Correction: Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB-N phase transition.

Correction for 'Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB-N phase transition' by D. O. López et al., Phys. Chem. Chem. Phys., 2016, 18, 4394-4404.

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB-N phase transition.

We report a calorimetric study of a series of mixtures of two twist-bend liquid crystal dimers, the 1'',7''-bis(4-cyanobiphenyl)-4'-yl heptane (CB7CB) and 1''-(2',4-difluorobiphenyl-4'-yloxy)-9''-(4-cyanobiphenyl-4'-yloxy) nonane (FFO9OCB), the molecules of which have different effective molecular curvatures. High-resolution heat capacity measurements in the vicinity of the NTB-N phase transition for a selected number of binary mixtures clearly indicate a first order NTB-N phase transition for all the investigated mixtures, the strength of which decreases when the nematic range increases. Published theories predict a second order NTB-N phase transition, but we have developed a self-consistent mean field Landau model using two key order parameters: a symmetric and traceless tensor for the orientational order and a short-range vector field which is orthogonal to the helix axis and rotates around of the heliconical structure with an extremely short periodicity. The theory, in its simplified form, depends on two effective elastic constants and explains satisfactorily our heat capacity measurements and also predicts a first-order NTB-N phase transition. In addition, as a complementary source of experimental measurements, the splay (K1) and bend (K3) elastic constants in the conventional nematic phase for the pure compounds and some selected mixtures have been determined.

Dielectric, calorimetric and mesophase properties of 1''-(2',4-difluorobiphenyl-4'-yloxy)-9''-(4-cyanobiphenyl-4'-yloxy) nonane: an odd liquid crystal dimer with a monotropic mesophase having the characteristics of a twist-bend nematic phase.

This paper reports a novel liquid crystal phase having the characteristics of a twist-bend nematic phase formed by a non-symmetric ether-linked liquid crystal dimer. The dimer 1''-(2',4-difluorobiphenyl-4'-yloxy)-9''-(4-cyanobiphenyl-4'-yloxy) nonane (FFO9OCB) exhibits two liquid-crystalline phases on cooling at a sufficiently high rate from the isotropic phase. The high temperature mesophase has been reported in the literature as nematic and confirmed in this study. The other mesophase is metastable and can be supercooled giving rise to a glassy state. Its identification and characterization are based on optical textures, broadband dielectric spectroscopy, calorimetry, measurements of both splay and bend elastic constants in the nematic phase and miscibility studies. It is concluded that the low temperature mesophase exhibits the characteristics of a twist-bend nematic phase. Dielectric measurements enable us to obtain the static permittivity and information about the molecular dynamics in the isotropic phase, in the nematic mesophase and across the isotropic-to-nematic phase transition. Two orientations, parallel and perpendicular to the director, have been investigated. In the high temperature nematic mesophase, the dielectric anisotropy is found to be positive. Measurements of the parallel component of the dielectric permittivity are well-explained by the molecular theory of dielectric relaxation in nematic dimers (M. Stocchero, A. Ferrarini, G. J. Moro, D. A. Dunmur and G. R. Luckhurst, J. Chem. Phys., 2004, 121, 8079). The dimer is modelled as a mixture of cis and trans conformers and the model allows an estimate of their relative populations at each temperature. The nematic-to-isotropic phase transition has been exhaustively studied from the accurate evolution of the heat capacity and the static dielectric permittivity data. It has been concluded that the transition is first order in nature, but close to tricritical. The nature of the nematic-to-the novel liquid crystal phase transition is difficult to analyze to the same extent because of insufficient precision. Only observations at cooling rates of 10 K min(-1) or higher were possible because on heating from the glassy state, the twist-bend nematic mesophase crystallizes at temperatures far below the nematic-nematic phase transition.

Overall dielectric study on the odd members of a highly nonsymmetric pyrene-based series of liquid crystal dimers.

