Matthew Blunt - Academia.edu (original) (raw)

Papers by Matthew Blunt

The Journal of Physical Chemistry C, 2018

The development of supramolecular synthons capable of driving hierarchical two-dimensional self-a... more The development of supramolecular synthons capable of driving hierarchical two-dimensional self-assembly is an important step towards the growth of complex and functional molecular surfaces. In this work the formation of nucleobase quartets consisting of adenine and thymine groups was used to control the 2D self-assembly of porphyrins. Tetra-(phenylthymine) zinc porphyrin (Zn-tetra-TP) and tetra-(phenyladenine) porphyrin (tetra-AP) were synthesised and scanning tunneling microscopy (STM) experiments performed to visualize their self-assembly at the liquid-solid interface between an organic solvent and a graphite surface. Mono-component solutions of both Zn-tetra-TP and tetra-AP form stable 2D structures with either thyminethymine or adenine-adenine hydrogen bonding. Structural models based on STM data were validated using molecular mechanics (MM) simulations. In contrast, bi-component mixtures showed the formation of a structure with p4 symmetry consisting of alternating Zn-tetra-TP and tetra-AP molecules in a chessboard type pattern. The relative positions of the porphyrin components were identified from STM images via contrast changes associated with the zinc atom present in Zn-tetra-TP. MM simulations suggest that hydrogen bonding interactions within these structures are based on the formation of adenine-thymine (ATAT) quartets with Watson-Crick base pairing between adenine and thymine groups.

Patterns and pathways in nanoparticle self-organization

Oxford Handbooks Online, 2017

This article reviews relatively recent forms of self-assembly and self-organization that have dem... more This article reviews relatively recent forms of self-assembly and self-organization that have demonstrated particular potential for the assembly of nanostructured matter, namely biorecognition and solvent-mediated dynamics. It first considers the key features of self-assembled and self-organized nanoparticle arrays, focusing on the self-assembly of nanoparticle superlattices, the use of biorecognition for nanoparticle assembly, and self-organizing nanoparticles. It then describes the mechanisms and pathways for charge transport in nanoparticle assemblies, with particular emphasis on the relationship between the current–voltage characteristics and the topology of the lattice. It also discusses single-electron conduction in nanoparticle films as well as pattern formation and self-organization in dewetting nanofluids.

Chemical communications (Cambridge, England), Jan 20, 2016

Two-dimensional covalent-organic frameworks (2D-COFs) on surfaces offer a facile route to new 2D ... more Two-dimensional covalent-organic frameworks (2D-COFs) on surfaces offer a facile route to new 2D materials. Schiff-base condensation reactions have proven to be an effective fabrication route for such materials. We present scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) studies of porphyrin 2D-COFs grown at a solid-vapour interface. XPS shows that covalent links between porphyrins consist of a mixture of imines and hemiaminals, a non-conjugated intermediate in the Schiff-base condensation reaction. These results demonstrate that environmental conditions during growth can have an important impact on the chemical composition of Schiff-base 2D-COFs.

This work is centered on the study of self-organisation and pattern formation in a prototypical n... more This work is centered on the study of self-organisation and pattern formation in a prototypical nanostructured system, namely colloidal nanoparticle assemblies. The particular system chosen for investigation, Au nanocrystals spin cast onto silicon substrates from a solvent, despite being chemically rather simple exhibits a rich variety of complex patterns. In the majority of experiments discussed in this thesis, far-from-equilibrium conditions are attained by a spin-casting process which drives rapid solvent evaporation. A systematic study was carried out to determine the various factors affecting the morphology of nanoparticle assemblies produced in this manner. These Thanks must also go to Dr. Mathias Brust (the

Chem. Sci., 2015

The synthesis and surface-based self-assembly of thymine-functionalised porphyrins is described.

Science, 2008

A molecular network that exhibits critical correlations in the spatial order that is characterist... more A molecular network that exhibits critical correlations in the spatial order that is characteristic of a random, entropically stabilized, rhombus tiling is described. Specifically, we report a random tiling formed in a two-dimensional molecular network of p -terphenyl-3,5,3′,5′-tetracarboxylic acid adsorbed on graphite. The network is stabilized by hexagonal junctions of three, four, five, or six molecules and may be mapped onto a rhombus tiling in which an ordered array of vertices is embedded within a nonperiodic framework with spatial fluctuations in a local order characteristic of an entropically stabilized phase. We identified a topological defect that can propagate through the network, giving rise to a local reordering of molecular tiles and thus to transitions between quasi-degenerate local minima of a complex energy landscape. We draw parallels between the molecular tiling and dynamically arrested systems, such as glasses.

