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- Spotting plants' microfilament morphologies and nanostructuresPublication . Almeida, Ana; Canejo, João; Mur, Urban; Copar, Simon; Almeida, Pedro L.; Zumer, Slobodan; Godinho, Maria HelenaThe 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 and nutrients from the roots to the leaves. Unveiling details about local interactions of tracheary elements with surrounding material, which varies between plants due to adaptation to different environments, is crucial for understanding ascending fluid transport and for tracheary mechanical strength relevant to potential applications. Here we show that plant tracheary microfilaments, collected from Agapanthus africanus and Ornithogalum thyrsoides leaves, have different surface morphologies, revealed by nematic liquid crystal droplets. This results in diverse interactions among microfilaments and with the environment; the differences translate to diverse mechanical properties of entangled microfilaments and their potential applications. The presented study also introduces routes for accurate characterization of plants' microfilaments.
- First curl, then wrinklePublication . Trindade, Ana C.; Canejo, João; Teixeira, Paulo; Patricio, Pedro; Godinho, Maria HelenaThe 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. Wrinkling only starts after the fibre has attained a well‐defined helical shape. A simple analytical model is proposed to find the curling curvature and wrinkle wavelength, as well as the transition between the “curling” and “wrinkling” regimes. This new instability resembles that found in the tendrils of climbing plants as they dry and lignify.
- Wrinkling Labyrinth Patterns on Elastomeric Janus ParticlesPublication . Trindade, A. C.; Canejo, João; Pinto, L. F. V.; Patricio, Pedro; Brogueira, Pedro; Teixeira, Paulo; Godinho, Maria HelenaWe describe a novel, low-cost and low-tech method for the fabrication of elastomeric Janus particles with diameters ranging from micrometers to millimeters. This consists of UV-irradiating soft urethane/urea elastomer spheres, which are then extracted in toluene and dried. The spheres are thus composed of a single material: no coating or film deposition steps are required. Furthermore, the whole procedure is carried out at ambient temperature and pressure. Long, labyrinthine corrugations ("wrinkles") appear on the irradiated portions of the particles' surfaces, the spatial periodicity of which can be controlled by varying the sizes of particles. The asymmetric morphology of the resulting Janus particles has been confirmed by scanning electron microscopy, atomic force microscopy, and optical microscopy. We have also established that the spheres behave elastically by performing bouncing tests with dried and swollen spheres. Results can be interpreted by assuming that each sphere consists of a thin, stiff surface layer ("skin") lying atop a thicker, softer substrate ("bulk"). The skin's higher stiffness is hypothesized to result from the more extensive cross-linking of the polymer chains located near the surface by the UV radiation. Textures then arise from competition between the effects of bending the skin and compressing the bulk, as the solvent evaporates and the sphere shrinks.
- Hierarchical wrinkling on elastometric Janus spheresPublication . Trindade, Ana C.; Canejo, João; Patricio, Pedro; Brogueira, Pedro; Teixeira, Paulo; Godinho, Maria HelenaHierarchical wrinkling on elastomeric Janus spheres is permanently imprinted by swelling, for different lengths of time, followed by drying the particles in an appropriate solvent. First-order buckling with a spatial periodicity (lambda(11)) of the order of a few microns and hierarchical structures comprising of 2nd order buckling with a spatial periodicity (lambda(12)) of the order of hundreds of nanometers have been obtained. The 2nd order buckling features result from a Grinfeld surface instability due to the diffusion of the solvent and the presence of sol molecules.
- Cellulose-based biomimetics and their applicationsPublication . Almeida, Ana; Canejo, João; Fernandes, Susete; Echeverria Zabala, Coro; Almeida, Pedro L.; Godinho, Maria HelenaNature 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.
- How to mimic the shapes of plant tendrils on the nano and microscale: spirals and helices of electrospun liquid crystalline cellulose derivativesPublication . Godinho, M. H.; Canejo, João; Pinto, L. F. V.; Borges, J. P.; Teixeira, PauloWe show that suspended nano and microfibres electrospun from liquid crystalline cellulosic solutions will curl into spirals if they are supported at just one end, or, if they are supported at both ends, will twist into a helix of one handedness over half of its length and of the opposite handedness over the other half, the two halves being connected by a short straight section. This latter phenomenon, known as perversion, is a consequence of the intrinsic curvature of the fibres and of a topological conservation law. Furthermore, agreement between theory and experiment can only be achieved if account is taken of the intrinsic torsion of the fibres. Precisely the same behaviour is known to be exhibited by the tendrils of climbing plants such as Passiflora edulis, albeit on a lengthscale of millimetres, i.e., three to four orders of magnitude larger than in our fibres. This suggests that the same basic, coarse-grained physical model is applicable across a range of lengthscales.
- Elastomeric patterns probed by a nematic liquid crystalPublication . Trindade, A.C.; Almeida, A. P. C.; Canejo, João; Patricio, Pedro; Pieranski, Pawel; Godinho, Maria HelenaSoft Janus elastomers have two surfaces with diverse characteristics. In this work, by tuning the chemical composition and the surface roughness we were able to vary the wettability of thin films (thickness of 100-200 mu m) and spheres (diameters in the order of 200 mu m to 2 mm) and evidence the multifunction of the opposite sides. We also describe a simple and inexpensive method to reveal the wrinkled-labyrinthine patterns that appear in the Janus particles by means of a nematic liquid crystal (LC). LC contact angle measurements associated with the swelling and anchoring characteristics of the surfaces were used to image the Janus particles opening new platforms for sensor applications from flexible free-standing LCs containers.
- Helical Twisting of Electrospun Liquid Crystalline Cellulose Micro- and NanofibersPublication . Canejo, João; Borges, João P.; Godinho, M. Helena; Brogueira, Pedro; Teixeira, Paulo; Terentje, Eugene M.Helically twisted fibers can be produced by electrospinning liquid-crystalline cellulose solutions. Fiber topographies are studied by atomic force microscopy, scanning electron microscopy (see figure) and polarized optical microscopy. The fibers have a nearly universal pitch-to-diameter ratio and comprise both right- and left-handed helices.
- Reversible water driven chirality inversion in cellulose-based helices isolated from Erodium awnsPublication . Almeida, Ana; Querciagrossa, Lara; Silva, Pedro; Gonçalves, Filipa; Canejo, João; Almeida, Pedro L.; Godinho, Maria Helena; Zannoni, ClaudioAmong 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 the Geraniaceae plant family. Here we report on a simple and efficient strategy to isolate and tune cellulose-based hygroscopic responsive materials from Erodium awns’ dead tissues. The stimuli-responsive material isolated forms left-handed (L) or right-handed (R) helical birefringent transparent ribbons in the wet state that reversibly change to R helices when the material dries. The humidity-driven motion of dead tissues is most likely due to a composite material made of cellulose networks of fibrils imprinted by the plant at the nanoscale, which reinforces a soft wall polysaccharide matrix. The inversion of the handedness is explained using computational simulations considering filaments that contract and expand asymmetrically. The awns of Erodium are known to present hygroscopic movements, forming R helices in the dry state, but the possibility of actuating chirality via humidity suggests that these cellulose-based skeletons, which do not require complicated lithography and intricate deposition techniques, provide a diverse range of applications from intelligent textiles to micro-machines.
- Espirais e Hélices - Do Polímero mais abundante da naturezaPublication . Godinho, M. H.; Canejo, João; Brogueira, P.; Teixeira, PauloA celulose é o polímero renovável mais abundante do mundo. É o principal constituinte das paredes celulares das plantas, as quais constituem a sua principal fonte.