Broadband dielectric spectroscopy (10(3) Hz-1.8 × 10(9) Hz) has been performed on the odd nonsymmetric liquid crystal dimers of the series α-(4-cyanobiphenyl-4'-oxy)-ω-(1-pyreniminebenzylidene-4'-oxy) alkanes (CBOnO.Py) with n ranging from 3 to 11, as a function of temperature. A previous thermal behavior study through heat capacity measurements has been made. Dielectric measurements enable us to obtain information about the molecular dynamics in the nematic mesophase as well as in the isotropic phase. Two orientations (parallel and perpendicular) of the molecular director with regard to the probe electric field have been investigated. In the nematic mesophase, the dielectric anisotropy is revealed to be positive for all studied compounds. Measurements of the parallel component of the dielectric permittivity are well-explained by means of the molecular theory of dielectric relaxation in nematic dimers (Stocchero, M.; Ferrarini, A.; Moro, G. J.; Dunmur, D. A.; Luckhurst, G. R. J. Chem. Phys., 2004, 121(16), 8079). The dimer is seen as a mixture of cis and trans conformers, and the model allows us to estimate their relative populations at each temperature. The main molecular motions are interpreted by the model as independent end-overend rotations of each terminal semirigid unit of the dimer.

Disentangling molecular motions involved in the glass transition of a twist-bend nematic liquid crystal through dielectric studies.

Broadband dielectric spectroscopy spanning frequencies from 10(-2) to 1.9 × 10(9) Hz has been used to study the molecular orientational dynamics of the glass-forming liquid crystal 1",7"-bis (4-cyanobiphenyl-4'-yl)heptane (CB7CB) over a wide temperature range of the twist-bend nematic phase. In such a mesophase two different relaxation processes have been observed, as expected theoretically, to contribute to the imaginary part of the complex dielectric permittivity. For measurements on aligned samples, the processes contribute to the dielectric response to different extents depending on the orientation of the alignment axis (parallel or perpendicular) with respect to the probing electric field direction. The low-frequency relaxation mode (denoted by µ(1)) is attributed to a flip-flop motion of the dipolar groups parallel to the director. The high-frequency relaxation mode (denoted by µ(2)) is associated with precessional motions of the dipolar groups about the director. The µ(1)-and µ(2)-modes are predominant in the parallel and perpendicular alignments, respectively. Relaxation times for both modes in the different alignments have been obtained over a wide temperature range down to near the glass transition temperature. Different analytic functions used to characterize the temperature dependence of the relaxation times of the two modes are considered. Among them, the critical-like description via the dynamic scaling model seems to give not only quite good numerical fittings, but also provides a consistent physical picture of the orientational dynamics on approaching the glass transition.

Relación entre el volumen espiratorio máximo en un segundo, el índice BODE y la calidad de vida percibida por el paciente de enfermedad pulmonar obstructiva crónica / Relation between maximum expiratory volume in one section, BODE index and quality of life perceived by the chronic obstructive pulmonary disease patient

Objetivo: Evaluar la correlación existente entre la calidad de vida percibida por los pacientes y dos parámetros objetivos de gravedad: a) la gravedad de la obstrucción por el volumen espiratorio máximo en el primer segundo (FEV1), y b) el índice BODE (Body Mass Index, Airflow Obstruction, Dyspnea and Exercice Capacity). Material y métodos: Estudio observacional descriptivo de corte transversal, realizado en 40 pacientes diagnosticados de la enfermedad pulmonar obstructiva crónica (EPOC) y clasificados según la escala GOLD (Global initiative for chronic obstructive lung disease) en moderados o graves, a los que se entrevistó mediante el cuestionario respiratorio de St. George (SGRQ). Se calculó el índice BODE, previa medición de los parámetros que lo componen. También se recogieron datos antropométricos y demográficos de los pacientes. Resultados: De los 40 pacientes del estudio, 38 eran varones (95%), con una edad media ± desviación estándar (DE) de 76,15 ± 5,82 años. Las medias ± DE obtenidas en referencia a la variable subjetiva del cuestionario SGRQ fueron de 33,58 ± 18,14. En referencia a los datos conseguidos de las variables objetivas, obtuvimos del FEV1 una media ± DE de 49,05 ± 15,731, y del índice BODE de 2,33 ± 1,8 y de sus parámetros integrantes: test de los 6 minutos, 440 ± 87,9; escala Medical Research Council, 1,4 ± 0,6; índice de masa corporal, 28,16 ± 4,4. Según los valores obtenidos observamos la existencia de correlación entre SGRQ y el índice BODE, al igual que entre la actividad, como subescala de la SGRQ y el índice BODE. Conclusiones: El resultado del índice BODE se correlaciona débilmente con los resultados de la SGRQ de forma conjunta, por lo que un elevado índice BODE afecta negativamente a la calidad de vida de los pacientes con EPOC moderados o graves (AU)

