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Electrical properties of a liquid crystal dispersed in an electrospun cellulose acetate network

Publication . MANAILA MAXIMEAN, DOINA; Danila, Octavian; Almeida, Pedro L.; Ganea, Constantin Paul

Electro-optical devices that work in a similar fashion as PDLCs (polymer-dispersed liquid crystals), produced from celulose acetate (CA) electrospun fibers deposited onto indium tin oxide coated glass and a nematic liquid crystal (E7), were studied. CA and the CA/liquid crystal composite were characterized by multiple investigation techniques, such as polarized optical microscopy, dielectric spectroscopy and impedance measurements. Dielectric constant and electric energy loss were studied as a function of frequency and temperature. The activation energy was evaluated and the relaxation time was obtained by fitting the spectra of the dielectric loss with the Havriliak–Negami functions. To determine the electrical characteristics of the studied samples, impedance measurements results were treated using the Cole–Cole diagram and the three-element equivalent model.

2018-01-15Journal article

Open access

Cellulose-based biomimetics and their applications

Publication . Almeida, Ana; Canejo, João; Fernandes, Susete; Echeverria Zabala, Coro; Almeida, Pedro L.; Godinho, Maria Helena

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.

2018-05-10Journal article

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Filling in the voids of electrospun hydroxypropyl celulose network: dielectric investigations

Publication . MANAILA MAXIMEAN, DOINA; Danila, Octavian; Ganea, Constantin Paul; Almeida, Pedro L.

Here we describe an organic electro-optic device, obtained using electrospun hydroxypropyl cellulose (HPC) polymer fibres and nematic liquid crystals (LC). Its working mechanism is similar to that of a classic polymer-dispersed liquid crystal (PDLC) device. The scanning electron microscopy of the HPC deposited fibres shows a mat of fibres with diameters in the nano and micron size range. Dielectric spectroscopy measurements allow the determination of the dependence of the dielectric constant and electric energy loss on frequency and temperature as well as the determination of the activation energy. The electro-optic study shows a very good optical transmission curve, with an “on”-“off” switching voltage of less than 1V/μ m.

2018-04-23Journal article

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Bactericidal efficacy of molybdenum oxide nanoparticles against antimicrobial-resistant pathogens

Publication . Lopes, Elizeth; Piçarra, S.; Almeida, Pedro L.; Lencastre, H. de; Aires-de-Sousa, Marta

Multidrug-resistant bacteria pose a major threat to effective antibiotics and alternatives to fight multidrug-resistant pathogens are needed. We synthetized molybdenum oxide (MoO3) nanoparticles (NP) and determined their antibacterial activity against 39 isolates: (i) eight Staphylococcus aureus, including representatives of methicillin-resistant S. aureus epidemic clones; (ii) six enterococci, including vancomycin-resistant isolates; and (iii) 25 Gram-negative isolates (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacter cloacae), including extended spectrum beta-lactamases and carbapenemases producers. All isolates showed a MoO3 NP MIC of 700–800 mg l−1. MoO3 NP produced a clear inhibition zone for S. aureus and all Gram-negative isolates at concentrations ≥25 mg ml−1 and ≥50 mg ml−1 for enterococci. When the NP solutions were adjusted to pH ~7, the biocidal activity was completely abolished. MoO3 NP create an acidic pH and show a universal antimicrobial activity against susceptible and resistant isolates belonging to the most relevant bacterial species responsible for hospital-acquired infections.

2018-08Journal article

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Molecular order and dynamics of water in hybrid cellulose acetate-silica asymmetric membranes

Publication . Beira, Maria Jardim; Condesso, Miguel; Pereira Da Silva, Miguel; Cosme, Pedro; Almeida, Pedro L.; Corvo, Marta C.; Sebastião, Pedro J.; Figueirinhas, João; De Pinho, Maria Norberta

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 compatible with typical pore dimensions in similar membranes.

2019-04-18Journal article

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