Fluctuations and Mixing State of an Aqueous Solution of the Ionic Liquid Tetrabutylphosphonium Trifluoroacetate around the Critical Point

2019 ◽  
Vol 72 (2) ◽  
pp. 93 ◽  
Author(s):  
Ayako Nitta ◽  
Takeshi Morita ◽  
Hiroyuki Ohno ◽  
Keiko Nishikawa
Keyword(s):  
Phase Transition ◽  
Aqueous Solution ◽  
Critical Point ◽  
Ion Pairs ◽  
Partial Molar Volumes ◽  
Density Fluctuations ◽  
Solution Temperature ◽  
X Ray Scattering ◽  
Mixing States ◽  
The Relationship

Aqueous solutions of ionic liquids have unique mixing states. Fluctuations are useful for understanding the inhomogeneity of the mixing states. In this study, an aqueous solution of tetrabutylphosphonium trifluoroacetate, ([P4,4,4,4]CF3COO), which exhibits a lower-critical-solution-temperature-type phase transition, was investigated. Focussing on the concentration and temperature range near the critical point, the fluctuations were evaluated by combining three kinds of experimentally obtained data: small-angle X-ray scattering intensity, partial molar volumes, and isothermal compressibility. Using Kirkwood–Buff integrals, individual density fluctuations of water and [P4,4,4,4]CF3COO were calculated, and these suggested that a large number of water molecules hydrated [P4,4,4,4]CF3COO ion pairs, and the hydrated ion pairs aggregated near the critical point. The relationship between the mesoscopic fluctuations and the macroscopic phase transition was clarified by drawing counter maps of the fluctuations in the phase diagrams.

Modified Poly (N-Isopropylacrylamide) Hydrogels for Drug Delivery

2010 ◽  
Author(s):  
Guoguang Fu ◽  
Winston Soboyejo
Keyword(s):  
Phase Transition ◽  
Drug Delivery ◽  
Aqueous Solution ◽  
Drug Release ◽  
Lower Critical Solution Temperature ◽  
Environmental Temperature ◽  
Swelling Behavior ◽  
Solution Temperature ◽  
Critical Solution Temperature ◽  
Release Profiles

Thermo-responsive hydrogel can change their swelling behavior and drug release characteristics in response to environmental temperature [1–5]. Poly(N-isopropylacrylamide) (PNIPA) hydrogel undergoes a phase transition when the temperatue is lower than a lower critical solution temperature (LCST) of ∼32°C in aqueous solution [8], and drug release profiles in PNIPA hydrogel can be controlled by the alternation of their solution temperatures.

Polyamorphism and the universal liquid–liquid critical point in the supercooled state

2010 ◽  
Vol 1 (SRMS-7) ◽  
Author(s):  
G.N. Greaves
Keyword(s):  
Critical Point ◽  
Critical Phenomena ◽  
Three Dimensional ◽  
Density Fluctuations ◽  
Molecular Fluids ◽  
X Ray Scattering ◽  
Universal Power Law ◽  
Critical Point Phenomena ◽  
Low Entropy

The physics of critical phenomena is well established in systems as diverse as molecular fluids, crystalline alloys and magnetic materials. As the critical point is approached, the susceptibility increases anomalously and fluctuations give rise to dramatic opalescence. Evidence has recently emerged for the existence of a second critical point in the liquid state at supercooled temperatures, below which polyamorphic phases coexist differing in density but sharing the same composition. Whilst much attention has been paid to supercooled water, polyamorphic phases have been observed in many elemental and oxide liquids potentially offering routes to low-entropy glasses. Our recent direct observation of a polyamorphic phase transition in levitated molten yttria–alumina offers the first opportunity to study the associated critical point in a real supercooled system. In situ small-angle X-ray scattering records sharp rises in the average correlation length of density fluctuations and in the compressibility as the transition is approached. Both increases approximate to the universal power-law relations predicted by the three-dimensional Ising model in common with all critical point phenomena. The observation brings the second critical point predicted in liquids into line with other critical phenomena.

Synthesis and thermo-responsive behavior of helical polyacetylenes derived from proline

2018 ◽  
Vol 54 (85) ◽  
pp. 12081-12084 ◽  
Author(s):  
Ge Shi ◽  
Sheng Wang ◽  
Xiaoyan Guan ◽  
Jie Zhang ◽  
Xinhua Wan
Keyword(s):  
Phase Transition ◽  
Aqueous Solution ◽  
Lower Critical Solution Temperature ◽  
Solution Temperature ◽  
Critical Solution Temperature ◽  
Responsive Behavior

Structurally simple, biomass-based helical polyacetylene exhibits an unexpected lower critical solution temperature in an aqueous solution with a narrow phase-transition window and a small hysteresis.

The Effects of Drying Techniques on Clay-Rich Soil Texture

1974 ◽  
Vol 32 ◽  
pp. 466-467
Author(s):  
T. G. Naymik
Keyword(s):  
Critical Point ◽  
Liquid Nitrogen ◽  
Liquid Nitrogen Temperature ◽  
Drying Methods ◽  
Air Drying ◽  
Freeze Dried ◽  
Critical Point Drying ◽  
Set Up ◽  
The Relationship ◽  
Quartz Grains

Three techniques were incorporated for drying clay-rich specimens: air-drying, freeze-drying and critical point drying. In air-drying, the specimens were set out for several days to dry or were placed in an oven (80°F) for several hours. The freeze-dried specimens were frozen by immersion in liquid nitrogen or in isopentane at near liquid nitrogen temperature and then were immediately placed in the freeze-dry vacuum chamber. The critical point specimens were molded in agar immediately after sampling. When the agar had set up the dehydration series, water-alcohol-amyl acetate-CO2 was carried out. The objectives were to compare the fabric plasmas (clays and precipitates), fabricskeletons (quartz grains) and the relationship between them for each drying technique. The three drying methods are not only applicable to the study of treated soils, but can be incorporated into all SEM clay soil studies.

Temperature Effect on the Two-Dimensional Phase Transition Kinetics of Adenine Adsorbed at the Hg Electrode/Aqueous Solution Interface

2003 ◽  
Vol 68 (8) ◽  
pp. 1407-1419 ◽  
Author(s):  
Claudio Fontanesi ◽  
Roberto Andreoli ◽  
Luca Benedetti ◽  
Roberto Giovanardi ◽  
Paolo Ferrarini
Keyword(s):  
Phase Transition ◽  
Aqueous Solution ◽  
Phase Change ◽  
Temperature Effect ◽  
Transition Rate ◽  
Effect Of Temperature ◽  
Two Dimensional ◽  
Solution Interface ◽  
Phase Transition Kinetics ◽  
Kinetics Of

The kinetics of the liquid-like → solid-like 2D phase transition of adenine adsorbed at the Hg/aqueous solution interface is studied. Attention is focused on the effect of temperature on the rate of phase change; an increase in temperature is found to cause a decrease of transition rate.

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