Objective: To measure the correlation between perceived quality of life and two objective severity parameters: forced expiratory volume in one second (FEV1) and body mass, airflow obstruction, dyspnea and exercise capacity (BODE) index. Material and methods: Observational descriptive cross-sectional study involving 40 Chronic Obstruction Pulmonary Disease (COPD) patients. They were classified using the Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification system into moderate or severe. The Saint George Respiratory Questionnaire (SGRQ) was carried out by interview and the BODE value was analyzed after measurement of the parameters included in it. Anthropometry and demography data were also collected. Results: A study including 40 patients, 38 of them men 38 (95%), with mean age 76.15 ± 5.82 was performed. The means obtained for the subjective variable of the SGRQ was 33.58 ± 18.14. Regarding the data obtained for the objective variables, the FEV1 had a mean of 49.05 ± 15.731, and the BODE index showed 2.33 ± 1.8. The parameters making it up were: 6-minute exercise test 440 ± 87.9, mean MRC score: 1.4 ± 0.6, and body mass index (BMI) 28.16 ± 4.4. According to the values obtained, we observed the existence of a correlation between SGRO and the BODE index and between the activity, and subscale of the SGRO and BODE index. Conclusions: The BODE index are weakly correlative with the results of the SGRO combined. High index BODE negatively affects the perceived quality of life of moderate/severe COPD patients (AU)

Phase behavior and properties of the liquid-crystal dimer 1'',7''-bis(4-cyanobiphenyl-4'-yl) heptane: a twist-bend nematic liquid crystal.

The liquid-crystal dimer 1'',7''-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB) exhibits two liquid-crystalline mesophases on cooling from the isotropic phase. The high-temperature phase is nematic; the identification and characterization of the other liquid-crystal phase is reported in this paper. It is concluded that the low-temperature mesophase of CB7CB is a new type of uniaxial nematic phase having a nonuniform director distribution composed of twist-bend deformations. The techniques of small-angle x-ray scattering, modulated differential scanning calorimetry, and dielectric spectroscopy have been applied to establish the nature of the nematic-nematic phase transition and the structural features of the twist-bend nematic phase. In addition, magnetic resonance studies (electron-spin resonance and (2)H nuclear magnetic resonance) have been used to investigate the orientational order and director distribution in the liquid-crystalline phases of CB7CB. The synthesis of a specifically deuterated sample of CB7CB is reported, and measurements showed a bifurcation of the quadrupolar splitting on entering the low-temperature mesophase from the high-temperature nematic phase. This splitting could be interpreted in terms of the chirality of the twist-bend structure of the director. Calculations using an atomistic model and the surface interaction potential with Monte Carlo sampling have been carried out to determine the conformational distribution and predict dielectric and elastic properties in the nematic phase. The former are in agreement with experimental measurements, while the latter are consistent with the formation of a twist-bend nematic phase.

Dielectric and thermodynamic study on the liquid crystal dimer α-(4-cyanobiphenyl-4'-oxy)-ω-(1-pyreniminebenzylidene-4'-oxy)undecane (CBO11O·Py).

Broadband dielectric spectroscopy (10(3) to 1.8 × 10(9) Hz) and specific heat measurements have been performed on the odd nonsymmetric liquid crystal dimer α-(4-cyanobiphenyl-4'-oxy)-ω-(1-pyreniminebenzylidene-4'-oxy)undecane (CBO11O·Py), as a function of temperature. The mesogenic behavior is restricted to a nematic mesophase which can be supercooled down to its corresponding glassy state if the cooling rate is fast enough (no less than 15 K·min(-1)). Dielectric measurements enable us to obtain the static permittivity and information about the molecular dynamics in the nematic mesophase as well as in the isotropic phase and across the isotropic-to-nematic phase transition. Two orientations (parallel and perpendicular) of the molecular director with regard to the probe electric field have been investigated. In the nematic mesophase, the dielectric anisotropy is revealed to be positive. Measurements of the parallel component of the dielectric permittivity are well explained by means of the molecular theory of dielectric relaxation in nematic dimers (J. Chem. Phys. 2004, 121 (16), 8079). The dimer is seen as a mixture of cis and trans conformers, and the model allows us to estimate their relative populations at each temperature. The main molecular motions are interpreted by the model as independent end-overend rotations of each terminal semirigid unit of the dimer. The nematic-to-isotropic phase transition has been exhaustively studied from the accurate evolution of the specific-heat and the static dielectric permittivity data. It has been concluded that the transition is first order in nature and follows the tricritical hypothesis. As a consequence, the nematic mesophase has been characterized as uniaxial despite the biaxiality and flexibility of the dimer molecule.

