Maria Helena Godinho

Maria Helena Godinho
Universidade NOVA de Lisboa | NOVA · Centre of Materials Research (CENIMAT)

Professor

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187
Publications
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Publications

Publications (187)
Article
A new photonic structure is produced from cellulose nanocrystal iridescent films reflecting both right and left circularly polarized light. Micrometer-scale planar gaps perpendicular to the films’ cross-section between two different left-handed films’ cholesteric domains are impregnated with a nematic liquid crystal. This photonic feature is revers...
Article
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The colloidal suspensions of aqueous cellulose nanocrystals (CNCs) are known to form liquid crystalline 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. H...
Chapter
The generic experiment started with the homeotropic texture filling the droplet, except for an annular domain of residual dowser texture in vicinity of the meniscus. Since the discovery of its persistence, the dowser texture was studied with the particular aim of generating and manipulating monopoles. The experiments started by the generation of a...
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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...
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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...
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Due to its low symmetry C2v, the dowser texture is characterised by a 2D unitary vector field or alternatively by a unitary complex field. For the same symmetry reasons, the dowser texture is sensitive, in first order, to perturbations such as thickness gradients, electric fields or flows. We will focus on corresponding properties called respective...
Article
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 nea...
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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 keepin...
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Dowsons are ±2π point singularities of the unitary complex order parameter eiφ characterizing the so-called dowser texture in a thin nematic layer with homeotropic boundary conditions. Dowsons are therefore similar to disclinations in freely-standing smectic C films or to vortices in two-dimensional superfluids or superconductors. Using especially...
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Mesoporous structures made of cellulose nanocrystals (CNCs) and their self-assembly into films is of great interest not only due to their abundancy and sustainability but also due to their ease of chemical modification and nanoscale bio mimicry capabilities. However, their implementation in (opto)electronic devices requires further understanding on...
Article
The structural support of plant cells is provided by the cell wall, which major load-bearing component is an array of hierarchical orientedhierarchical-oriented cellulose nano-, micro- and meso-structures of cellulose microfibrils. Cellulosic structures can respond to humidity changes by expanding or shrinking and this allows, for example, the disp...
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The tracheary system of plant leaves is composed of a cellulose skeleton with diverse hierarchical structures. It is built of polygonally bent helical microfilaments of cellulose-based nanostructures coated by different layers, which provide them high compression resistance, elasticity, and roughness. Their function includes the transport of water...
Article
Due to its low symmetry, the long-lived pseudo-planar texture, dubbed “the dowser texture”, has a flexo-electric spontaneous polarisation \(\mathbf{P}_{fe}\). Being degenerated, the dowser texture is easily aligned by the electric torque \(\Gamma = \mathbf{P}_{fe}\times \mathbf{E}\) acting on \(\mathbf{P}\). The dowser texture can also be aligned b...
Chapter
Helices appear in nature at many scales, ranging from molecules to tendrils in plants. Organisms take advantage of the helical shape to fold, propel and assemble. For this reason, several applications in micro and nanorobotics, drug delivery and soft-electronics have been suggested. On the other hand, biomolecules can form complex tertiary structur...
Article
Among the movements observed in some cellulosic structures produced by plants are those that involve the dispersion and burial of seeds, as for example in Erodium from Geraniaceae plant family. Here we report on a simple and efficient strategy to isolate cellulose-based hygroscopic responsive materials from Erodium awns dead tissues. The stimuli-re...
Article
Disclination loops threaded on a polymeric fiber with planar axial anchoring are shown to be sensitive to magnetic fields. In particular, a homogeneous magnetic field oblique to the fiber drives translation of disclination loops along it. The velocity of translation depends on the intensity of the field and on the angle between the field and the fi...
Chapter
Static and dynamic periodic patterns (stripes, wrinkles, and dots) are ubiquitous in nature, ranging from small wrinkles in soft materials (such as pumpkins, melons, nuts, and dehydrated fruits or even on animal’s skin) to much larger wavelength buckles (such as in lava flows or in geological structures, as in the desert sand).
Article
The persistent quasi-planar nematic texture known also as the dowser texture is characterized by a 2D unitary vector field d. We show here that the dowser texture is sensitive, in first order, to electric fields. This property is due to the flexo-electric polarisation P collinear with d expected from R.B. Meyer's considerations on flexo-electricity...
Article
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...
Article
The production of fibres and films with enhanced mechanical properties, from liquid crystalline cellulose-based systems, has always been a challenge. Previous works indicate that the use of spinning and electrospinning allows the fabrication of non-woven membranes with optical and mechanical characteristics distinct from casting films. The subseque...
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Well-defined temperature-responsive cellulose acetate (CA) grafted with a temperature-responsive polymer (TRP) was synthesized using a grafting-to approach. The TRP obtained by reversible addition–fragmentation chain transfer polymerization (RAFT), with Mn = 17700 and dispersity Đ = 1.10, is a random copolymer of di(ethylene glycol) methyl ether me...
