191 results found
Quirke N, Cheng D, Huo F, 2022, Frontiers of multiscale modeling and simulation, MOLECULAR SIMULATION, Vol: 48, Pages: 827-827, ISSN: 0892-7022
Rouse I, Power D, Brandt EG, et al., 2021, First principles characterisation of bio-nano interface, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 23, Pages: 13473-13482, ISSN: 1463-9076
Kokot H, Kokot B, Sebastijanović A, et al., 2020, Prediction of chronic inflammation for inhaled particles: the impact of material cycling and quarantining in the lung epithelium, Advanced Materials, Vol: 32, ISSN: 0935-9648
On a daily basis, people are exposed to a multitude of health-hazardous airborne particulate matter with notable deposition in the fragile alveolar region of the lungs. Hence, there is a great need for identification and prediction of material-associated diseases, currently hindered due to the lack of in-depth understanding of causal relationships, in particular between acute exposures and chronic symptoms. By applying advanced microscopies and omics to in vitro and in vivo systems, together with in silico molecular modeling, it is determined herein that the long-lasting response to a single exposure can originate from the interplay between the newly discovered nanomaterial quarantining and nanomaterial cycling between different lung cell types. This new insight finally allows prediction of the spectrum of lung inflammation associated with materials of interest using only in vitro measurements and in silico modeling, potentially relating outcomes to material properties for a large number of materials, and thus boosting safe-by-design-based material development. Because of its profound implications for animal-free predictive toxicology, this work paves the way to a more efficient and hazard-free introduction of numerous new advanced materials into our lives.
Contini C, Hindley J, Macdonald T, et al., 2020, Size dependency of gold nanoparticles interacting with model membranes, Communications Chemistry, Vol: 3, Pages: 1-12, ISSN: 2399-3669
The rapid development of nanotechnology has led to an increase in the number and variety of engineered nanomaterials in the environment. Gold nanoparticles (AuNPs) are an example of a commonly studied nanomaterial whose highly tailorable properties have generated significant interest through a wide range of research fields. In the present work, we characterise the AuNP-lipid membrane interaction by coupling qualitative data with quantitative measurements of the enthalpy change of interaction. We investigate the interactions between citrate-stabilised AuNPs ranging from 5 to 60 nm in diameter and large unilamellar vesicles acting as a model membrane system. Our results reveal the existence of two critical AuNP diameters which determine their fate when in contact with a lipid membrane. The results provide new insights into the size dependent interaction between AuNPs and lipid bilayers which is of direct relevance to nanotoxicology and to the design of NP vectors.
Hosier I, Vaughan A, Quirke N, 2019, Electrical conductivity of waxes as model systems for polyethylene: Role of water, JOURNAL OF APPLIED POLYMER SCIENCE, Vol: 137, ISSN: 0021-8995
Ren Y, Wu K, Coker DF, et al., 2019, Thermal transport in model copper-polyethylene interfaces, Journal of Chemical Physics, Vol: 151, ISSN: 0021-9606
Thermal transport through model copper-polyethylene interfaces is studied using two-temperature nonequilibrium molecular dynamics. This approach treats electronic and phonon contributions to the thermal transport in the metallic region, but only phonon mediated transport is assumed in the polymer. Results are compared with nonequilibrium molecular dynamics simulations of heat transport in which only phonon contributions are incorporated. The influence of the phase of the polymer component (crystalline, amorphous, and lamella) and, where relevant, its orientation relative to the metallic interface structure is explored. These computational studies suggest that the thermal conductivity of the metal-polymer interface can be more than 40 times greater when the polymer chains of the lamella are oriented perpendicular to the interface than the situation when the interface is formed by an amorphous polymer or a crystalline polymer phase in which the chains orient parallel to the interface. The simulations suggest that the phonon contribution to the thermal conductivity of the copper region can be increased by as much as a factor of three when coupling between the electrons and phonons in the metal region is incorporated. This, combined with the explicit inclusion of the purely electronic component of the thermal transport in the metal region, can lead to a substantial increase in the heat flux promoted by the interface while maintaining a constant temperature drop. These simulation results have important implications for designing materials that have excellent electrical insulation properties but can also be highly effective in heat conduction.
