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High-resolution Peltier-element-based adiabatic scanning calorimetry (pASC) has been used to investigate the temperature dependence of the specific heat capacity and specific enthalpy of two mixture systems of the liquid crystal smectic A1 compound 5-n-nonyl-2-(4′-isothiocyanatophenyl)dioxane-1.3 (9DBT), and one of the smectic Ad compounds 4-n-octyloxy-4′-cyanobiphenyl (8OCB) and 4-nonyloxy-4′cyanobiphenyl (9OCB). For both mixture systems, measurements have been carried out over a large temperature range, from the crystalline solid phase over the smectic and nematic phases into the isotropic liquid phase. Both systems exhibit substantial, mixing-induced, enhanced nematic ranges and large changes in the composition dependence of the transition temperatures between the different phases. In both systems, eutectic melting points have been located and, for the different mixtures, the melting and eutectic transition heats have been obtained. The nematic to isotropic (NI) transitions are weakly first order with latent heat values in the range usually observed for this transition in other liquid crystals. The critical behavior of the specific heat capacity at the NI transition is described by exponent values near the tricritical one of 0.5. Along the smectic A to nematic (AN) transition lines, strong composition dependence was observed for the latent heat, from almost zero to values comparable to those observed at the nematic to isotropic transition. The concentration dependence of these AN latent heats was adequately fitted with a crossover function consistent with a mean-field free-energy expression that has a nonzero cubic term; the latter is induced by the Halperin-Lubensky-Ma coupling between the smectic A order parameter and orientational order director fluctuations. The fitting analysis resulted in the location of a Landau-tricritical point along one branch of the transition line in the system 9DBT-8OCB and one in each branch (for low and high 9OCB mole fractions) of, SCOPUS: ar.j, info:eu-repo/semantics/published

We address the question on the validity of the ideal volumetric mixing approximation, a customarily used approach to analyze liquid-liquid phase transitions. Thus, liquid-liquid coexistence curves for the binary mixture composed by nitromethane and 3-pentanol were obtained from direct single-phase mass density measurements as a function of temperature. A reasonable agreement with previously reported data obtained from refractive index measurements has been found, indicating that assuming ideal mixing is rather reasonable. Furthermore, the implications of the ideal volumetric mixing approximation on asymmetric liquid-liquid criticality are explored in the framework of complete scaling formulation, with emphasis on the coexistence curves in the mole fraction-temperature and volume fraction-temperature planes as well as on the behaviour of the isobaric heat capacity per particle and per unit volume and the associated Yang-Yang-type anomalies., SCOPUS: ar.j, info:eu-repo/semantics/published

The first studies of critical phenomena date back to the second half of the nineteenth century and resulted in the first half of the twentieth century in the comprehensive picture of the so called mean-field theory. As more precise experimental techniques were developed it became apparent in the middle of the last century that the behavior of real systems was inconsistent with the mean-field predictions. The anomalous specific heat capacity behavior at critical points obtained from high-resolution calorimetry played a major role in this insight. In the following decades, major progress was made and new concepts such as universality, critical exponents and the renormalization group theory emerged. In particular, universality united critical phenomena in seemingly unrelated systems. In the whole process, high-resolution calorimetry in fluid systems substantially contributed. The many phase transitions in liquid crystals constituted testing ground for the investigation of general concepts of statistical physics. In this evolution the possibility of adiabatic scanning calorimetry (ASC) to measure simultaneously the temperature dependence of the enthalpy and heat capacity played a major role in the determination of the order of transitions and the power law behavior. In this chapter, the role of ASC is exemplified by presenting results, in particular of the enthalpy, for liquid–liquid criticality and for phase transitions in liquid crystals., info:eu-repo/semantics/published

