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Interstellar dust grains are non-spherical and, in some environments,partially aligned along the direction of the interstellar magnetic field.Numerous alignment theories have been proposed, all of which examine the grainrotational dynamics. In 1999, Lazarian & Draine introduced the importantconcept of thermal flipping, in which internal relaxation processes induce thegrain body to flip while its angular momentum remains fixed. Through detailednumerical simulations, we study the role of thermal flipping on the graindynamics during periods of relatively slow rotation, known as `crossovers', forthe special case of a spheroidal grain with a non-uniform mass distribution.Lazarian & Draine proposed that rapid flipping during a crossover would lead to`thermal trapping', in which a systematic torque, fixed relative to the grainbody, would time average to zero, delaying spin-up to larger rotational speeds.We find that the time-averaged systematic torque is not zero during thecrossover and that thermal trapping is not prevalent. As an application, weexamine whether the classic Davis-Greenstein alignment mechanism is viable, forgrains residing in the cold neutral medium and lacking superparamagneticinclusions. We find that Davis-Greenstein alignment is not hindered by thermaltrapping, but argue that it is, nevertheless, too inefficient to yield thealignment of large grains responsible for optical and infrared starlightpolarization. Davis-Greenstein alignment of small grains could potentiallycontribute to the observed ultraviolet polarization. The theoretical andcomputational tools developed here can also be applied to analyses of alignmentvia radiative torques and rotational disruption of grains.

The alignment of interstellar dust grains: thermal flipping and the Davis-Greenstein mechanism