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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.

Cellulose-based systems are useful for many applications. However, the issue of self-organization under non-equilibrium conditions, which is ubiquitous in living matter, has scarcely been addressed in cellulose-based materials. Here, we show that quasi-2D preparations of a lyotropic cellulose-based cholesteric mesophase display travelling colourful patterns, which are generated by a chemical reaction-diffusion mechanism being simultaneous with the evaporation of solvents at the boundaries. These patterns involve spatial and temporal variation in the amplitude and sign of the helix´s pitch. We propose a simple model, based on a reaction-diffusion mechanism, which simulates the observed spatiotemporal colour behaviour. Cellulose is a naturally occurring system of interest for its chiral macromolecular structure. Here, colourful structural patterns are observed in a cellulose-based lyotropic cholesteric system, attributed to conformational self-adjustment of the cellulose chain to its environment.

This work is funded by FEDER funds through the COMPETE 2020 Program, National Funds through FCT - Portuguese Foundation for Science and Technology and POR Lisboa2020 , under the projects with references POCI- 01-0145-FEDER-007688 (Reference UID/CTM/50025), UID/BIA/00329/2013, PTDC/CTM-BIO/6178/2014, M-ERA-NET2/0007/2016 (CellColor) and PTDC/CTM-REF/30529/2017. S.N. Fernandes and L.F. Lopes acknowledge the Minister of Science, Technology and Higher Education for National Funds , European Social Funds and FCT for fellowships number SFRH/BDP/78430/2011 and SFRH/BPD/84478/2012 , respectively. This work was supported by the Histology and Comparative Pathology laboratory [Electron Microscopy service] of the Instituto de Medicina Molecular João Lobo Antunes, specifically Andreia Pinto for her kind support. We would like to thank Carlos Silva for providing the C. chrysina specimen. The C. aurata specimen observed was provided by the Insect Collection of the National Museum of Natural History and Science, University of Lisbo Significant advances have been made to control the iridescence and the selective reflection of left circularly polarised (LCP) light, and transmission of right circularly polarised (RCP) light of solid films prepared from cellulose nanocrystals (CNCs). However the manipulation of the photonic properties of the CNCs films, which reflect both RCP and LCP light is less investigated. Solid films prepare from natural sources as CNCs have advantageous characteristics that are absent in other synthetic structures, such as wide availability and renewability. Here we review and compare recent research activity involving the production and characterization of photonic band gap structures resulting from an anisotropic layer inserted between two cholesteric layers with different helical pitches but the same handedness. We make connections between systems existing in Nature and synthetic ones with the hope of advancing in the production and manipulation of CNCs-based photonic structures. authorsversion published

The colloidal suspensions of aqueous cellulose nanocrystals (CNCs) are known to form liquid crystalline (LC) systems above certain critical concentrations. From an isotropic phase, tactoid formation, growth, and sedimentation have been determined as the genesis of a high-density cholesteric phase, which, after drying, originates solid iridescent films. Herein, the coexistence of a liquid crystal upper phase and an isotropic bottom phase in CNC aqueous suspensions at the isotropic-nematic phase separation is reported. Furthermore, isotropic spindle-like domains are observed in the low-density LC phase and high-density LC phases are also prepared. The CNCs isolated from the low- and high-density LC phases are found to have similar average lengths, diameters, and surface charges. The existence of an LC low-density phase is explained by the presence of air dissolved in the water present within the CNCs. The air dissolves out when the water solidifies into ice and remains within the CNCs. The self-adjustment of the cellulose chain conformation enables the entrapment of air within the CNCs and CNC buoyancy in aqueous suspensions.

