Presentation and improvement of an AFM-based system for the measurement of adhesion forces.

International audienceThe aim of this paper is the presentation and improvement of an AFM-based system dedicated to measure adhesion forces. Because an AFM-lever presents a high linearity and a high resolution, it can be used to characterize forces that appears between two micro-objects when their relative distance is small. In this paper, an AFM is used to evaluate the adhesion forces versus the distance. Especially, the pull-off and the Van Der Waals forces can be quantified. Unfortunately, the presence of the hysteresis on the piezotube distorts the measurement and makes the whole system imprecise. Hence, a Prandtl-Ishlinskii hysteresis compensator is introduced. To show the efficiency of the improved measurement system, experiments on different materials where performed

Nanocomposite electrical insulation: multiscale characterization and local phenomena comprehension

Dans le domaine de l'isolation électrique, il a été démontré que les matériaux hybrides organiques/inorganiques nanocomposites (NC) assurent une nette amélioration de leur fonctionnement à haute température/haute tension et permettent aux systèmes d'isolation électrique de renforcer leurs propriétés diélectriques. Récemment, il a été démontré que certaines modifications des propriétés électriques telles que la permittivité, la rupture diélectrique, la résistance aux décharges partielles ou la durée de vie étaient souvent attribuées à l'interphase nanoparticule/matrice, une région où la présence des nanoparticules modifie les propriétés de la matrice. De plus, des études récentes montrent qu'une fonctionnalisation de la surface des nanoparticules permet une meilleure dispersion dans la matrice hôte. Cette meilleure dispersion affecte la zone d'interphase et joue également un rôle majeur dans l'amélioration des propriétés des nanocomposites. Cependant, le rôle de l'interphase reste théorique et peu de résultats expérimentaux existent pour décrire ce phénomène. Par conséquent, en raison de l'échelle nanométrique de l'interphase, une caractérisation de ses propriétés demeure un défi. Au cours de cette thèse, deux études principales sont menées afin de mieux comprendre la relation structure-propriété dans les polymères nanocomposites. Tout d'abord, la microscopie à force atomique (AFM) est utilisée pour effectuer simultanément des mesures qualitatives et quantitatives de ces zones d'interaction dans le nanocomposite polyimide/nitrure de silicium (PI/Si3N4). Le mode Peak Force Quantitative Nano Mechanical (PF QNM) dérivé de l'AFM révèle la présence de l'interphase en mesurant les propriétés mécaniques (module de Young, déformation ou adhérence). Le mode microscopie à force électrostatique (EFM) est utilisé pour détecter et mesurer la permittivité locale de la matrice et de l'interphases. Par ailleurs, l'objectif de ce travail est de présenter l'effet de la fonctionnalisation de surface des nanoparticules de nitrure de silicium (Si3N4) sur les régions d'interphase. Ces résultats quantitatifs, à la fois mécaniques et électriques, permettent de comparer la dimension et les propriétés des interphase autour des nanoparticules traitées et non traitées. Par conséquent, cette nouvelle approche de caractérisation de cette zone confronte les résultats expérimentaux à des modèles théoriques. Un nouveau modèle basé sur les résultats expérimentaux obtenus est proposé. De plus, la deuxième partie de cette étude présente une caractérisation macroscopique des propriétés et de la rigidité diélectrique des films de polyimide pur, du nanocomposite avec des particules traitées et non traités. Les résultats révèlent le rôle de l'interphase sur la réduction du phénomène de polarisation de l'électrode (PE) dû aux mouvements ioniques surtout à haute température. Pour les nanoparticules non traitées, ces effets sont moins importants en raison de la formation d'agrégats. En revanche, une diminution nette de la PE est obtenue en fonctionnalisant la surface des nanoparticules avec le silane comme agent de couplage. Enfin, la rigidité diélectrique de l'ensemble des échantillons est mesurée et montre une augmentation considérable de la performance diélectrique des nanocomposites à haute température par rapport au PI pur.In the electrical insulation field, it was demonstrated that nanocomposite (NC) organic/inorganic hybrid materials assure a distinct improvement of their high temperature/high voltage functioning and allow the electrical insulation to strengthen its dielectric properties. Recently, it was shown that some modifications of the electrical properties such as permittivity, dielectric breakdown, partial discharges resistance or lifetime are often awarded to the nanoparticle/matrix interphase, a region where the presence of the nanoparticle changes the matrix properties. Moreover, recent studies show that the nanoparticle surface functionalization allows a better dispersion of the particles within the host matrix. This better dispersion affects the interphase zone and plays a major role in the nanocomposite properties improvement as well. However, the role of the interphase remains theoretical and few experimental results exist to describe this phenomenon. Accordingly, because of its nanometer scale, the interphase properties characterization remains a challenge. Two main studies are carried out, during this thesis work, that can provide a better understanding of structure-properties relationships in polymer nanocomposite. First, Atomic Force Microscopy (AFM) is employed to make at the same time qualitative and quantitative measurements of these interaction zones within Polyimide/Silicon Nitride (PI/Si3N4) nanocomposite. The Peak Force Quantitative Nano Mechanical (PF QNM) AFM mode reveals the presence of the interphase by measuring mechanical properties (Young modulus, deformation or adhesion). Electrostatic force microscope (EFM) mode is used in order to detect and measure the matrix and interphase local permittivity. Moreover, the aim of this work is to present the effect of the surface functionalization of silicon nitride (Si3N4) nanoparticles on the interphase regions. Mechanical and electrical quantitative results permit comparing the interphase dimension and properties between treated and untreated Si3N4 nanoparticles. As a result, this new approach to characterize the nanocomposite interphase zone using local measurements confronts experimental results with theoretical models. A new model based on the obtained experimental results is proposed. In addition, the second part of this study presents a macroscopic investigation on the dielectric properties and breakdown strength of neat polyimide, untreated and treated nanocomposite films. Results reveal the interphase role on the reduction of the electrode polarization (EP) phenomenon due to ionic movements especially at high temperatures. For untreated nanoparticles, these effects are less important due to the aggregate formation. In contrast, an EP drastic decrease is obtained by functionalizing the nanofiller surface with a silane coupling agent. Finally, the high temperature breakdown strength for all samples is investigated and shows a considerable increase of nanocomposites dielectric performance at high temperature compared to neat PI