Schneemilch M, Quirke N, 2019, Free energy of adhesion of lipid bilayers on titania surfaces, Journal of Chemical Physics, Vol: 151, ISSN: 0021-9606
The adhesion strength between a flexible membrane and a solid substrate (formally the free energy of adhesion per unit area) is difficult to determine experimentally, yet is a key parameter in determining the extent of the wrapping of a particle by the membrane. Here, we present molecular dynamics simulations designed to estimate this quantity between dimyristoylphosphatidylcholine (DMPC) bilayers and a range of low-energy titanium dioxide cleavage planes for both anatase and rutile polymorphs. The average adhesion strength across the cleavage planes for rutile and anatase is relatively weak ∼-2.0 ± 0.4 mN m-1. However, rutile has two surfaces (100 and 101) displaying relatively strong adhesion (-4 mN m-1), while anatase has only one (110). This suggests a slightly greater tendency for bilayers to wrap rutile particles compared to anatase particles but both would wrap less than amorphous silica. We also estimate the adsorption free energies of isolated DMPC lipids and find that only the rutile 101 surface shows significant adsorption. In addition, we estimate the adhesion enthalpies and infer that the entropic contribution to the adhesion free energy drives adhesion on the rutile surfaces and opposes adhesion on the anatase surfaces.
Schneemilch M, Quirke N, 2019, Free energy of adhesion of lipid bilayers on silica surfaces (vol 148, 194704, 2018), JOURNAL OF CHEMICAL PHYSICS, Vol: 150, ISSN: 0021-9606
Saiz F, Quirke N, 2018, The excess electron in polymer nanocomposites, Physical Chemistry Chemical Physics, Vol: 20, Pages: 27528-27538, ISSN: 1463-9076
We have used ab initio molecular dynamics and density-functional theory (DFT) calculations at the B3LYP/6-31G** level of theory to evaluate the energy and localisation of excess electrons at a number of representative interfaces of polymer nanocomposites. These modelled interfaces are made by combining liquid water and amorphous slabs of polyethylene and silica. The walls of the amorphous silica slabs are built with two surface chemistries: Q4 or fully-dehydroxylated and Q3/Q4 or partially-hydroxylated with a silanol content between 1.62 and 6.86 groups per nm2. Our results indicate that in silica/polyethylene systems an excess electron would sit at the interface with energies between −1.75 eV with no hydroxylation and −0.99 eV with the highest silanol content. However, in the presence of a free water film, the chemistry of the silica surface has a negligible influence on the behaviour of the excess electron. The electron sits preferentially at the water/vapour interface with an energy of minus a few tenths of an eV. We conclude that the moisture content in a wet polymer nanocomposite has a profound influence on the electron trapping behaviour as it produces much lower trapping energies and a higher excess-electron mobility compared to the dry material.
Quirke N, Saiz F, Cubero D, 2018, The excess electron at polyethylene interfaces, Physical Chemistry Chemical Physics, Vol: 20, Pages: 25186-25194, ISSN: 1463-9076
This work investigates the energy and spatial properties of excess electrons in polyethylene in bulk phases and, for the first time, at amorphous vacuum interfaces using a pseudopotential single-electron method (Lanczos diagonalisation) and density functional theory (DFT). DFT calculations are made employing two approaches: with pseudopotentials/plane waves and the local-density approximation; and with all-electron Gaussian basis functions at the B3LYP level of theory, supplemented with a lattice of ghost atoms. All three methods predict similar spatial localisation of the excess electron, but a reliable comparison of its energy can only be made between the Lanczos and DFT using Gaussian bases. While Lanczos predicts that an excess electron would preferentially localise in nanovoids with diameters smaller than 1 nm, DFT suggests that it would localise on surfaces in nanovoids larger than 1 nm. Overall we conclude that in DFT studies of polyethylene/vacuum interfaces at the current level of theory, orbital-based methods provide a useful representation of excess electron properties.
