The buildup mechanism of polypeptide multilayers prepared by the layer-by-layer deposition of a polyanion (poly(L-glutamic acid) (PGA)) and polycations (poly(L-lysine) (PLL), poly(D-lysine) (PDL), and copoly(DL-lysine)(PDLL)) was reinvestigated by using in situ ATR-IR spectroscopy. A difference spectral technique applied to analyze the spectra indicated that the deposition of both the PGA and PLL (PDL) layers accompanies the formation of secondary structures consisting mainly of the antiparallel pleated sheet (the beta-sheet) structure, and that the formation of the beta-sheet structure cannot always be explained in terms of polyanion/polycation complex formation or charge compensation between the polyanion and polycations, although it has been considered as a major process in the multilayer buildup process. Instead, the present paper proposes the following mechanism. During the deposition of the polyelectrolyte, a small amount of the beta-sheet structures are produced at the interface as a result of charge compensation between a polyelectrolyte and an oppositely charged polyelectrolyte in the multilayer. The beta-sheets act as nuclei from which further propagation of the structure takes place at the solution/multilayer interfaces. The driving force of the buildup process in the new mechanism is a kinetically favorable insolubilization of each polyelectrolyte in solution at the interfaces.

Molecular structures at the free surface of liquid n-heptadecane (n-C 17 H 36 ; freezing point (T f ) 22 °C, surface freezing point (T s ) 24 °C) were studied by infrared external reflection spectroscopy. Upon successively cooling the liquid sample from 28 °C, at which the sample assumes an isotropic state, to 26, 25, and 24 °C, the infrared external reflection spectra exhibited drastic changes, indicating changes in the orientation and conformation of surface species. At 26 °C, an irregular structure of n-C 17 H 36 with a gauche conformation changes into a regular one with a mainly trans conformation, and simultaneously the symmetry axis of the terminal methyl group tilts away from the surface normal. At 25 °C, the hydrocarbon chain raises its axis to the direction of the surface normal, and the carbon skeleton plane inclines to the direction of the surface plane. At 24 °C (T s ), the molecular axis is raised further to the direction of the surface normal, and the surface species form a rotator phase at the surface. Thus, upon cooling from a temperature a few degrees above T s , surface freezing of n-C 17 H 36 proceeds through discrete structural and orientation changes of the surface species, contrasting with the explanations of previous studies in terms of an abrupt structural change at the free surface occurring at T s .

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This study presents experimental measurements of the vapor pressures and pressure–volume–temperature (PVT) properties of trans-1,1,1,3-tetrafluoro-2-butene, also known as HFO-1354mzy­(E). This substance is expected to be a candidate working fluid for high-temperature heat pumps. The densities were measured by magnetic levitation densimeter (MLD). Vapor pressures were measured over the temperature range from (340 to 410) K, at pressures from (0.5 to 2.5) MPa. Liquid-phase PVT properties were measured at temperatures between (280 and 420) K at pressures up to 20 MPa. Gas-phase PVT properties were measured in the temperature range from (340 to 420) K at pressures from (0.5 to 2.5) MPa. The experimental uncertainties of the present measurements were estimated to be within ±18 mK in temperature, ±2.9 kPa in pressure, and ±0.012 % in density, respectively. The vapor pressure correlation and equations of state (EoS) for the liquid-phase and gas-phase PVT properties were derived. The vapor pressure correlation and the proposed EoS were found to well represent the set of measurements within a deviation of ±0.13 % in vapor pressure, ±0.2 % in liquid phase density, and ±0.3 % in pressure for the gas-phase PVT properties, respectively.