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1H spin-lattice relaxation time (T1) measurements were performed to probe the dynamic behavior of water in aqueous suspensions of cellulose nanocrystals (CNCs) and a layered smectite clay mineral with different degrees of concentration. 1H-T1 experiments were carried out over a wide frequency domain, ranging from a few kilohertz to 500 MHz, with the aid of conventional and fast field cycling nuclear magnetic resonance (NMR) techniques. The experimental relaxometry data illustrate differences between the dynamic behavior of bulk water and that confined in the vicinity of CNC-clay surfaces. Clay alone in moderate concentration was found to enforce almost no effect on the water dynamics, whereas introducing CNCs to the system presented a significantly enhanced relaxivity. The modeling of the relaxation dispersions allowed the determination of dynamical processes and variables explaining the dynamic behavior of water in CNC-clay suspensions. It turned out that reorientations mediated by translational displacements are a leading NMR relaxation mechanism for water interacting with the surfaces of CNC-clay particles in the low-frequency domain. In the high-frequency regime, however, the inner-sphere paramagnetic relaxation mechanism dominates, which is caused by the interaction of water protons with dissolved Fe ions.

Permanent memory effect (PME) in polymer dispersed liquid crystal (PDLC) allows a greater applicability range than traditional PDLCs. One of the most interesting application could be the possible s...

Molecular order and dynamics of the CB-C9-CB liquid crystalline dimer exhibiting the nematic (N) and the twist bend nematic (Ntb) phases were investigated by proton NMR spectroscopy, using fields of 0.78 T and 7.04 T, and relaxometry. The first relaxometry experiments for a very wide Larmor frequency domain (8 kHz-300 MHz) on this system, using a combination of standard and fast field cycling NMR techniques, were performed. The spectroscopy results in the Ntb phase allowed us to probe the local molecular orientation relative to the Ntb helix axis. The relaxation data were analyzed considering order director fluctuations (ODF), molecular self-diffusion (SD) and local molecular rotations/reorientations (R) relaxation mechanisms. Global fits of theoretical relaxation models, as a function of temperature and Larmor frequency, for the phases under investigation, allowed for the determination of rotational correlation times, diffusion coefficients, viscoelastic parameters, correlation lengths and activation energies (in the case of thermally activated mechanisms). A clear difference between the structures of the N and Ntb phases was detected from the results of proton spin-lattice relaxation through distinct temperature and frequency dependencies' signatures of the collective modes. Significant pre-transitional effects were observed at the N-Ntb phase transition both from relaxometry and spectroscopy data. The experimental results correlate to data and models for comparable liquid crystalline systems. Fil: Aluculesei, Alina. Universidade de Lisboa; Portugal Fil: Cachitas, Hugo. Universidade de Lisboa; Portugal Fil: Carvalho, José. Universidade de Lisboa; Portugal Fil: Vaca Chávez Fornasero, Fabián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidade de Lisboa; Portugal Fil: Figueirinhas, Joaõ L.. Universidade de Lisboa; Portugal Fil: Sebastiaõ, Pedro José. Universidade de Lisboa; Portugal Fil: Cruz, Carlos. Universidade de Lisboa; Portugal Fil: Tamba, Maria Gabriela. University of Hull; Reino Unido Fil: Kohlmeier, Alexandra. University of Hull; Reino Unido Fil: Mehl, Georg H.. University of Hull; Reino Unido

Understanding the behavior of a chemical compound at a molecular level is fundamental, not only to explain its macroscopic properties, but also to enable the control and optimization of these properties. The present work aims to characterize a set of systems based on the ionic liquids [Aliquat][Cl] and [Aliquat][FeCl4] and on mixtures of these with different concentrations of DMSO by means of 1H NMR relaxometry, diffusometry and X-ray diffractometry. Without DMSO, the compounds reveal locally ordered domains, which are large enough to induce order fluctuation as a significant relaxation pathway, and present paramagnetic relaxation enhancement for the [Aliquat][Cl] and [Aliquat][FeCl4] mixture. The addition of DMSO provides a way of tuning both the local order of these systems and the relaxation enhancement produced by the tetrachloroferrate anion. Very small DMSO volume concentrations (at least up to 1%) lead to enhanced paramagnetic relaxation without compromising the locally ordered domains. Larger DMSO concentrations gradually destroy these domains and reduce the effect of paramagnetic relaxation, while solvating the ions present in the mixtures. The paramagnetic relaxation was explained as a correlated combination of inner and outer-sphere mechanisms, in line with the size and structure differences between cation and anion. This study presents a robust method of characterizing paramagnetic ionic systems and obtaining a consistent analysis for a large set of samples having different co-solvent concentrations.

