ATR FTIR can provide information on the chemistry of new materials and the kinetics of chemical reactions. In FTIR spectra peaks are obtained that are associated with different chemical groups. Since the absorbance or height of the peak is proportional to the concentration of the chemical group, in a mixture changes in height with time can provide information on the relative rates of formation of different products.
The Perkin Elmer series 2000 FTIR spectrometer is equipped with a temperature controlled (25-200 ºC) diamond ATR unit and both Spectrum and Timebase software that allow determination of individual spectra or spectra as a function of time respectively. These spectra can be converted to profiles of absorbance versus time at chosen wavenumbers. The instrument can also be used to generate Raman spectra.
Examples Of Work Undertaken At The Institute
A variety of projects are currently utilising this technique for standard characterisation of new materials for example phosphate glasses and degradable polymers. The technique is also being applied to assess and quantify various possible reactions between dentine and chemicals used in dentistry. Reaction kinetic studies have included polymerisation of polymers and composites as well as setting kinetics of various cements for tooth and bone repair. In Figure 1 for example spectra of a brushite forming bone cement at different times after mixing are shown. In Figure 2 absorbance at the 980cm-1 peak is provided as a function of time for this cement with 2 different powder liquid ratios (PLR) and 2 temperatures. Such data can be converted into percentage conversion of a component or relative levels of reaction. For example in Figure 3 the percentage of monomer polymerised in 4 different methacrylate containing dental restorative materials determined using FTIR is given and Figure 4 the relative levels of acid reaction in four dental cements. These results can be used to explain macroscopic properties of the materials as they set.
Figure 1 ATR FTIR spectra of a brushite forming
Figure 2 Absorbance profiles for a brushite cement with PLR of 3.3 and 2.0 cement as a function of time after mixing
Figure 3 Percentage polymerisation of 4 hybrid dental restorative materials
Figure 4 Relative levels of acid neutralisation in 4 dental restorative materials