Structural Behavior of n-Tricosane and n-Pentacosane Mixtures at 20°C

New insights on the crystalline forms in binary systems of n-alkanes: Characterization of the solid ordered phases in the phase diagram tricosane + pentacosane

“…Jouti et al 34,35 who worked, like us, with the C 25 purchased from Aldrich with the same stated purity did not detect this phase.…”

“…Indeed, experimental results on this system and on other binary systems and, in particular, on C 26 1 C 28 (the subject of another paper) have enabled us to characterize for the first time the three intermediate forms and to propose, therefore, a new phase diagram for the binary system C 23 -C 25 . The scope of this work is even wider since these phases are also observed in other binary systems [31][32][33][34][35][36][37][38][39][40][41] of n-alkanes [with a chain-length difference ͑Dn͒ equal to 1 or 2]. In other words, this paper leads to a complete characterization of all solid ordered forms observed in all binary systems of n-alkanes (the components belonging to the range C 16 to C 28 ).…”

“…The study of binary phase diagrams (temperature versus composition) has revealed a complex structural behavior of the mixed samples [28][29][30][31][32][33][34][35][36][37][38][39][40][41] where other forms than those seen in the components are observed and which are stabilized by mixing. The earliest binary phase diagram showing multiple one-phase domains at low temperature (temperature domain where the ordered phases are observed) is that of Lüth et al 28 for the system C 20 -C 22 .…”

“…A complete miscibility both at high and low temperature was proposed. Complex structural behavior of the mixed samples in this system was recently observed by Jouti et al 34,35 At room temperature, these authors have shown the existence of seven one-phase regions in the binary system and they supposed that all the phases are orthorhombic and are denoted by them as b0(C 23 ), b′0(C 23 ), b″1, b′1, b″2, b′0(C 25 ), b0(C 25 ). The two couples b0 and b′0 come from the polymorphism of the components C 23 and C 25 while the three other forms b″1, b′1, and b″2 are observed only in the mixed samples.…”

“…Polymorphism of n-alkanes (C n H 2n12 ; hereafter denoted by C n ) and determination of binary phase diagrams [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] in the alkane family have been reported on in recent years in numerous publications. The polymorphism of n-alkanes is rather well known where many solid-solid phase transitions have been observed as a function of temperature.…”