Cellulose nano crystals (CNCs) are promising materials for energy efficient buildings related to the control of reflectivity and heat absorption/reflection of light. In this sense it is important to improve CNCs films fire retardant properties, which can be achieved by adding clays. Cellulose nanocrystals (CNCs) and nanolayers obtained from Sodium Fluorohectorite (NaFh) synthetic clay are both known to form liquid crystalline phases in aqueous suspensions. CNCs form cholesteric phases, which structure is preserved after water evaporation, while dry NaFh nanolayers aligned films collapse. In this initial work, it is shown that CNCs are compatible with NaFh clay. We demonstrate that the liquid crystalline phase of CNCs in water is not destroyed by the presence of NaFh nanolayers. The NaFh nanolayers act as planar anchoring surfaces to the cellulose nanorods and, after evaporation of the water coloured films are obtained. The precursor solutions and the photonic films were investigated by Describe several techniques. Open Access This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

POCI- 01-0145-FEDER-007688 (Reference UIDB/50025/2020-2023) PTDC/CTM-BIO/6178/2014 M-ERA-NET2/0007/2016 PTDC/CTM-REF/30529/2017 EUTOPIA CA17139 Slovenian Research Agency Grant Z1-5441 P1-0099 Structural vivid colours can arise from the interference of light reflected from structures exhibiting periodicity on scales in the range of visible wavelengths. This effect is observed with light reflected from cell-walls of some plants and exoskeletons of certain insects. Sometimes the colour sequence observed for these structures consists of nearly circular concentric rings that vary in colour from Red, Orange, Yellow, Green, Cyan to Blue, from the periphery to the centre, similarly to the colour scheme sequence observed for the rainbow (ROYGB). The sequence of colours has been found for solid films obtained from droplets of aqueous cellulose nanocrystals (CNCs) suspensions and attributed to a "coffee ring"effect. In this work, coloured lyotropic solutions and solid films obtained from a cellulose derivative in the presence of trifluoroacetic acid (TFA), which acts as a "reactive solvent", are revisited. The systems were investigated with spectroscopy, using circularly and linearly polarised light, coupled with a polarised optical microscope (POM) and scanning electron microscopy (SEM). The lyotropic cholesteric liquid crystalline solutions were confined in capillaries to simplify 1D molecular diffusion along the capillary where an unexpected sequence of the structural colours was observed. The development and reappearance of the sequence of vivid colours seem consistent with the reaction-diffusion of the "reactive solvent"in the presence of the cellulosic chains. The strong TFA acts as an auto-catalyst for the chemical reaction between TFA and the hydroxyl groups, existing along the cellulosic chain, and diffuses to the top and bottom along the capillaries, carrying dissolved cellulosic chains. Uncovering the precise mechanism of colour sequence and evolution over time in cellulosic lyotropic solutions has important implications for future optical/sensors applications and for the understanding of the development of cellulose-based structures in nature. This journal is authorsversion published

FCT – Portuguese Foundation for Science and Technology through the Ph.D. scholarship SFRH/BD/125191/2016. project PapEl, reference PTDC/CTM-NAN/5172/2014. project CHIHC, reference PTDC/NAN-MAT/32558/2017. project PTDC/CTM-BIO/6178/2014, M-ERA-NET2/0007/2016 (CellColor). POR Lisboa2020 through project PTDC/CTM-REF/30529/2017. D.G. acknowledges the support from FCT – Portuguese Foundation for Science and Technology through the AdvaMTech PhD program scholarship PD/BD/52627/2014. Mesoporous structures made of cellulose nanocrystals (CNCs) and their self-assembly into films are of great interest not only due to their abundancy and sustainability but also due to their ease of chemical modification and nanoscale biomimicry capabilities. However, their implementation in (opto)electronic devices requires further understanding on how these self-assembled twisted mesoporous superstructures respond to electrical stimulus. In this regard, this work focuses on the infiltration of solid CNC droplets with three distinct alkali ions (Li+, Na+, and K+) to yield films with improved electrochemical response when compared to pristine ones, while preserving their photonic character. Electrochemical characterization shows capacitances of up to 2.5 μF cm–2 allowing for their integration as solid-state gate electrolytes in amorphous indium–gallium–zinc–oxide transistors, resulting in low operating voltages (10 cm2 V–1 s–1. Devices fabricated on Na+ and K+ infiltrated CNC films present the best characteristics, indicating pure capacitive charging of the semiconductor. The insights presented here contribute to applications in solid-state ionics in mesoporous structures or the combination of optically active electrolytes capable of providing unique functionalities in ion-gated transistors and circuitry. publishersversion published

