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A reliable, accurate, and inexpensive optical detector for table-top applications is described here. Based on a commercial high resolution office scanner coupled to a projection plate, the detector offers a large image plate surface, allowing recording of sizeable images without systematic errors associated with coupling optics aberrations. Several tests on distance-dependent and steady interference patterns are presented and discussed. The extension to other types of optical measurements by substituting the projection plate is proposed.

The vibrational spectrum of liquids constituted of chain molecules is difficult to analyze because it may have contributions of different rotational isomers. In turn, with a proper vibrational assignment, this feature allows us to extract information about the effect of temperature or pressure on the molecular conformations in the liquid state. In this regard, the information on the vibrational spectrum in the solid phase greatly simplifies the vibrational analysis of the different rotational conformers existing in the liquid, as the molecules usually present all-trans conformations in the crystalline state. Here we report room-temperature Raman experiments on n-pentanol performed in a sapphire-anvil cell up to 3 GPa. A detailed analysis of the liquid-solid phase transition occurring at 1.3 GPa is provided. The analysis of the Raman spectrum in the solid phase allows the identification of the bands due to the different rotational isomers present in the liquid. The analysis of the spectral region corresponding to skeletal vibrations of the carbon chain (800-1200 cm(-1)) indicates that gauche conformers are promoted by the application of pressure. The analysis of the intensity ratio of those bands assigned to trans and gauge conformations is used to calculate the change in molecular volume ascribed to the trans-gauge isomerization process. We find a value similar to that found in n-alkanes, i.e., -0.88 cm(3) mol(-1). In addition, we find indication that pressure varies the proportions of the different gauge conformers. Thus, it appears that the GTTt to TGTt transition in the carbon chain is favored at high pressures. As expected, a smaller change in the molecular volume accompanies this conformation change.

Mechanical coeffecients of liquids play an important role in the understanding of the physics of fluids. There is a relative small number of undergraduate experiments dealing with thermodynamic properties of pure liquids and liquid mixtures. In fact, it is difficult to find experiments other than direct determination of liquid molar volumes or the molar excess volume for binary mixtures, which are usually measured by pyknometry. This paper describes a simple experiment designed to measure the isothermal compressibility and the thermal expansion coefficient of liquids. The experiment is based on an expansion principle and can be carried out with a rather simple experimental device. Additional features of the method and advanced experiments are discussed.

Vapour pressures and excess volumes for the hexafluorobenzene—n-hexadecane system and vapour pressures for the hexafluorobenzene—benzene—n-hexadecane system have been measured at 298.15 K. Thermodynamic consistency of the data has been checked using a Pade approximation for the binary system, and a new expression for the excess Gibbs energy of the ternary system. The new expression compares favourably with others previously proposed in the literature.

The Rayleigh ratio has been obtained for the following mixtures of non-electrolytes that show “w-shape” CEp vs. x curves: Nitrobenzene + n-Heptane, 1,4-Dichlorobutane + n-Heptane and Acetone + n-Dodecane. From them, the concentration-concentration correlation function Scc(0) has been calculated, as well as the excess Gibbs energy. It has been found that a clear tendency to homocoordination is present in all the mixtures studied. There is a rough correspondence between the concentration at which the maximum of the Scc(0) curves occur and those at which the negative curvature regions exist in the CEp curves. Also the larger the value of max. Scc(0) the more intense the “w-shape” effect. Despite size differences between the components and specific interactions which complicate the connection between Scc(0) and CEp, an analysis in terms of simple mean field models supports the view that the systems which show “w-shape” CEp curves still feel the effects of the more or less distant UCST. Hence Scc(0) is proposed as an indicator of the “w-shape” CEp.

Determination des coefficients osmotiques: la methode du point de gel est utilisee. On en deduit les coefficients d'activite

Excess heat capacities, CEp have been obtained through the concentration range at 25°C for five sets of systems of type An + B: hexafluorobenzene + 2,2,4-trimethylpentanc and 2,2,4,4,6,8,8-heptamethylnonane; hexafluorobenzene + cyclohexane (10° W) and dicyclohexyl (W); 1-chloronaphthalene + 2,2-dimethylbutane, 2,2,4-trimethylpentane (W) and 2,2,4,4,6,8,8-heptamethylncnane (W), 1-chloronaphthalene + n-hexadecane; 1-chloronaphthalene + cyclohexane and dicyclohexyl (15°, W). For the systems indicated, CEp has a W-shape, i.e., two minima separated by a maximum or two changes of sign of the curvature. The W-shape does not occur for hexafluorobenzene + cyclohexane at 25° but appears at 10°. Temperature and molecular size act on CEp through the degree of solution non-randomness as indicated by GE and the concentration-concentration correlation function, Scc which is a good predictor for the W-shape and of the concentration at which the maximum appears. The W-shape corresponds to an Scc value greater than 0.7 and GE > 800 J mol−1, the temperature being within 100 K of the UCST.

