50 research outputs found
Multiscale Poromechanics of Wet Cement Paste
Capillary effects such as imbibition-drying cycles impact the mechanics of
granular systems over time. A multiscale poromechanics framework was applied to
cement paste, that is the most common building material, experiencing broad
humidity variations over the lifetime of infrastructure. First, the liquid
density distribution at intermediate to high relative humidities is obtained
using a lattice gas density functional method together with a realistic
nano-granular model of cement hydrates. The calculated adsorption/desorption
isotherms and pore size distributions are discussed and compare well to
nitrogen and water experiments. The standard method for pore size distribution
determination from desorption data is evaluated. Then, the integration of the
Korteweg liquid stress field around each cement hydrate particle provided the
capillary forces at the nanoscale. The cement mesoscale structure was relaxed
under the action of the capillary forces. Local irreversible deformations of
the cement nano-grains assembly were identified due to liquid-solid
interactions. The spatial correlations of the nonaffine displacements extend to
a few tens of nm. Finally, the Love-Weber method provided the homogenized
liquid stress at the micronscale. The homogenization length coincided with the
spatial correlation length nonaffine displacements. Our results on the solid
response to capillary stress field suggest that the micronscale texture is not
affected by mild drying, while local irreversible deformations still occur.
These results pave the way towards understanding capillary phenomena induced
stresses in heterogeneous porous media ranging from construction materials,
hydrogels to living systems.Comment: 6 figures in main text, 4 figures in the SI appendi
The crucial effect of early-stage gelation on the mechanical properties of cement hydrates.
Gelation and densification of calcium-silicate-hydrate take place during cement hydration. Both processes are crucial for the development of cement strength, and for the long-term evolution of concrete structures. However, the physicochemical environment evolves during cement formation, making it difficult to disentangle what factors are crucial for the mechanical properties. Here we use Monte Carlo and Molecular Dynamics simulations to study a coarse-grained model of cement formation, and investigate the equilibrium and arrested states. We can correlate the various structures with the time evolution of the interactions between the nano-hydrates during the preparation of cement. The novel emerging picture is that the changes of the physicochemical environment, which dictate the evolution of the effective interactions, specifically favour the early gel formation and its continuous densification. Our observations help us understand how cement attains its unique strength and may help in the rational design of the properties of cement and related materials.This work was supported by the SNSF (Grants No. PP00P2 126483/1 and PP00P2 150738) and George town University, by the Fundamental Research Funds for the Central Universities of P. R. China, ERC Advanced Grant 227758 (COLSTRUCTION), ITN grant 234810 (COMPLOIDS) and by EPSRC Programme Grant EP/I001352/1. KI thanks the French National Research Agency (ICoME2 Labex Project ANR-11-LABX- 0053 and A*MIDEX Project ANR-11-IDEX-0001-02) for support.This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/ncomms1210
A series of Notch3 mutations in CADASIL; insights from 3D molecular modelling and evolutionary analyses
CADASIL disease belongs to the group of rare diseases. It is well established that the Notch3 protein is primarily responsible for the development of CADASIL syndrome. Herein, we attempt to shed light to the actual molecular mechanism underlying CADASIL via insights that we have from preliminary in silico and proteomics studies on the Notch3 protein. At the moment, we are aware of a series of Notch3 point mutations that promote CADASIL. In this direction, we investigate the nature, extent, physicochemical and structural significance of the mutant species in an effort to identify the underlying mechanism of Notch3 role and implications in cell signal transduction. Overall, our in silico study has revealed a rather complex molecular mechanism of Notch3 on the structural level; depending of the nature and position of each mutation, a consensus significant loss of beta-sheet structure is observed throughout all in silico modeled mutant/wild type biological systems
Ion specificity of confined ion-water structuring and nanoscale surface forces in clays
Ion specificity and related Hofmeister effects, ubiquitous in aqueous
systems, can have spectacular consequences in hydrated clays, where
ion-specific nanoscale surface forces can determine large scale cohesive,
swelling and shrinkage behaviors of soil and sediments. We have used a
semi-atomistic computational approach and examined sodium, calcium and aluminum
counterions confined with water between charged surfaces representative of clay
materials, to show that ion-water structuring in nanoscale confinement is at
the origin of surface forces between clay particles which are intrinsically
ion-specific. When charged surfaces strongly confine ions and water, the
amplitude and oscillations of the net pressure naturally emerge from the
interplay of electrostatics and steric effects, which can not be captured by
existing theories. Increasing confinement and surface charge densities promote
ion-water structures that increasingly deviate from the ions' bulk hydration
shells, being strongly anisotropic and persistent, and self-organizing into
optimized, nearly solid-like assemblies where hardly any free water is left. In
these conditions, strongly attractive interactions can prevail between charged
surfaces, due to the dramatically reduced dielectric screening of water and the
highly organized water-ion structures. By unravelling the ion-specific nature
of these nanoscale interactions, we provide evidence that ion-specific
solvation structures determined by confinement are at the origin of ion
specificity in clays and potentially a broader range of confined aqueous
systems.Comment: Main text: 14 pages and 6 figures. Supporting information: 5 figures.
