Cédric Plassard

Conformation of Adsorbed Comb Copolymer Dispersants

Comb copolymers with an adsorbing backbone and nonadsorbing side chains can be very effective dispersants, particularly when a high ionic strength strongly penalizes electrostatic stabilization. For this reason, they have become essential components of concrete over the past decade. This article examines the steric hindrance characteristics of such polymers through the use of atomic force microscopy (AFM) on calcium silicate hydrate, the main hydration product of Portland cement. It is found that solution and surface properties (hydrodynamic radius, radius of gyration, surface coverage, steric layer thickness) and force-distance curves obtained during AFM measurements can be well described by a scaling approach derived in this paper. This represents the first real quantitative step in relating these properties directly to the molecular structure of such comb copolymer dispersants.

The Role of Adsorption Energy in the Sulfate-Polycarboxylate Competition

This paper describes how the interaction between sulfates and polycarboxylate polymers has become a subject of much discussion and occasional concern over the past years. Laboratory studies have shown that sulfates may prevent some polycarboxylate polymers from adsorbing, which causes a reduction in flow properties of cementitious materials. This seems to have led to the belief that this phenomenon is generally true for all polycarboxylates. In fact, it depends very much on the detailed polymer structure. Examples of this will be shown both with flow examples on paste, and experiments by atomic forces microscopy that illustrate in a very convincing way that this competition does not always turn to the advantage of sulfate ions. Furthermore, it is discussed how the outcome of this competition is governed by variations in the adsorption energy of the polymers.

Mode-synthesizing atomic force microscopy for 3D reconstruction of embedded low-density dielectric nanostructures

Challenges in nanoscale characterization call for non-invasive, yet sensitive subsurface characterization of low-density materials such as polymers. In this work, we present new evidence that mode-synthesizing atomic force microscopy can be used to detect minute changes in low-density materials, such as those engendered in electro-sensitive polymers during electron beam lithography, surpassing all common nanoscale mechanical techniques.Moreover, we propose 3D reconstruction of the exposed polymer regions using successive high-resolution frames acquired at incremental depths inside the sample. In addition, the results clearly show the influence of increasing dwell time on the depth profile of the nano-sized exposed regions. Hence, the simple approach described here can be used for achieving sensitive nanoscale tomography of soft materials with promising applications in material sciences and biology.

Polymer Physics and Superplasticizers

This paper describes how the increased performance of polycarboxylate superplasticizers is generally explained by the steric hindrance they are intended to develop between cement particles. In fact, direct evidence of this is relatively scarce. The only direct measurements to date have been made by atomic force microscopy on model surfaces of magnesium oxide. This paper reports very recent measurements using the same technique but on surfaces of calcium silicate hydrate that constitute a more realistic model system. Furthermore, it is shown that the measured interfacial behavior of superplasticizers can be quantified by a scaling law approach borrowed and extended from polymer physics.

Mode-synthesizing atomic force microscopy for volume characterization of mixed metal nanoparticles.

Atomic force microscopy (AFM) and other techniques derived from AFM have revolutionized the understanding of materials and biology at the nanoscale, but mostly provide surface properties. The observation of subsurface nanoscale features and properties remains a great challenge in nanometrology. The operating principle of the mode‐synthesizing AFM (MSAFM) is based on the interaction of two ultrasonic waves, one launched by the AFM probe fp, a second launched by the sample fs, and their resulting nonlinear frequency mixing. Recent developments highlighted the need for quantitative correlation between the role of the frequency actuation of the probe fp and the sample fs. Here we present the great potential of MSAFM for advanced volume characterization of metallic nanoparticles presenting a multilayered structure composed of a nickel core surrounded by a gold envelope.

SOLID SOLUTION CHARACTERIZATION IN METAL BY ORIGINAL TOMOGRAPHIC SCANNING MICROWAVE MICROSCOPY TECHNIQUE

A general challenge in metallic components is the need for materials research to improve the service lifetime of the structural tanks or tubes subjected to harsh environments or the storage medium for the products. One major problem is the formation of lightest chemical elements bubbles or different chemical association, which can have a significant impact on the mechanical properties and structural stability of materials. The high migration mobility of these light chemical elements in solids presents a challenge for experimental characterization. Here, we present work relating to an original non-destructive, with high spatial resolution, tomographic technique based on Scanning Microwave Microscopy (SMM), which is used to visualize in-depth chemical composition of solid solution of a light chemical element in a metal. The experiments showed the capacity of SMM to detect volume. Measurements realized at different frequencies give access to a tomographic study of the sample.