The Molecular Mechanism of α-Resorcinol’s Asymmetric Crystal Growth from the Melt

Abstract

Polar crystals are characterized by an axis that has a nonzero dipole due to the nature of the molecular packing. For these crystals, the growth rates of the faces delineating the polar axis are generally expected to be equal. Recent experiments, however, have revealed a few exceptions where the growth of these faces from the vapor phase is asymmetric, a notable case being crystals of resorcinol. Here, we present the mechanics of resorcinol crystal growth from the melt for the hemihedral faces (011) and (01̅ 1̅ ) delineating the polar axis as revealed by molecular dynamics simulations. The simulations reveal asymmetric growth consistent with experiment. The asymmetry is attributed to the slow-growing (011) face being less able to direct the correct alignment of the oncoming molecules and the presence of an alternate resorcinol conformation that readily incorporates into the lattice at this surface, serving to poison and retard subsequent growth. Putting the issue of the rogue conformation aside, the identified factors that influence molecular recognition are considered to be applicable to other polar crystals, which suggest asymmetric growth along the polar axis to be a common feature. ■ SIGNIFICANCE STATEMENTPolar crystals form the basis for important functional materials. For these crystals, we do not understand the nature and mechanism of crystal growth along the polar axis, which is considered to be identical at both ends. Recent experiments have revealed a few exceptions where the growth of these faces from the vapor phase is asymmetric. We have carried out molecular dynamics simulations on one of these exceptional cases, resorcinol. The simulations reveal the molecular processes involved and explain the asymmetric growth. The molecular recognition processes at play and the associated dynamics of molecule alignment during crystal growth suggest asymmetric growth along the polar axis to be a common feature.

Resorcinol Crystallization from the Melt: A New Ambient Phase and New “Riddles”

“…They show that the α phase in equilibrium with melt slabs capping the polar axis, do indeed grow with asymmetric rates as expected at temperatures below 60 °C. 80 Is this the last words on the resorcinol riddle? We are afraid not.…”

“…In the very latest simulation, the same authors open the door to experiments in the melt. They show that the α phase in equilibrium with melt slabs capping the polar axis, do indeed grow with asymmetric rates as expected at temperatures below 60 °C …”

Kinetics of Crystallization and Orientational Ordering in Dipolar Particle Systems

“…Different from the traditional way of imposing thermodynamic driving forces (i.e., temperature and pressure), the microscopic tuning of the dipolar orientational dissipative flux (the collective rotation dynamics and the polarization at CMIs) would usher in a new level of engineered polar particle crystal growth. Finally, the combined nonequilibrium theory/simulation approach proposed in this work could also have profound implications for the quantitative study of more complex crystallization kinetics, including i) solidification of alloys [38] (or under static magnetic fields [39]), ii) crystallization of molecules with permanent dipole moments [34,40,41] and nano-sized crystallites with net dipole moments [42,43], iii) in-plane growth of two-dimensional surface (or confined) layers of crystalline silicon [44] or ice [45,46], iv) crystal growth in fluid flows [47], v) novel phase transitions (analogous to crystallization) of particles with multiple attributes, e.g., freezing of active polar colloids [48,49], and deformable colloids [50], or orientational ferroelastic transition of rodlike dipolar particles [51].…”

Tailor‐Made Auxiliaries for Polar Growth from Melts

“…[30] Attachment energies ought not depend on the direction of the polar axis and it inspired a long discussion, many experiments, and computations directed at whether the hydrophilic or hydrophobic end of α resorcinol in solutions and vapors was faster growing. [31][32][33][34][35][36][37][38][39] These were not the last words on the resorcinol riddle. We extended the discussion to resorcinol growth from the melt while deflecting attention from the polar axis of the α phase to the polar axis of the β phase, [22] a high temperature form shortlived in solution.…”