10Nanomaterials have become a widely used group of materials in many chemical engineering 11 applications owing to their ability to provide an enhanced level of functional properties 12 compared to their crystalline and bulk counterparts. Here we report fundamental level 13 advancements on how the anatase and rutile phase of TiO2 nanoparticles chemo-thermally 14 respond between room temperature and the melting temperature under both vacuum and water 15 environments. The current study is based on using molecular dynamics (MD) simulations. We 16 present results on the equilibrium crystal morphology of these phases, structural and surface 17 energy of TiO2 nanoparticles in the size range of 2-6 nm under different temperatures. 18Thermodynamic and structural properties, in the form of potential energy and Radial 19Distribution Functions (RDF's) respectively, are calculated for both forms of TiO2 20 nanoparticles. The temperature associated with the melting transition increased with an 21 increase in the particle size in both the phases. The potential energy change associated with 22 the melting transition for anatase was seen to be less than that for rutile nanoparticles. Also 23 the temperature at which the RDF's began to stretch and broaden was observed to be lower for

Numerical investigations are conducted to study the effect of factors such as particle clustering and interfacial layer thickness on thermal conductivity of nanofluids. Based on this, parameters including Kapitza radius, and fractal and chemical dimension which have received little attention by previous research are rigorously investigated. The degree of thermal enhancement is analysed for increasing aggregate size, particle concentration, interfacial thermal resistance, and fractal and chemical dimensions. This analysis is conducted for water-based nanofluids of Alumina (Al 2 O 3 ), CuO and Titania (TiO 2 ) nanoparticles where the particle concentrations are varied up to 4vol%. Results from the numerical work are validated using available experimental data. For the case of aggregate size, particle concentration and interfacial thermal resistance; the aspect ratio (ratio of radius of gyration of aggregate to radius of primary particle, Rg/a) is varied between 2 to 60. It was found that the enhancement decreases with interfacial layer thickness. Also the rate of decrease is more significant after a given aggregate size. For a given interfacial resistance, the enhancement is mostly sensitive to Rg/a <20 indicated by the steep gradients of data plots. Predicted and experimental data for thermal conductivity enhancement are in good agreement.On the influence of fractal and chemical dimensions (d l and d f ) of Alumina-water nanofluid, the Rg/a was varied between 2-8, d l between 1.2-1.8 and d f between 1.75-2.5. For a given concentration, the enhancement increased with the reduction of d l or d f . It appears a distinctive sensitivity of the enhancement to d f , in particular in the range 2-2.25, for all values of Rg/a. However the sensitivity of d l was largely depended on the value of Rg/a. The information gathered from present work on the sensitivity of thermal conductivity enhancement to aggregate size, particle concentration, interfacial resistance, and fractal and chemical dimensions will be useful in manufacturing highly thermally conductive nanofluids. Further research on the refine cluster evolution dynamics as a function of particle-scale properties is underway.

Fracture toughness measures the resistance of a material to fracture. This fundamental property is used in diverse engineering designs including mechanical, civil, materials, electronics and chemical engineering applications. In spite of the advancements made in the past 40 years, the evaluation of this remains challenging for extremely heterogeneous materials such as composite concretes. By taking advantage of the optical properties of a thin birefringent coating on the surface of opaque, notched composite concrete beams, here we sense the evolution of the maximum shear stress distribution on the beams under loading. The location of the maximum deviator stress is tracked ahead of the crack tip on the experimental concrete samples under the ultimate load, and hence the effective crack length is characterised. Using this, the fracture toughness of a number of heterogeneous composite beams is evaluated and the results compare favourably well with other conventional methods using combined experimental and numerical/analytical approaches. Finally a new model, correlating the optically measured shear stress concentration factor and flexural strength with the fracture toughness of concretes is proposed. The current photonics-based study could be vital in evaluating the fracture toughness of even opaque and complex heterogeneous materials more effectively in future.

Article:Okeke, G, Hammond, R and Antony, SJ (2013) Influence of size and temperature on the phase stability and thermophysical properties of anatase TiO2 nanoparticles: molecular dynamics simulation. Journal of Nanoparticle Research, 15. 1584Research, 15. . 1584Research, 15. -1592. ISSN 1388-0764 https://doi.org/10.1007/s11051-013-1584-7 eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. AbstractNanoparticles have attracted the attention of researchers in a number of multidisciplinary fields as they possess enhanced structural and physical properties, which make them desirable to a wide range of industries. These enhancements have mostly been attributed to their large surface area-to-volume ratio. However, the effect of temperature on the structural and surface properties of nanoparticles of different sizes is still not well understood, an aspect addressed in the present work. Using molecular dynamics simulations, we have performed investigations on Anatase TiO 2 nanoparticles with sizes ranging between two and six nm and at different temperatures. Structural and surface properties including surface energies are reported for the different nanoparticle sizes, temperature and simulation time step. Comparisons of surface energies for the different nanoparticle sizes show that surface energy increases to a maximum (optimum value) especially for temperatures between 300 -1500 K, as the particle size increases after which no further significant increase is observed. Studies conducted on the 2 change of final structure with respect to the initial structure of the particles, revealed that atomic structural disordering is more visible at the surface layer compared to the bulk or core of the final structure. Further studies conducted on the sphericity of the nanoparticles showed that the particles became less spherical with increase in temperature.

This is a repository copy of Structures and orientation-dependent interaction forces of titania nanowires using molecular dynamics simulations.