Melting and glass transition temperatures may be determined from plots of which property versus temperature?

• A. Elastic modulus versus temperature.
• B. Stress versus strain.
• C. Temperature versus time.
• D. Specific volume versus temperature graphs.

Answer: (D)

The key idea is that phase transitions reveal themselves most directly in how a material expands with temperature. For the glass transition, the material changes from a stiff, low-expansion glassy state to a more compliant, higher-expansion rubbery state, so the specific volume vs temperature plot shows a noticeable change in slope at Tg. For melting, the solid and liquid phases have different densities and thermal expansion behavior, so the plot of specific volume versus temperature exhibits a discontinuity or a distinct intersection between the solid-branch and liquid-branch curves at the melting temperature. Together, these features make specific volume versus temperature the clearest way to identify both melting and glass transition temperatures. Other plots, like elastic modulus versus temperature or stress versus strain, can hint at Tg or melting but do not provide as direct or unambiguous a signature for both transitions.