TY - JOUR

T1 - Phase transitions of n-alkanes as rotator crystals

AU - Chazhengina, S. Y.

AU - Kotelnikova, E. N.

AU - Filippova, I. V.

AU - Filatov, S. K.

PY - 2003/2/28

Y1 - 2003/2/28

N2 - Phase transitions of n-alkane homologues with n = 17-24, their solid solutions, two-phase mixtures and multicomponent mixtures with n = 17-37, of biological, geological and technological origin have been studied by high-temperature X-ray powder diffraction. In keeping with the rotator nature of n-alkanes, their thermal deformations and polymorphic transformations are discussed as a function of the thermal torsional motion of the molecules. We have shown that not only orthorhombic n-alkanes but also triclinic n-alkanes undergo consistent phase transitions from the crystal state (cryst) to the low-temperature (rot.1) and high-temperature (rot.2) rotator states. When molecules (atoms) of different kinds combine in a structure one more rotator state of n-alkanes (rot. 1 + 2), intermediate between the low-temperature (rot.1) and high-temperature (rot.2) rotator states, was identified. Each of these states is characterized by a specific form of the molecular thermal oscillation motion. The existence of crystal phase V and rotator phase RV is discussed on the basis of X-ray powder diffraction and literature data. Phase transitions of the mixtures of two crystal phases were shown to depend on the molecular symmetry (parity) of the mixed components and the difference in chain length (Δn). The distinguishing feature of the phase transition to the rotator state of multicomponent mixtures is step-wise phase separation of the solid solution during heating.

AB - Phase transitions of n-alkane homologues with n = 17-24, their solid solutions, two-phase mixtures and multicomponent mixtures with n = 17-37, of biological, geological and technological origin have been studied by high-temperature X-ray powder diffraction. In keeping with the rotator nature of n-alkanes, their thermal deformations and polymorphic transformations are discussed as a function of the thermal torsional motion of the molecules. We have shown that not only orthorhombic n-alkanes but also triclinic n-alkanes undergo consistent phase transitions from the crystal state (cryst) to the low-temperature (rot.1) and high-temperature (rot.2) rotator states. When molecules (atoms) of different kinds combine in a structure one more rotator state of n-alkanes (rot. 1 + 2), intermediate between the low-temperature (rot.1) and high-temperature (rot.2) rotator states, was identified. Each of these states is characterized by a specific form of the molecular thermal oscillation motion. The existence of crystal phase V and rotator phase RV is discussed on the basis of X-ray powder diffraction and literature data. Phase transitions of the mixtures of two crystal phases were shown to depend on the molecular symmetry (parity) of the mixed components and the difference in chain length (Δn). The distinguishing feature of the phase transition to the rotator state of multicomponent mixtures is step-wise phase separation of the solid solution during heating.

KW - High-temperature X-ray diffraction

KW - N-alkane

KW - Phase transition

KW - Rotator phases

UR - http://www.scopus.com/inward/record.url?scp=0037469581&partnerID=8YFLogxK

U2 - 10.1016/S0022-2860(02)00531-8

DO - 10.1016/S0022-2860(02)00531-8

M3 - Article

AN - SCOPUS:0037469581

VL - 647

SP - 243

EP - 257

JO - Journal of Molecular Structure

JF - Journal of Molecular Structure

SN - 0022-2860

IS - 1-3

ER -