Nobuyasu Hiramatsu

Pressure effect on transformation of cis-unsaturated fatty acid polymorphs 2. Palmitoleic acid (cis-9-hexadecenoic acid)

Abstract The existence of two polymorphs of palmitoleic acid was observed by differential scanning calorimetry. Powder X-ray diffraction pattern showed that the two polymorphs correspond to the α and γ forms, which have bee observed in other cis -monounsaturated fatty acids, oleic acid and erucic acid. γ reversibly transformed to α at −18.7°C on heating and α melted at 2.0°C. The effect of hydrostatic pressure on the γ-α transformation temperature, T tr and the α-melt transition temperature, T m , were studied by means of high-pressure differential thermal analysis. T tr and T m were elevated by pressure, as expreessed by d T /d p at atmospheric pressures of 0.190 and 0.202 K/MPa, respectively. The volume increases were estimated to be 5.6 cm 3 /mol for the γ-α transformation and 23/.6 cm 3 /mol for the α-melt transition by applying the Clausius-Clapeyron equation. The results were discussed compared with those observed in oleic acid.

Phase behavior of binary mixture of palmitoleic acid (cis-9-hexadecenoic acid) and asclepic acid (cis-11-octadecenoic acid)

The influence of difference in Δ chain length of cis-monounsaturated fatty acids on the phase behavior of their binary mixtures was examined based on the phase diagram of the mixture composed of palmitoleic acid (C16; ω7, Δ9) and asclepic acid (C18; ω7, Δ11). The phase diagram exhibited a ‘eutectic-like’ pattern, which demonstrates that the two components are perfectly miscible in liquid phase but much less miscible in solid phase (α-phase). This is in contrast to the case of binary mixtures composed of counter-combination of fatty acids with the same Δ- but different ω-chain length, where it was found that the molecular compounds are formed in the solid phase and the compounds are miscible with each component at least in the α phase. The present results provide further evidence for the critical importance of the matching in Δ chain length for determining the phase behavior of cis-monounsaturated fatty acid mixtures.

Phase behavior of binary mixtures of cis-monounsaturated fatty acids with different ω-chain length

Abstract Phase diagrams of binary mixtures of oleic acid (OA)/palmitoleic acid (POA) and OA/myristoleic acid (MOA) were constructed by differential scanning calorimetry to examine the mixing behavior of cis-monounsaturated fatty acids with different ω-chain length in polymorphic phases. The phase diagram for OA/POA mixtures demonstrates that the molecular compounds of OA3POA2 and of OA1POA2 are formed in α phase and in γ phase, respectively. The compound forms solid solutions with OA and also with POA in the α phase, whereas both OA1POA2/OA and OA1POA2/POA in γ phase are perfectly immiscible. As for OA/MOA mixtures, the compound OA2MOA3 is formed from MOA and the α polymorph of OA. The solid solution is formed between the compound and MOA, while the miscibility between the compound and OA is much poorer. The present study reveals that the conformational state of the ω-chain, i.e. ordered (γ-form) or disordered (α-form), strongly affects the phase behavior of binary mixtures of cis-monounsaturated fatty acids.

Pressure study on thermal transitions of oleic acid polymorphs by high-pressure differential thermal analysis

Transition temperatures for oleic acid polymorphs (alpha, beta and gamma) and the melt were measured under various pressures up to 200 MPa by means of high-pressure differential thermal analysis. The pressure dependences of the transition temperatures were analyzed by applying the Clapeyron equation, and the volume changes associated with the phase transitions were estimated as follows; delta V gamma-alpha = 5.9 cm3/mol, delta V alpha-melt = 29.2 cm3/mol and delta V beta-melt = 41.1 cm3/mol. The volume changes for the gamma-alpha and alpha-melt transitions were discussed in relation to the crystal structures of the alpha and gamma modifications. The experiments showed that the beta modification, whose structural data are lacking, is the most dense. This correlates with the fact that the beta form is thermodynamically most stable among the three modifications of oleic acid.

