28 research outputs found
A novel non-intrusive microcell for sound-speed measurements in liquids. Speed of sound and thermodynamic properties of 2-propanone at pressures up to 160 MPa
A novel high-pressure, ultrasonic cell of extremely reduced internal dimensions ( 0.8 10 6 m3) and good precision for the
determination of the speed of propagation of sound in liquids was conceived and built. It makes use of a non-intrusive methodology
where the ultrasonic transducers are not in direct contact with the liquid sample under investigation. The new cell was used to carry
out speed of sound measurements in 2-propanone (acetone) in broad ranges of temperature (265 < T =K < 340) and pressure
(0:1 < p=MPa < 160). (p; q; T ) data for acetone were also determined but in a narrower T ; p range (298 to 333 K; 0.1 to 60 MPa). In
this interval, several thermodynamic properties were thus calculated, such as: isentropic (js) and isothermal (jTÞ compressibility,
isobaric thermal expansivity (ap), isobaric (cp) and isochoric (cv) specific heat capacity, and the thermal pressure coefficient (cv).
Comparisons with values found in the literature generally show good agreement.info:eu-repo/semantics/publishedVersio
Thermophysical and thermodynamic properties of ionic liquids over an extended pressure range: [bmim][NTf2] and [hmim][NTf2]
The current study focuses on 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [bmim][NTf2], and 1-hexyl-3-
methylimidazolium bis(trifluoromethylsulfonyl)amide, [hmim][NTf2]. The objective is to study the influence of pressure as well as
that of the cation s alkyl chain length on several properties of this type of ionic liquids. Speed of propagation of ultrasound waves
and densities in pure ionic liquids (ILs) as a function of temperature and pressure have been determined. Several other thermody namic properties such as compressibilities, expansivities and heat capacities have been obtained. Speed of sound measurements have
been carried out in broad ranges of temperature (283 < T/K < 323) and pressure (0.1 < p/MPa < 150), using a non-intrusive micro cell. Density measurements have been performed at broad ranges of temperature (298 < T/K < 333) and pressure (0.1 < p/MPa < 60)
using a vibrating tube densimeter. The pressure dependence of heat capacities, which is generally mild, is highly dependent on the
curvature of the temperature dependence of density.info:eu-repo/semantics/publishedVersio
Intra-molecular coupling as a mechanism for a liquid-liquid phase transition
We study a model for water with a tunable intra-molecular interaction
, using mean field theory and off-lattice Monte Carlo simulations.
For all , the model displays a temperature of maximum
density.For a finite intra-molecular interaction ,our
calculations support the presence of a liquid-liquid phase transition with a
possible liquid-liquid critical point for water, likely pre-empted by
inevitable freezing. For J=0 the liquid-liquid critical point disappears at
T=0.Comment: 8 pages, 4 figure
Liquid-liquid equilibrium data of poly(N-isopropylacrylamide-co-1-deoxy-methacrylamido-d-glucitol) in water
Densities and derived thermodynamic properties of ionic liquids. 3. Phosphonium-based ionic liquids over an extended pressure range
Phase behavior of (polyacrylamides + water) solutions: concentration, pressure and isotope effects
Phase diagrams of poly(N-isopropylacrylamide) (PNIPAAM) as well as of hydrophilically-modified copolymers in aqueous solution were determined. A high-accuracy He-Ne Laser scattering technique was used for the detection of operational spinodal (sp) and cloud-point (cp) curves. Polymer concentration was varied from 0.5 to 20 wt.%. In the case of copoly(PNIPAAM/vinylsaccharide) several different chain lengths were considered. Pressure (up to 400 bar) and solvent isotope effects were studied. We predict a closed-loop type phase diagram for the copolymers, which presents an estimated hypercritical point in H2O solutions at Mw~0.5×105, although only lower critical solution temperature (LCST) is experimentally accessible. At lower molecular weights, the solutions are always in the one-phase region.http://www.sciencedirect.com/science/article/B6TG2-43MC9F5-N/1/63fb7dd8bec4ff798723b9bcb318a0a