Schneemilch M, Quirke N, 2018, Free energy of adhesion of lipid bilayers on silica surfaces, Journal of Chemical Physics, Vol: 148, ISSN: 0021-9606
The free energy of adhesion per unit area (hereafter referred to as the adhesion strength) of lipid arrays on surfaces is a key parameter that determines the nature of the interaction between materials and biological systems. Here we report classical molecular simulations of water and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayers at model silica surfaces with a range of silanol densities and structures. We employ a novel technique that enables us to estimate the adhesion strength of supported lipid bilayers in the presence of water. We find that silanols on the silica surface form hydrogen bonds with water molecules and that the water immersion enthalpy for all surfaces varies linearly with the surface density of these hydrogen bonds. The adhesion strength of lipid bilayers is a linear function of the surface density of hydrogen bonds formed between silanols and the lipid molecules on crystalline surfaces. Approximately 20% of isolated silanols form such bonds but more than 99% of mutually interacting geminal silanols do not engage in hydrogen bonding with water. On amorphous silica, the bilayer displays much stronger adhesion than expected from the crystalline surface data. We discuss the implications of these results for nanoparticle toxicity.
Engineered nanomaterials have a wide range of applications and as a result, are increasingly present in the environment. While they offer new technological opportunities, there is also the potential for adverse impact, in particular through possible toxicity. In this review, we discuss the current state of the art in the experimental characterisation of nanoparticle-membrane interactions relevant to the prediction of toxicity arising from disruption of biological systems. One key point of discussion is the urgent need for more quantitative studies of nano-bio interactions in experimental models of lipid system that mimic in vivo membranes.
Xie L, Chan K-Y, Quirke N, 2017, Poly(ethylene glycol) (PEG) in a Polyethylene (PE) Framework: A Simple Model for Simulation Studies of a Soluble Polymer in an Open Framework., Langmuir, Vol: 33, Pages: 11746-11753, ISSN: 0743-7463
Canonical molecular dynamics simulations are performed to investigate the behavior of single-chain and multiple-chain poly(ethylene glycol) (PEG) contained within a cubic framework spanned by polyethylene (PE) chains. This simple model is the first of its kind to study the chemical physics of polymer-threaded organic frameworks, which are materials with potential applications in catalysis and separation processes. For a single-chain 9-mer, 14-mer, and 18-mer in a small framework, the PEG will interact strongly with the framework and assume a more linear geometry chain with an increased radius of gyration Rg compared to that of a large framework. The interaction between PEG and the framework decreases with increasing mesh size in both vacuum and water. In the limit of a framework with an infinitely large cavity (infinitely long linkers), PEG behavior approaches simulation results without a framework. The solvation of PEG is simulated by adding explicit TIP3P water molecules to a 6-chain PEG 14-mer aggregate confined in a framework. The 14-mer chains are readily solvated and leach out of a large 2.6 nm mesh framework. There are fewer water-PEG interactions in a small 1.0 nm mesh framework, as indicated by a smaller number of hydrogen bonds. The PEG aggregate, however, still partially dissolves but is retained within the 1.0 nm framework. The preliminary results illustrate the effectiveness of the simple model in studying polymer-threaded framework materials and in optimizing polymer or framework parameters for high performance.
Quirke N, Jiang C, 2017, Preface, MOLECULAR SIMULATION, Vol: 43, Pages: 479-479, ISSN: 0892-7022
Saiz F, Quirke N, Bernasconi L, et al., 2016, Excess electron states in fluid methane: Density-functional versus Lanczos approaches, Chemical Physics Letters, Vol: 664, Pages: 143-148, ISSN: 1873-4448
We compare density-functional theory (DFT) electronic structure calculations at the hybrid B3LYP level for fluid methane with experiments and a pseudo-potential Lanczos method. We generate fluid configurations from classical/ab initio molecular dynamics and use DFT to determine one-particle orbital and total energies. Our results show that DFT predicts excess electron energies that qualitatively agree with experiments over a density range, provided these values are determined from total energy differences between charged and neutral systems. By contrast, orbital energies of the lowest unoccupied state of the N-electron system provide qualitatively incorrect excess electron energies as a function of the fluid density.