Understanding the behavior of a chemical compound at a molecular level is fundamental, not only to explain its macroscopic properties, but also to enable the control and optimization of these properties. The present work aims to characterize a set of systems based on the ionic liquids [Aliquat][Cl] and [Aliquat][FeCl4] and on mixtures of these with different concentrations of DMSO by means of 1H NMR relaxometry, diffusometry and X-ray diffractometry. Without DMSO, the compounds reveal locally ordered domains, which are large enough to induce order fluctuation as a significant relaxation pathway, and present paramagnetic relaxation enhancement for the [Aliquat][Cl] and [Aliquat][FeCl4] mixture. The addition of DMSO provides a way of tuning both the local order of these systems and the relaxation enhancement produced by the tetrachloroferrate anion. Very small DMSO volume concentrations (at least up to 1%) lead to enhanced paramagnetic relaxation without compromising the locally ordered domains. Larger DMSO concentrations gradually destroy these domains and reduce the effect of paramagnetic relaxation, while solvating the ions present in the mixtures. The paramagnetic relaxation was explained as a correlated combination of inner and outer-sphere mechanisms, in line with the size and structure differences between cation and anion. This study presents a robust method of characterizing paramagnetic ionic systems and obtaining a consistent analysis for a large set of samples having different co-solvent concentrations.

In this work we have used lattice Monte Carlo to determine the orientational order of a system of biaxial particles confined between two walls inducing perfect order and subjected to an electric field perpendicular to the walls. The particles are set to interact with their nearest neighbors through a biaxial version of the Lebwohl-Lasher potential. A particular set of values for the molecular reduced polarizabilities defining the potential used was considered; the Metropolis sampling algorithm was used in the Monte Carlo simulations. The relevant order parameters were determined in the middle plane of the sample and for some cases across the whole thickness of the sample. We have determined the temperature--electric field phase diagram for this system and found, as expected, five different system configurations corresponding to three different mesophases. At low temperatures and low fields the system finds itself in an undistorted biaxial phase. On increasing the field at low temperatures, a Freedericksz transition takes place and the secondary directors reorient towards the field while the primary director stays undistorted and parallel to the walls. On increasing the field further, a second Freedericksz transition occurs and the primary director orients also towards the field direction. The orientational order measured at the field strengths tested is not affected by the field. On increasing the temperature, a transition to a uniaxial phase occurs and within the range of this phase a field increase leads also to a Freedericksz transition where the main director reorients towards the field. At higher temperature a transition to a disordered phase is found. We have performed finite size scaling analysis for the Freedericksz critical fields and found that they scale with the distance $L$ between the walls as ${L}^{--1}$ as expected from continuum theory. From these fields we have also determined the temperature dependence of two elastic constant ratios. Critical exponents and critical temperatures for the order parameter and the correlation length for the biaxial-uniaxial phase transition and the uniaxial to disordered phase transition were also determined by finite size scaling and are discussed.

In this work 2H NMR spectroscopy and 1H NMR relaxometry and diffusometry were used to characterise water order and dynamics in cellulose acetate/silica asymmetric membranes. Two hydrated membranes were characterised allowing the identification of extra ordering of the water molecules and the presence in each membrane of up to two spectral components with different degrees of order and different T1 values. The mechanism behind this order increase was ascribed to the rapid exchange of the water molecules between the pore walls and its interior. T1 relaxometry dispersions allowed for the identification of the relevant mechanisms of pore-confined water motion, with rotations mediated by translational displacements (RMTD) as the dominant mechanism in the low frequency region. Using the RMTD low cut off frequency along with the in situ directly measured diffusion constant it was possible do determine characteristic lengths of correlated water motion in both membranes studied, which fall in ranges compat...

A set of five manuscripts written by Sister Lucia between 1941 and 1944 were under study. Among them is the one that contains the description of the third part of the Secret of Fatima also known as the Third Secret of Fatima. In this work, a characterization of the paper and the ink used in these documents was achieved using micro-X-ray fluorescence spectrometry. Quantitative results were obtained for P, K, Ca, Fe, Cu and Zn, revealing different paper composition and Zn in the inks. 2D elemental maps confirmed that Zn was present in the five documents ink and that the manuscript revealing the Third Secret of Fatima contained no erasures or alteration attempts to the original manuscript.

