Temperature modulated optical refractometry: A quasi-isothermal method to determine the dynamic volume expansion coefficient

in Thermochimica Acta (2013), 555

The volume expansion coefficient is a thermodynamic key parameter yielding insight into molecular cohesion and organization of condensed matter. We present here the novel experimental technique ... [more ▼]

The volume expansion coefficient is a thermodynamic key parameter yielding insight into molecular cohesion and organization of condensed matter. We present here the novel experimental technique temperature modulated optical refractometry (TMOR) to determine not only the static but also the dynamic volume expansion coefficient of transparent condensed matter of cubic or isotropic symmetry. A specialty of TMOR is its capability to measure the volume expansion coefficient under quasi-isothermal conditions. In this experimental mode TMOR is able to differentiate between static, dynamic and kinetic contributions to the volume expansion coefficient. Due to these features TMOR especially qualifies for the investigation of structural changes provoked by structural phase transitions, glass transitions and other structure-related transformations in transparent condensed matter. The scientific potential of this novel experimental technique is demonstrated by evidencing anomalies of the complex volume expansion coefficient accompanying the chemically induced glass transition occurring during the formation of a covalently cross-linked epoxy network. [less ▲]

Optical Refraction: an alternative view on the effect of nanoparticles on polymeric network formation and the resulting nanocomposites

Presentation (2011, January 14)

Thermal and chemical glass transition of thermosets in the presence of two types of inorganic nanoparticles

in Thermoplastic and thermosetting polymers and composites (2011)

Interactions between silica nanoparticles and an epoxy resin before and during network formation.

in Polymer (2009), 50(14), 3211-3219

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica ... [more ▼]

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica nanoparticles and an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) have been studied before and during network formation (curing). Rheology and mainly temperature modulated differential scanning calorimetry (TMDSC) have been used to investigate interactions between the silica nanoparticles and molecules of the epoxy oligomer or molecules of the growing epoxy network. Measurements of the complex specific heat capacity before curing showed that interactions between the nanoparticles and DGEBA molecules are very weak. An expression for an effective specific heat capacity of the silica nanoparticles could be deduced. Examination of the isothermal curing process after addition of an amine hardener yielded evidences for a restricted molecular mobility of the reactants in the cause of network formation. These restrictions could be overcome by increasing the curing temperature. No evidences for an incorporation of the silica nanoparticles into the epoxy network, i.e. for a strong chemical bonding to the network, were found. Interactions between the silica nanoparticles and the epoxy resins under study are assumed to be of a physical nature at all stages of network formation. [less ▲]