Common mechanism of thermodynamic and mechanical origin for ageing and crystallisation of glasses

The glassy state is known to undergo slow structural relaxation, where the system progressively explores lower free-energy minima which are either amorphous (ageing) or crystalline (devitrification). Recently, there is growing interest in the unusual intermittent collective displacements of a large number of particles known as "avalanches". However, their structural origin and dynamics are yet to be fully addressed. Here, we study hard-sphere glasses which either crystallise or age depending on the degree of size polydispersity, and show that a small number of particles are thermodynamically driven to rearrange in regions of low density and bond orientational order. This causes a transient loss of mechanical equilibrium which facilitates a large cascade of motion. Combined with previously identified phenomenology, we have a complete kinetic pathway for structural change which is common to both ageing and crystallisation. Furthermore, this suggests that transient force balance is what distinguishes glasses from supercooled liquids.Comment: 13 pages, 13 figure

From ultra-fast growth to avalanche growth in devitrifying glasses

During devitrification, pre-existing crystallites grow by adding particles to their surface via a process which is either thermally activated (diffusive mode), or happens without kinetic barriers (fast crystal growth mode). It is yet unclear what factors determine the crystal growth mode, and how to predict it. With simulations of repulsive hard-sphere glasses, we show for the first time that the same system at the same volume fraction and temperature can devitrify via both modes depending on the preparation protocol of the glass. We prepare two types of glass, a conventional glass (CG) via fast quenching and a uniform glass (UG) via density homogenization. Firstly, we bring either glass into contact with a crystal (X) and find the inherent structure (CGX/UGX). During energy minimization, the crystal front grows deep into the CG interface, while the growth is minimal for UG. When thermal noise is added, this behavior is reflected in different crystallization dynamics. CGX exhibits a density drop at the crystal growth front, leading to enhanced dynamics at the interface and a fast growth mode. This mechanism may explain the faster crystal growth observed below the glass transition experimentally. In contrast, UGX grows via intermittent avalanche-like dynamics localized at the interface, a combination of localized mechanical defects and the exceptional mechanical stability imposed by the UG glass phase.Comment: 23 pages, 8 figure

Towards glasses with permanent stability

Unlike crystals, glasses age or devitrify over time, reflecting their non-equilibrium nature. This lack of stability is a serious issue in many industrial applications. Here, we show by numerical simulations that the devitrification of quasi-hard-sphere glasses is prevented by suppressing volume fraction inhomogeneities. A monodisperse glass known to devitrify with `avalanche'-like intermittent dynamics is subjected to small iterative adjustments to particle sizes to make the local volume fractions spatially uniform. We find that this entirely prevents structural relaxation and devitrification over aging time scales, even in the presence of crystallites. There is a dramatic homogenization in the number of load-bearing nearest neighbors each particle has, indicating that ultra-stable glasses may be formed via `mechanical homogenization'. Our finding provides a physical principle for glass stabilization and opens a novel route to the formation of mechanically stabilized glasses.Comment: 6 pages, 4 figures, 1 ancillary video file, 1 supplementary PD

Interactions between colloids induced by a soft cross-linked polymer substrate

Using video-microscopy imaging we demonstrate the existence of a short-ranged equilibrium attraction between heavy silica colloids diffusing on soft surfaces of cross-linked polymer gels. The inter-colloid potential can be tuned by changing the gel stiffness or by coating the colloids with a polymer layer. On sufficiently soft substrates, the interaction induced by the polymer matrix leads to large-scale colloidal aggregation. We correlate the in-plane interaction with a colloid-surface attraction

Reconstruction of submarine eruption processes from FTIR volatile analysis of marine tephra: Example of Oomurodashi volcano, Japan

Tephra layers in marine sediments are widely used to correlate and date paleoclimate and paleoceanography records, and to determine spatiotemporal changes in magmatic evolution and eruption frequency. Dissolved matrix glass H2O contents of marine tephra could potentially inform understanding of eruption processes but are rarely used due to the issue of secondary hydration after deposition. Recent advancements in Fourier transform infrared spectroscopy (FTIR) volatile analysis have enabled reconstruction of original water contents of hydrated volcanic glasses. These new Fourier transform infrared spectroscopy analysis methods offer a new way to investigate tephra stored in marine sedimentary archives. We present a case study of the Od-1 tephra layer in marine sedimentary core C9010E, drilled ∼40 km south of the Boso peninsula in Japan. This tephra was erupted by the shallow silicic submarine Oomurodashi volcano in the northern Izu-Bonin arc at ∼13.5 ka. Our Fourier transform infrared spectroscopy volatile data show it has been affected by secondary hydration, with the extent of hydration controlled by grain size and porosity characteristics. Numerical modelling of low temperature hydration suggests Fourier transform infrared spectroscopy data offer an additional method for estimating eruption ages of marine tephra. OH contents, unaltered by low temperature secondary hydration, record low ambient eruptive pressures for all grain sizes and tephra types i.e., blocky and dense or pumiceous. Consideration of hydrostatic pressure gradients and past sea level at Oomurodashi shows that the majority of tephra volatile data cannot be explained by quench within a submarine eruption plume. Instead, OH contents record quench fragmentation within the shallow submarine edifice. Physical characteristics of the tephra are consistent with the formation of these tephra by explosive phreatomagmatic eruption processes. Together these OH data and tephra characteristics support the interpretation that the Od-1 tephra layer was formed by the same shallow phreatomagmatic eruption that formed the existing Oomuro Hole crater and that produced subaerial tephra deposits on nearby Izu-Oshima and Toshima islands. This study demonstrates the crucial contribution that imaging Fourier transform infrared spectroscopy analysis can make to the interpretation of degassing and eruption processes of volcanic glasses, particularly vesicular pyroclasts and/or glasses affected by secondary hydration, adding an important new dimension to marine tephra research

