Isothermal Conditions Research Articles

A predictive mesoscale model for continuous dynamic recrystallization

Thermomechanical processing of titanium alloys often requires complex routes to achieve the desired final microstructure. Recent advances in modeling and simulation tools have facilitated the optimization of these processing routes. However, existing models often fail to accurately predict microstructural changes at large deformations. In this study, we refine the physical principles of an existing mean-field model and propose a calibration method that uses experimental results under isothermal conditions, accounting for the actual local deformation within the workpiece. This new approach improves the predictability of microstructural changes due to continuous dynamic recrystallization during torsion and compression experiments. Additionally, we integrate the model into the commercial FEM-based DEFORM™ 2D software to predict the local microstructure evolution within hot torsion specimens thermomechanically treated by resistive heating. Validation using non-isothermal deformation tests demonstrates that the model provides realistic simulations at high strain rates, where adiabatic heat modifies temperature, flow stress and microstructure. This study demonstrates the intrinsic correlation between microstructure, flow behavior, and workpiece geometry, considering the impact of deformation history in thermomechanical processes.

A cavitation enabled green leaching of metals from spent lithium-ion batteries

As the world dabbles with increasing quantities of spent lithium-ion batteries (LIBs) and the need to recover valuable metals therein, sustainable approaches to achieving this need have become a necessity. In this work, we present the findings of an ultrasound-assisted intensification of a leaching process for the recovery of cobalt, nickel, manganese and lithium from spent LIBs. Molasses, methanesulfonic acid and ultrasonication were used together to enhance the leaching of the metals. The influence of ultrasonic modes, namely, sonication under isothermal and non-isothermal conditions, and leaching parameters, such as temperature, sonication amplitude, time, solid-liquid ratio, and reductant dosage, were evaluated. The leaching of metals was found to be strongly dependent on amplitude, temperature, and time. Compared to conventional mechanical stirring, the application of ultrasonic waves improves the leaching of metals by ∼22–74 %, with the degree of enhancement dependent on the temperature and the metal. The non-isothermal sonication mode (sonication without temperature control) has a lower energy input yet can yield a similar leaching performance as sonication under controlled temperature (isothermal mode). The results suggest that the introduction of ultrasonic waves created cavitation bubbles, which caused solid fragmentation, enhanced the mass transfer and diffusion of the reactants, and formed products that led to significant improvements in the leaching efficiency.

Topology of thermodynamic potentials using physical models: Helmholtz, Gibbs, Grand, and Null.

Thermodynamic potentials play a substantial role in numerous scientific disciplines and serve as basic constructs for describing the behavior of matter. Despite their significance, comprehensive investigations of their topological characteristics and their connections to molecular interactions have eluded exploration due to experimental inaccessibility issues. This study addresses this gap by analyzing the topology of the Helmholtz energy, Gibbs energy, Grand potential, and Null potential that are associated with different isothermal boundary conditions. By employing Monte Carlo simulations in the NVT, NpT, and μVT ensembles and a molecular-based equation of state, methane, ethane, nitrogen, and methanol are investigated over a broad range of thermodynamic conditions. The predictions from the two independent methods are overall in very good agreement. Although distinct quantitative differences among the fluids are observed, the overall topology of the individual thermodynamic potentials remains unaffected by the molecular architecture, which is in line with the corresponding states principle-as expected. Furthermore, a comparative analysis reveals significant differences between the total potentials and their residual contributions.

Comparison of structural and in vitro digestive properties of autoclave-microwave treated maize starch under different retrogradation temperature conditions

Retrogradation is a critical step in the physical production of resistant starch. This study aimed to examine the effects of isothermal and temperature-cycled retrogradation on the structural, physicochemical properties, and digestibility of resistant starch type-III (RS3) under various thermal conditions. To create RS3, normal maize starch (NM) and Hylon VII (HAM) were treated by autoclave-microwave and then retrograded at isothermal (4 °C) or various temperature conditions (4/10 °C, 4/20 °C, 4/30 °C, 4/40 °C, and 4/50 °C). We found that temperature-cycled retrogradation possessed greater potential than isothermal retrogradation for producing short-range ordering and crystalline structures of RS3. Also, retrograded starch prepared via temperature cycling exhibited higher double helix content, lower amorphous content, reduced swelling power, and less amylose leaching in water. Furthermore, the starch digestibility was affected by structural alterations, which were more significant in HAM-retrograded starch. While, HAM-4-40 (39.27 %) displayed the highest level of resistant starch (RS).

