Which term best describes the combination of viscous and elastic characteristics in polymers?

The term that best describes the combination of viscous and elastic characteristics in polymers is viscoelasticity. This phenomenon occurs in materials that exhibit both viscous (time-dependent) and elastic (time-independent) behaviors when subjected to stress or strain.

In a viscoelastic material, the response to deformation involves both the ability to return to its original shape when the stress is removed (elastic behavior) and the ability to change shape over time under constant stress (viscous behavior). This dual characteristic is crucial for understanding how polymers behave under different loading conditions, making them versatile for various applications where both elasticity and damping properties are desired.

In contrast, pseudoplasticity refers to materials that become less viscous under shear stress but do not exhibit the elastic properties of viscoelastic materials. Isotropic behavior describes materials that have identical mechanical properties in all directions, which does not specifically denote any elastic or viscous characteristics. Thermal expansion refers to the tendency of materials to change shape and size with temperature changes, without addressing the viscous or elastic properties inherent to polymers.

Thus, viscoelasticity is the most accurate term for describing the interplay of viscous and elastic characteristics in polymers.