Hydroxypropylcellulose (HPC) is an important cellulose derivative that has been widely studied due to its water-solubility, biocompatibility and biodegradability, but even more significant due to its ability to form liquid crystalline phases. HPC is able to form, under certain conditions, chiral nematic (cholesteric) structures in water solutions. Previous work confirmed that films prepared from liquid crystalline HPC/water solutions (LC-HPC) gave rise to anisotropic networks, with similar mechanical and optical characteristics of Liquid Crystalline Elastomers (LCE), capable to respond to humidity. It was also demonstrated that the incorporation of carbon nanotubes (CNTs) significantly improved the actuator responsiveness. In the work presented herein, we investigate how the incorporation of carbon nanotubes affects the flow behavior of LC-HPC solutions, and thus the structure-properties relationship, through a detailed Rheo-NMR study. As observed from the results, when shearing the samples, the degree of order reached (maximum quadrupolar peak splitting) by LC-HPC solutions increases with CNT content. Regarding the subsequent relaxation process, only the incorporation of 0.01 wt% of CNTs (lowest content) contributes to a faster recovery of cholesteric structure., The authors acknowledge funding from FEDER through the COMPETE 2020 Program and National Funds through FCT-Portuguese Foundation for Science and Technology under projects UID/CTM/ 50025/2013 and M-ERA-NET2/0007/2016 (CellColor). P.L.A. acknowledges financial support from Portuguese Foundation for Science and Technology through the project PTDC/FIS-NAN/0117/2014. J.L.F acknowledges financial support from Portuguese Foundation for Science and Technology through CeFEMA strategic project UID/CTM/ 04540/2019. C.E. acknowledges the Portuguese Ministry of Science, Technology and Higher Education for National Funds, European Social Funds and FCT for the PostDoc fellowship with reference SFRH/BPD/ 88779/2012 and the Spanish Ministry of Science, Innovation, and Universities for her IJCI-2015-26432 contract. The authors declare no competing interests. All data is available in the main text or the supplementary Information

Using proton and deuterium NMR spectroscopy, this work provides a description of the molecular orientational order of the mesogenic groups in both the Ntb and the classical nematic phase (N) of the liquid crystal dimer CB–C9–CB. The proton NMR data were collected at high field (7 T) with the nematic domains aligned by the field. Deuterium NMR data obtained from aligned samples at 11.7 T, published by Hoffmann, A. Soft Matter 2015, 11, 850, were also considered in this study. Using the first-order perturbation theory, we carried out detailed simulations of the proton spectra from the terminal mesogenic groups along with the quadrupolar splittings from the carbon–deuterium bonds in the first chain positions, which allow for the determination of the Saupe order tensor for the mesogenic groups. We show that the main mechanism that induces the change of the 1H NMR spectrum and the quadrupolar splittings at the N–Ntb phase transition is the change of the orientation of the most ordered molecular frame (eigenfra...

A molecular recognition process has been used to form new mesogenic molecular structures, where intermolecular hydrogen bonding occurs between 4-(octyloxy)benzoic acid (8BAO) and four 4-alkylbenzoic acids (nBAs, n = 2, 5, 6, 7). The synthesis of these complexes has been attained by resorting to mechanochemistry. The resulting materials have been characterized by polarizing optical thermal microscopy, differential scanning calorimetry, vibrational spectroscopy, X-ray powder diffraction, and 1H NMR relaxometry. All the elements of the series show the formation of a mesophase. For one of the complexes, its electro-optical properties have also been assessed, resulting comparable to those of other widely used liquid crystals.

Cellulose and its derivatives, such as hydroxypropylcellulose (HPC) have been studied for a long time but they are still not well understood particularly in liquid crystalline solutions. These systems can be at the origin of networks with properties similar to liquid crystalline (LC) elastomers. The films produced from LC solutions can be manipulated by the action of moisture allowing for instance the development of a soft motor (Geng et al., 2013) driven by humidity. Cellulose nanocrystals (CNC), which combine cellulose properties with the specific characteristics of nanoscale materials, have been mainly studied for their potential as a reinforcing agent. Suspensions of CNC can also self-order originating a liquid–crystalline chiral nematic phases. Considering the liquid crystalline features that both LC-HPC and CNC can acquire, we prepared LC-HPC/CNC solutions with different CNC contents (1, 2 and 5 wt.%). The effect of the CNC into the LC-HPC matrix was determined by coupling rheology and NMR spectroscopy – Rheo-NMR a technique tailored to analyse orientational order in sheared systems.