Proceedings of the National Academy of Sciences, 2009

We have recently shown that p -terphenyl-3,5,3′,5′-tetracarboxylic acid adsorbed on graphite self... more We have recently shown that p -terphenyl-3,5,3′,5′-tetracarboxylic acid adsorbed on graphite self-assembles into a two-dimensional rhombus random tiling. This tiling is close to ideal, displaying long-range correlations punctuated by sparse localized tiling defects. In this article we explore the analogy between dynamic arrest in this type of random tilings and that of structural glasses. We show that the structural relaxation of these systems is via the propagation–reaction of tiling defects, giving rise to dynamic heterogeneity. We study the scaling properties of the dynamics and discuss connections with kinetically constrained models of glasses.

Physical Review Letters, 2007

We have achieved highly localized control of pattern formation in two-dimensional nanoparticle as... more We have achieved highly localized control of pattern formation in two-dimensional nanoparticle assemblies by direct modification of solvent dewetting dynamics. A striking dependence of nanoparticle organization on the size of atomic force microscope-generated surface heterogeneities is observed and reproduced in numerical simulations. Nanoscale features induce a rupture of the solvent-nanoparticle film, causing the local flow of solvent to carry nanoparticles into confinement. Microscale heterogeneities instead slow the evaporation of the solvent, producing a remarkably abrupt interface between different nanoparticle patterns.

Physical Review Letters, 2008

The growth of fingering patterns in dewetting nanofluids (colloidal solutions of thiol-passivated... more The growth of fingering patterns in dewetting nanofluids (colloidal solutions of thiol-passivated gold nanoparticles) has been followed in real-time using contrast-enhanced video microscopy. The fingering instability on which we focus here arises from evaporatively-driven nucleation and growth in a nanoscopically thin "precursor" solvent film behind the macroscopic contact line. We find that well-developed isotropic fingering structures only form for a narrow range of experimental parameters. Numerical simulations, based on a modification of the Monte Carlo approach introduced by Rabani et al. [Nature 426, 271 (2003)], reproduce the patterns we observe experimentally.

Physical Review E, 2010

The assembly of molecular networks into structures such as random tilings and glasses has recentl... more The assembly of molecular networks into structures such as random tilings and glasses has recently been demonstrated for a number of two-dimensional systems. These structures are dynamicallyarrested on experimental timescales so the critical regime in their formation is that of initial growth. Here we identify a transition from energetic to entropic stabilisation in the nucleation and growth of a molecular rhombus tiling. Calculations based on a lattice gas model show that clustering of topological defects and the formation of faceted boundaries followed by a slow relaxation to equilibrium occurs under conditions of energetic stabilisation. We also identify an entropicallystabilised regime in which the system grows directly into an equilibrium configuration without the need for further relaxation. Our results provide a methodology for identifying equilibrium and nonequilibrium randomness in the growth of molecular tilings, and we demonstrate that equilibrium spatial statistics are compatible with exponentially slow dynamical behaviour.

Physical Review E, 2008

Various experimental settings that involve drying solutions or suspensions of nanoparticles-often... more Various experimental settings that involve drying solutions or suspensions of nanoparticles-often called nanofluids-have recently been used to produce structured nanoparticle layers. In addition to the formation of polygonal networks and spinodal-like patterns, the occurrence of branched structures has been reported. After reviewing the experimental results we use a modified version of the Monte Carlo model first introduced by Rabani et al. [Nature 426, 271 (2003)] to study structure formation in evaporating films of nanoparticle solutions for the case that all structuring is driven by the interplay of evaporating solvent and diffusing nanoparticles. After introducing the model and its general behavior we focus on receding dewetting fronts which are initially straight but develop a transverse fingering instability. We analyze the dependence of the characteristics of the resulting branching patterns on the driving effective chemical potential, the mobility and concentration of the nanoparticles, and the interaction strength between liquid and nanoparticles. This allows us to understand the underlying instability mechanism.

Nature Chemistry, 2010

Self-assembly of planar molecules on a surface can result in the formation of a wide variety of c... more Self-assembly of planar molecules on a surface can result in the formation of a wide variety of close-packed or porous structures. Two-dimensional porous arrays provide host sites for trapping guest species of suitable size. Here we show that a non-planar guest species (C 60) can play a more complex role by promoting the growth of a second layer of host molecules (p-terphenyl-3,5,3 ′′ ,5 ′′-tetracarboxylic acid) above and parallel to the surface so that self-assembly is extended into the third dimension. The addition of guest molecules and the formation of the second layer are co-dependent. Adding a planar guest (coronene) can displace the C 60 and cause reversion to a monolayer arrangement. The system provides an example of a reversible transformation between a planar and a non-planar supramolecular network, an important step towards the controlled self-assembly of functional, three-dimensional, surface-based supramolecular architectures.