High-resolution enthalpy data are a useful tool in the study of phase transitions. Alkanes of intermediate chain length show a complex melting behaviour, with phases with rotational degrees of freedom appearing between the crystalline and liquid phases. The results presented here show that for tricosane (C23), tetracosane (C24) and pentacosane (C25), the transitions between these rotator phases are first order. Recently, the attention on phase change materials (PCMs) in energy-saving applications has strongly increased. PCMs are used to store energy, and the selection is largely based on the phase transition properties (notably the transition temperature and transition heat) of these materials. These properties are naturally quantified by the enthalpy, as illustrated for a selection of potential PCMs, mostly mixtures of alkanes., info:eu-repo/semantics/published

Adiabatic scanning calorimetry (ASC) is a technique that aims to simultaneously measure the temperature dependence of the enthalpy and the heat capacity of a liquid or solid condensed matter sample. The basic concept of ASC resides in applying a constant heating or cooling power to a sample holder containing the material to study. Although the ASC concept was first implemented in the late 1970s and further improved over the years, instruments remained largely limited to specific research applications because they required operation by skilled and trained personnel. This was not least due to elaborate construction and control to impose adiabatic conditions, as well as complicated sample cell mounting. In this chapter we describe a novel implementation, incorporating a Peltier element between the sample cell and the adiabatic shield. The new user-friendly Peltier-element-based adiabatic scanning calorimeter (pASC) allows measurements over large temperature ranges on milligram-sized samples with high resolution in temperature, enthalpy, and heat capacity. In addition to the heating and cooling modes of the pASC, it can also be used as a classical heat step calorimeter and in differential scanning calorimetry (DSC) type heat-flux or power-compensated modes. As examples, enthalpy results are presented for the melting transitions of gallium and water, and for phase transitions in an aqueous lipid vesicle suspension and in a liquid crystal., info:eu-repo/semantics/published

Peltier-element-based adiabatic scanning calorimetry was used to obtain equilibrium enthalpy and heat capacity curves for pure water and water–NaCl mixtures, up to the eutectic mass concentration of 23.2%, in the temperature range from –30 to 5∘C 5∘C ,including both the eutectic and the ordinary ice melting. From these equilibrium data, information about the transition temperatures and the heats of fusion was extracted. The transition temperatures are consistent with literature data for the phase diagram. The heats of fusion were rescaled with respect to the fraction of the sample that changes phase at each transition. These rescaled values for the eutectic transition are independent of the overall salt concentration, whereas for the ice melting there is an indication of slight decrease with increasing salt concentration., info:eu-repo/semantics/published

The phase transitions of binary lipid mixtures are studied by a combination of Peltier-element-based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM-D). pASC, a novel type of calorimeter, provides valuable and unambiguous information on the heat capacity and the enthalpy, whereas QCM-D is proposed as a genuine way of determining phase diagrams by analysing the temperature dependence of the viscosity. Two binary mixtures of phospholipids with the same polar head and differing in the alkyl chain length, DMPC + DPPC and DMPC + DSPC, are discussed. Both techniques give consistent phase diagrams, which compare well with literature results, showing their capability to map the phase behaviour of pure lipids as well as lipid mixtures. This work can be considered as a departure point for further investigations on more complex lipid mixtures displaying relevant phases such as the liquid-ordered phase and solid-lipid interfaces with biologically functional importance., info:eu-repo/semantics/published

Simultaneously measured high-resolution enthalpy and heat capacity data are obtained by means of a novel type Peltier-element-based adiabatic scanning calorimeter that can also operate as a classical adiabatic heat-step calorimeter. Specific enthalpy and specific heat capacity results with 2% uncertainty and sub-mK temperature resolution are presented for the melting transition of the calorimetric reference materials biphenyl and phenyl salicylate. The simultaneously obtained enthalpy and heat capacity data allow for a simplified and reliable purity analysis, info:eu-repo/semantics/published

A novel type of adiabatic scanning calorimeter (ASC) based on Peltier elements (PEs) is used to obtain high-resolution enthalpy and heat capacity data on the melting transition of gallium. The accuracy of the specific heat capacity and specific enthalpy is about 2 %, for a sub-mK temperature resolution. The simultaneously determined equilibrium specific heat capacity and specific enthalpy are used to determine the heat of fusion and the purity. In addition, the use of the PE-based ASC as a classical heat step calorimeter and as a constant rate (DSC-type) calorimeter is discussed. A comparison of the ASC results with literature data and DSC data shows the advantages of ASC for the study of phase transitions., info:eu-repo/semantics/published