A number of polymer dispersed liquid crystal (PDLC) films based on dimethacrylate monomers were synthesised by polymer-induced phase separation (PIPS) using polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (TX-100) as an additive up to total solution weight of 10% aiming to modify the initial anchorage force of the liquid crystal (LC) molecules to the polymeric matrix. The effects of the addition of this additive to the PDLC films were studied resorting to electro-optical studies. Using a fitting model, several parameters were correlated such as the permanent memory effect (PME), the voltage required to achieve 90% of maximum transmittance (E90), the average elastic constant (K) and the rotational viscosity of the director (γ). The use of TX-100 results on an increase on the PME and γ, and decrease on the E90 and K.

BACKGROUND Polymer dispersed liquid crystal (PDLC) films have a range of applications varying from switchable windows to new optical memory devices. They switch from an opaque state, when liquid crystal molecules are randomly dispersed, to a transparent state, when liquid crystal molecules are aligned, simply by applying a small voltage. On some PDLC films, the transparent state is retained even when the voltage is switched off; this is called permanent memory effect (PME). This process is totally reversible, returning to the initial opaque state either through heating or applying a higher frequency electric field when using a two frequency liquid crystal. RESULTS In this work, the impact on the electro-optical response of PDLC films as a result of adding an additive was studied. This performance is affected by several factors, the most important being the anchorage force. This anchorage force is modified with the addition of an additive such as TX-100. As a result, it was verified that the addition of TX-100, increased the PME up to 98.7% and decreased the voltage required to achieve 90% of maximum transmittance to 2 V µm−1. CONCLUSIONS The addition of a surfactant, as TX-100 in this case, was shown to be a valuable method to control the PME in PDLC systems in particular those prepared by PIPS from the oligomer polyethylene glycol dimethacrylate and the monomer triethylene glycol dimethacrylate in mixture with the nematic LC E7. This new advance on liquid crystal field also allows development of a new memory device based on a write–read–erase cycle. © 2015 Society of Chemical Industry

Water-based cellulose cholesteric liquid crystalline phases at rest can undergo structural changes induced by shear flow. This reflects on the deuterium spectra recorded when the system is investigated by rheo-nuclear magnetic resonance (rheo-NMR) techniques. In this work, the model system hydroxypropylcellulose (HPC)+water is revisited using rheo-NMR to clarify unsettled points regarding its behavior under shear and in relaxation. The NMR spectra allow the identification of five different stable ordering states, within shear and relaxation, which are well integrated in a mesoscopic picture of the system’s structural evolution under shear and relaxation. This picture emerging from the large body of studies available for this system by other experimental techniques, accounts well for the NMR data and is in good agreement with the three distinct regions of steady shear flow recognized for some lyotropic LC polymers. Shear rates in between 0.1 and 1.0 s–1 where investigated using a Taylor–Couette flow and de...

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The objective of this work was to develop solid dosage forms using powders containing inclusion complexes (ibuprofen with β-cyclodextrin) which were used to produce tablets (direct compression without additional excipients) and pellets (extrusion/spheronization) from wet mass containing 40% (w/w) of microcrystalline cellulose. The pellets also demonstrated that during preparation of the wet mass, the inclusion process occurred in a same yield that when pre-complexation was used. The particles characteristics were evaluated after being obtained through different complexation methods. The results showed that the tensile strength and profile dissolution were as expected for both dosage forms. Tablets containing inclusion complexes showed higher solubility when compared with a reference formulation and with two commercial formulations. The ibuprofen released from the two pellets formulations didn't show relevant differences between them. The drug released was analyzed considering different dissolution parameters. The advantages of these new methodologies can be summarized as: (a) tablets were produced at a lower cost for the total process; and (b) in the pellet's preparation there was no need of the previous complexation method resulting in a decrease in time and energy required.