Pressure effect on transformation of cis-unsaturated fatty acid polymorphs. 3. Erucic acid (cis-ω9-docosenoic acid) and asclepic acid (cis-ω7-octadecenoic acid)

Abstract The effect of hydrostatic pressure on the polymorphic transformation and melting of erucic acid and asclepic acid was investigated by means of a high-pressure differential thermal analysis. The volume changes, Δ V , associated with the polymorphic transformation and melting at atmospheric pressure were evaluated by applying the Clausius-Clapeyron equation. The value of Δ V for the γ-α transformation of asclepic acid (5.3 cm 3 /mol) is well comparable to those obtained for the corresponding transformations of oleic acid (5.9 cm 3 /mol) and palmitoleic acid (5.6 cm 3 /mol). This result indicates that the extent of disordering in ω-chain resulting from the γ-α transformation is rather insensitive to the lengths of both ω-chain and Δ-chain of cis -unsaturated fatty acids. On the other hand, a significantly large Δ V value (7.5 cm 3 /mol) was obtained for the γ 1 -α 1 transformation of crucic acid irrespective of its nature of order-disorder transformation similar to the γ-α transformation, reflecting the difference in the crystallographic structure between γ, α and their counterparts γ 1 , α 1 . For asclepic acid, the melt-crystallization under high pressures above about 110 MPa lead to the formation of new polymorphs which are not observed at atmospheric pressure. This demonstrates that the diversity of polymorphism observed in cis -unsaturated fatty acids is extended by applying high pressure.

Pressure effect on phase behavior of binary mixtures of cis-unsaturated fatty acids

Abstract The solid-to-liquid phase transition of binary mixtures of cis-monounsaturated fatty acids was investigated as a function of their composition under various pressures up to about 200 MPa by means of a high pressure differential thermal analysis. Two mixture systems were examined; one is the mixture composed of oleic acid (OA; cis-9-octadecenoic acid) and palmitoleic acid (POA; cis-9-hexadecenoic acid), and the other is that composed of asclepic acid (APA; cis-11-octadecenoic acid) and POA. The components in the former mixture differ in the length of ω-chain (the aliphatic chain segment between the double bond and methyl end group) by two methylene units, whereas those in the latter mixture differ in the length of Δ-chain (the chain segment between double bond and carboxyl group) by two methylene units. In both mixtures, the temperature of solid-liquid phase boundary, i.e. solidus and liquidus lines, was drastically increased by the increase in pressure. On the other hand, the shape of the phase boundary remained almost unaltered regardless of the pressure. The characteristic features in solid phase of these fatty acid mixtures, i.e. the molecular compound formation for OA/POA mixture and the highly restricted mutual miscibility for APA/POA mixture, are retained even under high pressure. This indicates that the intermolecular interaction of cis-monounsaturated fatty acids responsible for determining the phase behavior of binary mixture systems is rather insensitive to pressure, at least in the range up to 200 MPa.

Formation of α Form Nylon 12 under High Pressure

The formation conditions of α form Nylon 12 under high pressure from the melt and from the quenched state were investigated by means of high-pressure differential thermal analysis and wide-angle X-ray diffraction. The α form was formed by crystallization from the melt above 200 MPa, and the γ form disappeared in the sample obtained above 500 MPa. The quenched state was transformed into the α form at lower temperature than the melting point of the α form under high pressure, whereas the γ form was hardly transformed at all. The thermal behavior of the α form at atmospheric pressure was also studied. Two endotherms due to the meltings of the α and γ forms and one exotherm due to the α to γ form transformation were observed. This transformation occurred without melting of the α form at a slow heating rate and was regarded as a monotropic transition.

Device for high‐pressure differential thermal analysis for liquid samples

The simple high‐pressure DTA cell that can be used for liquid samples was constructed. The advantage of this device is the facility of its operation. The utility was demonstrated by measuring the freezing temperature of n‐tetradecane under various pressures up to 300 MPa.

Microphase separation in dehydrated N-isopropylacrylamide/sodium acrylate gel

The first small-angle X-ray scattering (SAXS) measurements were carried out in order to examine the mesoscopic structure in the N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel. By the SAXS measurements, a prominent peak was found in the dehydrated gel around 0.026 A-1. Taking into account of the cross section magnitude against X-ray, the concentration fluctuation of Na+ ions was a probable candidate for making contrast for the SAXS profile, which depends on the distribution of the hydrophilic group. Therefore, it was concluded that the mesoscopic structure found in the present study is due to the hydrophilic domains in the dehydrated gel which capture the Na+ ions and the remnant water inside the gel.

Ultrasonic Spectroscopy for Teflon/Glass Bead Composite System

To investigate the frequency characteristics of ultrasonic waves transmitted through samples containing some foreign particles, ultrasonic Spectroscopy was carried out for Teflon/glass bead composite samples where bead sizes were varied from 850 ?m to 25 ?m. With the decrease of the bead size, the spectral amplitude first decreases over the whole frequency range, and the low frequency pattern recovers. The spectral amplitude takes minimum at a particular bead size depending on the frequency, and this minimum shifts to the small bead size side with the increase of frequency. Those behaviors are discussed with the theory of acoustic wave scattering.