Liquid crystals (LCs) are important materials for flat panel display and photonic devices. Most LC devices use electrical field-, magnetic field-, or temperature-induced refractive index change to modulate the incident light. Molecular constituents, wavelength, and temperature are the three primary factors determining the liquid crystal refractive indices: ne and no for the extraordinary and ordinary rays, respectively. In this dissertation, we derive several physical models for describing the wavelength and temperature effects on liquid crystal refractive indices, average refractive index, and birefringence. Based on these models, we develop some high temperature gradient refractive index LC mixtures for photonic applications, such as thermal tunable liquid crystal photonic crystal fibers and thermal solitons. Liquid crystal refractive indices decrease as the wavelength increase. Both ne and no saturate in the infrared region. Wavelength effect on LC refractive indices is important for the design of direct-view displays. In Chapter 2, we derive the extended Cauchy models for describing the wavelength effect on liquid crystal refractive indices in the visible and infrared spectral regions based on the three-band model. The three-coefficient Cauchy model could be used for describing the refractive indices of liquid crystals with low, medium, and high birefringence, whereas the two-coefficient Cauchy model is more suitable for low birefringence liquid crystals. The critical value of the birefringence is deltan~0.12. Temperature is another important factor affecting the LC refractive indices. The thermal effect originated from the lamp of projection display would affect the performance of the employed liquid crystal. In Chapter 3, we derive the four-parameter and three-parameter parabolic models for describing the temperature effect on the LC refractive indices based on Vuks model and Haller equation. We validate the empirical Haller equation quantitatively. We also validate that the average refractive index of liquid crystal decreases linearly as the temperature increases. Liquid crystals exhibit a large thermal nonlinearity which is attractive for new photonic applications using photonic crystal fibers. We derive the physical models for describing the temperature gradient of the LC refractive indices, ne and no, based on the four-parameter model. We find that LC exhibits a crossover temperature To at which dno/dT is equal to zero. The physical models of the temperature gradient indicate that ne, the extraordinary refractive index, always decreases as the temperature increases since dne/dT is always negative, whereas no, the ordinary refractive index, decreases as the temperature increases when the temperature is lower than the crossover temperature (dno/dT<0 when the temperature is lower than To) and increases as the temperature increases when the temperature is higher than the crossover temperature (dno/dT>0 when the temperature is higher than To ). Measurements of LC refractive indices play an important role for validating the physical models and the device design. Liquid crystal is anisotropic and the incident linearly polarized light encounters two different refractive indices when the polarization is parallel or perpendicular to the optic axis. The measurement is more complicated than that for an isotropic medium. In Chapter 4, we use a multi-wavelength Abbe refractometer to measure the LC refractive indices in the visible light region. We measured the LC refractive indices at six wavelengths, lamda=450, 486, 546, 589, 633 and 656 nm by changing the filters. We use a circulating constant temperature bath to control the temperature of the sample. The temperature range is from 10 to 55 oC. The refractive index data measured include five low-birefringence liquid crystals, MLC-9200-000, MLC-9200-100, MLC-6608 (delta_epsilon=-4.2), MLC-6241-000, and UCF-280 (delta_epsilon=-4); four middle-birefringence liquid crystals, 5CB, 5PCH, E7, E48 and BL003; four high-birefringence liquid crystals, BL006, BL038, E44 and UCF-35, and two liquid crystals with high dno/dT at room temperature, UCF-1 and UCF-2. The refractive indices of E7 at two infrared wavelengths lamda=1.55 and 10.6 um are measured by the wedged-cell refractometer method. The UV absorption spectra of several liquid crystals, MLC-9200-000, MLC-9200-100, MLC-6608 and TL-216 are measured, too. In section 6.5, we also measure the refractive index of cured optical films of NOA65 and NOA81 using the multi-wavelength Abbe refractometer. In Chapter 5, we use the experimental data measured in Chapter 4 to validate the physical models we derived, the extended three-coefficient and two-coefficient Cauchy models, the four-parameter and three-parameter parabolic models. For the first time, we validate the Vuks model using the experimental data of liquid crystals directly. We also validate the empirical Haller equation for the LC birefringence delta_n and the linear equation for the LC average refractive index . The study of the LC refractive indices explores several new photonic applications for liquid crystals such as high temperature gradient liquid crystals, high thermal tunable liquid