Symmetrical Ketone/n-Alkane Systems. 1. Phase Diagrams from DSC

Abstract

Binary phase diagrams have been determined for solution-crystallized samples of two long-chain symmetrical ketones (Kn) and n-alkanes (Cn) with the same carbon numbers of n ) 25 and 39 from differential scanning calorimetry (DSC) measurements. Toluene was used as the solvent for crystallization of K39/C39 samples and hexane for K25/C25. They are found to form a solid solution which exhibits the solid-solid phase transition behaviors characteristic of a crystal of the pure n-alkane component, when the molar fraction f m of Kn is lower than a critical value f m,c , being dependent on n. For f m > f m,c , K39/C39 samples have formed another type of solid solution which melts after a rather broad solid-liquid equilibrium at elevated temperatures. On the other hand, K25/C25 samples have given eutectic mixtures for f m > f m,c , and the phase diagram is found to agree with that of the same samples crystallized from melt. We apply the Flory-Huggins theory for reproducing the phase diagrams using the interaction parameter 12 between Kn and Cn molecules and discuss effects of solvent which gave rise to these anomalous phase behaviors in terms of 12 and 0i (i ) 1, 2) between solvent and Kn (or Cn) estimated from their solubility curves.

Crystal Structures of n-Alkanes with Branches of Different Size in the Middle

“…Linear n -alkanes with carbon numbers less than 80 are known to take the extended chain conformation as the energetically most favored form in the crystalline state, and the smooth flat interface is always formed between lamellae. − Introduction of small functional groups such as the carbonyl or hydroxyl group to the middle of those linear chains hardly disturbs the crystalline structure of their linear homologues. − The subcell structure is the same for all samples examined, and their melting temperatures become higher than those of the linear homologues because of dipole−dipole interaction or hydrogen bonding, whereas the solid−solid phase transitions characteristic of pure linear alkanes disappear due to this interaction. ,− …”

“…[1][2][3][4][5][6][7] Introduction of small functional groups such as the carbonyl or hydroxyl group to the middle of those linear chains hardly disturbs the crystalline structure of their linear homologues. [8][9][10][11][12][13][14][15][16][17] The subcell structure is the same for all samples examined, and their melting temperatures become higher than those of the linear homologues because of dipole-dipole interaction or hydrogen bonding, whereas the solid-solid phase transitions characteristic of pure linear alkanes disappear due to this interaction. 3,[18][19][20][21][22] Among various branching effects on morphologies and crystalline structures of alkane molecules, the size effect can be most effectively studied introducing groups having only the van der Waals interaction to the main chain, and where the methyl group is the smallest unit.…”

6 Recent developments in calorimetry

“…Also calorimetric evaluation of phase change materials for use as thermal interface materials was made by Liu and Chung. 204 With the use of DSC Nakasone et al 205 have made phase diagrams for binary symmetrical (ketoneϩ n-alkane) systems. Lerdkanchanaporn et al 206 have elaborated similar diagrams for the system (ibuprofen ϩ stearic acid) in order to help in pharmaceutical formulations.…”

Systematic Study of Aggregation Structure and Thermal Behavior of a Series of Unique H-Shape Alkane Molecules

“…Center-Branched Alkanes. Introduction of small functional groups such as carbonyl or hydroxyl group at the middle point of the linear chains, H 3 C(CH 2 ) n –CO–(CH 2 ) n CH 3 or H 3 C(CH 2 ) n –CHOH–(CH 2 ) n CH 3 , modifies the regular packing structure of the original linear n -alkane homologues. − The subcell structure of the methylene parts is essentially the same as that of linear homologues. The melting temperature becomes higher than that of the corresponding linear n -alkane because of the existence of strong dipole–dipole interactions between the neighboring CO bonds or relatively strong intermolecular hydrogen bonds between the OH groups.…”

“…The melting temperature becomes higher than that of the corresponding linear n -alkane because of the existence of strong dipole–dipole interactions between the neighboring CO bonds or relatively strong intermolecular hydrogen bonds between the OH groups. The solid-state phase transitions detected for linear alkanes are not observed for the center-substituted alkane derivatives due to these additional interactions. − …”