Schneemilch M, Quirke N, 2016, Free energy of adsorption of supported lipid bilayers from molecular dynamics simulation, CHEMICAL PHYSICS LETTERS, Vol: 664, Pages: 199-204, ISSN: 0009-2614
Shen Y, Quirke N, Zerulla D, 2016, Ultra-low frequency Raman spectroscopy of SWNTs under high pressure, Proceedings of SPIE, Vol: 9932, ISSN: 0277-786X
Radial deformation phenomena of carbon nanotubes (CNTs) are attracting increased attention because evenminimal changes of the CNT’s cross section can result in significant changes of their electronic and optical properties.It is therefore important to have the ability to sensitively probe and characterize this radial deformation.High pressure Raman spectroscopy offers a general and powerful method to study such effects in SWNTs. In thisexperimental work, we focus in particular on one theoretically predicted Raman vibrational mode, the so-called”Squash Mode” (SM), named after its vibrational mode pattern, which has an E2g symmetry representation andexists at shifts below the radial breathing mode (RBM) region. The Squash mode was predicted to be moresensitive to environmental changes than the RBM.Here we report on a detailed, experimental detection of SMs of aligned SWNT arrays with peaks as close as18 cm−1to the laser excitation energy. Furthermore, we investigate how the SM of aligned CNT arrays reactswhen exposed to a high pressure environment of up to 9 GPa. The results confirm the theoretical predictionsregarding the angular and polarization dependent variations of the SM’s intensity with respect to their excitation.Furthermore, clear Raman upshifts of SM under pressures of up to 9 GPa are presented. The relative changes ofthese upshifts, and hence the sensitivity, are much higher than that of RBMs because of larger radial displacementof some of the participating carbon atoms during the SM vibration.
Shen Y, Quirke N, Zerulla D, 2016, Ultra-low frequency Raman spectroscopy of SWNTs under high pressure, Conference on Carbon Nanotubes, Graphene, and Emerging 2D Materials for Electronic and Photonic Devices IX, Publisher: Society of Photo-optical Instrumentation Engineers (SPIE), ISSN: 1996-756X
Radial deformation phenomena of carbon nanotubes (CNTs) are attracting increased attention because even minimal changes of the CNT's cross section can result in significant changes of their electronic and optical properties. It is therefore important to have the ability to sensitively probe and characterize this radial deformation. High pressure Raman spectroscopy offers a general and powerful method to study such effects in SWNTs. In this experimental work, we focus in particular on one theoretically predicted Raman vibrational mode, the so-called "Squash Mode" (SM), named after its vibrational mode pattern, which has an E2g symmetry representation and exists at shifts below the radial breathing mode (RBM) region. The Squash mode was predicted to be more sensitive to environmental changes than the RBM.Here we report on a detailed, experimental detection of SMs of aligned SWNT arrays with peaks as close as 18 cm-1 to the laser excitation energy. Furthermore, we investigate how the SM of aligned CNT arrays reacts when exposed to a high pressure environment of up to 9 GPa. The results confirm the theoretical predictions regarding the angular and polarization dependent variations of the SM's intensity with respect to their excitation. Furthermore, clear Raman upshifts of SM under pressures of up to 9 GPa are presented. The relative changes of these upshifts, and hence the sensitivity, are much higher than that of RBMs because of larger radial displacement of some of the participating carbon atoms during the SM vibration.These novel ultra-sensitive Raman SM shifts of SWNTs provide enhanced sensitivity and demonstrate new opportunities for nano-optical sensors applications.
Lau KY, Vaughan AS, Chen G, et al., 2016, Polyethylene/silica nanocomposites: absorption current and the interpretation of SCLC, JOURNAL OF PHYSICS D-APPLIED PHYSICS, Vol: 49, ISSN: 0022-3727
Virtanen S, Vaughan AS, Yang L, et al., 2016, Dielectric Breakdown Strength and Electrical Conductivity of Low Density Polyethylene Octylnanosilica Composite, IEEE Conference on Electrical Insulation and Dielectric Phenomena (IEEE CEIDP), Publisher: IEEE, Pages: 58-61, ISSN: 0084-9162
Shen Y, Quirke N, Zerulla D, 2015, Polarisation dependence of the squash mode in the extreme low frequency vibrational region of single walled carbon nanotubes, Applied Physics Letters, Vol: 106, ISSN: 1077-3118
There is considerable interest in the vibrational modes of carbon nanotubes as they can be used to determine interaction potentials. In particular, theory predicts the appearance of so called squash modes (SMs, with E 2 g symmetry representation) at very low frequencies. These SMs are expected to be extremely sensitive to environmental changes and thus ideal as nanoscale probes. Here, we report clear experimental evidence for the existence of SMs of ordered, dry, single walled carbon nanotube (SWNT) arrays with peaks as close as 18 cm−1 to the laser excitation. Furthermore, we confirm the theoretical predictions regarding the angular and polarisation dependent variations of the SM's intensity with respect to the excitation. Additionally, using both SM and radial breathing mode data, we unambiguously assign the chirality and diameter of the SWNTs in our sample.