Sickle Cell Disease Erythrocyte Stiffness and Cytoadhesion Investigated via Atomic Force Microscopy

The biomechanical properties of red blood cells (RBCs), including increased stiffness and abnormal cytoadherence, are integral components in the cascade of events resulting to vasoocclusive episodes (VOEs) in sickle cell disease (SCD). VOEs are the main cause of morbidity in SCD and sickle cell trait (SCT). Using experimental techniques based on atomic force microscopy (AFM), we studied the stiffness and adhesion of RBCs from SCD patients and from subjects with SCT. We found that SCD and SCT RBCs are three-fold stiffer than normal RBCs. Further, a ten-fold increase in the stiffness of sickled RBCs was measured upon deoxygenation. In an effort to rectify the increased stiffness of sickle RBCs, mice were fed a diet supplemented with docosahexanoic acid (DHA), an omega-3 fatty acid. A decrease in RBC stiffness was measured suggesting therapeutic benefits of DHA. Cytoadherence of RBCs to subendothelial laminin via the basal cell adhesion molecule/Lutheran (BCAM/Lu) is implicated in vasculopathy, a common condition in SCD patients. We established the in vitro technique of single-molecule force spectroscopy (SMFS) which enables detection of single BCAM/Lu proteins on the RBC surface via measurement of the unbinding force with laminin. It was shown that epinephrine, acting through the cyclic adenosine monophosphate (cAMP) signaling pathway, increases the population of active BCAM/Lu receptors on SCT RBCs, suggesting a role in exercise-induced VOEs. The sensitivity of the SMFS system was validated in a neuronal system to quantitatively map SK channels and then employed to investigate the effects of cAMP pathway targeting on BCAM/Lu receptor expression on normal and SCD RBCs. We illustrated that A-kinase anchoring proteins are crucial for BCAM/Lu receptor activation. To examine the relevance of results based on SMFS in the cytoadhesion of entire RBCs, single-cell force spectroscopy (SCFS) was established to measure the adhesion of whole cells with a functionalized substrate. We established a correspondence between the SMFS and SCFS results. Both techniques were able to detect significant changes in the adhesive response of RBCs to cAMP pathway modulation and variability was measured amongst human subjects, suggesting that RBCs maintain diverse intracellular levels of tonic protein kinase A

Accelerating development of suspension pressurized metered dose inhaler formulations: innovative techniques to evaluate particle stability