Increasing effect of biocrusts on evaporation is evidenced by simulating evaporation and diffusion experiments and water stable isotope analysis

Evaporation, one of the main components of the water and energy balance between soil and atmosphere, plays a key role in hydrological processes particularly in semi-arid and arid climate regions. As critical living organism communities inhabiting the soil-atmosphere boundary, biocrusts are capable of modifying near-surface soil properties and structure in drylands. However, the roles of biocrusts in mediating soil evaporation still remain greatly controversial, and the literature yet lacks in a systematic assessment. In this study, evaporation experiments were conducted under simulated isothermal and non-isothermal conditions for bare soil and three types of biocrusts (cyanobacterial, moss, and their mixture) sampled from a semi-arid climate region of the Chinese Loess Plateau. During the evaporation, soil temperature and moisture were measured at depths 2, 5, 10, and 15 cm for those biocrusts and bare soil. Their water vapor diffusion process and stable isotopic composition were also analyzed in the laboratory. We found that the measured evaporation yielded 4.9%, 17.5%, and 31.6% higher average evaporation rate for cyanobacterial, cyano-moss, and moss crusts, respectively, when compared to the bare soil. In comparison to bare soil, all types of biocrusts markedly reduced the rate of temperature rise, prolonged the duration of wetting time, and delayed the formation of dry surface layer. The largest regulating effects on soil temperature and moisture were found in the moss crusts instead of cyanobacterial or cyano-moss crusts. The increasing evaporation in biocrusts was attributed to their higher fine particle content, lower bulk density, and greater water holding capacity. Moreover, the water vapor diffusion rate and diffusivity of biocrusts were 18.2% and 16.4% higher than those of bare soil, respectively, which is attributable to the increased total porosity and better soil structure. Additionally, the isotopic composition of soil water (0–50 cm) in bare soil and moss crusts was distributed below the local meteoric water line. The mean δ18O and δ2H in soil water gradually decreased with increasing soil depth, and the moss crusts were more isotopically enriched than bare soil. Based on the enhanced soil evaporation rate, improved vapor diffusivity, and enriched isotopic composition of biocrusts in contrast to bare soil, we conclude that biocrusts exacerbate vapor transport and evaporative loss, and consequently they are crucial surface cover in rebalancing surface ecohydrological and biochemical processes in global drylands. These findings improve our understanding of the complexity of dryland hydrology, and a full consideration should be given in future biocrust studies.

Isothermal reduction and comparative analysis of reaction kinetics of sponge iron produced from hematite-charcoal reaction using non-contact direct reduction method