crystal photonic crystal fibers, the laser induced 2D+1 thermal solitons in nematic crystals, determination for the infrared refractive indices of liquid crystals, comparative study for refractive index between liquid crystals and photopolymers for polymer dispersed liquid crystal (PDLC) applications, and so on. In Chapter 6, we introduce these applications one by one. First, we formulate two novel liquid crystals, UCF-1 and UCF-2, with high dno/dT at room temperature. The dno/dT of UCF-1 is about 4X higher than that of 5CB at room temperature. Second, we infiltrate UCF-1 into the micro holes around the silica core of a section of three-rod core PCF and set up a highly thermal tunable liquid crystal photonic crystal fiber. The guided mode has an effective area of 440 ƒÝm2 with an insertion loss of less than 0.5dB. The loss is mainly attributed to coupling losses between the index-guided section and the bandgap-guided section. The thermal tuning sensitivity of the spectral position of the bandgap was measured to be 27 nm/degree around room temperature, which is 4.6 times higher than that using the commercial E7 LC mixture operated at a temperature above 50 degree C. Third, the novel liquid crystals UCF-1 and UCF-2 are preferred to trigger the laser-induced thermal solitons in nematic liquid crystal confined in a capillary because of the high positive temperature gradient at room temperature. Fourth, we extrapolate the refractive index data measured at the visible light region to the near and far infrared region basing on the extended Cauchy model and four-parameter model. The extrapolation method is validated by the experimental data measured at the visible light and infrared light regions. Knowing the LC refractive indices at the infrared region is important for some photonic devices operated in this light region. Finally, we make a completely comparative study for refractive index between two photocurable polymers (NOA65 and NOA81) and two series of Merck liquid crystals, E-series (E44, E48, and E7) and BL-series (BL038, BL003 and BL006) in order to optimize the performance of polymer dispersed liquid crystals (PDLC). Among the LC materials we studied, BL038 and E48 are good candidates for making PDLC system incorporating NOA65. The BL038 PDLC cell shows a higher contrast ratio than the E48 cell because BL038 has a better matched ordinary refractive index, higher birefringence, and similar miscibility as compared to E48. Liquid crystals having a good miscibility with polymer, matched ordinary refractive index, and higher birefringence help to improve the PDLC contrast ratio for display applications. In Chapter 7, we give a general summary for the dissertation.

Thin-film-transistor (TFT) liquid crystal display (LCD) has been widely used in smartphones, pads, laptops, computer monitors, and large screen televisions, just to name a few. A great deal of effort has been delved into wide viewing angle, high resolution, low power consumption, and vivid color. However, relatively slow response time and low transmittance remain as technical challenges. To improve response time, several approaches have been developed, such as low viscosity liquid crystals, overdrive and undershoot voltage schemes, thin cell gap with a high birefringence liquid crystal, and elevated temperature operation. The state-of-the-art gray-to-gray response time of a nematic LC device is about 5 ms, which is still not fast enough to suppress the motion picture image blur. On the other hand, the LCD panel's transmittance is determined by the backlight, polarizers, TFT aperture ratio, LC transmittance, and color filters. Recently, a fringe-field-switching mode using a negative dielectric anisotropy (Δε) LC (n-FFS) has been demonstrated, showing high transmittance (98%), single gamma curve, and cell gap insensitivity. It has potential to replace the commonly used p-FFS (FFS using positive Δε LC) for mobile displays. With the urgent need of submillisecond response time for enabling color sequential displays, polymer-stabilized blue phase liquid crystal (PS-BPLC) has become an increasingly important technology trend for information display and photonic applications. BPLCs exhibit several attractive features, such as reasonably wide temperature range, submillisecond gray-to-gray response time, no need for alignment layer, optically isotropic voltage-off state, and large cell gap tolerance. However, some bottlenecks such as high operation voltage, hysteresis, residual birefringence, and slow charging issue due to the large capacitance, remain to be overcome before their widespread applications can be realized. The material system of PS-BPLC, including nematic LC host, chiral dopant, and polymer network, are discussed in detail. Each component plays an essential role affecting the electro-optic properties and the stability of PS-BPLC. In a PS-BPLC system, in order to lower the operation voltage the host LC usually has a very large dielectric anisotropy (Δε > 100), which is one order of magnitude larger than that of a nematic LC. Such a large Δε not only leads to high viscosity but also results in a large capacitance. High viscosity slows down the device fabrication process and