This thesis presents several innovative techniques to rapidly evaluate particle stability in suspension-based pressurized metered dose inhalers (pMDIs). Chapter 1 reviews techniques available to evaluate particle stability in pMDIs, discussing categories such as particle properties, suspension quality, polymorphism, and long term stability. Emerging techniques such as Liquid Colloidal Probe Microscopy (CPM), Nano X-ray Computer Tomography (NanoXCT), and Pressurized Isothermal Microcalorimetry possess the potential for accelerating pMDI formulation and are developed through the work embodied within this thesis. Chapters 2, 3, and 4 discuss the improvement and application of liquid CPM to evaluate nano-scale interactions between particles of various porosities in a model propellant. Particle porosity/morphology was found to have a significant effect on these interactions; however, direct measurement of internal particle architecture can be challenging. Thus, in chapter 5, a novel technique using NanoXCT was developed to visualize and quantify the internal porosity of inhalable sized particles with a resolution of 50 nm. It is necessary to control morphology through various manufacturing processes such as freeze and spray drying, since these processes can affect particle physical stability in propellant; thus, in chapter 6 an innovative technique using isothermal microcalorimetry was developed to directly evaluate particle stability in actual pMDI formulations. The versatility of the technique is further demonstrated in Chapter 7, through the evaluation of various other pMDI particle parameters such as amorphicity, excipient compatibility, and moisture ingress

Accelerating development of suspension pressurized metered dose inhaler formulations: innovative techniques to evaluate particle stability

This thesis presents several innovative techniques to rapidly evaluate particle stability in suspension-based pressurized metered dose inhalers (pMDIs). Chapter 1 reviews techniques available to evaluate particle stability in pMDIs, discussing categories such as particle properties, suspension quality, polymorphism, and long term stability. Emerging techniques such as Liquid Colloidal Probe Microscopy (CPM), Nano X-ray Computer Tomography (NanoXCT), and Pressurized Isothermal Microcalorimetry possess the potential for accelerating pMDI formulation and are developed through the work embodied within this thesis. Chapters 2, 3, and 4 discuss the improvement and application of liquid CPM to evaluate nano-scale interactions between particles of various porosities in a model propellant. Particle porosity/morphology was found to have a significant effect on these interactions; however, direct measurement of internal particle architecture can be challenging. Thus, in chapter 5, a novel technique using NanoXCT was developed to visualize and quantify the internal porosity of inhalable sized particles with a resolution of 50 nm. It is necessary to control morphology through various manufacturing processes such as freeze and spray drying, since these processes can affect particle physical stability in propellant; thus, in chapter 6 an innovative technique using isothermal microcalorimetry was developed to directly evaluate particle stability in actual pMDI formulations. The versatility of the technique is further demonstrated in Chapter 7, through the evaluation of various other pMDI particle parameters such as amorphicity, excipient compatibility, and moisture ingress

Tools to study cytoadhesion of P. falciparum-infected erythrocytes under flow

Plasmodium falciparum infected erythrocytes are able to bind to a multitude of extracellular receptors through adhesins expressed on their membrane. The molecular interactions involved in parasite binding to these receptors are only partly understood, although the trait itself is well-known and used as an early indicator of severe malaria diagnosis and progress of infection. Binding to the microvasculature of blood vessels or the intervillous spaces of the placenta, ensures the survival of the parasite as it avoids splenic clearance in the later stages of maturation. In this thesis, the importance of sheer flow and cell morphology in binding dynamics of parasitized erythrocytes is further highlighted. While static adhesion assays would showcase similar amounts of cells adhering in different maturation stages, when observed in flow, this picture changes drastically. Trophozoite stage parasites seem to bind less frequently but more efficiently onto the simulated endothelium. In the last stage of maturation, schizont stage parasites alter the cell morphology to such an extent that adhesion is more likely but with less contact area and density of involved receptors. Changes in the membrane morphology between AA and AS erythrocytes also underline the significance of receptor presentation and accessibility influencing binding efficiency. The effects of a P. falciparum infection during primigravida are threatening to both the mother and the foetus, as infected erythrocytes sequester to the maternal side of the syncytiotrophoblast that lines the placenta. Despite the tremendous efforts in the field, the adhesive tropism of infected erythrocytes that leads to placental sequestration remains unsolved. In this thesis, I determined that measurements are not possible without the full length protein and interactions between the receptor and its erythrocyte-expressed ligand are not specific enough to distinguish from negative control experiments. Another form of cell adhesion investigated in this thesis is the formation of so-called rosettes, that form when an infected erythrocyte binds to non-infected erythrocytes. Rosette formation is considered either an indication of severe malaria or a symptom of progressed infection and is believed to propagate the severity of infection by obstructing smaller vasculature and normal blood flow. in this thesis, I developed a platform to study the position of rosettes within a channel in flow, in order to determine their margination tendance. In those experiments, I verified that regardless of haematocrit value and size of rosette, rosettes remain in flow and do not marginate towards the walls of the flow chamber

