Higher crystallinity increases thermal conductivity because of which mechanism?

• A. Increased electron mobility
• B. Increased chain stiffness
• C. Increased coordination of molecular chain vibrations
• D. Decreased phonon scattering

Answer: (C)

Heat is carried in solids mainly by phonons, the lattice vibrations. When a polymer has more crystalline regions, the chains are arranged in a regular, orderly way, so neighboring chains can vibrate together more coherently. This coordinated vibration lets vibrational energy move across the material with fewer interruptions, effectively increasing the phonon mean free path and raising thermal conductivity. Electron transport isn’t the main heat mechanism in polymers, so options tied to electron mobility aren’t the driving factor here. While chain stiffness and reduced scattering relate to heat flow, the essential mechanism highlighted by higher crystallinity is the improved coordination of molecular chain vibrations across the crystal network.