Wang Y, Wu K, Cubero D, et al., 2014, Molecular Modeling and Electron Transport in Polyethylene, IEEE Transactions on Dielectrics and Electrical Insulation, Vol: 21, Pages: 1726-1734, ISSN: 1558-4135
Polyethylene is commonly used as an insulator for AC power cables. However it is known to undergo chemical and physical change which can lead to dielectric breakdown. Despite almost eighty years of experimental characterization of its electrical properties, very little is known about the details of the electrical behaviour of this material at the molecular level. An understanding of the mechanisms of charge trapping and transport could help in the development of materials with better insulating properties required for the next generation of high voltage AC and DC cables. Molecular simulation techniques provide a unique tool with which to study dielectric processes at the atomic and electronic level. Here we summarise simulation methodologies which have been used to study the properties of PE at the molecular level, elucidating the role of morphology in the trapping of excess electrons. We find that polyethylene has localised states due to conformational trapping extending below the mobility edge (above which the electrons are delocalised), at -0.1¿¿0.1eV with respect to the vacuum level. These trap states with localisation lengths between 0.3 and 1.2nm have energies as low as -0.4+0.1eV in the amorphous and interfacial regions of polyethylene with more positive values in lamella structures. Crystalline regions have a mobility edge at +0.46 +0.1eV, so we would expect transport by electrons excited above the mobility edge to delocalised states to be predominantly through amorphous regions if they percolate the sample.
We report computer simulations of an excess electron in various structural motifs of polyethylene at room temperature, including lamellar and interfacial regions between amorphous and lamellae, as well as nanometre-sized voids. Electronic properties such as density of states, mobility edges, and mobilities are computed on the different phases using a block Lanczos algorithm. Our results suggest that the electronic density of states for a heterogeneous material can be approximated by summing the single phase density of states weighted by their corresponding volume fractions. Additionally, a quantitative connection between the localized states of the excess electron and the local atomic structure is presented.
de Frein C, Lestini E, Quirke N, et al., 2013, Environmental effects on the Raman spectra of single walled carbon nanotubes, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, Vol: 250, Pages: 2635-2638, ISSN: 0370-1972
de Frein C, Quirke N, Zerulla D, 2013, Finite length and solvent analysis effects on the squash mode of single walled carbon nanotubes, APPLIED PHYSICS LETTERS, Vol: 103, ISSN: 0003-6951
Wang Y, Wu K, Cubero D, et al., 2013, Electron Trapping in Polyethylene, 11th IEEE International Conference on Solid Dielectrics (ICSD), Publisher: IEEE, Pages: 19-22, ISSN: 1553-5282
Groombridge M, Schneemilch M, Quirke N, 2011, Slip boundaries in nanopores, MOLECULAR SIMULATION, Vol: 37, Pages: 1023-1030, ISSN: 0892-7022
Schneemilch M, Quirke N, 2010, Molecular dynamics of nanoparticle translocation at lipid interfaces, MOLECULAR SIMULATION, Vol: 36, Pages: 831-835, ISSN: 0892-7022
Zhang Q, Chan K-Y, Quirke N, 2009, Molecular dynamics simulation of water confined in a nanopore of amorphous silica, MOLECULAR SIMULATION, Vol: 35, Pages: 1215-1223, ISSN: 0892-7022
Whitby M, Cagnon L, Thanou M, et al., 2008, Enhanced fluid flow through nanoscale carbon pipes, NANO LETTERS, Vol: 8, Pages: 2632-2637, ISSN: 1530-6984
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