The challenge of making sponge iron, or direct reduced iron (DRI), is hard to overstate. These are a key feed for metallurgical operations while iron extraction sets these limits, which include scarcity of metallurgical coke, poor environmental impact, and high production cost. Thus, the non-contact direct reduction process of DRIs has the potential to significantly reduce carbon deposition and CO2 emission from the ironmaking process. This work produced sponge iron from commercially acquired hematite ore using an alternative reducing agent (i.e. charcoal) under specified isothermal conditions. Comparative analysis of reaction kinetics models including Ginstein−Brounshtein and Shrinking core models was also performed to ascertain the resistances that control the reaction rate for reduction degree up to 98.1%. The reduction kinetics were found to be described by reaction control time and activation energies based on a shrinking core model as the reduction time lasted for 120 min at temperatures 843–1273 K. At temperatures above 973–1073 K, the rate-limiting step was found to be solely an interfacial chemical reaction process, with an apparent activation energy of 196.1 kJ/mol. In addition, a slowing trend was observed for iron ore sample sizes 10–20 mm as a result of ash layer infiltration around the inner-core structure of the DRI metal matrix. The DRI morphological characteristics were performed using Scanning Electron Microscopy (SEM) and Electron Dispersive Spectrometry (EDS) to ascertain the mineralogical and morphological properties of the DRI samples. The XRF analysis confirms that the raw iron ore sample is hematite. Its iron content is 70.04% metallic iron (TFe) which has 83.59% Fe2O3 The SEM/EDS image also revealed the presence of micropores on the DRI morphology. This indicates that the reduction ratio and swelling extent rise with the temperature and time. This happens for all DRI sizes. However, the EDS result confirms the presence of gangue elements within the DRI metal matrix and mineralogical structure. The DRI contains very high silicon content up to 33.90%. So, a fluxing experiment is needed using limestone (CaCO3) or quicklime (CaO) quicklime to remove gangue (silicate, aluminate) from the DRI matrix. At the set reduction temperatures, the largest metallization degree of 93.05% at 1273 K for a reduction time of 120 min was achieved. This showed that the overall reduction process still follows the expected chronological order since the NDR process uses CO gas from preheated charcoal. This makes DRI be produced from raw hematite under non-contact reduction bases. Therefore, the NDR technique offers a viable option for sponge iron production in modern-day iron and steelmaking processes.

Ultra-sensitive colorimetric detection of SARS-CoV-2 by novel gold nanoparticle (AuNP)-assisted loop-mediated isothermal amplification (LAMP) and freezing methods.

Loop-mediated isothermal amplification (LAMP) is a molecular diagnosis technology with the advantages of isothermal reaction conditions and high sensitivity. However, the LAMP reactions are prone to producing false-positive results and thus are usually less reliable. This study demonstrates a gold nanoparticle (AuNP)-assisted colorimetric LAMP technique for diagnosing SARS-CoV-2, which aims to overcome the false-positive results. The AuNPs were functionalized with E gene probes, specifically tailored to bind to the amplified E-gene LAMP product, using the freezing method. Varied salt concentration and AuNP/probe combinations were tested for the highest visual performance. The experiments were conducted on synthetic SARS-CoV-2 RNA (Omicron variant), as well as on clinical samples. The assay showed an exceptional sensitivity of 8.05fg of LAMP amplicon mixture (0.537fg/µL). The average reaction time was ~ 30min. In conclusion, AuNP-assisted LAMP detection will not identify any potential unspecific amplification, which helps to improve the efficiency and reliability of LAMP assays in point-of-care applications. The freezing method to functionalize the AuNPs with probes simplifies the assay, which can be utilized in further diagnostic studies.

Chemical Composition of Larch Oleoresin before and during Thermal Modification

Larch is a strong timber, which grows rapidly in the UK climate, but can contain abundant resin pockets. To address the resin exudation issue, a mild thermal modification process has been developed, promoting the curing of the resin. This paper reports a series of studies which characterised the chemical profile of larch oleoresin before and after the mild thermal treatment, explaining the changes which occur when resin is dried. Further experiments were used to simulate specific points in time during the mild treatment process. The non-polar components of the fresh (untreated) and treated larch oleoresin were profiled using gas chromatography mass spectrometry (GC-MS). Fresh larch oleoresin was also subjected to isothermal experiments at different temperatures in a thermogravimetric analyser–differential scanning calorimeter (TGA/DSC), followed by re-analysing the resin composition. This demonstrated the loss of monoterpenes at temperatures of 120 °C and above, with complete loss by isothermal conditions of 150 °C and 60 min. The partial loss of sesquiterpene alkanes and alkenes were also observed at all temperatures, although completeness of this loss was achieved at isothermal temperatures of 150 °C and above. The diterpene composition was seen to change for isothermal experiments conducted at 150 °C and above, with a dehydration of terpenols to form the equivalent terpene alkenes. The observed physical changes in the TGA/DSC experiment were in good agreement with observations of the oleoresin sampled from thermally modified larch planks.