Apparent heat capacities have been measured for fifteen branched and cyclic alcohols in dilute n-decane solution at 25 °C. The alcohols were 2-methyl-2-propanol, cyclohexanol, 3-methyl-3-pentanol, trans-, cis-, and mixed isomer 2-methylcyclohexanol, 1-methylcyclohexanol, 3-ethyl-3-pentanol, cyclooctanol, 3,7-dimethyl-1-octanol, 5-decanol, 4-propyl-4-heptanol, cyclododecanol, 5-butyl-5-nonanol, and 8-hexadecanol (in n-hexane). Excess heat capacities CpE throughout the concentration range were measured at 25 °C for: 1-hexanol + n-hexadecane (n-C16) and + 2,2,4,4,6,8,8-heptamethylnonane (br-C16), 4-propyl-4-heptanol, and 1-decanol + n-decane, 3-methyl-3-pentanol + n-C16 and + br-C16 and at 27 °C for cyclohexanol + n-C16 and + br-C16. Also, for 3-methyl-3-pentanol + n-decane CpE was measured at 10, 25, 40, and 50 °C. For a series of isomeric alcohols, the apparent molar heat capacities show a maximum against concentration which decreases and moves to higher alcohol concentration as the hydroxyl group on the alcohol becomes increasingly hindered, effectively reducing the alcohol self-association capabilities. This situation is also reflected by the heat capacities of the pure alcohols which increase strongly in magnitude in going from a linear 1-alcohol to an isomeric alcohol which has its hydroxyl group on a quaternary carbon atom. CpE of the mixtures are negative at low alcohol concentrations turning positive at increasingly higher alcohol concentrations as the steric hindrance on the hydroxyl group increases. Throughout most of the concentration range CpE for the branched or cyclic alcohols is considerably more positive than for the corresponding isomeric 1 -alcohol. For the highly hindered 3-methyl-3-pentanol CpE(T) passes through a maximum. All of the above behaviour is explained by the Treszczanowicz–Kehiaian model for self-associated liquids + inert solvents which has been applied to the present data. Equilibrium constants have been obtained for alcohol association and are sensitive to alcohol structure. At low alcohol concentrations, while for the linear 1-alcohols tetramers are the predominant species and dimer are almost absent, for the corresponding isomeric alcohols the concentration of tetramers is severely reduced and the lower species, i.e. trimers and dimers, are more important. For the highly hindered alcohols, monomers are the predominant species in dilute solution reflecting the decrease in self-association ability that steric hindrance of the hydroxyl group imposes on them.

Solutions containing both poly(4-vinylpyridine) (P4VP) and poly(acrylic acid) (PAA) in 50% v/v metanol-water have been studied at room temperature by means of fluorescence studies, spectrophotometry and potentiometry. The results show the formation of a polycomplex between the polymers. Its stoichiometry is 0.5–0.6 PAA:1 P4VP and only slightly depends on polymer concentration for a range of very dilute solutions (10−3–10−4 M in monomeric units). The polycomplex is largely stabilized through hydrogen bonds but there is some proton transfer and the resulting coulombic interactions also contribute to the stabilization. The role of hydrophobic interactions is also discussed.