We report on the use of the heat transfer method, a novel surface-sensitive technique based on heat transfer through solid–liquid interfaces, to detect phase transitions of model lipid membranes. We selected the lipid DPPC because of its rich phase behavior in an experimentally accessible temperature range. The vesicles were adsorbed on nanocrystalline diamond films, known as a versatile platform material for biosensing with outstanding heat-conduction properties. Complementary Peltier-element-based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements were carried out to monitor the phase transitions in multilamellar and small unilamellar vesicles, respectively. The heat-transfer measurements revealed reversible jumps upon heating and cooling in the thermal resistance in the vicinity of the expected transition temperature and they agree qualitatively with molecular simulations of the thermal conductivity across a lipid bilayer. The results show the capability of the heat transfer method to detect the main phase transition in DPPC, opening new perspectives for the study of more complex lipid systems and different solid platforms. This work confirms QCM-D as a useful tool for the assessment of the structural changes upon the phase conversion and shows the capability of pASC to provide high-resolution thermodynamic information on biophysical systems., info:eu-repo/semantics/published

We report optical birefringence data by two different methods with high temperature resolution for octylcyanobiphenyl (8CB) near the smectic-Ato nematic (Sm-A-N) phase transition temperature TAN. Within the resolution of our experiments, we find that the Sm-A-Nphase transition is continuous. For a possible discontinuity in the orientational order parameter S(T)at TAN, we arrive at an upper limit of 0.0002, which is substantially smaller than other estimates in literature, but consistent with the value of 0.00008 derived from the upper limit of the latent heat from high-resolution adiabatic scanning calorimetry (ASC), which is itself consistent with the Halperin-Lubensky-Ma theory. The temperature derivative of the order parameter exhibits a power law divergence with a critical exponent that is consistent with the value α=0.31±0.03for the specific heat capacity obtained by ASC., info:eu-repo/semantics/published

It is demonstrated that interactions between nanoparticles and topological defects induce a twist-grain boundary phase in a chiral liquid crystal. The occurrence of this phase, the analogue of the Shubnikov phase in type-II superconductors, is driven by direct interactions between surface-functionalized CdSe quantum dots and screw dislocations. It is shown that, within an adaptive-defect-core-targeting mechanism, nanoparticles of appropriate size and functionalization adapt to qualitatively different cores of topological defects such as disclination lines and screw dislocations. This mechanism enables the effective reduction of the energetically costly, singular defect core volume, while the surrounding phase ordering remains relatively weakly affected. The findings suggest new pathways towards the controlled assembly of superstructures in diverse, symmetry-broken, condensed-matter systems, ranging from nanoparticle-decorated liquid crystals to superconductors., info:eu-repo/semantics/published

The high-resolution adiabatic scanning calorimetric technique has been used to investigate the nematic-smectic A transition (N-SmA in binary mixtures of the non-smectogenic liquid crystal heptyloxycyanobiphenyl (7OCB) and heptane, exhibiting a so-called injected smectic A phase. With the exception of a mixture with the lowest heptane mole fraction for which only an upper limit of 0.2 ± 0.2 J kg−1 for a possible latent heat could be obtained, for all other mixtures finite latent heats were obtained. The mole fraction dependence of the latent heat could be well fitted with a crossover function consistent with a mean-field free energy expression with a non-zero cubic term arising from the Halperin-Lubensky-Ma (HLM) coupling between the SmA order parameter and the orientational director fluctuations. The mole fraction dependence of the heat capacity effective critical exponents is similar to that observed in mixtures of the two liquid crystals octyloxycyanobiphenyl (8OCB) and nonylcyanobiphenyl (9OCB). The thermal behavior observed along the N-SmA phase transition line yields further strong evidence for the HLM coupling effect., info:eu-repo/semantics/published