In this work we study the strain-induced deformation of both isotropic and anisotropic liquid droplets dispersed in a liquid crystalline cellulose matrix. We have produced two types of acetoxypropylcellulose (APC) solid films one with a droplet dispersion of the commercial liquid crystal E7 from Merck, and another with a droplet dispersion of silicone oil. To produce the solid films a solution of APC (60%wt) in dimethylacetamide (DMAc) with 15%wt of either the commercial nematic liquid crystal E7 or the silicone oil was prepared. After homogenization the phase separated solutions were submitted to a shear flow mechanical field and casted onto a Teflon plate. We performed mechanical uniaxial stress-strain tests in the free standing films recording continuously the strain and images of the deformed droplets. The mechanical tests were carried out using a mini stress-strain testing machine apparatus and an Olympus optical polarizing microscope with an attached CCD camera. The images obtained from the mechanical tests for each value of the imposed strain were then analyzed comparing the images of deformed droplets with those of the undeformed ones, extracting in this way the local strain field. The droplet deformation data obtained show, as expected, significant differences in the local strain field when stretching parallel and perpendicular to the initial shear direction. No significant differences were found in the local strain fields obtained from the silicone oil and the E7 droplets films. The local strain fields variation with the imposed strain are compared with the predictions of the theory developed for nematic elastomers by Warner and Terentjev (Liquid crystal elastomers. Clarendon Oxford Press, Oxford, 2003).

A cellulose derivative/liquid crystal composite‐type electro‐optical cell using a commercial cholesteric liquid crystal (CLC) was investigated. The electro‐optical properties of the system were examined, i.e. the dependence on applied voltage of the reflected wavelength and the minimum and maximum transmissions. A thin film of the CLC was dispersed with a cross‐linked cellulose film of 25 µm thickness. In the voltage dependence of the reflected wavelength it was verified that there is a hysteresis in the reflected wavelength. The variation of the reflected wavelength with temperature was also determined. The results are analysed in the framework of similar systems described in the literature for CLC dispersed in a polymer matrix.

Mesogenic cellulose derivative chains cross-linked into free-standing thin films were prepared by a shear-casting technique from anisotropic precursor solutions of thermotropic (acetoxypropyl)cellulose. After shear cessation a macroscopically oriented serpentine structure with the director in average along the shear direction is locked resulting in anisotropic optical and mechanical properties of the material. These films were submitted to an external uniaxial mechanical field perpendicular and parallel to the shear direction. Stretching perpendicular to the shear direction produced significant director rotations and a reset of order of the director order parameter for a deformation in the range 2–3 as detected by X-rays and optical microscopy. The different response found for strains imposed parallel and perpendicular to the initial average director orientation indicates that even though our system shows a serpentine director modulation that is either attenuated or reinforced by deformations parallel or perpendicular to the shear direction, its behaviour is similar to theoretical predictions for monodomain nematic elastomers described in the literature.

This work describes the process of fabrication of 3D topography membranes and the fully quantitative characterisation of their topography using atomic force microscopy (AFM), small-angle light scattering (SALS), scanning electron microscopy (SEM) and polarizing optical microscopy (POM). The use of these membranes and the impact of the 3D membrane topography on the enhancement of mass transport during solute recovery (hexyl acetate) from a viscous room temperature ionic liquid 1-n-butyl-3-methyl-imidazolium tetrafluoroborate ([C4mim] [BF4]) by organophilic pervaporation is presented and discussed. A quantitative analyses of the results obtained allow to conclude that the use of the surface-modified membrane led to an increase of solute flux of 14%, which is well above the value of 4% that may be attributed to an augment of membrane surface area due to the increased membrane roughness. This increase of solute flux has to be granted to improved fluid dynamic conditions due to micro-turbulence at the membrane surface. This work illustrates how the design of three-dimensional relief microstructures at the membrane surface, with topographic modulation of features with characteristic dimensions, may lead to improved momentum and mass transport conditions at the membrane surface through promotion of local micro-turbulence.

The effect was investigated of an applied magnetic field on the stability of the shear flow of a nematic polymer liquid crystal of the tumbling type with respect to the formation of transient bands. For a given Ericksen number of the flow, the critical field that suppresses the thermally generated and shear amplified perturbations is calculated. The boundary in the control parameter space between the homogeneous and the band formation regime is calculated using a numerical simulation of the flow based on a time‐dependent perturbative analysis. It is also found that the critical wavevector of the bands increases with the field and decreases with the Ericksen number of the flow and with the shear strain when a magnetic field is applied.