Nature Chemistry, 2011

Homochirality is essential to many biological systems, and plays a pivotal role in various techno... more Homochirality is essential to many biological systems, and plays a pivotal role in various technological applications. The generation of homochirality and an understanding of its mechanism from the single-molecule to supramolecular level have received much attention. Two-dimensional chirality is a subject of intense interest due to the unique possibilities and consequences of confining molecular self-assembly to surfaces or interfaces. Here, we report the perfect generation of twodimensional homochirality of porous molecular networks at the liquid-solid interface in two different ways: (i) by selfassembly of homochiral building blocks and (ii) by self-assembly of achiral building blocks in the presence of a chiral modifier via a hierarchical structural recognition process, as revealed by scanning tunnelling microscopy. The present results provide important impetus for the development of two-dimensional crystal engineering and may afford opportunities for the utilization of chiral nanowells in chiral recognition processes, as nanoreactors and as data storage systems.

Nano Letters, 2007

The transport of electrons through topologically complex two-dimensional Au nanoparticle networks... more The transport of electrons through topologically complex two-dimensional Au nanoparticle networks has been investigated using a combination of low temperature (4.5 K) direct current I(V) measurements and numerical simulations. Intricate, spatially correlated nanostructured networks were formed via spin-casting. The topological complexity of the nanoparticle assemblies produces I(V) curves associated with nonlinearity exponents, ∼ 4.0. Simulations based on tunneling transport in sparse and inhomogeneous planar networks are used to elucidate the influence of topology on the value of .

Langmuir, 2010

The effect on 2D molecular crystallization caused by the addition of propylthioether side groups ... more The effect on 2D molecular crystallization caused by the addition of propylthioether side groups to the 3,4,9,10perylenetetracarboxylic dianhydride (PTCDA) molecule is investigated using scanning tunneling microscopy (STM). The molecule was deposited from 1-phenyloctane onto highly oriented pyrolytic graphite (HOPG) and imaged at the liquid-solid interface. We observe a different structure to previously reported arrangements of PTCDA due to the presence of the propylthioether side groups which inhibits the formation of the herringbone phase. A model, supported by calculations based on density functional theory, is proposed in which molecules form rows stabilized by hydrogen bonding.

Journal of the American Chemical Society, 2011

Journal of Physics: Condensed Matter, 2009

We review recent experiments on dewetting thin films of evaporating colloidal nanoparticle suspen... more We review recent experiments on dewetting thin films of evaporating colloidal nanoparticle suspensions (nanofluids) and discuss several theoretical approaches to describe the ongoing processes including coupled transport and phase changes. These approaches range from microscopic discrete stochastic theories to mesoscopic continuous deterministic descriptions. In particular, we focus on (i) a microscopic kinetic Monte Carlo model, (ii) a dynamical density functional theory and (iii) a hydrodynamic thin film model. Models (i) and (ii) are employed to discuss the formation of polygonal networks, spinodal and branched structures resulting from the dewetting of an ultrathin 'postcursor film' that remains behind a mesoscopic dewetting front. We highlight, in particular, the presence of a transverse instability in the evaporative dewetting front which results in highly branched fingering structures. The subtle interplay of decomposition in the film and contact line motion is discussed. Finally, we discuss a simple thin film model (iii) of the hydrodynamics on the mesoscale. We employ coupled evolution equations for the film thickness profile and mean particle concentration. The model is used to discuss the self-pinning and de-pinning of a contact line related to the 'coffee-stain' effect. In the course of the review we discuss the advantages and limitations of the different theories, as well as possible future developments and extensions.

Journal of Materials Chemistry, 2011

Atomic force microscopy measurements as a function of annealing temperature, time of exposure to ... more Atomic force microscopy measurements as a function of annealing temperature, time of exposure to a high relative humidity environment, and scan duration/parameters have been used to ascertain the stability of assemblies of thiol-passivated Au nanoparticles on silicon substrates. Striking changes in the morphology of self-organised nanoparticle patterns are observed following the exposure of samples to atmospheres with a relative humidity of 80%. The nanoparticle film dewets the underlying silicon substrate on exposure to water, forming locally thicker regions. Time-lapse imaging shows that the dewetting proceeds via layer-by-layer growth, and there is no evidence for classical coarsening mechanisms involving self-similar film morphologies. Annealing at temperatures between 100 C and 160 C produces a rather different dewetting effect for the highest temperatures and/or annealing times, where significant nanoparticle sintering promotes the break-up of the two-dimensional assembly. The morphology of the initial 2D film plays a key role in determining the time scale on which annealing promotes nanoparticle dewetting. Dewetting can also be induced by a scanning probe such that localised (micron-scale) areas of the nanoparticle assembly can be converted from 2D to 3D character.