Cylindrical sub-micrometer confinement results for the odd-symmetric dimer alpha,omega-bis[(4-cyanobiphenyl)-4'-yloxy]undecane (BCB.O11).

Broadband dielectric spectroscopy (10(2) Hz to 1.9 x 10(9) Hz) and specific heat measurements have been performed on the odd-symmetric dimer alpha,omega-bis[(4-cyanobiphenyl)-4'-yloxy]undecane (BCB.O11) in the isotropic (I) and nematic (N) phases confined to 200 nm diameter parallel cylindrical pores of Anopore membranes. Unlike previous studies on liquid crystal monomers, untreated and hexadecyltrimethylammonium bromide-treated membranes give rise to radial and axial confinements, respectively. An attempt is made to explain these unexpected results by means of a qualitative model for the dimer arrangement on alumina substrates. The model suggests that the population of conformers, which follow the bulk-like dynamics, is modified by confinement. Such a fact seems to be consistent with other distinctive features attributed to confinement, as for example, the increasing of the entropy change at the N-to-I phase transition for both axial and radial confinements. Specific-heat measurements have shown how confinement affects the N-to-I phase transition by a downward shift in transition temperature as well as by broadened and rounded specific-heat peaks. However, these modifications are revealed to be substantially different from what has been found previously in similar studies on liquid crystal monomers. Dynamic dielectric measurements have probed the different molecular motions in both confinements and how these motions are developed in a way similar to the bulk-dimer. Dielectric results have also proved that the surface-pinned molecular layer (where molecular motions are very restricted) adjacent to the pore-wall is temperature-dependent as already found previously for liquid crystal monomers.

Estudio de prevalencia de la deficiencia de yodo en una población escolarizada de 6 años / Prevalence study of iodine deficiency in a 6-year-old school population

Introducción: El yodo es un oligoelemento cuyo déficit provoca diferentes complicaciones agrupadas bajo el nombre de trastornos por déficit de yodo. La ingesta de alimentos ricos en yodo es la única vía de administración del mismo. Se considera déficit leve de yodo una yoduria inferior a 100μg/l; aumentando la posibilidad de trastornos por déficit de yodo. Objetivo: Determinar la prevalencia de déficit de yodo en los niños de 6 años de la provincia de Lleida. Métodos: Estudio trasversal de selección aleatoria, en niños escolarizados en la provincia de Lleida. Tras la aceptación, se cumplimentó un cuestionario y se realizó un análisis de orina para determinar el nivel de yodo. Resultados: Inclusión de 328 niños (5 sin muestra de orina), 46,8% varones, 54,27% en escuelas públicas, 17,2% inmigrantes y 40,95% utilizaba el comedor escolar. El 62,42% comía pescado 2 o más veces a la semana, sal yodada el 60,98% y el 90,65% leche diariamente. La yoduria media se situó en 234,4μg/l (DT=133,7). El déficit de yodo fue establecido al 9,29% (6,12–12,45%) de la muestra, relacionándose significativamente con el tipo de centro (concertado o público), origen del niño, sal yodada, consumo de pescado y leche. Conclusiones: La prevalencia de déficit leve de yodo en Lleida es inferior a la de estudios parecidos anteriores, mostrando unos buenos parámetros nutricionales. El déficit de yodo es superior en niños inmigrantes, aunque se presentan modificaciones nutricionales que pueden establecer mejoras superiores a la de la población autóctona (AU)

Introduction: Iodine is a dietary element, a deficiency of which leads to complications grouped with the name Iodine Deficiency Disorders (IDD). The intake of foods rich in iodine is the only route of iodine administration. Iodine is considered to deficient when its concentration is less than 100μg/L in urine, thus increasing the possibility of IDD. Aim: To determine the prevalence of iodine deficiency in 6-year-old school children in the region of Lleida. Methods: A randomised cross-sectional study of 6-year-old school children in the area of Lleida was selected. After the acceptance, a questionnaire had to be filled in and a urine sample was collected to determine the urinary iodine. Results: A total of 328 subjects were included (5 without urine sample), 46.8% boys, 54.27% in public schools, 17.2% immigrants and 40.95% had lunch at school. The majority (62.42%) ate fish twice or more a week, 60.98% used iodised salt and 90.65% drank milk daily. The iodine mean was 234.4μg/l (SD=133.7). Only 9.29% (6.12–12.45%) had iodine deficiency which was associated to the type of school the children attended (private or public), immigrant origin, iodised salt, fish and milk nutrition. Conclusions: The prevalence of iodine deficiency in Lleida is lower than in previous publications, shown by the good nutrition parameters. The shortage of iodine is higher in immigrant boys, although better nutrition measures could be taken to improve their situation (AU)

[Prevalence study of iodine deficiency in a 6-year-old school population]. / Estudio de prevalencia de la deficiencia de yodo en una población escolarizada de 6 años.