increases device response time. On the other hand, large capacitance causes slow charging time to each pixel and limits the frame rate. To reduce viscosity, we discovered that by adding a small amount (~6%) of diluters, the response time of the PS-BPLC is reduced by 2X-3X while keeping the Kerr constant more or less unchanged. Besides, several advanced PS-BPLC materials and devices have been demonstrated. By using a large Δε BPLC, we have successfully reduced the voltage to <10V while maintaining submillisecond response time. Finally we demonstrated an electric fieldindeced monodomain PS-BPLC, which enables video-rate reflective display with vivid colors. The highly selective reflection in polarization makes it promising for photonics application. Besides displays in the visible spectral region, LC materials are also very useful electro-optic media for near infrared and mid-wavelength infrared (MWIR) devices. However, large absorption has impeded the widespread application in the MWIR region. With delicate molecular design strategy, we balanced the absorption and liquid crystal phase stability, and proposed a fluoro-terphenyl compound with low absorption in both MWIR and near IR regions. This compound serves as an important first example for future development of low-loss MWIR liquid crystals, which would further expand the application of LCs for amplitude and/or phase modulation in MWIR region.

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The twin screw extrusion technique has been explored to produce lyotropic liquid crystal coated powder precursor by exploiting Pluronic F127 thermoreversible gelation property to get powder precursor without granular aggregates or with less compacted granular aggregates. The highly soluble chlorpheniramine maleate loaded in Pluronic F127 solution coated MCC particles prepared through twin screw extrusion was examined to produce the cubic phase (gel) for the development of controlled release formulation and for coating of very fine particles which cannot be achieved by traditional bead coaters. Controlled release formulations are beneficial in reducing the frequency of administration of highly soluble drugs having short half life and also to address the problem of polypharmacy in old age patients by reduction of dosage frequency. An unusual refrigerated temperature (5 C) profile for twin screw extrusion was selected based on the complex viscoelastic flow behaviour of Pluronic F127 solution which was found to be highly temperature sensitive. The Pluronic F127 solution was found to be Newtonian in flow and less viscoelastic at low temperature, such that low temperature (5 C) conditions were found to be suitable for mixing and coating the MCC particles to avoid compacted aggregates. At higher temperatures (35-40 C) Pluronic F127 solution exhibited shear thinning and prominent viscoelasticity, properties which were exploited to force CPM containing Pluronic F127 solution to stick over the MCC surface. This was achieved by elevating the temperature of the last zone of the extrusion barrel. It was found that to avoid compacted aggregates the MCC must be five times the weight of the Pluronic F127 solution and processed at a screw speed of 400 RPM or above at refrigerated temperature. Processing was not found to be smooth at ambient temperature with frictional heat and high torque generation due to significant compaction of coated particles which can be attributed to the elastic behaviour of Pluronic F127 solution at temperatures between ambient to typical body temperature. PLM images confirmed the cubic phase formation (gel) by Pluronic F127 coating which was found to be thick with maximum Pluronic F127 concentration (25%). SEM images showed smoothing of surface topography, and stretching and elongation of MCC fibres after extrusion which is indicative of coating through extrusion processing. Plastic deformation was observed for the lower Pluronic F127 concentration and higher MCC proportions. There was a significant decrease in work done for cohesion by the powder flow analyser observed in the batches with more aggregates compared with batches with least aggregates. A regression analysis study on factorial design batches was conducted to investigate the significant independent variables and their impact on dependent variables for example % torque, geometric mean diameter and work done for cohesion, and to quantitatively evaluate them. From the regression analysis data it was found that the coefficient of determination for all three dependent variables was in the range of 55-62%. The pharmaceutical performance of the prepared coated LLC precursor through twin screw extrusion in terms of controlled release was found to be very disappointing. Almost 100% chlorpheniramine maleate was released within 10-15mins, defined as providing burst release. The MDSC method was developed within this work to detect Pluronic F127 solution cubic phase formation. The MDSC method was developed to consider sample size, effect of heating and cooling, sample heat capacity, and the parameters for highest sensitivity which can be followed by sample accurately without the phase lag to produce accurate repeatable results.