FEDER funds through the COMPETE 2020 Program, National Funds through FCT -Portuguese Foundation for Science and Technology and POR Lisboa2020, PTDC/CTM-BIO/6178/2014, M-ERA-NET2/0007/2016 (CellColor) and PTDC/CTM-REF/30529/2017 (NanoCell2SEC). Lyotropic colloidal aqueous suspensions of cellulose nanocrystals (CNCs) can, after solvent evaporation, retain their chiral nematic arrangement. As water is removed the pitch value of the suspension decreases and structural colour-generating films, which are mechanically brittle in nature, can be obtained. Increasing their flexibility while keeping the chiral nematic structure and biocompatible nature is a challenging task. However, if achievable, this will promote their use in new and interesting applications. In this study, we report on the addition of different amounts of hydroxypropyl cellulose (HPC) to CNCs suspension within the coexistence of the isotropic-anisotropic phases and infer the influence of this cellulosic derivative on the properties of the obtained solid films. It was possible to add 50 wt.% of HPC to a CNCs aqueous suspension (to obtain a 50/50 solids ratio) without disrupting the LC phase of CNCs and maintaining a left-handed helical structure in the obtained films. When 30 wt.% of HPC was added to the suspension of CNCs, a strong colouration in the film was still observed. This colour shifts to the near-infrared region as the HPC content in the colloidal suspension increases to 40 wt.% or 50 wt.% The all-cellulosic composite films present an increase in the maximum strain as the concentration of HPC increases, as shown by the bending experiments and an improvement in their thermal properties. publishersversion published

The conference ‘Twisted’, held in Luxembourg from 10th to 12th of May 2017, was organised at the University of Luxembourg, Campus Limpertsberg, in BâtimentdesSciences surrounded by a beautiful and ...

The authors acknowledge the support from the FCT – Portuguese Foundation for Science and Technology through the Ph.D. scholarship SFRH/BD/125191/2016. The authors would like to acknowledge the European Commission under project NewFun (ERC‐StG‐2014, GA 640598) and BET‐EU (H2020‐TWINN‐2015, GA 692373). This work was also supported by the FEDER funds through the COMPETE 2020 Program, Portugal2020 project CelSmartSense number 17862 and the National Funds through the FCT – Portuguese Foundation for Science and Technology under the Project No. POCI‐01‐0145‐FEDER‐007688, Reference UID/CTM/50025, project FunPaper, reference EXPL/CTM‐NAN/1184/2013, project PapEl, reference PTDC/CTM‐NAN/5172/2014, project PTDC/CTM‐BIO/6178/2014 and M‐ERA‐NET2/0007/2016 (CellColor). S.N.F. acknowledges the MCTES, the European Social Funds, and the FCT for fellowships SFRH/BDP/78430/2011. D.G. acknowledges the support from the FCT – Portuguese Foundation for Science and Technology through the AdvaMTech PhD program scholarship PD/BD/52627/2014. The integration of bioinspired chiral cellulose nanocrystal (CNC) films into transistor devices with distinct sensing properties for left- and right-handed circular polarized light (LCPL and RCPL, respectively) is reported. The CNC films with a left-handed internal long-range order are infiltrated with sodium ions to yield solid-state electrolytes with photonic properties capable of LCPL reflection and RCPL transmission. They are employed as gate dielectrics in sputtered amorphous indium–gallium–zinc oxide (a-IGZO) transistors. The obtained devices operate in depletion mode at low voltages (

In the field of cellulosic liquid crystals, attempts to establish the relationship between structure/properties have been developed. Above a critical concentration in an aqueous solution, hydroxypropylcellulose self-assembles in order to form cholesteric liquid crystal phases (LC-HPC). In this work we aim to understand how the incorporation of a low content of cellulose nanocrystals (CNC) within LC-HPC/H 2 O (50 wt%), could influence the behaviour of the system when subjected to low shear rates, where the cholesteric phase still persists. The analysis of the deuterium spectrum and the T 2 (transversal relaxation) values confirm that the mobility of LC-HPC at low shear rates is restricted due to CNC, and consequently so is the flow of the cholesteric polydomains. These effects are more evident in the LC-HPC sample containing 2 wt% of CNC; besides needing more strain units to induce some degree of order, the achieved degree of order is recovered faster when compared to the reference sample.

