Nanomechanics

Résumé

Nanomechanics is a branch of nanoscience studying fundamental mechanical (elastic, thermal and kinetic) properties of physical systems at the nanometer scale. Nanomechanics has emerged on the crossroads of biophysics, classical mechanics, solid-state physics, statistical mechanics, materials science, and quantum chemistry. As an area of nanoscience, nanomechanics provides a scientific foundation of nanotechnology. Nanomechanics is that branch of nanoscience which deals with the study and application of fundamental mechanical properties of physical systems at the nanoscale, such as elastic, thermal and kinetic material properties. Often, nanomechanics is viewed as a branch of nanotechnology, i.e., an applied area with a focus on the mechanical properties of engineered nanostructures and nanosystems (systems with nanoscale components of importance). Examples of the latter include nanomachines, nanoparticles, nanopowders, nanowires, nanorods, nanoribbons, nanotubes, including carbon n

Source officielle

https://en.wikipedia.org/wiki/Nanomechanics

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Publications associées (26)

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In this course we will see an overview of the exciting field of Micro and Nanomechanical systems. We will go over the dfferent scaling laws that dominate the critical parameters, how size affects material properties, how these devices are manufactured, designed and later used.

This course explains the origin of optical and electrical properties of semiconductors. The course elaborates how they change when the semiconductors are reduced to sizes of few nanometers. The course provides also the basis to use software to calculate the properties of hetero/nanostructures.

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Adaptation of Pseudomonas aeruginosa to constant sub-inhibitory concentrations of quaternary ammonium compounds

Myriam Borgatta, Florian Frédéric Vincent Breider, Giovanni Dietler, Sandor Kasas, Leonardo Venturelli, Urs von Gunten

Quaternary ammonium compounds (QACs) are widely used in consumer products for disinfection purposes. QACs are frequently detected in aquatic systems at sub-inhibitory concentrations and were found to affect the development of antimicrobial resistance if bacteria are exposed to increasing concentrations. However, the effect of a constant sub-inhibitory concentration on the development of bacterial resistance is unknown. A constant exposure to 88% of the minimum inhibitory concentration (MIC) of benzalkonium chloride (BAC) led to an increase of the MIC of P. aeruginosa. It increased from 80 mg l-1 to 150 mg l-1 after 10 cycles of exposure and remained stable after removal of BAC. When P. aeruginosa was exposed to cetyltrimethyl ammonium chloride (CTMA), the MIC increased from 110 mg l-1 to 160 mg l-1 after 10 cycles of exposure and decreased to 120 mg l-1 after removal of CTMA. Additionally, cross-resistance between the QACs was observed. When exposed to BAC, the MIC for CTMA increased from 110 mg l-1 to 200 mg l-1, and when exposed to CTMA, the MIC for BAC increased from 80 mg l-1 to 160 mg l-1. In contrast, the susceptibility to 16 antibiotics was not significantly affected by exposure to QACs. Finally, analyses of the membranes’ nanomechanical properties of P. aeruginosa with atomic force microscopy (AFM) showed increases in cell roughness, adhesion and stiffness after treatment with CTMA. Since sub-inhibitory concentrations of QACs can be detected in aquatic systems, this may lead to a dissemination of bacteria with higher QAC resistance in the environment.

2020

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This thesis presents, develops and applies new methodologies that can quantitatively probe the mechanical and viscoelastic properties of biomaterials at the nanoscale. Elastic and viscous properties are important characteristics of materials, such as many kinds of polymers and polymer solutions, colloidal solutions, but also many biological materials like cells or tissues. Very often, especially biological samples are difficult to obtain in large quantities, and measuring their mechanical properties requires the use of novel techniques that are based on local probing down to the nanoscale, like Atomic Force Microscopy (AFM) or Optical Trapping Interferometry (OTI). First we present a study on the mechanical properties of a single vimentin intermediate filament by elastically deforming it with the tip of an AFM. The resulting deflection gives a direct information on the elastic deformation of the filament itself. The bending modulus of native, non-stabilized IFs was found to be between 300 and 400 MPa. Our results together with the ones of previous works, suggest that IFs present axial sliding between their constitutive dimers, and therefore have a bending stiffness that depends on the filament length. To reduce the axial sliding between subunits, we stabilized vimentin by crosslinking with glutaraldehyde, which allowed us to conclude on a lower limit estimate of the filaments' Young's modulus. After, we present the development of a new tool for one-particle microrheology to measure locally viscoelastic properties of complex fluids with unprecedented bandwidth and resolution. Microrheology allows the characterization of very small quantities of a soft sample in a minimally invasive way, by tracking the Brownian motion of an embedded micron-sized spherical probe only driven by thermal energy. The storage modulus quantifies the elastic energy stored in the system, whereas the loss modulus is a measure for the damping due to viscosity. The method of choice to record the trajectory of the Brownian probe embedded in a complex fluid is Optical Trapping Interferometry (OTI). The optical trap has a twofold function: it ensures that the particle remains within the detector range, and it provides a light source for the position detection. By correctly calibrating the position signal of our detector, we validated a recently developed method, which is independent of any a priori assumption on the medium's viscosity and we could show that OTI can be used as a true in situ viscometer. By achieving considerable improvement in the spatio-temporal resolution of OTI, down to the nanometer and microsecond range, we could access timescales at which the inertia of the probed fluid becomes detectable. The high sensitivity of our set-up allowed us to calculate the velocity autocorrelation function (VAF) of the Brownian particle's motion at short times, where the VAF is very sensitive to the dynamics of thermal fluctuations, and hence to the nature of the structures interacting in the immediate vicinity of the probe. With such advance, we were able to track the dynamics of our Brownian microsphere, confined by a viscoelastic model polymer. Additionally to the viscoelastic modulus G*(ω), characteristic to each solution that we studied, we found that the velocity correlation function exhibits a positive or negative power-law behavior, which is strongly dependant on the solution's morphology, like polymer concentration, length, and mesh size of the network.

EPFL2008

Chargement

Swelling Behavior and Nanomechanical Properties of (Peptide-Modified) Poly(2-hydroxyethyl methacrylate) and Poly(poly(ethylene glycol) methacrylate) Brushes

Solenne Desseaux, Juan Pablo Hinestrosa Salazar, Harm-Anton Klok, Nicolas Bertrand Schüwer, Kislon Voitchovsky

Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(poly(ethylene glycol) methacrylate) (PPEGMA) brushes represent a class of thin, surface-tethered polymer films that have been extensively used e.g. to generate non-biofouling surfaces or as model systems to study fundamental biointerfacial questions related to cell-surface interactions. As the properties of PHEMA and PPEGMA brushes depend on the hydration and swelling of these thin films, it is important to understand the influence of basic structural parameters such as the composition of the polymer brush, the film thickness, or grafting density on these phenomena. This article reports results of a series of experiments that were performed to investigate the swelling behavior and mechanical properties of a diverse library of PHEMA and PPEGMA brushes covering a range of film thicknesses and grafting densities. The swelling ratios of the PHEMA and PPEGMA brushes were determined by ellipsometry and neutron reflectivity experiments and ranged from similar to 1.5 to similar to 5.0. Decreasing the grafting density and decreasing the film thickness generally results in an increase in the swelling ratio. Modification of the PHEMA and PPEGMA brushes with the cell adhesive RGD peptide ligand was found to result in a decrease in the swelling ratio. The neutron reflectivity experiments further revealed that solvated PHEMA and PPEGMA brushes are best described by a two-layer model, consisting of a polymer-rich layer close to the substrate and a second layer that is swollen to a much higher degree at the brush water interface.

2016

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EPFL2008