This dissertation is focused on theoretical and experimental studies of optical properties of materials and multilayer structures composing liquid crystal displays (LCDs) and electrochromic (EC) devices. By applying spectroscopic ellipsometry, we have determined the optical constants of thin films of electrochromic tungsten oxide (WOx) and nickel oxide (NiOy), the films’ thickness and roughness. These films, which were obtained at spattering conditions possess high transmittance that is important for achieving good visibility and high contrast in an EC device. Another application of the general spectroscopic ellipsometry relates to the study of a photo-alignment layer of a mixture of azo-dyes SD-1 and SDA-2. We have found the optical constants of this mixture before and after illuminating it by polarized UV light. The results obtained confirm the diffusion model to explain the formation of the photo-induced order in azo-dye films. We have developed new techniques for fast characterization of twisted nematic LC cells in transmissive and reflective modes. Our techniques are based on the characteristics functions that we have introduced for determination of parameters of non-uniform birefringent media. These characteristic functions are found by simple procedures and can be utilised for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving associated optimization problems. Cholesteric LCD that possesses some unique properties, such as bistability and good selective scattering, however, has a disadvantage – relatively high driving voltage (tens of volts). The way we propose to reduce the driving voltage consists of applying a stack of thin (~1µm) LC layers. We have studied the ability of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. We have demonstrated that in order to accomplish good color characteristics and high brightness of the display, one or two retardation plates are sufficient.

Ce mémoire de thèse porte sur la caractérisation de l'effet électrocalorique des matériaux ferroélectriques solides et cristaux liquides. La découverte récente d'un effet électrocalorique qualifié de "géant" a relancé l'intérêt pour l'étude et la caractérisation des propriétés électrocaloriques des matériaux. Au-delà de la recherche des matériaux performants, ce domaine de recherche concerne également le développement des techniques de caractérisations appropriées et la réalisation des prototypes de réfrigération électrocalorique. Dans ce contexte, notre étude se focalise sur le développement de nouvelles techniques de caractérisation, la méthode photopyroélectrique (indirecte) et la calorimétrie (directe). La technique photopyroélectrique, développée au sein du laboratoire a été utilisée pour la détermination des propriétés thermiques du matériau pyroélectrique lui-même. L'exploitation de cette technique nous a permis également de déterminer les propriétés pyroélectriques du matériau, en particulier le rapport entre le coefficient pyroélectrique et la capacité calorifique, en fonction de la température et du champ électrique appliqué, nécessaire pour une évaluation indirecte de l'effet électrocalorique. Plusieurs matériaux ferroélectriques solides et liquides ont été étudiés à l'aide de cette méthode, en particulier, un monocristal de TriGlycine Sulfate et deux cristaux liquides. L'effet électrocalorique a été évalué autour de la température de transition de phase que présentent chacun de ces matériaux. Pour valider les résultats obtenus, nous avons procédé à des mesures indirectes de la polarisation par la méthode usuelle du courant de dépolarisation. Dans ce travail, nous avons également développé une technique de mesure indirecte de l'effet électrocalorique, par mesure calorimétrique, à l'aide d'un nouveau dispositif. Outre l'étude des transitions de phase et de la capacité calorifique, cet instrument permet une mesure directe de la température et de la quantité de chaleur absorbée ou cédée avec le milieu environnant. Une première étude de l'effet électrocalorique a été réalisée sur un matériau multicouche à base de titanate de baryum. Les résultats obtenus par cette approche ont été ensuite comparés à d'autres techniques directes et indirectes existantes dans la littérature. Ces deux nouvelles approches permettent d'élargir les possibilités d'étude de futurs matériaux électrocaloriques et de mesurer à la fois les propriétés thermiques et pyroélectriques nécessaires pour l'étude de l'effet