A torsional dilatometer for volume change measurements on deformed glasses: Instrument description and measurements on equilibrated glasses

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Abstract
An automated mercury dilatometer has been designed and built for the purpose of making volume change measurements on cylindrical samples subjected to torsional deformations. In its current configuration the instrument takes readings of torque, normal force, and volume change upon application of a twist at one end of the sample. Volume change sensitivity of approximately 2× 10−6cm3 makes possible relative volume change measurements of the order of ΔV/V 0≂10−7 given the sample geometry. Over long times temperaturestability limits this to approximately 2.5×10−5. The instrument is described and preliminary measurements are presented for epoxy glasses which have been equilibrated by annealing near to the glass transition. The results show that the volume of the sample tested at temperatures ranging from 10 K below the conventionally measuredglass transitiontemperatureT g to T g increases upon application of a torsional deformation. This result is contrary to results reported in the literature for samples tested well below T g .

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