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NEW RESEARCH TOOL _ NEW method enabling detailed and precise study of phase equilibria in critical systems.
On approaching the critical consolute point, the critical opalescence appears. The mixture becomes milky and opaque, indicating the presence of critical fluctuations. In the analysis, the meniscus position is quantified using the fractional meniscus height, which is the height of the meniscus normalized by the total height of the sample.
The NEW visual method for determining phase equilibria involves photo-registration of the volume occupied by coexisting phase, followed by the analysis recalling issues of critical phenomena physics supported by statistical analysis.
It yielded concentrations or densities characterizations of the coexistence curve, critical point parameters, and relevant critical exponents. Tested mixtures of limited miscibility for a set of concentrations are placed in calibrated ampoules sealed by a torch flame. Subsequently, they are placed in a large, transparent, and thermostated vessel with computer-controlled temperature changes. The shift of menisci and then coexisting phase volume are registered by high-resolution photo apparatus. The whole measurement cycle, covering ca. 20 K temperature range, requires 10 to 30 hours. It is ‘automatic’ and does not require permanent staff assistance, except for the remote online control.
Jakub KALABIŃSKI designed and constructed the NOVEL VISUAL METHOD with photo registration, exploring menisci position changes (coupled to the volume of existing phases) with temperature shift. It provides data for precisely determining the coexistence curve (binodal). The set-up is computer-controlled, which the requirement of permanent staff presence and improves the accuracy and reliability of output data.
Advanced setups allow for automated measurements over several days, reducing the need for constant manual observation and improving the accuracy and reliability of the data.
Phase Equilibria and Critical Behavior in Nematogenic MBBA—Isooctane Monotectic-Type Mixtures
Critical concentration in binary mixtures of limited miscibility.
The report presents the new method, fast & simple in use, to determine the coexistence curve (binodal) and the critical concentration. Notable is the experimental simplicity of the technique: for the preliminary estimation it is enough to prepare two samples with different total concentrations or densities and observe relative volumes occupied by coexisting phases (or fractional meniscus heights) for two different temperatures. The method is illustrated based on experimental studies in nitrobenzene–hexane mixtures of limited miscibility. Notable is the importance of this result for a variety of practical implementations, ranging from chemical physics to foods and pharmaceutical technologies. Additionally, the manifestations of various stages of critical opalescence, from dark-navy-blue to bluish and whitish, in a broad range of temperatures and concentrations, are shown and discussed.
In the authors' opinion, the method offers a simple, reliable, and ‘fast in applications’ experimental tool, solving problems emerging after the cancellation of the CM law of rectilinear diameter. A brief discussion of some hardly indicated aspects of the critical opalescence is also given.
The photos show the formation of the two-phase after the temperature quenches for NLC + Sol samples placed between two parallel glass plates, enabling polarization-related insight. In such a case, there is no gravitational separation of coexisting phases. Note the emergence of nematic ‘seeds/nuclei’, with a visible texture, which number and size increase with the observation time. For such a configuration, the assisted opalescence is not detected (the sample is ‘thin’). The authors used the processing consisting of rotating and cropping the image and a levels manipulation tool. This tool allows changing the image’s tones through brightness, contrast, and gamma correction.
The sole purpose of the operations was to highlight the visibility of the effects by the opalescence. This paper shows the results of such analysis, enabling explicit insight into the formation of the two-phase isotropic-nematic domain.
Four decades ago, the CM law of rectilinear diameter ceased to be the omnipotent tool for estimating the critical concentration in critical binary mixtures. No alternative concept of its precise and easy determination has appeared since then. This report presents the new and reliable experimental tool for the fast estimation of the critical concentration and temperature. This report presents a set of new dependencies, which can portray changes of the critical consolute temperature and concentration, as the function of pressure and within homologous series of low-molecular liquids composed of a nitro compound and n-alkanes. It is shown that it is even possible to prepare a critical mixture for which dTC/dP ≈ 0 in a broad range of pressures. All these can be significant for fundamental modeling and practical implementations exploring unique near-critical features.
Impact of Pressure on Low-Molecular Weight Near-Critical Mixtures of Limited Miscibility.
The photos show phase equilibria and critical opalescence into 3-picoline–-deuterium oxide (D2O) mixtures of limited miscibility, for which the two-phase domain appears on heating from the homogeneous phase. The developed novel visual method enabled the first-ever precise estimation of the coexistence curve for such. Notable is the explicit evidence for the pretransitional anomaly of the binodal diameter, i.e., the cancellation of the rectilinear ‘law’ for the diameter occurrying also for such unique mixtures of limited miscibility.
To the best of the authors' knowledge, it is the first example of such analysis for the low-critical-temperature (LCT) type mixture of limited miscibility.
New insight into 3-picoline–-deuterium oxide (D2O) mixtures of limited miscibility withthe lower critical consolute temperature.
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This WEBSITE was created to realize the following, main GOALS:
Soft Matter systems have common features, such as the dominance of elements or local structures on the mesoscale, combined with their relatively weak interactions, which turns out to be sufficient to obtain a tendency to self-organize with even a small change in parameters. This additionally leads to extraordinary sensitivity to even minor endogenous and exogenous factors, e.g., nanoparticles and pressure. In the case of the latter, relatively low pressures P~1 GPa, or even much lower ones, can lead to phases/states with exotic features, often persisting after decompression.
Worth stressing, that for "classical hard matter" systems, a pressure similar to that at the Earth's core (~300 GPa) is typically required, and the resulting "exotic" properties most often disappear upon decompression.
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