Expansion coefficients (α), thermal pressure coefficients (γ), isothermal compressibilities, densities and heat capacities have been measured at 25 °C for pure components and the following mixtures: 1-chloronaphthalene with the series of normal alkanes (n-Cn) where n= 6, 8, 10, 12, 14, 15 and 16, and with a series of highly branched alkanes (br-Cn), 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane and 2,2,4,4,6,8,8-heptamethylnonane. With these data the following first- and second-order mixing quantities are reported: VE, dVE/dT, dVE/dP, Δ(γVT), CEp, Δ(αγVT) and ΔCν. Excess enthalpies, HE, for 1-chloronaphthalene–br-Cn, CEp for p-xylene–n-Cn(n= 8, 10 and 14), 1-chloronaphthalene–cyclohexane and 1-methylnaphthalene–n-C12 are also reported. VE and dVE/dT are strongly negative, and dVE/dP are positive, for the lower n- and br-Cn, becoming smaller for higher alkanes. Flory theory gives excellent predictions for each quantity with both series. The mixing function, Δ(γVT), deviates from the equality Δ(γVT)=–HE which is predicted by the Flory theory and other theories which assume van der Waals behaviour. Contrasting with cyclohexane–n-Cn and benzene–n-Cn, where –Δ(γVT) > HE, 1-chloronaphthalene with n-Cn gives –Δ(γVT) 8. The excess heat capacity CEp is anomalously positive for the n-Cn series and has higher values than for br-Cn. CEp equimolar values show a maximum against the carbon number n; similar behaviour was found for Δ(αγVT). ΔCν=CEp–Δ(αγVT) values are strongly positive for both series of alkanes. The results are explained by temperature-sensitive ordering of (2–2) and (1–2) contacts. The (2–2) order between long-chain alkanes is destroyed on mixing, giving negative contributions to dVE/dT, Δ(γVT) and CEp, as in cyclohexane and benzene–n-Cn. For 1-chloronaphthalene–n-Cn(1–2) compensatory order formed in solution has the opposite effect, producing –Δ(γVT) 0.

We recently proposed an isothermal equation of state that was successfully applied to study the high-pressure behavior of solids. Later, we developed a simple model to include temperature effects on the equation of state. In the present work we consider the prediction capabilities of the complete equation of state in the entire p-V-T surface of a solid. Our predictions have been compared with experimental data up to pressures of several GPa and temperatures between zero and temperatures rather higher than those of melting. We also compare the performance of our equation against the most successful equations of state proposed in the literature, with excellent results. The isothermal equation of state provides us an adequate representation of experimental pressure-volume data and a simple volume dependence for the Gr\"uneisen parameter. The equation needs only four parameters evaluated at room pressure at a single reference temperature. \textcopyright{} 1996 The American Physical Society.

The excess volumes of C6F6 and C6H5F+an octane isomer (n-octane, cyclooctane, 2,2,4-trimethylpentane) have been measured at 25°C. The equimolar values increase from 2,2,4-trimethylpentane to n-octane to cyclooctane. The present results cannot be explained in terms of the scheme developed by Patterson for other alkane mixtures. Comparing the present results with others in the literature, the effect of the dipolar moment of the aromatic compound seems to be more complex than in previous studies of polar+non-polar components. The results have been analyzed in terms of two generalized van der Waals models, and a semiempirical equation of state. The results range from poor to fair.

We have recently shown that the high-pressure behavior of the isothermal compressibility, κT, and the thermal expansion coefficient, αp, can be characterized for molecular liquids from low-pressure measurements of these quantities together with surface tension data. The quality of the estimation was good enough to characterize the pressure behavior of the molar volume using a reference volume measured under orthobaric conditions. The same scheme is used here to predict the molar volume of some binary mixtures at different compositions as a function of pressure. Agreement with experimental data is good enough to predict the high-pressure behavior of the molar excess volume. © 1995 American Chemical Society.

The excess volume of hexafluorobenzene (C6F6)–2,2,4-trimethylpentane (2,2,4-TMP) has been measured at 298.15 K as well as the vapour pressures at 298.15, 323.15 and 348.15 K. From the latter, the excess Gibbs energies have been calculated, and the excess enthalpies have been estimated through the Gibbs–Helmholtz equation. The comparison with similar data for binary systems involving benzene (C6H6), C6F6, 2,2,4-TMP and cyclohexane (c-C6H12) shows that c-C6H12 and 2,2,4-TMP have quite different volumetric and entropic behaviours when mixed with C6F6, whilst they are almost equivalent when mixed with C6H6. Finally, the vapour pressures have been measured and the excess Gibbs energies calculated at 298.15 and 323.15 K for the ternary system C6F6–C6H6–2,2,4-TMP.