Predictive model for the growth of Shiga toxin-producing Escherichia coli in Minas Frescal cheese

This study aims to develop and evaluate a predictive model for Shiga toxin-producing Escherichia coli (STEC) growth on Minas Frescal cheese across varied temperature conditions. A pool of five STEC strains (3–4 log CFU/g) was inoculated onto 10 g Minas Frescal cheese portions (%moisture = 68.30 ± 0.47,%fat in dry basis = 26.55 ± 0.37, pH = 6.86 ± 0.02) stored at isothermal conditions (4, 8, 15, 25, 37, and 42 °C). STEC concentrations increased at 8 °C and above, persisting throughout the 504-hour study period at 4 °C, showing minimal cell loss. The growth curves were fitted with the primary model of Baranyi and Roberts using Combase DMFit, showcasing robust alignment between predicted and experimental data (R2 ≥ 0.98). Further, the µmax and λ values were fitted as a function of temperature to modified Ratkowsky equations, resulting in R2 of 0.99 and 0.96, and RMSE of 0.03 and 0.08, respectively, for the secondary models. Model validation was performed under isothermal conditions at 20 and 30 °C. The Ratkowsky equations can reliably predict STEC growth rate and lag phase in Minas Frescal cheese at diverse temperatures (8 to 42 °C), evidenced by accuracy and bias factors of 1.06 and 1.06. These findings offer insights into cold chain management for STEC control during Minas Frescal cheese production, distribution, and storage, emphasizing the need for robust post-pasteurization manufacturing practices to prevent STEC survival even at lower temperatures.

Diffusion in multicomponent mixed solvent electrolyte systems

Thermodynamic ideality is often assumed in diffusion calculation, implying concentrations are assumed equal to the activities with activity coefficients of one. A general set of diffusion flux and molar flux equations are developed, incorporating equilibrium thermodynamic models for non-ideal conditions in well-known non-equilibrium diffusion theory. Derivations are based on the Maxwell-Stefan friction theory with the chemical potential as the driving force. Isothermal and isobaric conditions are assumed, and the theory does not include the Soret coefficient or the Onsager formalism.In this work, Fick's law is derived from the general diffusion theory, also as a function of activity gradients. The results illustrate that concentration cannot just be substituted by activity. Using a similar approach demonstrates that the Nernst-Planck (NP) equation may be derived from the general theory incorporating terms for migration and convection. An extended NP equation is derived including the thermodynamic correction factors (TCF) to account for the non-ideality of the liquid. The derived equation shows the improvement of the self-diffusion terms and friction coefficients in the NP equation and that the TCF enhances the observed effective diffusivities.Examples of TCF are presented using the extended UNIQUAC thermodynamic model. This is done for the CO2-NaOH-monoethyleneglycol-water system, which is typically found in wet natural gas pipeline CO2 corrosion systems. pH-stabilization is classically used in the prevention of corrosion, but the results show that glycol has a noticeable effect of the diffusion on key components in the corrosion mechanism. A TCF of 0.4 to 1.3 may be expected. This indicates that the flux calculation deviates up to 60 % from the real-life scenario if ideality is assumed. The thermodynamic model may therefore improve the diffusion calculations considerably.

Special RCA based sensitive point‐of‐care detection of HPV mRNA for cervical cancer screening

AbstractDeveloping the sensitive point‐of‐care testing (POCT) of oncogenic nucleic acids from human papillomavirus (HPV) infection is essential in preventing cervical cancer, especially in resource‐limited settings. Rolling circle amplification (RCA) is attractive in achieving POCT via nucleic acid‐based aggregation under isothermal conditions. However, the influence of RCA product structure on the aggregation remains unexplored resulting in limited sensitivity. Here, a minimum secondary structured RCA technique (MSS‐RCA) is developed by designing a unique circular template, demonstrating significantly enhanced detection sensitivity with only one amplification step and one primer under isothermal conditions. The amplification efficiency of MSS‐RCA could be kinetically manipulated by controlling the secondary structure of the circular template. Introducing the invertase probe to MSS‐RCA, HPV16 E6/E7 nucleic acid target was detected with a personal glucose meter (PGM) with a sensitivity of 5 fm (50 zmol in 10 µL). This integrated MSS‐RCA‐PGM detection system was successfully applied to detect HPV16 E6/E7 mRNA extracted from 54 cervical swab samples reaching a positive predictive value of 100.00% and negative predictive values of 96.00% (77.77% to 99.40%, 95% CI). MSS‐RCA‐PGM provides a sensitive POCT platform for the detection of nucleic acid biomarkers for screening of cervical cancer or other diseases.