In this work we used hydroxypropylcellulose (HPC) and acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) for electro-optical devices. Cellulose derivatives films were prepared from crosslinked both HPC and APC isotropic and liquid crystalline solutions without and with a low molecular weight nematic liquid crystal mixture (LC) E7. Films prepared from anisotropic solutions presented a band texture and E7 droplets of micron and submicron size were found to coexist with the band texture in the films prepared with E7. The optical cells were composed by the cellulose derivatives films covered on both free surfaces by a layer of the LC E7 and placed between two transparent conducting substrates. All the electro-optical cells prepared showed switching times in the range of some milliseconds to hundreds of milliseconds. The on-voltage ( V on ) is lowered for cells prepared with the ester derivative film obtained from isotropic solutions. The maximum transmission values show a clearly tendency to decrease for the cellulosic matrix prepared from anisotropic solutions with and without nematic liquid crystal droplets.

In this work we address new results obtained with a thin free standing flexible film (approximately 120 microm) of a urethane/urea copolymer related to the formation of micro and nano size structures [M.H. Godinho, A.C. Trindade, J.L. Figueirinhas, L.V. Melo, P. Brogueira, Synthetic Metals, 147(1-3), 209 (2004); M.H. Godinho, A.C. Trindade, J.L. Figueirinhas, L.V. Melo, P. Brogueira, Molecular Crystals and Liquid Crystals (2005)]. The copolymer was synthesized from a polypropylene oxide-based prepolymer with three isocyanate terminal groups (PU) and polybutadienediol (PBDO) with PBDO content of 40% wt. After casting and curing the film was cut into different samples and each exposed to UV radiation for different periods of time; 23, 25, 26, 31 and 49 h (lambda=254 nm) and later extracted with toluene and dried. The dried films were then studied by polarising optical microscopy (POM), small angle light scattering (SALS) and the surfaces exposed to UV radiation analyzed by means of atomic force microscopy (AFM). Before extraction with toluene a nanometer-flat surface, characterized by a mean roughness value Ra=0.59 nm, was obtained. Depending on exposure time to UV radiation and after extraction with toluene a corrugated surface, with features mum-sized in all axes, resulting in an increase of the overall mean roughness value to Ra=50.7 nm, starts to develop after 25 h of exposure time. This work gives evidence of the non-monotonous time behavior of the wrinkled surface growth that develops under the action of ultraviolet radiation. As the exposure time increases the free-standing films directly exposed surfaces show a decreasing density of the structures observed and an increasing characteristic peak-to-valley height. The peak-to-valley height measured for samples exposed for 23, 25, 26, 31 and 49 h, respectively 193, 383, 381, 1550 and 2039 nm and the corresponding mean roughness values are Ra=50.7 nm, 105.4, 116.8, 438.3 and 515.4 nm, respectively. Between 26 and 31 h exposure time a leap in both values, peak-to-valley and Ra, was observed. The sudden increase in these values is correlated to fabrication of wrinkles by uniaxially stretching PU/PBDO elastomer films.

Since long ago cellulosic lyotropic liquid crystals were thought as potential materials to produce fibers competitive with spidersilk or Kevlar, yet the processing of high modulus materials from cellulose-based precursors was hampered by their complex rheological behavior. In this work, by using the Rheo-NMR technique, which combines deuterium NMR with rheology, we investigate the high shear rate regimes that may be of interest to the industrial processing of these materials. Whereas the low shear rate regimes were already investigated by this technique in different works [1] , [2] , [3] , [4] , the high shear rates range is still lacking a detailed study. This work focuses on the orientational order in the system both under shear and subsequent relaxation process arising after shear cessation through the analysis of deuterium spectra from the deuterated solvent water. At the analyzed shear rates the cholesteric order is suppressed and a flow-aligned nematic is observed which for the higher shear rates develops after certain time periodic perturbations that transiently annihilate the order in the system. During relaxation the flow aligned nematic starts losing order due to the onset of the cholesteric helices leading to a period of very low order where cholesteric helices with different orientations are forming from the aligned nematic, followed in the final stage by an increase in order at long relaxation times corresponding to the development of aligned cholesteric domains. This study sheds light on the complex rheological behavior of chiral nematic cellulose-based systems and opens ways to improve its processing.

Magnetic nanoparticles from magnetic colloidal suspensions were incorporated in the urethane/urea elastomer (PU/PBDO) by adding to the prepolymers solution in toluene diverse amounts of magnetite grains. It is shown that ferrofluid grains can be efficiently incorporated into the elastomer according to this procedure. Mechanical and optical experiments performed show that the elastomer preparation procedure (casting) introduces a structural anisotropy on the optically isotropic sample. This fact is put in evidence by the measurements of the Young's moduli and orientation of the sample's optical axis under stress. The dependence of the phase shift of both the pure and ferrofluid-doped elastomer samples under strain is linear, and the strain-optic coefficient is show to be linear with the ferrofluid concentration.

