FOURIER-TRANSFORM INFRARED MICROSPECTROSCOPY OF PHASE-SEPARATED MIXED BIOPOLYMER GELS

We present results which show how Fourier transform infrared (FTIR) microspectroscopy can be used as a valuable tool in the study of phase-separated mixed biopolymer solutions and gels. The work in this paper deals specifically with the ternary amylopectin-gelatin-D2O system which forms thermoreversible gels when a hot mixed solution is cooled to room temperature. First, we show how the integrated area of particular infrared absorption peaks from the two polymers can be used as an estimate for composition, and we use this approach to monitor the spatial fluctuations in composition by tracking across a sample and also to monitor changes in composition with time at fixed position. We also use this approach to establish the scale upon which phase separation takes place by taking the infrared spectrum over a range of sampling sizes at fixed position. Second, we use FTIR microspectroscopy coupled with partial least-squares analysis to determine quantitatively polymer concentration in the micro-phase-separated domains of a mixed gel. From a comparison of these concentrations with the previously determined equilibrium phase diagram of this system, we find that for samples held for long enough above the gelation temperature of either component before quenching, the concentration in the phase-separated domains of the gel are the same as those found at equilibrium in the liquid-liquid bulk phase-separated phases.