électrocalorique. / This thesis work deals with the characterization of the electrocaloric effect in solid and liquid crystal ferroelectric materials. Following the 2006 discovery of Mischenko and al., the characterization techniques of the electrocaloric effect and the exploration of new caloric materials have attracted much attention. This discovery showed also that electrocaloric materials can be used for efficient innovative solution for refrigeration devices. This PhD dissertation focuses on the development of new techniques used to evaluate the electrocaloric effect by the photopyroelectric technique and by calorimetry. Few years ago, a new particular configuration based on the photopyroelectric technique, developed in our laboratory, was described for measuring thermal parameters of pyroelectric materials themselves. By means of this technique, we indirectly investigate the electrocaloric effect in ferroelectric materials by measuring the ratio of the pyroelectric coefficient to the volumetric heat capacity, as function of temperature and applied field, using Maxwell's relation. Measurements were carried out on ferroelectric solid materials (TriGlycine Sulfate) and liquid crystals. Electrocaloric effect has been evaluated around the phase transition temperature of each sample. To further validate the accuracy to the evaluated adiabatic temperature changes, we proceeded to indirect measurements by using the polarization reversal current technique. In the present work, we also developed a calorimeter in order to directly evaluate the electrocaloric effect. This technique is mainly used to measure with high resolution the heat capacity and enthalpy near phase transition temperature. In addition, this technique allows us to directly measure the temperature and the amount of heat absorbed or transferred from the material to the surrounding environment. A primary study of the electrocaloric effect was carried out on a multilayer material based on barium titanate. The results obtained by this approach have been then compared to conventional direct and indirect measurements. Those two new approaches give access to the measurement of both thermal and pyroelectric properties allowing the evaluation of the electrocaloric effect.

Le remplacement des électrolytes liquides conventionnels des batteries lithium-ion est un enjeu majeur pour améliorer leurs performances et leur sécurité. Dans ce contexte, ce travail de thèse est focalisé sur la synthèse d’une nouvelle classe d’électrolytes solides organiques : les cristaux liquides ioniques thermotropiques, ainsi que la caractérisation multi-échelle des nanostructures obtenues et du transport ionique. Tout d’abord, nous présentons les structures chimiques choisies pour créer des assemblages de molécules cristal liquide à conduction « single-ion ». Ensuite, nous détaillons l’étude structurale et fonctionnelle, qui a permis d’établir l’organisation supramoléculaire sous forme de phase colonnaire avec des canaux de conduction ionique nanométriques. Des conductivités pouvant atteindre 10-4 S.cm-1 à 70°C ont été obtenues. La dynamique des ions au sein de ces électrolytes a été étudiée à l’échelle moléculaire et nous avons mis en évidence un mécanisme de conduction par saut. La polymérisation des cristaux liquides ioniques pourrait permettre le développement d’électrolytes polymères de type single-ion pour les batteries. / One major issue towards large-scale application of lithium-based batteries concerns their safety which is directly related to the nature of the electrolyte. Solid electrolytes are at present considered as a promising approach to avoid the risks related to the commonly employed liquids. Herein we report the synthesis and the characterization of a promising class of electrolytes: Thermotropic Ionic Liquid Crystals (TILCs). We describe the design and the synthesis of new self-assembled single-ion materials in function of their chemical architecture. We performed a systematic structural and functional properties study, demonstrating the crystal-liquid properties as well as the supramolecular organization into columnar phases. One of the most promising TILC shows a conductivity of 10-4 S.cm-1 at 70°C. The ion dynamics was probed at molecular scale to establish the main features of hopping conduction mechanism. Further polymerization of the TILCs could be applied to develop high performance single-ion polymer electrolytes for Li-ion batteries.