The present work deals with the preparation of new liquid crystalline cellulose dispersed liquid crystal films (100 μm) using a shearing casting technique. The matrix of the films presents the so-called band texture perpendicular to the shear direction. The nematic low molecular weight liquid crystal is encapsulated in micron and submicron size ellipsoids. The ratio between the lengths of the main axis and the short axis is around 1.23. The main axis is oriented, on average, 28° away from the shear direction. The evolution of the band texture and of the ellipsoidal liquid crystal droplets is investigated by polarizing optical microscopy and light scattering techniques as a function of the strain imposed along and perpendicular to the shear direction. Stretch along shear with strain equal to 0.8 seems to have no effect on the banded structure of the matrix, while the nematic liquid crystal ellipsoids slightly orient the main axis to the stress direction and their shape anisotropy increases by a factor of 2...

New cellulose‐derived dispersed liquid crystal free‐standing thin films were prepared by a shear‐casting technique from anisotropic and isotropic solutions of thermotropic (acetoxypropyl)cellulose in N,N‐dimethylacetamide with different amounts of the nematic E7. For films prepared from anisotropic solutions, dispersed nematic E7 droplets of micron and submicron size were found to coexist, with the band texture characteristic of polymer liquid crystals after shearing. Mechanical properties including Young's modulus and stress–strain curves were determined along and perpendicular to the shear direction, and revealed the anisotropic behaviour of films prepared from lyotropic solutions. The nematic E7 component appears to promote chain mobility and rearrangement of the polymer matrix and to modify the viscoelastic properties of the matrix.

In this work we address new results obtained with free thin flexible films (60–100 μm) of urethane/urea elastomers related to the formation of micro- and nano-patterns. The samples were synthesised from a polypropylene oxide-based prepolymer with three isocyanate terminal groups (PU) and polybutadienediol (PBDO) with different PBDO content of 30, 40 and 60 wt.% After casting and curing the films were exposed to UV radiation ( λ = 254 nm) and extracted with toluene. The dried films were studied by polarising optical microscopy (POM), small angle light scattering (SALS) and the surfaces exposed to UV radiation were analysed by means of atomic force microscopy (AFM). Before extraction with toluene a nanometer-flat surface, characterized by a mean roughness value R a = 0.59 nm, was obtained. The sample with 40 wt.% of PBDO, after exposed to UV and extracted with toluene shows a corrugated surface, with features μm-sized in all axes, resulting in a dramatic increase of the overall mean roughness. As the PBDO concentration decreases the free films surfaces show an increasing density of the structures observed and a decreasing characteristic peak-to-valley height. This work suggests that the PBDO/PU samples exposed to UV radiation can be nano to micromodulated by tuning the PBDO/PU relative content. These structures can be revealed with toluene from the original nanometer-flat surface.

New experimental results on urethane/urea free standing thin films (60 μm) prepared from a polypropylene oxide isocyanate terminated triol prepolymer (PU) and polybutadiene diol (PBDO) in the amount of 60% (PU/60PBDO) by weight of polybutadiene, which exhibit periodic patterns upon the application of a mechanical field are used to critically analyse these systems. We focus in this work on the analysis of the casting conditions and on the solid film characterization before and after UV irradiation. The casting of the different solutions was observed by polarizing optical microscopy (POM) coupled to a shearing system. The stress–strain and swelling data collected for the film before UV irradiation allowed the detection of an orientational order induced by the solution casting conditions, involving shear and evaporation of the solvent, which manifests itself in the anisotropy of the stress–strain and swelling film's properties in toluene. After UV irradiation of the elastomeric film, the interlinking of PBDO chains and amines linkages enhances the orientational order enabling instabilities to appear and the mesophase to become evident in the system as shown by POM, stress–strain and small angle light scattering data. Segregated soft and hard parts of the copolymer are thought to constitute the material unit, which is anisotropically distributed. The results here presented reinforce the earlier made claim that these systems do have an anisotropic structure akin to liquid crystallinity.