In this work, we developed and investigated a random laser based on rhodamine6G (Rh6G) in ethylene glycol (EG) solution with varying cellulose nanocrystalline (CNC) needles as scatterers in the lasing media. Besides the suspension-in-cuvette scheme, an alternative configuration was also employed: a dye-CNC flexible self-supported thick-film (70 µm) random laser made by drop casting of the C N C s + R h 6 G + h y d r o x y p r o p y l cellulose suspension. In relation to conventional scatterers, the biodegradable cellulose nanocompounds showed a comparable reduction in both the spectral full width at half-maximum and the energy threshold values, with an optimal concentration of 5 mg [CNC]/ml[EG] in suspension. Its performance was also compared with other cellulose-based random lasers, presenting advantages for some parameters. The flexible film configuration showed similar results, but contained 10% less Rh6G than the suspension.

One strategy that has gained much attention in the last decades is the understanding and further mimicking of structures and behaviours found in nature, as inspiration to develop materials with additional functionalities. This review presents recent advances in stimuli-responsive gels with emphasis on functional hydrogels and microgels. The first part of the review highlights the high impact of stimuli-responsive hydrogels in materials science. From macro to micro scale, the review also collects the most recent studies on the preparation of hybrid polymeric microgels composed of a nanoparticle (able to respond to external stimuli), encapsulated or grown into a stimuli-responsive matrix (microgel). This combination gave rise to interesting multi-responsive functional microgels and paved a new path for the preparation of multi-stimuli “smart” systems. Finally, special attention is focused on a new generation of functional stimuli-responsive polymer hydrogels able to self-shape (shape-memory) and/or self-repair. This last functionality could be considered as the closing loop for smart polymeric gels., This work is funded by National Funds through FCT—Portuguese Foundation for Science and Technology, Reference UID/CTM/50025/2013 and FEDER funds through the COMPETE 2020 Program under the project number POCI-01-0145-FEDER-007688. C. Echeverria acknowledges the Juan de la Cierva contract (IJCI-2015-26432) from MINECO—Spanish Ministry of Economy, Industry and Competitiveness.

Nature has been producing cellulose since long before man walked the surface of the earth. Millions of years of natural design and testing have resulted in cellulose-based structures that are an inspiration for the production of synthetic materials based on cellulose with properties that can mimic natural designs, functions, and properties. Here, five sections describe cellulose-based materials with characteristics that are inspired by gratings that exist on the petals of the plants, structurally colored materials, helical filaments produced by plants, water-responsive materials in plants, and environmental stimuli-responsive tissues found in insects and plants. The synthetic cellulose-based materials described herein are in the form of fibers and films. Fascinating multifunctional materials are prepared from cellulose-based liquid crystals and from composite cellulosic materials that combine functionality with structural performance. Future and recent applications are outlined.

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A detailed study of the cross-relaxation effects between the 1H and 2H spins systems is presented in the nematic phase of a 5-cyanobiphenyl (5CB) liquid crystal, partially deuterated at α position (5CB-αd2). The proton spin–lattice relaxation time was measured at a frequency range from 5 kHz to 100 MHz at a temperature 5 K below the nematic–isotropic phase transition. In the low frequency domain, the spin–lattice relaxation rate (T1–1) dispersion clearly differs from that of the fully protonated 5CB homologue. At two distinct frequencies, T1–1 presents two distinct local maxima and for low frequencies T1–1 presents a stronger frequency dependence when compared with what is observed for 5CB. The T1–1 dispersion obtained for 5CB-αd2 for frequencies above 60 kHz was interpreted in terms of the relaxation mechanisms usually accepted to interpret the spin–lattice relaxation in nematic phases in general and 5CB in particular. For lower frequencies it was necessary to consider cross-relaxation contributions betw...