Expansion coefficients (α), thermal pressure coefficients (γ), isothermal compressibilities, densities and heat capacities have been measured at 25 °C for pure components and the following mixtures: 1-chloronaphthalene with the series of normal alkanes (n-Cn) where n= 6, 8, 10, 12, 14, 15 and 16, and with a series of highly branched alkanes (br-Cn), 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane and 2,2,4,4,6,8,8-heptamethylnonane. With these data the following first- and second-order mixing quantities are reported: VE, dVE/dT, dVE/dP, Δ(γVT), CEp, Δ(αγVT) and ΔCν. Excess enthalpies, HE, for 1-chloronaphthalene–br-Cn, CEp for p-xylene–n-Cn(n= 8, 10 and 14), 1-chloronaphthalene–cyclohexane and 1-methylnaphthalene–n-C12 are also reported. VE and dVE/dT are strongly negative, and dVE/dP are positive, for the lower n- and br-Cn, becoming smaller for higher alkanes. Flory theory gives excellent predictions for each quantity with both series. The mixing function, Δ(γVT), deviates from the equality Δ(γVT)=–HE which is predicted by the Flory theory and other theories which assume van der Waals behaviour. Contrasting with cyclohexane–n-Cn and benzene–n-Cn, where –Δ(γVT) > HE, 1-chloronaphthalene with n-Cn gives –Δ(γVT) 8. The excess heat capacity CEp is anomalously positive for the n-Cn series and has higher values than for br-Cn. CEp equimolar values show a maximum against the carbon number n; similar behaviour was found for Δ(αγVT). ΔCν=CEp–Δ(αγVT) values are strongly positive for both series of alkanes. The results are explained by temperature-sensitive ordering of (2–2) and (1–2) contacts. The (2–2) order between long-chain alkanes is destroyed on mixing, giving negative contributions to dVE/dT, Δ(γVT) and CEp, as in cyclohexane and benzene–n-Cn. For 1-chloronaphthalene–n-Cn(1–2) compensatory order formed in solution has the opposite effect, producing –Δ(γVT) 0.

We have measured VE at 298.15 K for the systems formed by 2,2,4-trimethylpentane or n-octane or cyclo-octane, with chlorobenzene, 1,2-dichlorobenzene and 1,3-dichlorobenzene. The results can be qualitatively understood in terms of the p* and free-volume contributions to the excess functions. However, the effects of polarity and of the shape of the molecules are not as clear as in other studies reported in the literature.Whereas Deiters' equation of state fits the results of each system well, it does not predict the observed change in VE when the octane isomer is changed. On the other hand, generalized van der Waals, and a lattice-with-holes model, correctly predicts such a variation, although the quantitative agreement is poor.

The apparent molar heat capacities, ΦC, and excess heat capacities, CpE, have been obtained at 25 °C for the following alkan-1-ols, Cm H2m+1 OH at low mole fraction, x1 < 0.1, in n-alkanes, Cn H2n+2, (m,n): (1,6), (1,7), (2,10), (4,10), (6,6), (6,9), (6,10), (6,12), (6,16), (7,10), (10,6), (10,10), (10,16), (11,10), (12,10), (14,6), (16,6) and (16,16). The Treszczanowicz–Kehiaian (TK) association theory was applied to the associative part of the apparent heat capacity, ΦC(assoc), obtaining ΔH° for hydrogen-bond formation and the volume-fraction equilibrium constant, K4Φ, for formation of tetramers which are the dominant multimers. K4Φ are related to K4, an equilibrium constant for hydrogen-bond formation in tetramers, which is found to be independent of alkan-1-ol chain length from m= 4 to 16, while K4 for m= 2 and 1 are larger. A common K4 implies a single corresponding states curve (CSC) of ΦC(assoc) either against ψ1, the number of moles of alcohol per mole of segments in the solution, as introduced by Pouchly, or against molarity. The CSC is obeyed by the dilute solution data, with some deviation for methanol and ethanol systems, and also by ΦC(assoc) measured throughout the whole concentration range at 25 °C for m= 6 with n= 7, 8, 12 and 16 and for m= 1 (high and low concentration only), 4, 6 and 10 with n= 7 and m= 2, 4, 6 and 10 with n= 12 (again with m= 2 as exception). The CSC in reduced form allows the determination of the size of the dominant multimer from experimental ΦC data and should be followed by alkan-1-ol–inert solvent data at any temperature. CpE for constant m increases with n, and this is a consequence of the adherence to a CSC as well as being predicted by the TK theory. Together with literature results for other systems it is found that for n= constant, CpE increases as m decreases, reaching a maximum at m= 3, then decreasing again for m= 2 and 1. The behaviour of m= 10–3 is a consequence of the CSC, whereas m= 2 and 1 represent deviations from the CSC.