INTRODUCTION: Iodine is a dietary element, a deficiency of which leads to complications grouped with the name Iodine Deficiency Disorders (IDD). The intake of foods rich in iodine is the only route of iodine administration. Iodine is considered to deficient when its concentration is less than 100 microg/L in urine, thus increasing the possibility of IDD. AIM: To determine the prevalence of iodine deficiency in 6-year-old school children in the region of Lleida. METHODS: A randomised cross-sectional study of 6-year-old school children in the area of Lleida was selected. After the acceptance, a questionnaire had to be filled in and a urine sample was collected to determine the urinary iodine. RESULTS: A total of 328 subjects were included (5 without urine sample), 46.8% boys, 54.27% in public schools, 17.2% immigrants and 40.95% had lunch at school. The majority (62.42%) ate fish twice or more a week, 60.98% used iodised salt and 90.65% drank milk daily. The iodine mean was 234.4 microg/l (SD=133.7). Only 9.29% (6.12-12.45%) had iodine deficiency which was associated to the type of school the children attended (private or public), immigrant origin, iodised salt, fish and milk nutrition. CONCLUSIONS: The prevalence of iodine deficiency in Lleida is lower than in previous publications, shown by the good nutrition parameters. The shortage of iodine is higher in immigrant boys, although better nutrition measures could be taken to improve their situation.

Study of the critical behavior and scaling relationships at the N-to-I phase transition in hexyloxycyanobiphenyl.

An exhaustive analysis of the critical behavior of the nematic to isotropic (N-to-I) phase transition on the liquid crystal hexyloxycyanobiphenyl (6OCB) has been performed. To do so, the accurate evolution of various physical magnitudes (static dielectric permittivity data together with specific heat and volumetric determinations) around the N-to-I transition has been required. The specific heat data with the isobaric thermal expansion coefficient and the derivative of the static dielectric permittivity with temperature have been proven to be related to each other by a scaling relationship. However, some discrepancies have been observed for the dielectric data in relation to such a scaling relationship and the critical behavior of the N-to-I phase transition. All information has been used to get some insight on the strength of the first-order N-to-I phase transition of the 6OCB in relation to the other counterparts in the nOCB series of compounds.

Thermodynamic assessment of smectic A-nematic tricritical points through the equal gibbs energy analysis.

A complete thermodynamic analysis on four two-component phase diagrams between liquid crystals belonging to the nCB and nOCB series of compounds, the so-called cyanobiphenyls, has been performed through the Oonk's equal Gibbs energy method. The binary systems dealt with in this paper show as a common feature the existence of a tricritical point at the SmA-to-N phase transition, all of which reported elsewhere. As a singular finding of the work proposed in this paper, the Oonk's method is extended in order to account for second-order phase transitions. Likewise, this extension allows performing calculations of the tricritical temperature.

Influence of cylindrical submicrometer confinement on the static and dynamic properties in nonyloxycyanobiphenyl (9OCB).

Broadband dielectric spectroscopy (10(2)-1.9 x 10(9) Hz) and specific heat measurements have been performed on nonyloxycyanobiphenyl (9OCB) in the isotropic (I), nematic (N), and smectic A (SmA) phases confined to 200 nm diameter parallel cylindrical pores of Anopore membranes. Untreated and HTBA-treated membranes have been found to obtain axial and radial confinements, respectively. However, structural or configurational transitions in untreated membranes have been reported to exist in the SmA-mesophase of 9OCB. Both confinements clearly affect the N-I and SmA-N phase transitions. In the axial confinement, the analysis of the specific heat and static dielectric permittivity data leads to a second order SmA-N phase transition, which is known to be weakly first order for bulk 9OCB. Dynamic dielectric measurements have accounted for the different molecular motions in both confinements. On both mesophases, either N or SmA, the relaxation processes in axial configuration are faster than in the bulk. However, in radial confinement, they are either equal or slower than in the bulk. Additionally, there are no differences in the energy barrier hindering the molecular motions between the axial and radial confinements and even in relation to bulk. Likewise, dielectric results suggest that the extension inside the pores of the surface pinned molecular layer (proved to be temperature-dependent) persists at high enough temperature as a residual-thin layer adjacent to the pore wall.