DNA-colloid systems and micro-rheology

This thesis is not available on this repository until the author agrees to make it public. If you are the author of this thesis and would like to make your work openly available, please contact us: [email protected] Library can supply a digital copy for private research purposes; interested parties should submit the request form here: http://www.lib.cam.ac.uk/collections/departments/digital-content-unit/ordering-imagesPlease note that print copies of theses may be available for consultation in the Cambridge University Library's Manuscript reading room. Admission details are at http://www.lib.cam.ac.uk/collections/departments/manuscripts-university-archivesWe investigate the behaviour of DNA-colloid systems using micro-rheology, with a view to demonstrating the efficacy of passive particle-tracking methodologies and developing entirely new systems. Chapter 1 introduces the fields of DNA coated colloids (DNACCs) and passive micro-rheology, with a particular fo cus on the challenges of creating an equilibrating DNACC system and the practicalities and limitations of passive microrheology in gaining access to valid rheological information. In Chapter 2, we present a newly developed realtime monitoring algorithm for complex moduli in optical tweezer micro-rheology sys,tems. Further to eliminating high frequency artefacts, our method is memory light and computationally efficient. Chapter 3 investigates the dynamics of ADNA coated colloids using Brownian Dynamics simulation and a theoretical model, also applying the algorithm developed in Chapter 2. A two-regime diffusivity is identified, in contrast to previous works, which simply found an increased hydrodynamic size. Chapter 4 looks at tuning the hydrophobicity of silica particles using poly(L)lysinepolyethylene glycol (PLL-PEG). We find an incubation pH dependence on their coverage. From analysing video microscopy trajectories, PLL-PEG coated beads sedimented onto A-DNA brushes are found to be significantly more diffusive. In Chapter 5, we int roduce an entirely new DNACC system, the functionalised fd bacteriophage, where high aspect ratio filamentous virions are coated with short oligonucleotides. Aggregation behaviour is confirmed with Atomic Force Microscopy and Dynamic Light Scattering, and systems where rods can act as a linker between spherical particles are also briefly investigated

Diffusive behaviour of PLL–PEG coated colloids on λ-DNA brushes – tuning hydrophobicity

We find ‘sticky’ 2D diffusion of poly-L-lysine–polyethylene glycol (PLL–PEG) coated silica colloids sedimented onto a brush of long, double stranded λ-DNA. The interaction is hypothesised to be hydrophobic, due to known physical properties of single and double stranded DNA and the systematic elimination of other known forces. The colloids are found to have variable affinity to the surface when prepared at different pH, even when the electrostatic environment of the brush is kept identical. Varied diffusive behaviour is observed: the diffusivity increases when the incubation pH is higher, and fewer beads are stuck to the brush surface. This sensitivity is found to agree with a simple model for the adsorption conditions of the PLL on the silica spheres. The significance of hydrophobicity is confirmed by capping the ssDNA ‘sticky’ end of the DNA, leading to a drastic enhancement of diffusivity of the particles on the brush

Influence of hydrodynamic interactions on colloidal crystallization

One of the biggest unresolved problems in crystallization phenomena is the significant discrepancy in the nucleation rate between experiments and simulations even for the simplest liquid, i.e., the hard-sphere system. A popular explanation for this discrepancy is the neglect of hydrodynamic interactions (HI) in simulation studies. By comparing simulations with and without HI, we show that the long-time diffusive dynamics of the colloids is slowed down more rapidly by hydrodynamic lubrication effects with increasing volume fraction. We find that the kinetics of both nucleation and growth are controlled by this long-time diffusion and that it is possible to account for most of the effects of HI by rescaling with this timescale. Therefore, we conclude that HI is not the primary cause of the accelerated nucleation rates observed in experiments