Corrosion effects of Na2CO3/NaCl molten salt eutectic on 316L stainless steel under isothermal and cycling conditions

Using phase-change materials in thermal energy storage systems for concentrating solar thermal plants can significantly reduce the volume of storage media and, therefore, the cost of the system. However, this approach introduces new material compatibility issues between the thermal energy storage material and the containment vessel in the form of corrosion and thermal transients, which are inherent in these systems. Rods and sheet coupons of stainless steel 316L were corroded for up to 768 h in 59.4/40.6 wt% Na2CO3/NaCl eutectic salt under isothermal (650 °C) and cycled conditions (between 600 and 650 °C). The testing methodologies correspond to actual service conditions, as isothermal degradation may not represent material loss under typical solar thermal cycling conditions. Mass losses were calculated via the Dynamic Gravimetric Analysis technique while Scanning Electron Microscopy utilizing Energy Dispersive Spectroscopy was used to analyze the corrosion layers. Isothermal mass loss plateaued at 75 mg/cm2 at 96 h with no further measurable loss after this time, while cycled samples had a fast initial mass loss rate of 60 mg/cm2 in the first 96 h and lost 0.0331 mg/cm2 every hour thereafter. The results indicate that isothermal samples corrode more slowly than the predominant industry cases of thermal cycling. Spalling is responsible for the degradation in both sets; the continual temperature changes in the cycled samples lead to additional stresses, exacerbating the effect.

Temperature-gradient and isothermal creep tests on 2024 aluminum alloy: A novel approach to creep failure evaluation aided by image processing

In high-temperature working conditions, the temperature difference between parts is common, and it is necessary to perform a temperature gradient test to predict creep behavior of alloy in real working conditions. In this study, a novel temperature gradient creep (TGC) test aided by an image processing method (IPM) was designed and performed on 2024-T3 aluminum alloy. The tests were performed under the conditions of isothermal tensile creep (ITC) and TGC in the temperature range of 285–315 °C under two stresses of 90 MPa and 125 MPa. Several experimental investigations were conducted to evaluate the creep failure of the specimens. The results showed that the temperature gradient during the TGC test leads to changes in strain, strain rate, stress exponent, microstructure and damage amount in the samples. The creep strain and strain rate of the TGC are greater than those of the ITC at 300 °C and 285 °C, and the rupture life is shorter. Finally, the Larson–Miller parameter is calculated, and the mathematical relationships between the strain rates of the TGCs and ITCs in 90 MPa and 125 MPa, which can be used to predict the creep strain rate under isothermal conditions, are proposed.

Experimental study on co-combustion of domestic garbage and sewage sludge: Evaluation of synergistic effect and thermo-kinetic behavior

A persistent increase in domestic garbage (DG) has become a significant worldwide issue due to its negative impact on the ecosystem. The co-combustion way of DG and sewage sludge (SS) in a garbage incineration plant has been deemed a viable option. The study aims to quantify co-combustion behaviors, interaction effects, and thermo-kinetic properties between DG and SS at isothermal conditions by a thermogravimetric analyzer. The results showed that co-combustion of DG with 20 % SS could boost the combustion performance indices, and exhibit the synergistic effect. In addition, at the various SS blending ratios (10, 20 and 35 %) under an air atmosphere, combustion performance indices gradually decreased with an increased SS blending ratio but the synergistic effects were inhibited with a 35 % SS blending ratio. Coat-Redfern method was used to determine the combustion kinetics and thermodynamic properties. The apparent activation energy in the DG-SS (80 %/20 %) blend exhibited a non-linear relationship but increased proportionally with higher SS blending ratio. The lowest activation energy (34.70 kJ/mol) was obtained at the DG-SS (90 %/10 %) blend. The results suggest that the co-combustion of DG and SS can improve the overall combustion performance with an optimal blending ratio of 20 % SS for the co-combustion application.