The rheological and structural characteristics of acetoxypropylcellulose (APC) nematic melt are studied at shear rates ranging from 10 s 1 to 1000 s 1 which are relevant to extrusion based processes. APC shows a monotonic shear thinning behavior over the range of shear rates tested. The negative extrudate-swell shows a minimum when a critical shear rate g_ c is reached. For shear rates smaller than g_ c, the flowinduced texture consists of two set of bands aligned parallel and normal to the flow direction. At shear rates larger than g_ c, the flow induced texture is reminiscent of a 2 fluids structure. Close to the shearing walls, domains elongated along the flow direction and stacked along the vorticity are imaged with POM, whereas SALS patterns indicate that the bulk of the sheared APC is made of elliptical domains oriented along the vorticity. No full nematic alignment is achieved at the largest shear rate tested. Below g_ c, the stress relaxation is described by a stretched exponential. Above g_ c, the stress relaxation is described by a fast and a slow process. The latter coincides with the growth of normal bands thicknesses, as the APC texture after flow cessation consists of two types of bands with parallel and normal orientations relative to the flow direction. Both bands thicknesses do not depend on the applied shear rate, in contrast to their orientation., This work was partially supported by the Portuguese Science and Technology Foundation through projects, PTDC/CTM/099595/2008, PTDC/CTM/101776/2008, PTDC/CTM-POL/1484/2012 and UID/CTM/500025/2013. S.N. Fernandes and J.P. Canejo acknowledge FCT for grants SFRH/BPD/78430/2011 and SFRH/BPD/101041/2014, respectively. Funding for project "Matepro e Optimizing Materials and Processes", with reference NORTE-07-0124-FEDER-000037 FEDER COMPETE, is also acknowledged.

The nickel complexes {bis[ N , N ′-di(2- t -butylphenyl)imino]acenaphthene} dibromonickel ( 1 -NiBr 2 ) and {bis[ N , N ′-di(2-phenylphenyl)imino]acenaphthene} dibromonickel ( 2 -NiBr 2 ) were studied in homo-, co- and terpolymerization of ethylene and propylene with polar monomers and the results compared to those previously obtained with another catalyst precursor [bis( N , N ′-dimesitylimino)acenaphthene] dibromonickel ( 3 -NiBr 2 ). In order to understand the effect of the ligand in the activity and rate of comonomer incorporation some theoretical studies, using both a semi-empirical molecular orbital method and a density-functional theory model, were performed. Good agreement was found between the computed parameters and the experimental results for the order of homo-polymerization, the differences in polymer molecular weight distribution, and, in some cases, the incorporation of functionalized copolymers in the case of copolymerization, and also on the inhibition effects caused by these copolymers.

The syntheses of ketimide titanium complexes of the type Ti(N CtBu2)3X (X = Cl, Cp, Ind), Ti(N CtBu2)4 and the zirconium complex CpZr(N CtBu2)2Cl are described. When activated by MAO, all compounds are ethylene polymerisation catalysts. In the conditions studied, the most active catalyst is CpZr(N CtBu2)2Cl, with an activity of 2.7 × 105 kg/(molZr [E] h). Titanium complexes are less active by about two orders of magnitude. The polyethylene produced is linear, as determined by NMR spectroscopy. Molecular structures of Ti(N CtBu2)3X (X = Cl, Cp, Ind) and Ti(N CtBu2)4 were determined by X-ray single crystal diffraction.

The synthesis of [TiInd(NCtBu2)Cl2] and the applications of [TiCp′(NCtBu2)Cl2] (Cp′=Ind, Cp*, Cp) as ethylene and propylene homopolymerisation catalysts, as well as its behaviour as catalysts of ethylene and 10-undecen-1-ol copolymerisation are described. The optimisation of the catalytic reactions showed that all compounds are very active homopolymerisation catalysts, particularly [TiInd(NCtBu2)Cl2] that gives 123.37 × 106 g/(molTi [E] h) and 50.77 × 106 g/(molTi [P] h) of linear polyethylene and atatic polypropylene, respectively. The less active homopolymerisation catalyst, [TiCp(NCtBu2)Cl2], is the most effective ethylene/10-undecen-1-ol copolymerisation catalyst, leading to the highest degree of polar monomer incorporation. The polymers obtained were characterised by NMR and DSC. The molecular structures of [TiCp′(NCtBu2)Cl2] (Cp′=Ind, Cp*) were determined by X-ray diffraction studies.

