Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 11: New Instruments and Methods
CPP 11.4: Vortrag
Dienstag, 27. März 2012, 10:30–10:45, C 243
Temperature modulated optical refractometry: a novel access to structural changes in isotropic media coupling to the optical refractive index — •Ulrich Müller1, Martine Philipp2, Roland Sanctuary1, Peter Müller-Buschbaum2, and Jan-Kristian Krüger1 — 1Université du Luxembourg, Laboratoire de physique des matériaux avancés, , 162a av. de la faiencerie, Luxembourg, Luxembourg — 2TU München, LS Funktionelle Materialien, Garching, Germany
Temperature modulated optical refractometry (TMOR) is a novel technique that provides access to the dynamic thermo-optic coefficient φ*(ω)=1/ndn/dT(ω). Similar to temperature modulated calorimetry small sinusoidal temperature perturbations are applied to the sample and their effect on its refractive index n is measured. By applying linear response theory the usually complex susceptibility φ*(ω) is obtained. Simultaneously, the mean refractive index yields information about kinetically induced structural changes. Using the Lorenz-Lorentz equation to relate the refractive index to the mass density the complex coefficient of thermal expansion α*(ω) can be calculated out of n and φ*(ω). This novel technique is especially suited for the investigation of (isothermal) structure-changing processes like polymerization, solvent evaporation, and isostructural phase transitions (e.g. glass transitions or volume phase transitions), where it allows for an easy discrimination of kinetic and dynamic contributions. Investigations of the chemically induced glass transition in an epoxy and of the volume phase transition in PNIPAM/water are presented as applications.