Thermal Reading of Texts Buried in Historical Bookbindings.

In the manufacture of ancient books, it was quite common to insert written scraps belonging to earlier library material into bookbindings. For scholars like codicologists and paleographers, it is extremely important to have the possibility of reading the text lying on such scraps without dismantling the book. In this regard, in this paper, we report on the detection of these texts by means of infrared (IR) pulsed thermography (PT), which, in recent years, has been specifically proven to be an effective tool for the investigation of Cultural Heritage.

Communication: Optically induced decoupling of the smectic-A and nematic order parameters at the AN phase transition in phototropic liquid crystals.

In the present work, by means of the photopyroelectric calorimetric investigations in liquid crystal/naphtopyran (NP) molecule mixtures, the effect of the photoisomerization of NP by UV light on the critical behavior of specific heat could be studied over the smectic-nematic phase transition. It is shown that the UV light irradiation of the sample can shift the critical exponent from a non-universal value typical of the non-irradiated mixture to one close to that of the 3D-XY universality class, predicted for such a transition. This witnesses the optically triggered reduction of the coupling between the smectic and nematic order parameters responsible for the deviation from the XY-like behavior.

Simultaneous specific heat, thermal conductivity and imaging evaluations in thin samples of 8CB liquid crystal dispersed with microemulsion of DDAB/water micelles.

In this work we use a photopyroelectric calorimetric set up to analyze the transformations occurring in thin samples of liquid crystal-microemulsion system by combining the results of the simultaneously performed high temperature resolution polarization microscopy observations and the temperature dependence of the specific heat, and of the thermal conductivity. This enabled an accurate direct correlation of the observations concerning the different measured quantities for a most comprehensive interpretation of the obtained results. It is found that the I-N conversion progresses in the entire nematic range because of the micelles expelled from the nucleating nematic volumes remaining confined in the residual isotropic material.

Simultaneous calorimetric and polarization microscopy investigations of light induced changes over phase transitions in a liquid crystal-napthopyran mixture.

We have studied the specific heat and the thermal conductivity in a 4-(n-octyl)-4'-cyanobiphenyl liquid crystal (LC)-photochromic molecules mixture, before, during, and after the photo-activation of the dispersed photochromic molecules, over both the smectic A-nematic and the nematic-isotropic phase transitions. The evaluation of the specific heat has enabled the determination of the changes of the phase transition characteristics induced by the photochromic molecules photoisomerization, while that of the thermal conductivity could be used to monitor the modifications induced in the average LC molecular orientation. The polarization microscopy imaging of the sample texture constituted a valuable support for the interpretation of the obtained thermal conductivity results.

Dual beam differential photopyroelectric setup for broadband thermal effusivity investigation of glass transitions in polymers.

The behaviour of the thermal effusivity squared over the glass transition in polystyrene is measured over a considerable frequency range using a novel dual beam front detection photopyroelectric configuration, which ensures a very effective processing of the obtained signal. This has enabled the detection of the very small changes taking place in such a parameter, despite the non-favourable sensitivity conditions due to the large mismatch between the thermal effusivities of the pyroelectric transducer and of the sample. The effect of the thermal contact resistance between the sample and the pyroelectric detector is also considered and discussed.

Study of the smecticA-hexaticB phase transition in homeotropic single domain samples of 65OBC liquid crystal by photopyroelectric calorimetry.

The smecticA-hexaticB phase transition was studied in a homeotropic single domain sample and in a non-aligned sample of n-hexyl-4'-n-pentyloxybiphenyl-4-carboxylate liquid crystal compound to probe the effect of different amount of defects on the phase transition. The specific heat, the thermal diffusivity and the enthalpy exchange were monitored over the transition and, at the same time, polarization microscopy observations could be carried out. The transition during the first cooling run was found to be accompanied by a considerably larger defect annealing in the non-aligned sample than in the homeotropic one, but the critical behaviour of the specific heat remained substantially the same.

Invited review article: Photopyroelectric calorimeter for the simultaneous thermal, optical, and structural characterization of samples over phase transitions.

The study of thermophysical properties is of great importance in several scientific fields. Among them, the heat capacity, for example, is related to the microscopic structure of condensed matter and plays an important role in monitoring the changes in the energy content of a system. Calorimetric techniques are thus of fundamental importance for characterizing physical systems, particularly in the vicinity of phase transitions where energy fluctuations can play an important role.

Effect of quenched disorder on the RI-RV, RII-RI, and liquid-RII rotator phase transitions in alkanes.

The ability of disorder to reduce the coupling between the distortion and tilt angle order parameters was tested over the R(I)-R(V) phase transition by measuring the specific heat in alkanes with different R(I) phase temperature range mixed with various concentrations of silica nanoparticles. It was found that the disorder significantly affects the character of the R(I)-R(V) transition, driving it toward a second-order character. The features about the R(II)-R(I) transition were progressively attenuated for increasing disorder in both alkanes, becoming very faint for the largest particle concentration, but the first-order character was maintained.