The salient feature of liquid crystal elastomers and networks is strong coupling between orientational order and mechanical strain. Orientational order can be changed by a wide variety of stimuli, including the presence of moisture. Changes in the orientation of constituents give rise to stresses and strains, which result in changes in sample shape. We have utilized this effect to build soft cellulose-based motor driven by humidity. The motor consists of a circular loop of cellulose film, which passes over two wheels. When humid air is present near one of the wheels on one side of the film, with drier air elsewhere, rotation of the wheels results. As the wheels rotate, the humid film dries. The motor runs so long as the difference in humidity is maintained. Our cellulose liquid crystal motor thus extracts mechanical work from a difference in humidity.

Shear transparent cellulose free-standing thin films can develop iridescence similar to that found in petals of the tulip “Queen of the Night.” The iridescence of the film arises from the modulation of the surface into bands periodically spread perpendicular to the shear direction. Small amounts of nanocrystalline cellulose (NCC) rods in the precursor liquid-crystalline solutions do not disturb the optical properties of the solutions but enhance the mechanical characteristics of the films and affects their iridescence. Smaller bands periodicity, not affected by the NCC rods, slightly deviated from the shear direction is also observed. NCCs are crucial to tune and understand the film's surface features formation. Our findings could lead to new materials for application in soft reflective screens and devices.

This work was funded by FEDER funds through the COMPETE 2020 Program and National Funds through FCT - Portuguese Foundation for Science and Technology under the Projects No, PTDC/FIS-NAN/0117/2014, and PTDC/CTM-BIO/6178/2014. S.N.F. acknowledges the Minister of Science, Technology and Higher Education for National Funds, European Social Funds and FCT for fellowship number SFRH/BDP/78430/2011. The authors also acknowledge FAPESP, CNPq, INCT-FCx from Brazil. Researchers reported a new cellulose-based photonic structure, which reflected both right circularly polarized (RCP) and left circularly polarized (LCP) light that can be tuned by temperature variation and the application of an external electric field. The optical properties of the cellulose nanocrystal (CNC) samples were investigated both in terms of their microstructure by scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS) and spectroscopically, using circularly and linear polarized light coupled with a polarized optical microscope (POM). The nanocrystals used in this work were prepared by acid hydrolysis of microcrystalline cellulose. Aqueous suspensions of CNCs in the acid form were used, resulting in freestanding iridescent films after drying with colors depending on the viewing angle. authorsversion published

We acknowledge support from the Portuguese Science and Technology Foundation through grants SFRH/BD/63574/2009, SFRH/BPD/78430/2011 to Y. Geng and S.N. Fernandes respectively, projects PTDC/CTM/099595/2008, PTDC/FIS/110132/2009, PEst-C/CTM/LA0025/2011 (Strategic Project - LA 25 - 2011-2012) and from the U.S. National Science Foundation IIP 1114332. The salient feature of liquid crystal elastomers and networks is strong coupling between orientational order and mechanical strain. Orientational order can be changed by a wide variety of stimuli, including the presence of moisture. Changes in the orientation of constituents give rise to stresses and strains, which result in changes in sample shape. We have utilized this effect to build soft cellulose-based motor driven by humidity. The motor consists of a circular loop of cellulose film, which passes over two wheels. When humid air is present near one of the wheels on one side of the film, with drier air elsewhere, rotation of the wheels results. As the wheels rotate, the humid film dries. The motor runs so long as the difference in humidity is maintained. Our cellulose liquid crystal motor thus extracts mechanical work from a difference in humidity. publishersversion published