L'essentiel de ce travail est l'étude de l'étalement de nano-gouttes smectiques sur un substrat de silicium rendu hydrophile par oxydation sous UV-ozone. De nombreuses expériences ont été menées à l'aide la récente technique SEEC (surface-enhanced ellipsometric contrast) qui permet la visualisation directe et en temps réel de couches moléculaires sur les surfaces. Cette technique offre couramment une résolution verticale supérieure à 0,1 nm. Un des cristaux liquides les plus utilisés dans ce travail est le 4’-n-Octyl-4-cyanobiphényle (8CB). Les expérimentations ont été conduites dans une gamme de température comprise entre 21,5°C et 33,5°C, dans cet intervalle de température le 8CB est en mésophase smectique.La dernière étape de l'étalement d'une gouttelette stratifiée dans le cas d'un mouillage impair est l'évolution à partir d'une tricouche vers une monocouche, par la disparition de la dernière bicouche dans la pile. Nous parlons de mouillage impair lorsque les milieux extérieurs sont hydrophile-hydrophobes (comme c'est le cas de nos mesures avec un substrathydrophile et un milieu extérieur (l'air) hydrophobe) et de mouillage pair lorsque les milieux extérieurs sont soit tous les deux hydrophiles soit tous les deux hydrophobes. Nous avons étudié le mouillage impair dans le cas des cristaux liquides smectiques 8CB sur une surface hydrophile. Le recul de la dernière bicouche est accompagné, lorsque la température est plus élevée de plusieurs degrés de celle de la transition Solide/Smectique A, par la formation de nucléations, qui apparaissent préférentiellement dans la partie extérieure de la bicouche. Sinon (lorsque l'on est près de la température de transition) on observe une rétraction de la bicouche sans nucléation. Les données expérimentales ne sont pas conformes à la seule théorie disponible (modèle de P.G. de Gennes et A.M. Cazabat), qui couvre les liquides faiblement stratifiés. Unnouveau modèle est proposé, en accord remarquable avec les expériences. Dans ce modèle le mécanisme de propagation semble être un processus quasi-statique gouverné par les interactions liquide/solide, la pression de Laplace à deux dimensions, et la distinction entre les coefficients de perméabilité de bord et de surface. Ce modèle permet de mieux expliquer nos résultat expérimentaux. De l'analyse des observations expérimentales en temps réel dans le cas de la formation de pores (nucléation), nous démontrons que les lignes de dislocation des boucles qui forment les frontières des pores ne sont pas situés à la même hauteur dans l'empilement des trois couches que les lignes de dislocation qui bordent la bicouche. En outre, une analyse minutieuse de nos résultats en utilisant une approche théorique récemment développée pour expliquer l'étalement de nano-gouttes de cristal liquide smectique suggère fortement que la nucléation des pores est déclenchée par la différence des potentiels chimiques entre les couches adjacentes, ce qui contraste avec le schéma classique où la nucléation est attribuée à la tension latérale le long des couches. Nous avons aussi imaginé un modèle de formation de pré-pores pour expliquer la perméation dans les strates adjacentes d'un liquide smectique. Enfin, une étude toujours en cours porte sur le nucléation hétérogène. Nous forçons une nucléation centrale et étudions son évolution. La tricouche est alors un anneau avec un rayon intérieur croissant et un rayons extérieur décroissant. Le système évolue jusqu'à la disparition totale de la tricouche. Notre modèle propose une solution qui est encore en cours de test. Letravail est ouvert et de nombreuses questions attendent leurs réponses... / The aim of this work is the study of the spread of nanodrops smectic on a silicon substrate made hydrophilic by oxidation under UV-ozone. Many experiments have been conducted using the recent SEEC technique (Surface-enhanced ellipsometric contrast) that allows direct visualization and real-time of molecular layers on surfaces. This technique provides a common vertical resolution greater than 0.1 nm. One of the most used liquid crystals in this work is the 4'-n-octyl-4-cyanobiphenyl (8CB). The experiments were conducted in a temperature range between 21.5 ° C and 33.5 ° C, in this temperature range the 8CB is in smectic mesophase. The last stage of the spreading of a droplet stratified in the case of an odd wetting is changing from a three-layer to a monolayer, that is, vanishing of the last bilayer in the stack. We talk about odd wetting when external environments are hydrophilic-hydrophobic (as is the case of our measurements with a hydrophilic substrate and an external medium (air) hydrophobie) and wetting even when external environments are either all two hydrophilic or bath hydrophobie. We studied the spreading in the case of smectic liquid crystals 8CB on a hydrophilic surface (odd wetting). Receding of the last bilayer is accompanied by