Adiabatic scanning calorimetry was used to study four ionic liquid crystals whose phase sequences include highly ordered crystal smectic phases (crystal smectic E or T phases). The ionic liquids were based on piperidinium or morpholinium cations with long alkyl chains; the anions were tetrafluoroborate or hexafluorophosphate. High-resolution heat capacity and enthalpy data were obtained, from which the total transition heat and latent heat for the observed phase transitions were determined. All transitions displayed a non-zero latent heat and were thus found to be first order., info:eu-repo/semantics/published

The large critical anomaly in the isobaric heat capacity Cp,x(T) Cp,x(T) of the binary mixture nitromethane + 3-pentanol is measured using high-resolution adiabatic scanning calorimetry. The unique features of this technique provided an alternative approach to the study of the critical behavior of Cp,x(T) Cp,x(T) ,providing further Cp,x(T) Cp,x(T) related quantities from which valuable information could be extracted. Our data are in full agreement with the predictions of the Modern Theory of Critical Phenomena; specifically, 3D-Ising model values for the critical exponent α and the universal amplitude ratio values of the leading critical amplitudes, as well as for the first correction-to-scaling ones, provide the optimum fits to represent the experimental data. Evidence for the need of higher-order terms, i.e. first correction-to-scaling term, is given. The large value of the coefficient E for the linear temperature dependence of the background obtained is ascribed to a possible contribution of the regular linear background term, of a higher-order asymmetry term, and of the second correction-to-scaling term. Internal consistency of Cp,x(T) Cp,x(T) and its related quantities is successfully checked., info:eu-repo/semantics/published

Phase change materials (PCMs) are substances exhibiting phase transitions with large latent heats that can be used as thermal storage materials with a large energy storage capacity in a relatively narrow temperature range. In many practical applications the solid-liquid phase change is used. For applications accurate knowledge of different thermal parameters has to be available. In particular, the temperature dependence of the enthalpy around the phase transition has to be known with good accuracy. Usually, the phase transitions of PCMs are investigated with differential scanning calorimetry (DSC) at fast dynamic scanning rates resulting in the effective heat capacity from which the (total) heat of transition can be determined. Here we present adiabatic scanning calorimetry (ASC) as an alternative approach to arrive simultaneously at the equilibrium enthalpy curve and at the heat capacity. The applicability of ASC is illustrated with measurements on paraffin-based PCMs and on a salt hydrate PCM., info:eu-repo/semantics/published

Dielectric constant measurements have been carried out in the one- and two-phase regions near the critical point of the polar + polar binary liquid mixture nitromethane + 3-pentanol. In the two-phase region, evidence for the, info:eu-repo/semantics/published

The behavior of the dielectric constant ε of pure fluids and binary mixtures near liquid-gas and liquid-liquid critical points is studied within the concept of complete scaling of asymmetric fluid-fluid criticality. While mixing of the electric field into the scaling fields plays a role, pressure mixing is crucial as the asymptotic behavior of the coexistence-curve diameter in the ε—T plane is concerned. Specifically, it is found that the diameters, characterized by a, info:eu-repo/semantics/published

Detailed results are reported for the dielectric constant ϵ ϵ as a function of temperature, concentration, and frequency near the upper critical point of the binary liquid mixture nitrobenzene-tetradecane. The data have been analyzed in the context of the recently developed concept of complete scaling. It is shown that the amplitude of the low frequency critical Maxwell–Wagner relaxation (with a relaxation frequency around 10 kHz) along the critical isopleth is consistent with the predictions of a droplet model for the critical fluctuations. The temperature dependence of ϵ ϵ in the homogeneous phase can be well described with a combination of a (1−α) (1−α) power law term (with α α the heat capacity critical exponent) and a linear term in reduced temperature with the Ising value for α α .For the proper description of the temperature dependence of the difference Δϵ Δϵ between the two coexisting phases below the critical temperature, it turned out that good fits with the Ising value for the order parameter exponent β β required the addition of a corrections-to-scaling contribution or a linear term in reduced temperature. Good fits to the dielectric diameter ϵd ϵd require a (1−α) (1−α) power law term, a 2β 2β power law term (in the past considered as spurious), and a linear term in reduced temperature, consistent with complete scaling., info:eu-repo/semantics/published