AMPLON: Amplifying DNA with Multiarm Priming and Looping Optimization of Nucleic Acid.

Nucleic acid amplification, the bedrock of biotechnology and molecular diagnostics, surges in applications-especially isothermal approaches-heightening the demand for advanced and precisely engineered methods. Here, a novel approach for amplifying DNA with multiarm priming and looping optimization of nucleic acid (AMPLON) is presented. AMPLON relies on a novel polymeric material with unique set of multiarm polyethylene glycol-DNA primers for efficient DNA amplification under isothermal conditions. Each arm carries single-stranded DNA complementing the sense or antisense sequence of the target DNA. The amplification reaction begins with antisense arms binding to the target DNA, forming a template for sense-carrying arms to direct multiarm large DNA amplicon synthesis through successive DNA looping and unlooping steps. Using human immunodeficiency virus type 1 (HIV-1) as a model clinical target, AMPLON exhibits high sensitivity, detecting target concentrations as low as 100 copies mL-1. Compared to a quantitative real-time polymerase chain reaction assay using sensitive primers, AMPLON reliably identifies HIV-1 RNA in plasma samples (n = 20) with a significant agreement rate of 95%. With its ability to achieve highly specific and sensitive target amplification within 30 min, AMPLON holds immense potential to transform the field of nucleic acid research and unleashing new possibilities in medicine and biotechnology.

On-line cure monitoring of phenol formaldehyde resin using embedded fiber Bragg grating sensor

On-line cure monitoring techniques have shown advantages for identifying the stages of curing and can lead to smart curing process of resin system and its composites. In this study, an on-line measuring technique with fiber Bragg grating (FBG) sensors was used to gain clear understanding of the curing stages of phenolic resin, as well as to determine its chemical shrinkage level. The FBG sensors were embedded in phenolic resin and worked under temperature raising and isothermal conditions. Through the interface between FBG sensor and resin, curing shrinkage strain was transferred to the grating, changing the central wavelength of FBG and producing strain. The feasibility of FBG sensors for monitoring chemical shrinkage during curing was verified by employing epoxy and benzoxazine resins that exhibits low chemical shrinkage. For cure monitoring of phenolic resin, the results show that the strain signal can be corresponded to various responses, such as solvent volatilization, hydroxylation and dehydration condensation reactions during temperature raising curing process. Through these strain characteristics, the curing state of phenolic resin can be obtained, which degree of cure ranges from 0.05 to 0.9. In isothermal curing process of phenolic resin, an exponential correlation between chemical shrinkage induced compressive strain and degree of cure of resin was identified, indicating that the real-time compressive strain is proportional to the degree of cure of phenolic resin. By evaluating real-time curing shrinkage levels, the estimation of curing degree of phenolic resin can be achieved utilizing exponential correlation of curing degree and curing shrinkage level.

Heat Flux Prediction of Radiation Balance Wall by Deep Convolutional Neural Networks

Aerodynamic thermal prediction plays a crucial role in the design of a hypersonic vehicle, particularly with regard to the thermal protection system. Traditional methods of aerodynamic thermal prediction encounter several primary challenges, including slow convergence rates, rigorous computational grid requirements, and the need to simplify by assuming isothermal wall conditions. In this research, we propose using the Convolutional Neural Network (CNN) Hybrid Feature (HF) model to facilitate rapid aerothermal predictions for both isothermal wall conditions with varying wall temperatures and radiation balance wall conditions. The CNN HF model is trained separately for isothermal wall conditions under identical inflow conditions as well as for diverse inflow conditions and radiation balance wall temperature scenarios. The model’s predictions are then compared to numerical simulation results. Our findings demonstrate that the CNN HF model efficiently provides rapid aerothermal predictions by leveraging macroscopic converged flowfield data. In the majority of cases, the model achieves a threefold enhancement in computational efficiency while maintaining predictive accuracy within a 5% range when compared to numerical simulation results. The application of the CNN HF approach in aerothermal prediction for different wall temperatures and radiation balance scenarios has significantly reduced the time required to obtain aerodynamic heating results.