Article
In spite of its metastability, the pseudo-planar texture of a nematic layer confined between surfaces with homeotropic anchoring can be preserved indefinitely in certain conditions. The pseudo-planar texture, dubbed “the dowser texture”, is degenerated and therefore sensitive to perturbations. It has been shown recently that the dowser texture is c...
Article
Nature abounds with helical filaments designed for specific tasks. For instance, some plants use tendrils to coil and attach to the surroundings, while Spiroplasma, a helical bacterium, moves by inverting the helical handedness along the filament axis. Therefore, developing methods to shape filaments on demand to exhibit a diversity of physical pro...
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Cellulose, the most abundant natural polymer on earth, is used in numerous applications in our day-to-day life. However, the discovery that cellulose-based systems could lead to the formation of liquid crystalline phases only dates to the 1970s. Compared with all known applications of cellulose, the liquid crystalline behavior has been less conside...
Article
The discovery of a cholesteric liquid crystalline phase in concentrated aqueous solutions of (hydroxypropyl)cellulose (HPC) dates back to the 1970s. Due to its biocompatibility, low cost and ease of conversion to fibres and films, HPC is still the target of numerous studies. In this article, some of the properties of the HPC/water lyotropic system...
Article
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Back Cover: This work shows that it is possible to precisely shape, along the same microfilament, helices with different curvatures and handedness. Elastic electrospun microfilaments with distinct intrinsic curvatures, along their length, as found in tendrils produced by plants, are prepared. Further information can be found in article 1600700, by...
Article
We report on two effects observed in experiments with captive disclination loops on polymeric fibers immersed in nematics and submitted to electric and/or magnetic fields. We show that the magnetic field oblique to a fiber with axial or helicoidal anchoring on its surface induces translation of disclination loops. Fields orthogonal to fibers with h...
Article
There has been an intense research for developing techniques that can produce filaments with helical shapes, given the widespread of potential applications. In this work, how helices with different curvatures can be precisely imprinted in microfilaments is shown. It is also shown that using this technique, it is possible to produce, in a single fib...
Article
Inspired by chitin based hierarchical structures observed in arthropods exoskeleton, this work reports the capturing of chitin nanowhiskers’ chiral nematic order into a chitosan matrix. For this purpose, highly crystalline chitin nanowhiskers (CTNW) with spindle-like morphology and average aspect ratio of 24.9 were produced by acid hydrolysis of ch...
Article
Cellulose nanocrystals are isolated from plant cellulose structures, e.g., cotton. In article 1603560, M. H. Godinho and co-workers describe a tunable photonic material produced from these cellulose nanocrystals iridescent films, which reflects both right- and left-handed circularly polarized light, taking advantage of the gaps existing along the c...
Article
We show how to easily generate point defects called hedgehogs, in the so-called quasi-planar texture --the dowser state-- of a nematic layer confined between surfaces with homeotropic anchoring conditions. We point out that the dowser texture can be preserved infinitely in spite of its higher energy with respect to the homogeneous homeotropic textu...
Article
The nanostructure of urethane/urea elastomeric membranes was investigated by small-angle X-ray scattering (SAXS) in order to establish relationships between their structure and mechanical properties. The networks were made up of polypropylene oxide (PPO) and polybutadiene (PB) segments. The structural differences were investigated in two types of m...
Article
In the so-called quasiplanar texture of a nematic layer confined between parallel plates with homeotropic anchoring conditions, the director field rotates by π between limit surfaces so that field lines have the shape of a dowsing Y-shaped wooden tool. The orientation of the director field at midheight of the layer is arbitrary for symmetry reasons...
Article
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 lo...
Article
The hygroscopic method developed previously for studies of lyotropic liquid crystals is used for the first time in experiments with millimetric capillary bridges made of a hydroxypropylcellulose/water mixture. Composition of such very small samples is controlled via humidity of the surrounding air. By a slow and well-controlled drying of initially...
Article
In this work we report a new way of producing wrinkled soft Janus spheres by using scCO(2). The wrinkles appear in one of the half-hemispheres by the asymmetric UV irradiation of the particles followed by an anisotropic scCO(2) swelling. This treatment allows the fabrication of banded as well as sinusoidal packed wrinkles in the irradiated spheres...
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Perversions connecting two helices with symmetric handedness are a common occurrence in nature, for example in tendrils. These defects can be found in our day life decorating ribbon gifts or when plants use tendrils to attach to a support. Perversions arise when clamped elastic filaments coil into a helical shape but have to conserve zero overall t...
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Microfibers with their elongated shape and translation symmetry can act as important components in various soft materials, notably for their mechanics on the microscopic level. Here we demonstrate the mechanical response of a micro-object to imposed chirality, in this case, the tilt of disclination rings in an achiral nematic medium caused by the c...