Critical behavior and scaling relationships at the SmA(d)-N and N-I transitions in nonyloxycyanobiphenyl (9OCB).

Different kind of measurements were performed on the liquid crystal nonyloxycyanobiphenyl (9OCB) to carry out a study of the molecular dynamics in the smectic A (SmA), nematic (N), and isotropic (I) phases as well as an exhaustive analysis of both the SmA-to-N and N-to-I phase transitions. For the dynamic study, broadband dielectric spectroscopy (102 to 1.8 x 109 Hz) was used. Two orientations (parallel and perpendicular) of the molecular director with regard to the probing electric field were investigated. From this study, the static dielectric permittivity was obtained in both alignments and, in addition, the molecular motions that contribute to each one were discussed. The static dielectric data together with specific heat and volumetric determinations were analyzed, proving that both phase transitions are weakly first order, displaying a nearly tricritical behavior. However, the width of metastable regions seems to be dependent on the physical magnitude, although specific heat and volumetric determinations allow for comparable results. It should be noticed that the temperature derivative of the static dielectric permittivity, specific heat, and isobaric thermal expansion coefficient data derived from volumetric determinations are related to each other by scaling relationships.

Two-component system CCl4 + (CH3)3CBr: extrema in equilibria involving orientationally disordered phases.

Phase equilibria involving orientationally disordered (OD) and liquid phases of the two-component system between carbon tetrachloride (CCl4) and 2-methyl-2-bromomethane ((CH3)3CBr) have been determined by means of X-ray powder diffraction and thermal analysis techniques from 210 K up to the liquid state. The isomorphism relation between the OD stable face-centered cubic (FCC) phase of (CH3)3CBr and the metastable FCC phase of CCl4 has been demonstrated throughout the continuous evolution of the lattice parameters and the existence of the two-phase equilibrium [FCC + L] for the whole range of composition, despite the monotropy of the FCC phase for the CCl4 component with respect to its OD rhombohedral (R) stable phase. A continuous series of OD R mixed crystals is found, which confirms the R lattice symmetry of the OD phase II of (CH3)3CBr, for which the crystallographic results have been long-time misinterpreted. X-ray patterns of such a phase were indexed according to the recent single-crystal results obtained by Rudman (Rudman, R. J. Mol. Struct. 2001, 569, 157). In addition, some experimental evidences are given to confirm the number of molecules per unit cell (Z = 21). The thermodynamic assessment reproduces coherently the phase diagram for the stable [R + L] and [R + FCC] two-phase equilibria as well as for the partially metastable [FCC + L] two-phase equilibrium and provides a set of data for the thermodynamic properties of nonexperimentally available phase transitions of pure components. Surprisingly, the phase equilibrium involving R and FCC OD phases appears as one of the very few showing a solid-solid equilibrium with two extremes.

Thermodynamic and dielectric studies concerning the influence of cylindrical submicrometer confinement on heptyloxycyanobiphenyl.

Measurements of the specific heat and the static dielectric permittivity of heptyloxycyanobiphenyl (7OCB) confined to the 0.2 microm diameter parallel cylindrical pores of Anopore membranes in the isotropic phase and nematic mesophase, are presented. A comparison between the bulk and the confined 7OCB in treated and untreated pore wall surfaces using a chemical surfactant (HTBA) is performed. Both the treated and untreated membrane confinements seem to affect the nematic-to-isotropic phase transition by a downshift in transition temperature and some rounding at the specific-heat maximum, in a way similar to that which was earlier published for other liquid crystals confined in the same geometry. The static dielectric measurements clearly point out that untreated membrane confinement is axial, with the nematic director aligned parallel to the pore axis being homeotropic bulklike, i.e., with the nematic director aligned perpendicular to the electrode cell surfaces. After chemical surfactant treatment, the nematic director is constrained in a radial alignment being perpendicular to the pore walls. The dielectric measurements are revealed to be specially sensible to analyze the surface-induced nematic order due to the pore wall. The tricritical nature of the nematic-to-isotropic phase transition in bulk 7OCB as well as in treated and untreated Anopore confined geometries is discussed through both the specific heat and the static dielectric data.