The occurrence of periodically distorted director structures in planar and pre-tilted nematic slabs above the magnetically driven Freedericksz transition is investigated in the intermediate geometries between the pure splay, twist and bend Freedericksz transition geometries. Considering rigid boundary conditions the domain of existence of the periodic structures is determined as a function of the Frank elastic constants ratios K2/K1, K1/K3 and the magnetic field orientation. It is found that the periodic distorted state can be reached either directly from the undistorted state on increasing the magnetic field or indirectly through the homogeneously distorted state when pre-tilt is present. It is also found in pre-tilted slabs that the transition from the undistorted state to the homogeneously distorted state can be either continuous or discontinuous, and the corresponding lines of tricritical points are determined. PACS numbers: 61.30.Gd, 64.70Md

We present an analysis of the formation and evolution of the transient periodic pattern in the nematic director field reorientation in the magnetic non-Freedericksz twist geometry and compare with experiments. The stability analysis of the magnetically induced director reorientation in a planar oriented nematic slab with rigid anchoring and with the viscoelastic parameters of 5CB shows that, when the magnetic field is not normal to the undisturbed director n 0 , the transient hydrodynamic instability sets in for a periodic pattern that is oblique with respect to n 0 , in agreement with our experimental results for a nematic slab of 5CB. The analysis of the formation of the stripes show the equivalent of a tricritical point separating supercritical from subcritical bifurcations when the critical wavevector at the transition is plotted as a function of the reduced field. The analysis of the evolution of the stripes show that the amplitude of the periodic perturbations only grows significantly near the Freed...

In the present work we study pattern formation in a bi-soft segment urethane/urea elastomer. The material under study is a film prepared from a polypropylene oxide based isocyanate terminated triol prepolymer (PU) and polybutadiene diol (PBDO) with 60% by weight of PBDO. Small angle light scattering (SALS) patterns were recorded as a function of elongation for different rates of extension. It was found that the process of band and stripe formation is dependent upon the sample elongation and rate of extension with a strong increase of band and stripe amplitude with increasing elongation. The SALS data also reveals that the bands' periodicity is independent of the rate of extension within the range studied.

We study the effect of the amount of cross-linking agent upon the mechanical and electro-optical behaviour of several cells prepared from hydroxypropylcellulose (HPC) cross-linked with 1,4 diisocianatobutane (BDI) (0.0%, 3.1%, 7.6%, 12.3% w/w). The tensile properties and the sol/gel fractions were obtained as a function of the amount of the cross-linking agent used to prepare the solid films. The Young's modulus appears to be constant, over the range of concentrations studied. The electro-optical cells prepared with the nematic liquid crystal (E7) were analysed by light transmission. Several trends were observed, e.g. the cross-linking agent, at the percentages used, has a strong influence on the cells contrast but not on the cell's maximum transmission or turn on voltage, while the film thickness shows preponderantly its influence on the cell's maximum transmission and turn on voltage. The mechanical properties of the HPC films are important for a recent application that is now being developed [Liq. Cryst., in press], where a flexible substrate is used. The results obtained point out ways for the realisation of an optimum electro-optical cell.

In this work, we study the electro-optical behaviour of cellulose/liquid crystal-based composite systems, in particular the influence of the flexible substrates and its conductive layers in the electro-optical behaviour of these kind of cells. Four cells were made using, respectively, two different substrates (a flexible polymer (poly(ethylene terephthalate) (PET)) and a soda lime glass) and two different conductive layers (indium tin oxide (ITO) and aluminium zinc oxide (AZO)). The conductive layer (AZO) was deposited in both, flexible and rigid substrates, for the same conditions, and the same substrates coated with ITO are commercially available. The cells were prepared from solid films of hydroxypropylcellulose (HPC) (30 μm thick) cross linked with 1,4-diisocyanatobutane (BDI) (7% w/w) and the nematic liquid crystal E7 (Merck, UK). The four different substrates were electrically and morphologically characterised. We have analysed all samples by light transmission and determined the maximum transmission, contrast and V on . We show a comparison of the results obtained for both flexible and rigid cells and discuss them in terms of the proposed working mechanism for these systems.

This review focuses on two of our studied bent-core liquid crystals 2-methyl-3-[4-(4-octylbenzoyloxy)-benzylidene]-amino-benzoic acid 4-(4-dodecylphenylazo)-phenyl ester A131, and a shape-persistent fluorenone mesogen, F1a by means of temperature-dependent (13)C NMR spectra and deuterium NMR spectra, respectively. Orientational order parameters, molecular packing, and/or conformations in the nematic phases or nematic glass can be extracted from the observed NMR spectra. These will be discussed in terms of certain motional models. In particular, F1a has been found to form a biaxial nematic glass. The derived orientational order parameters would put the biaxial system of phase symmetry lower than orthorhombic.