Submitted to The Journal of Physical Chemistry
Capillary stress and structural relaxation in moist granular materials
We propose a theoretical framework to calculate capillary stresses in complex
mesoporous materials, such as moist sand, nanoporous hydrates, and drying
colloidal films. Molecular simulations are mapped onto a phase-field model of
the liquid-vapor mixture, whose inhomogeneous stress tensor is integrated over
Voronoi polyhedra in order to calculate equal and opposite forces between each
pair of neighboring grains. The method is illustrated by simulations of
moisture-induced forces in small clusters and random packings of spherical
grains using lattice-gas Density Functional Theory. For a nano-granular model
of cement hydrates, this approach reproduces the hysteretic water
sorption/desorption isotherms and predicts drying shrinkage strain isotherm in
good agreement with experiments. We show that capillary stress is an effective
mechanism for internal stress relaxation in colloidal random packings, which
contributes to the extraordinary durability of cement paste.Comment: 4 figure
Effect of Confinement on Capillary Phase Transition in Granular Aggregates
Using a 3D mean-field lattice-gas model, we analyze the effect of confinement on the nature of capillary phase transition in granular aggregates with varying disorder and their inverse porous structures obtained by interchanging particles and pores. Surprisingly, the confinement effects are found to be much less pronounced in granular aggregates as opposed to porous structures. We show that this discrepancy can be understood in terms of the surface-surface correlation length with a connected path through the fluid domain, suggesting that this length captures the true degree of confinement. We also find that the liquid-gas phase transition in these porous materials is of second order nature near capillary critical temperature, which is shown to represent a true critical temperature, i.e., independent of the degree of disorder and the nature of the solid matrix, discrete or continuous. The critical exponents estimated here from finite-size scaling analysis suggest that this transition belongs to the 3D random field Ising model universality class as hypothesized by F. Brochard and P.G. de Gennes, with the underlying random fields induced by local disorder in fluid-solid interactions
The Effect of Confinement on Capillary Phase Transition In Granular Aggregates
Utilizing a 3D mean-field lattice-gas model, we analyze the effect of
confinement on the nature of capillary phase transition in granular aggregates
with varying disorder and their inverse porous structures obtained by
interchanging particles and pores. Surprisingly, the confinement effects are
found to be much less pronounced in granular aggregates as opposed to porous
structures. We show that this discrepancy can be understood in terms of the
surface-surface correlation length with a connected path through the fluid
domain, suggesting that this length captures the true degree of confinement. We
also find that the liquid-gas phase transition in these porous materials is of
second order nature near capillary critical temperature, which is shown to
represent a true critical temperature, i.e. independent of the degree of
disorder and the nature of solid matrix, discrete or continuous. The critical
exponents estimated here from finite-size scaling analysis suggest that this
transition belongs to the 3D random field Ising model universality class as
hypothesized by P.G. de Gennes, with the underlying random fields induced by
local disorder in fluid-solid interactions
KardiaTool: An Integrated POC Solution for Non-invasive Diagnosis and Therapy Monitoring of Heart Failure Patients
The aim of this work is to present KardiaTool platform, an integrated Point of Care (POC) solution for noninvasive diagnosis and therapy monitoring of Heart Failure (HF) patients. The KardiaTool platform consists of two components, KardiaPOC and KardiaSoft. KardiaPOC is an easy to use portable device with a disposable Lab-on-Chip (LOC) for the rapid, accurate, non-invasive and simultaneous quantitative assessment of four HF related biomarkers, from saliva samples. KardiaSoft is a decision support software based on predictive modeling techniques that analyzes the POC data and other patient's data, and delivers information related to HF diagnosis and therapy monitoring. It is expected that identifying a source comparable to blood, for biomarker information extraction, such as saliva, that is cost-effective, less invasive, more convenient and acceptable for both patients and healthcare professionals would be beneficial for the healthcare community. In this work the architecture and the functionalities of the KardiaTool platform are presented