Analysis of the order character of the R(II)-R(I) and the R(I)-R(V) rotator phase transitions in alkanes by photopyroelectric calorimetry.

The character of the R(II)-R(I) and the R(I)-R(V) transitions was studied in alkane samples by analyzing the hysteresis the specific heat shows between heating and cooling measurements, using photopyroelectric calorimetry. The hysteresis systematically shows up in all the investigated samples over the R(II)-R(I) transition, similarly to what also observed over the liquid-R(II) and the R(V)-crystal phase transitions, thus confirming the first order character of all such phase transitions. Over the R(I)-R(V) transition a hysteresis is also present but with varying characteristics depending on the width of the temperature range of the R(I) phase, the first order character being smaller for decreasing R(I) range.

Effect of confinement and strain on the specific heat and latent heat over the nematic-isotropic phase transition of 8CB liquid crystal.

Simultaneous measurements of the specific heat, latent heat, light scattering, and polarization microscopy were carried out in 8CB liquid crystal confined in Aerosil and Millipore membranes networks, to assess the different properties of the nematic material nucleating over the nematic-isotropic transition under different strain conditions. In Aerosil networks, it was found that the higher temperature peak of the double-peaked structure observed in the specific heat survived up to silica concentration values considerably larger than previously reported. Moreover, the first-order character of the transition occurring over the lower temperature peak, where the involved strain is larger, was considerably smaller than that observed over the larger temperature one as observed in the latent heat detection and hysteretic behavior.

Simultaneous characterization of optical and thermal parameters of liquid-crystal nanocolloids with high-temperature resolution.

We report on the high-temperature resolution measurements of the optical and thermal parameters of a liquid-crystal-silica nanoparticle colloid, as well as its video inspection, simultaneously performed in an upgraded photopyroelectric calorimeter. Over the nematic-isotropic coexistence region, the determined nematic correlation length, obtained from turbidity measurements, showed the characteristic two-step nematic nucleation process previously reported only for the specific heat.

Strain effects at the hexatic-B-smectic-A transition in the 65OBC liquid crystal.

We have studied the hexatic-B-smectic-A (HexB-SmA) transition in n -hexyl- 4'-n -pentyloxybiphenyl-4-carboxylate (65OBC) by means of a high-resolution ac photopyroelectric (PPE) calorimetric technique. A procedure for the interpretation of the PPE data, which allows the detection of an internal heating source due to strain annealing and/or latent heat, has been applied. We have found that the strain present in the sample depends on the kinetics of formation of the smectic phase once the sample is cooled from the isotropic one.

Dynamics of nematic liquid crystal with quenched disorder in the random dilution and random field regimes.

By means of specific heat spectroscopy, we have studied the dynamics of nematic 8CB nucleated, in the presence of random disorder, as the temperature is lowered across the isotropic to nematic phase transition such that the crossover region of random dilution to random field regimes of disorder strength is explored. We show, in terms of frequency dependence, hysteretic behavior, and aging effects, that the out-of-equilibrium properties of the nematic nucleated in the random disorder regime are strongly reminiscent of the bulk material while the one grown in the random field regime shows a glassy behavior with aging leading to slower dynamics. The aging effect has been explained in terms of strain relaxation in analogy with observations in other soft glassy colloidal systems.

Thermal and optical study of the kinetics of the nematic-isotropic transition in octylcyanobiphenyl.

It is shown in this paper that the kinetics of the nematic-isotropic (NI) transition in 30-microm-thick octylcyanobiphenyl liquid crystal films is strongly affected by the cell walls. We have found that this is due to the modification of the wetting properties of the liquid crystal depending on the surface treatment. The results have been obtained with an experimental setup which allows the simultaneous high resolution study of the sample thermal properties and texture evolution with temperature.

Critical behavior of thermal parameters at the smectic-A-hexatic-B and smectic-A-smectic-C phase transitions in liquid crystals.

High temperature resolution measurements of thermal conductivity, thermal diffusivity, and specific heat, with simultaneous polarized light visual inspection of the sample, have been performed at two different liquid crystal phase transitions: the SmA-SmC (Smectic-A-Smectic-C) and the SmA-HexB (Smectic-A-hexatic-B) in racemic A7 [4-(3-methyl-2-chlorobutanoyloxy)-4(')-heptyloxybiphenyl] and 65OBC (n-hexyl-4(')-n-pentyloxybiphenyl-4-carboxylate) compounds, respectively. In the past, anomalies in the thermal conductivity at the transitions have been reported. Our results indicate a nonsingular behavior of the thermal conductivity at both transitions, similarly to what has been previously reported for the smectic-A-nematic phase transition.