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This paper describes the high-pressure volumetric properties of three commonly used poly(α-olefin) base oilsPAO 2, PAO 4, and PAO 8with nominal 100 °C kinematic viscosities of 2, 4, and 8 cSt. Using a special variable-volume view cell that permits continuous pressure scan and volume measurements, densities were determined at 298, 323, 348, 373, and 398 K at pressures up to 40 MPa. Isothermal compressibilities, isobaric thermal expansivities, thermal pressure coefficients, and internal pressures were then evaluated. At each temperature, density–pressure correlations were developed for the range from 10 to 40 MPa. Density–temperature correlations were developed at 10, 20, 30, and 40 MPa. It is shown that the densities of PAO 2 (which were in the range from 0.7364 to 0.8214 g/cm3) are lower than those of PAO 4 (in the range from 0.7663 to 0.8470 g/cm3) or PAO 8 (in the range from 0.7664 to 0.8498 g/cm3). The densities of PAO 4 and 8 were essentially the same. Isothermal compressibilities of each base oil were of the same order of magnitude at each temperature (with the range being from 6.8 to 10.2 × 10–4 MPa–1), with PAO 2 showing slightly higher values. Isobaric thermal expansivities were in the range (7.2–9.5) × 10–4 K–1. PAO 2 showed higher expansivity values at all pressures. Thermal pressure coefficients were in the range 0.8–1.2 MPa K–1. The values were higher for PAO 2 at 323 K and higher temperatures. PAO 8, while showing the highest thermal pressure coefficient at 298 K, became lower than that of PAO 2 at 323 K and lower than that of PAO 4 at 348 K and higher temperatures. At 398 K, PAO 4 shows the highest thermal pressure coefficients. The trends observed with the thermal pressure coefficients were also reflected in the internal pressures for the respective oils. The internal pressure values were in the range from 260 to 370 MPa. The internal pressure value in each system was observed to decrease with pressure. These observations were interpreted in terms of the differences in the carbon chain lengths, ease of packing, and relative significance of attractive versus repulsive forces that develop as a function of the pressure or temperature.

The phase, packing and dynamic behavior of model membrane systems consisting of lipids with completely deuterated chains is generally monitored by the temperature dependeuce of the line width of the methylene (CD,) symmetric stretching modes located at -2100 cm-'Alternative empirical spectral parameters derived from the peak-height intensity ratios of spectral features assto the chain C-D methylene and methyl stretching modes are introduced and evaluated. In particular, specific intensity ratios reflect a sensitivity to average inter-and intra-chain order4sorder properties of the portions of the lipid chains localized either near the methyl termini or near the head-groupacyl chain interface. The utility of these intensity parameters is evaluated by examining the bilayer behavior of binary mixtures of dipahnitoylphosphatidylcholine with fully deuterated lipid chains (DPPCJI,,) and dirlmitoylpbosphatidylebolioe with nondeuterated &ins (DPPC-do) in various physical states. We also assess the use of intensity parameters for clarifying the effects of ethanol on the inter-and intra-chain interactions of DPPCJI,, bilayers. In the DPPC-d,,-ethanol system particular emphasis is placed on the formation of the novel interdigitated chain gel phase.