formation of pores in it, which appear in the outer part of it, when the temperature is several degrees higher than that of the transition Solid / Smectic A. Otherwise (when it is near the transition temperature) there is a retraction of the bilayer without nucleation. The experimental data are consistent with the only available theory (PG de Gennes model and AM Cazabat) covering weakly stratified fluids. A new model is proposed in remarkable agreement with the experiments. In this model the propagation mechanism appear�� to be a quasi-static process governed by the interactions liquid / solid, the Laplace pressure in two dimensions, and the distinction between the coefficients of permeability of edge and surface. This model helps to explain our experimental results. Analysis of experimental observations in real time in the case of pore formation (nucleation), we demonstrate that the dislocation lines of the loops which form the pore boundaries are not located at the same height, in the stack of three layers, that dislocation lines bordering the bilayer. In addition, a careful analysis of our results using a recently developed theoretical approach to explain the spread of nana-drops of smectic liquid crystal strongly suggests that the pore nucleation is activated by the difference in chemical potential between adjacent layers, which contrasts with the conventional scheme in which nucleation is assigned to the lateral tension along the layers. We also imagined a pre-pore formation model to explain permeation in adjacent layers of a smectic liquid. Finally, still current study focuses on the heterogeneous nucleation. We force a central nucleation and study its evolution. The trilayer is then a ring with an increasing inner radius and an outer radius decreasing. The system evolvesuntil the complete disappearance of the three-layer. Our model offers a solution that is still being tested. The work is open and many questions awaiting answers ...

Misturas liotrópicas de laurato de potássio (KL)/ sulfato de potássio (K2SO4)/ álcool (CnH2n+1OH)/ água (H2O) apresentam fases no estado líquido cristalino nemático. Essas fases nemáticas foram colesterizadas através da adicão do agente quiral brucina à mistura. Este estudo foi realizado mantendo as frações molares de todos os constituintes das misturas constantes e variando o comprimento da mol´ecula de álcool entre oito (1-octanol) e dezesseis (1-hexadecanol) átomos de carbono. Três fases colestéricas foram identificadas: ChD (colestérica discótica), ChB (colestérica biaxial) e ChC (colestérica calamítica). O diagrama de fases foi construído em função do número de átomos de carbono n na molécula do álcool. As transições entre as fases colestéricas foram investigadas por medições das birrenfringências ópticas usando microscopia óptica de luz polarizada. As misturas com 9 n 12 apresentaram as três fases colestéricas como função da temperatura e uma região de crossover entre as fases ChD e ChB, com comprimento de correlação a temperatura nula maior do que as dimensões micelares típicas. Misturas com n=8 e n=13 apresentaram transição de fase de primeira ordem entre as fases ChD e ChC, sem a presença da fase ChB intermediária a elas. As misturas com n=14, 15 e 16 apresentaram somente a fase ChC como função da temperatura. Os resultados foram interpretados como consequência da nanosegregação das moléculas de álcool nas micelas com relação às moléculas do anfifílico principal. / Lyotropic mixtures of potassium laurate (KL)/ potassium sulphate (K2SO4)/ alcohol (CnH2n+1OH)/ water (H2O) present nematic liquid crystal phases. These nematic phases were cholesterized by the doping of the mixtures with the chiral agent brucine. This study was conducted by keeping constant the molar fractions of all constituents of the mixtures and varying the length of the alcohol molecule between eight (1-octanol) and sixteen (1-hexadecanol) carbon atoms. Three cholesteric phases were identified: ChD (discotic cholesteric), ChB (biaxial cholesteric), and ChC (calamitic cholesteric). The phase diagram was constructed as a function of the number of carbon atoms n in the alcohol molecule. The cholesteric-cholesteric phase transitions were investigated by measurements of the optical birefringences via polarized light microscopy. The mixtures with 9 n 12 presented the three cholesteric phases as a function of temperature and a crossover between the ChD and ChB phases, with a bare correlation length larger than the typical micellar dimensions. Mixtures with n =8 and n =13 exhibited first order phase transitions among the ChD and the ChC phases, without the presence of the intermediate ChB phase. Mixtures with n =14, 15 and 16 showed only the ChC phase as a function of temperature. These results were interpreted as a consequence of the nanosegregation of the alcohol molecules in the micelles with respect to the main amphiphilic molecules.