Structure and Crystallization Behavior of the β Phase of Oleic Acid

Abstract

Crystallization and crystal structure of the β phase of oleic acid (cis-9-octadecenoic acid) have been investigated with morphological observation, X-ray diffraction, and DSC (differential scanning calorimeter). The morphology of growing crystals of the β phase depends significantly on supercooling. It was found that the β phase could be classified into at least two solid modifications, β1 (mp 16.3 °C) and β2 (mp 16.0 °C). The crystal structure analysis of the β1 phase has been performed. The unit cell belongs to a triclinic system of P1̄, and the asymmetric unit contains two crystallographically independent molecules, A and B. The molecular layer is a unique interdigitated structure, where the methyl group of molecule A and the carboxyl group of molecules B (or vice versa) are located on the same plane. For the conformation around the cis-CC bond, both molecules approximate to trans−cis−trans conformation, the first case for a cis-monounsaturated fatty acid. The methyl and carboxyl side chains together form a T∥ subcell. On the basis of its crystal structure, it was speculated that the β1 phase has a unique surface structure at the (001) face. The factors for the characteristic properties of the β phase were also discussed.

Synthesis of Nanohole‐Structured Single‐Crystalline Platinum Nanosheets Using Surfactant‐Liquid‐Crystals and their Electrochemical Characterization

“…[9,25] This is because the oleic chains of Tween 80 molecules with their cis-unsaturated conformations prefer their loose packing compared with the close-packed straight-bilayered structure constructed by the stearyl chains of Tween 60 with their trans-zigzag conformation. [28] On the other hand, the C 12 EO 9 /Tween 80/H 2 O mixed surfactant compositions at a 1:1:x 2 molar ratio also formed a hexagonal LLC phase over a wide range of x 2 ¼ 60-120 and the parameter a increased from 7.3 to 8.0 nm with an increase of water content (Fig. 4B).…”

“…[29] The remarkable change of the stability field of hexagonal LLC phase by cooling the present mixture from 15 to 5 8C is due to suppression of the thermal motion of constituent molecules, particularly, oleic acid ones because the polymorphic phases of the cis-unsaturated fatty acid have the melting temperature of as low as 13-16 8C. [28,30] The borohydride reduction treatment as in the Tween 80 based systems was applied to the Pt-salts (Na 2 PtCl 6 ) doped in the x ¼ 0-0.2 or x ¼ 0-0.6 hexagonal LLC phases kept at 5 8C and15 8C, respectively. This led to the formation of nanoholed Pt nanosheets as a minor phase for the x ¼ 0.6 LLC template with a hexagonal structure of a ¼ 8.04 nm at 5 8C (Fig.…”

“…The oleic chains of Tween 80 molecules with their cis-unsaturated conformations prefer no close-packed bilayered structure as constructed by the stearyl chains of Tween 60 with their trans-zigzag conformation. [28] The conformational properties of hydrophobic tail group for Tween 80 strikingly different from those for Tween 60 might lead to the template growth of unknown Pt nanostructures using the former surfactant based LLC phases. Here we report the synthesis of single-crystalline Pt nanosheets of around 4-10 nm in central thickness, with nanoholes of $1.8 nm in size and typically hexagonal-shaped, by the borohydride reduction of Pt salts using hexagonal LLCs of Tween 80 mixed with or without C 12 EO 9 .…”

Ultrathin PbS Sheets by Two-Dimensional Oriented Attachment

“…Our results strongly support that the assembly of oleic acid in a highly ordered monolayer on the {100} surfaces plays a key role in the formation and further stacking of PbS sheets. Oleic acid is well known to assemble vertically on various substrates and to form bilayer structures [20][21][22]. The thickness of a monolayer was determined from single crystal data and ranges from 1.7 to 2.4 nm in the reported crystal structures.…”

New ways to synthesize lead sulfide nanosheets—substituted alkanes direct the growth of 2D nanostructures

“…13 Lead sulfide nanosheets are formed through oriented attachment where ultra-small nanoparticles merge via the {110} facets of the crystal to minimize the surface energy of the whole nanocrystal. Since oleate, which forms monolayers in the crystalline phase, 14 is also present in the reaction the oriented attachment takes place in two dimensions only because the monolayers of oleate are established on the {100} facets and prohibit a growth or attachment in this direction. The coligands (in this case FA, CH, and HA) are necessary to destabilize the {110} facets and to remove the oleate from these facets, such that oriented attachment can take place; otherwise the oleate would block the facet completely.…”