High-resolution adiabatic scanning calorimetry has been used to study the specific heat capacity anomaly of the nitrobenzene–tetradecane mixture near its upper critical point. The analysis, which is based on a method that uses heat capacity and enthalpy data, yields a value of the critical amplitude ratio A+/A− which is consistent with the universal, accepted one. The critical amplitude of the correlation length was derived via two-scale factor universality. All this information is compared to that reported in previous studies for nitrobenzene–alkane mixtures., info:eu-repo/semantics/published

We present experimental data of the isobaric heat capacity per unit volume Cp,xV−1 Cp,xV−1 for mixtures containing nitrobenzene and an alkane (CNH2N+2 CNH2N+2 ,with N ranging from 6 to 15) upon approaching their liquid-liquid critical points along a path of constant composition. Values for the critical amplitude A+ A+ have been determined. They have been combined with the previously reported ones for the leading term of the coexistence-curve width to obtain, with the aid of well-known universal relations, the critical amplitudes of the correlation length and of the osmotic susceptibility. The trends of all these critical parameters, which exhibit anomalous behavior in the low N region, are discussed in terms of particular microscopic phenomena characterizing NB-CNH2N+2 NB-CNH2N+2 mixtures. The work is completed with an analysis of the analog of the Yang-Yang anomaly in liquid-liquid criticality: the behavior of the partial molar heat capacities of the two liquid components is found to illustrate previously uncovered asymmetry effects., info:eu-repo/semantics/published

The phase transition behaviour of the chiral liquid crystal CE6 doped with spherical surface-functionalised CdSe nanoparticles has been examined by means of high-resolution adiabatic scanning calorimetry and polarising microscopy. The addition of nanoparticles results in an essentially stabilised blue phase III. The phase diagram is displayed upon heating and cooling and the enthalpy changes involved in the conversion between the blue phases are determined. The dispersion of functionalised nanoparticles is prominent for the stabilisation of blue phase III, which is potentially useful for applications, especially if applied on liquid crystals that exhibit blue phases close to room temperature., info:eu-repo/semantics/published

By means of laser ultrasonics, we have used Rayleigh waves to study four cast-iron samples with different morphology of graphite precipitation. The frequency dependence of the wave attenuation and velocity were obtained in the range 0-30 MHz. In this frequency range the ultrasonic attenuation for all samples was found to be proportional to the square of the frequency while the velocities, although clearly different between different samples were found non-dispersive. The mechanism of the attenuation for cast-iron is discussed and the link between microstructural sample properties and wave propagation properties is discussed. © 1999 Chin. Phys. Soc., SCOPUS: ar.j, info:eu-repo/semantics/published

By means of laser ultrasonics, we have used Rayleigh waves to study four cast-iron samples with different morphology of graphite precipitation. The frequency dependence of the wave attenuation and velocity were obtained in the range 0-30 MHz. In this frequency range the ultrasonic attenuation for all samples was found to be proportional to the square of the frequency while the velocities, although clearly different between different samples were found non-dispersive. The mechanism of the attenuation for cast-iron is discussed and the link between microstructural sample properties and wave propagation properties is discussed. © 1999 Chin. Phys. Soc., SCOPUS: ar.j, info:eu-repo/semantics/published

Surface acoustic waves generated and detected by a laser-ultrasonic system are used to characterize graphite precipitates in cast irons. Measurements of velocity and amplitude as a function of frequency are performed in samples with nodular, vermicular and lamellar forms of graphite. The results show that the ultrasonic parameters allow classifying very clearly these different cast iron types. © 1998 Elsevier Science S.A. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Surface acoustic waves generated and detected by a laser-ultrasonic system are used to characterize graphite precipitates in cast irons. Measurements of velocity and amplitude as a function of frequency are performed in samples with nodular, vermicular and lamellar forms of graphite. The results show that the ultrasonic parameters allow classifying very clearly these different cast iron types. © 1998 Elsevier Science S.A. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published