Article
Full-text available
Cellulose is the main constituent of plant cell walls and can be converted into a wide range of derivatives. The derivatives are produced by a chemical reaction of the primary and two secondary hydroxyl groups available in β-d-glucopyranose units, often in heterogeneous conditions, yielding, in many cases, <3 average degrees of substitution per glu...
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Probing the surface morphology of microthin fibers such as naturally occurring biofibers is essential for understanding their structural properties, biological function, and mechanical performance. The state-of-the-art methods for studying the surfaces of biofibers are atomic force microscopy imaging and scanning electron microscopy, which well cha...
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Right now you are probably sitting on a comfy cushion. This is most likely filled with polyurethane (PU) foam. PUs are very long molecules made up of many repeating units. If the repeating units are prepolymers-intermediate-mass building blocks-with more than two reactive end groups, a three-dimensional network will form-a rubber, or elastomer, whi...
Article
The strategy of confining stimuli-responsive microgels in electrospun fibres would allow the fabrication of polymeric networks that combine the microgels swelling ability and properties with the interest features of the electrospun fibres. Colloidal electrospinning is an emerging method in which fibres containing microgels can be produced by a sing...
Article
The incorporation of small amount of highly anisotropic nanoparticles into liquid crystalline hydroxypropylcellulose (LC-HPC) matrix improves its response when is exposed to humidity gradients due to an anisotropic increment of order in the structure. Dispersed nanoparticles give rise to faster order/disorder transitions when exposed to moisture as...
Article
Back Cover: Cellulose-based electrospun fibers are fragmented by sonication-induced cavitation in water. The fragmentation process reveals a hierarchical structure of the electrospun structures, which are composed of closely-packed nanofilaments aligned along the fiber main axis. The limiting length of the electrospun filaments, which is reached af...
Article
The tensile strength of single cellulose acetate electrospun fibers is determined through sonication-induced fragmentation in water using a model previously developed by Terentjev and co-workers. The fragmentation of the electrospun fibers results in a gradual shortening of their length until a constant modal length is achieved. A single electrospu...
Chapter
Cellulose is a linear syndiotactic homopolymer composed of d-anhydroglucopyranose units which are linked by β-(1 → 4)-glycosidic bonds. The primary and secondary free hydroxyl groups, which decorate the polysaccharide chains, can undergo chemical substitution given rise to a high range of cellulose derivatives. It is well known that cellulose deriv...
Chapter
Cellulose is the most abundant biopolymer on earth. It can be used in different applications, namely in the form of fibers, and cellulose can be converted into numerous cellulose derivatives. Cellulose micro- and nanofibers have been the subject of intense research in the field of composites. Cellulose derivatives can show liquid crystalline chiral...
Article
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Liquid crystalline cellulosic-based solutions described by distinctive properties are at the origin of different kinds of multifunctional materials with unique characteristics. These solutions can form chiral nematic phases at rest, with tuneable photonic behavior, and exhibit a complex behavior associated with the onset of a network of director fi...
Article
A detailed study of the cross-relaxation effects between the (1)H and (2)H spins systems is presented in the nematic phase of a 5-cyano-biphenyl (5CB) liquid crystal, partially deuterated at $\alpha$ 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 nem...
Article
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Cotton-based nanocrystalline cellulose (NCC), also known as nanopaper, one of the major sources of renewable materials, is a promising substrate and component for producing low cost fully recyclable flexible paper electronic devices and systems due to its properties (lightweight, stiffness, non-toxicity, transparency, low thermal expansion, gas imp...
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This work demonstrates the feasibility of using polymeric micro- and nanofiber-composed films and liquid crystals as electrically switchable scattering light shutters. We present a concept of electro-optic device based on an innovative combination of two mature technologies: optics of nematic liquid crystals and electrospinning of nanofibers. These...
Article
We consider a fiber made of a soft elastic material, encased in a stiff elastic shell (core-shell geometry). If the core and shell dimensions are mismatched, e.g., because the core shrinks while the shell does not, but the two remain attached, then an elastic instability is triggered whereby wrinkles may appear on the shell. The wrinkle orientation...
Article
Cellulose and cellulose derivatives have long been used as membrane fabrication. Langmuir monolayer behavior, which naturally mimics membranes, of acetoxypropyl cellulose (APC) and lead sulfide (PbS) nanowire mixtures at different volume ratios is reported. Surface pressure (π)-area (A) isotherms of APC and PbS nanowires mixtures at different volum...
Article
The excellent properties of elastomers are exploited to trigger wrinkling instabilities in curved shells. Micro- and nano-fibres are produced by electrospinning and UV irradiated: each fibre consists of a soft core and a stiff outer half-shell. Upon solvent de-swelling, the fibres curl because the shell and the core have different natural lengths....