The heat deflection temperature of polyvinyl formal is about 90 C and is dependent on the specific composition of this complex polymer. Because of the presence of residual hydroxyl groups, commercial polyvinyl formal has a water absorption of about 1%. Polyvinyl formal has a Tg of 10S . It has a solubility parameter of about 10 H and is soluble in solvents with similar solubility parameters, such as acetone. 

This system is a rapid-serial primary screen. It uses a probe to scan from sample to sample across a catalyst wafer, analyzing reaction products at each location via mass spectrometry and/or optical absorption [1, 2, 45, 46]. The mass spectrometer is a commercial quadruple system with a custom ionizer interface. The optical absorption cell is a custom device and uses the method of photo-thermal deflection (mirage) to measure very low levels of a specific analyte. 

A simplified method for determining rate constants by DSC was introduced by Rogers (166). The deflection of the DSC curve above the baseline, >, is directly proportional to the rate of energy evolution or absorption of the sample, dqjdi, which in turn is directly proportional to the rate of reaction, da/dt. Therefore,... 

Calvo and Etchenique summarized in their review some further in situ combinations of EQCM with non-electrochemical techniques (see [35] and references therein). For example, EQCM was also combined with ellipsometry in order to study the nucleation and growth of polyaniline films (reference 24 in [35]) or the viscoelastic behavior of poly(7-methyl-L-co y-n-octadecyl-L-glutamate) [17]. EQCM was combined with UV-visible absorption spectroscopy, in order to investigate the redox reactions of viologens. A combination of EQCM and probe beam deflection, PBD, was also reported in the literature (references 29, and 30 in [35], and [81]). PBD can discriminate between anion, cation, and solvent fluxes that might be generated on the electrode surface. 

Variants of these techniques are the Photothermal Deflection Spectroscopy (PDS or Mirage effect) and Photothermal Displacement Spectroscopy (102). These techniques are based on deflection of a light beam due to refractive index gradients either In a fluid (or air) in contact with a light absorbing solid or in the solid itself. If the fluid is inert the technique can be used to measure absorption spectra of solid materials and transport properties. A version of these techniques was applied to electrochemical and photoelectrochemical systems (103). The authors describe the experimental conditions needed to separate the contributions from the temperature and concentration gradients. Once this is done the results can be correlated with the kinetics and mechanism of the electrochemical reactions. 

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