High Temperature Solid Oxide Electrolyte Fuel Cell Formulation: Non-Steady State Utilization of Fuel and Oxidant

The formulation presented in this paper was developed with the objective of its application to investigate the transient behavior of a high temperature solid oxide fuel cell (SOFC); especially with respect to the non-steady state consumption of fuel and oxidant reactants. Specifically, the chemical species transient amounts, their mole fractions, and total pressures in the cell anode-side fuel- (hydrogen) and cathode-side oxidant- (oxygen of the air) chambers can be predicted under the isothermal condition at a fixed cell-current level. The developed formulation is also capable of predicting the transient mole fraction profiles of fuel (hydrogen) and oxidant (oxygen) in the cell porous anode and cathode, respectively; thus, providing insight into the reactant species' effective transport and their utilization, via electrochemical reactions, in the cell porous electrodes. The presented formulation can be adapted for any fuel and oxidant combinations in any high temperature SOFC.

Pressure studies of rod-like liquid crystals – experimental facts and theoretical deficiencies

ABSTRACT In the years 1990–2015, many liquid crystalline (LC) substances were studied under elevated pressure. The main aims of studies were to determine the P vs. T phase diagrams, the equation of state V(P,T) for isotropic and LC phases, measuring the dynamical properties of molecules (mainly the flip-flop motions) and analysing them at the isobaric, isothermal and isochoric conditions. The observed phenomena were discussed using existing theoretical models of LC state or – in the absence of them – models adopted from the field of glass-forming liquids. In the present review, the attention will be paid to a comparative data analysis for two rings compounds with the strongly polar terminal group (CN or NCS) at one site and the n-alkyl or n-alkoxy group at the other. Such molecules may well mimic the rod-like molecules commonly used in theoretical models of LC state.

Relation between characteristic temperature and elution temperature in temperature programmed gas chromatography – Part II: Influence of column properties

The method development process in gas chromatography can be accelerated by suitable computer simulation tools using knowledge about the solute-column interactions described by thermodynamic retention parameters. Since retention parameters usually are determined under isothermal conditions, the presented work offers a step to estimate one of the most important retention parameters, the characteristic temperature Tchar by less laborious temperature programmed measurements.In the first part an empirical multivariate model was introduced describing the correlation between the elution temperature Telu of a solute and its characteristic temperature Tchar. Now in the second part a simulation model of GC and available retention data from a retention database was used to investigate the correlation between Telu and Tchar for an expanded range of heating rates and initial temperatures. In addition to part I, the simulation is used to investigate the influences of different properties of the separation column such as different phase ratios and column geometries like length and diameter or various stationary phases including SLB-5 ms, SPB-50, Stabilwax, Rtx-Dioxin2, Rxi-17Sil MS, Rxi-5Sil MS, ZB-PAH-CT, DB-5 ms, Rxi-5 ms, Rtx5 and FS5ms. The fit model is valid for all investigated stationary phases. The influence of the phase ratio to the correlation could be determined. Therefore, the model was expanded to this parameter.The expanded range of heating rates and the normalization for the system independent dimensionless heating rate required a further modification of the previously presented correlation model. The model now fits also under isothermal conditions. The results were used for estimation of the Tchar of an analyte from the elution temperature in the temperature program. The prediction performance was investigated and evaluated for 20 different temperature program conditions and at two phase ratios (β=125 and β=250). Under best conditions the estimated and the measured Tchar values show relative differences <0.5 %. With this novel model estimations for Tchar are possible at 20 °C above the initial temperature, which expands the prediction range even for low and medium retained analytes compared to earlier approaches.