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Eloi J.-C.,H H Wills Physics Laboratory | Okuda M.,H H Wills Physics Laboratory | Correia Carreira S.,H H Wills Physics Laboratory | Correia Carreira S.,Bristol Center for Functional Nanomaterials | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2014

Isothermal magnetic relaxation measurements are widely used to probe energy barriers in systems of magnetic nanoparticles. Here we show that the result of such an experiment can differ greatly for aligned and randomly oriented nanoparticles. For randomly oriented cobalt-doped magnetite nanoparticles we observe a prominent low-energy tail in the energy barrier distribution that is greatly attenuated when the particles are magnetically aligned. Monte Carlo simulations show that this behaviour arises for nanoparticles with both cubic and uniaxial magnetic anisotropy energy terms even though for cubic or uniaxial anisotropy alone the energy barrier distribution is independent of nanoparticle orientation. © 2014 IOP Publishing Ltd.

Hernandez L.A.,University of Santiago de Chile | Del Valle M.A.,University of Santiago de Chile | Diaz F.R.,University of Santiago de Chile | Fermin D.J.,Bristol Center for Functional Nanomaterials | Risbridger T.A.G.,Bristol Center for Functional Nanomaterials
Electrochimica Acta | Year: 2015

Abstract Poly(1-amino-9,10-anthraquinone) (P1AAQ) nanowires have been directly electro-synthesized on a steel electrode, previously modified with a thin film of poly(P1AAQ-co-o-phenylenediamine), via a SiO2 mesoporous template. Nanostructures obtainment was verified by electrochemical techniques and TEM. After template removal, it was corroborated that the nanowires, about 30 nm in diameter and 200 nm in length, were attached to the P1AAQ surface. The reproducibility of the method exhibited a standard deviation 3.357.10-6 for Pox(0.8 V) and 3.901.10-6 for Pred(0.003 V) and, in addition, the response remains stable over ten successive voltammetric cycles. Characterization was conducted utilizing electrochemical techniques and visualized by SEM micrographs. Thus, to the pioneering methodology for obtaining polymeric nanowires utilizing just electrochemical techniques, this modification is now added in order to assure the adhesion of the polymeric nanostructures to the electrode surface; the feasibility of use of the device in the varied applications that these materials hold, is therefore envisaged. © 2015 Elsevier Ltd. All Rights reserved.

Rios de Anda I.,University of Bristol | Rios de Anda I.,Bristol Center for Functional Nanomaterials | Statt A.,University of Bristol | Statt A.,Johannes Gutenberg University Mainz | And 3 more authors.
Contributions to Plasma Physics | Year: 2015

Charged colloids can behave as Yukawa systems, with similar phase behaviour. Using particle-resolved studies, we consider a system with an unusually long Debye screening length which forms crystals at low colloid volume fraction ϕ ≈ 0.01. We quantitatively compare this system with the Yukawa model and find that its freezing point is compatible with the theoretical prediction but that the crystal polymorph is not always that expected. In particular we find body-centred cubic crystals where face-centred cubic crystals are expected. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kumarakuru H.,University of Bristol | Kumarakuru H.,Nelson Mandela Metropolitan University | Cherns D.,University of Bristol | Collins A.M.,Bristol Center for Functional Nanomaterials
Ceramics International | Year: 2014

The structure and electrical properties of nanostructured Al-doped ZnO (AZO)/ZnO bilayers grown as potential solar cell electrodes by pulsed laser deposition on (0001) sapphire substrates are investigated. Transmission and scanning electron microscopy and X-ray diffraction show a narrow temperature window around 350-450 °C where nanostructures are formed. 2-D mapping of electrical conductivity by tunnelling atomic force microscopy showed that these nanostructures provided low resistance pathways, but that the overall film resistivity increased for substrate temperatures above 350 °C. The reasons for this are discussed. © 2014 Elsevier Ltd and Techna Group S.r.l.

Beddoes C.M.,University of Bristol | Beddoes C.M.,Bristol Center for Functional Nanomaterials | Berge J.,University of Bristol | Bartenstein J.E.,University of Bristol | And 4 more authors.
Soft Matter | Year: 2016

Using high pressure small angle X-ray scattering (HP-SAXS), we have studied monoolein (MO) mesophases at 18 wt% hydration in the presence of 10 nm silica nanoparticles (NPs) at NP-lipid number ratios (ν) of 1 × 10-6, 1 × 10-5 and 1 × 10-4 over the pressure range 1-2700 bar and temperature range 20-60 °C. In the absence of the silica NPs, the pressure-temperature (p-T) phase diagram of monoolein exhibited inverse bicontinuous cubic gyroid (QGII), lamellar alpha (Lα), and lamellar crystalline (Lc) phases. The addition of the NPs significantly altered the p-T phase diagram, changing the pressure (p) and the temperature (T) at which the transitions between these mesophases occurred. In particular, a strong NP concentration effect on the mesophase behaviour was observed. At low NP concentration, the p-T region pervaded by the QGII phase and the Lα-QGII mixture increased, and we attribute this behaviour to the NPs forming clusters at the mesophase domain boundaries, encouraging transition to the mesophase with a higher curvature. At high NP concentrations, the QGII phase was no longer observed in the p-T phase diagram. Instead, it was dominated by the lamellar (L) phases until the transition to a fluid isotropic (FI) phase at 60 °C at low pressure. We speculate that NPs formed aggregates with a "chain of pearls" structure at the mesophase domain boundaries, hindering transitions to the mesophases with higher curvatures. These observations were supported by small angle neutron scattering (SANS) and scanning electron microscopy (SEM). Our results have implications to nanocomposite materials and nanoparticle cellular entry where the interactions between NPs and organised lipid structures are an important consideration. © 2016 The Royal Society of Chemistry.

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