Study of Thin-Film Surfaces

Disertační práce se zabývá studiem povrchových vlastností jedno a vícevrstvých filmů deponovaných z vinyltriethoxysilanových a tetravinylsilanových monomerů. Zabývá se také charakterizací adheze jednovrstvých filmů z tetravinylsilanu. Plazmaticky polymerizované tenké vrstvy byly připraveny na leštěných křemíkových substrátech pomocí plazmové depozice z plynné fáze za ustálených podmínek. Povrchové vlastnosti vrstev byly charakterizovány pomocí různých metod rastrovací sondové mikroskopie a nanoindentačních technik jako je konvenční a cyklická nanoindentace. Vrypový test byl použit pro charakterizaci vlastností adheze vrstev. Jednovrstvé filmy připravené za různých depozičních podmínek byly charakterizovány s ohledem na povrchové morfologie a mechanické vlastností (modul pružnosti, tvrdost). Výsledky morfologie povrchu, analýzy zrn, nanoindentace, analýzy konečných prvků a modulů mapování pomohly rozlišit hybridní charakter filmů, které byly deponovány při vyšších výkonech RF-výboje. Nový přístup byl použit v povrchové charakterizaci vícevrstvého filmu pomocí rastrovací sondové mikroskopie a nanoindentace. Adhezívní chování plazmaticky polymerizovaných vrstev různých mechanických vlastností a tloušťek bylo analyzováno pomocí normálních a laterálních síl, koeficientu tření, a snímků vrypů získaných pomocí mikroskopie atomárních sil.doctoral thesis deals with the study of surface properties of single-layer and multilayer thin films deposited from of vinyltriethoxysilane and tetravinylsilane monomers. It also deals with adhesion characterization of single layer tetravinylsilane films. The plasma polymerized thin films were prepared under steady-state deposition conditions on polished silicon wafers using plasma-enhanced chemical vapor deposition. The surface properties of the films were been characterized by different scanning probe microscopy methods and nanoindentation techniques such as conventional depth-sensing nanoindentation and load-partial-unload (cyclic) nanoindentation. While, the nanoscratch test was used to characterize the film adhesion properties. Single layer films prepared at different deposition conditions were characterized with respect to surface morphology and mechanical properties (Young’s modulus and hardness). The results of surface morphology, grain analysis, nanoindentation, finite elemental analysis and modulus mapping helped to know the hybrid nature of single layer films that were deposited at higher powers of RF-discharge. A novel approach was used in surface characterization of multilayer film by scanning probe microscopy and nanoindentation. The adhesion behavior of plasma polymer films of different mechanical properties and film thickness were analyzed by normal and lateral forces, friction coefficient, and scratch images obtained by atomic force microscopy.

Surface analysis of xGnP/PEI nanocomposite

Tato Diplomová práce se zabývá povrchovou analýzou nanokompozitní folie polyetherimidu (PEI) vyztuženého exfoliovanými grafitickými nanodestičkami (xGnP). Analyzovány byly take vzorky nevyztužené PEI folie a samostatné nanodestičky. Vzorky nanokompozitu a PEI folie byly plazmaticky leptány s využitím argonového plazmatu po dobu 1, 3 a 10 hod. Skenovací elektronová mikroskopie (SEM) byla použita pro charakterizaci samostatných nanodestiček rozptýlených na křemíkovém substrátu, původních či leptaných vzorků PEI folie a nanokompozitu. Nanodestičky byly identifikovány při povrchu leptané nanokompozitní folie. Mikroskopie atomárních sil (AFM) byla použita pro zobrazení povrchové topografie separovaných nanodestiček a odkrytých destiček při povrchu leptaného kompozitu. Povrchová drsnost (střední kvadratická hodnota, vzdálenost nejnižšího a nejvyššího bodu) leptaného nanokompozitu narůstala s prodlužující se dobou leptání. Akustická mikroskopie atomárních sil (AFAM) byla použita pro charakterizaci elastické anizotropie leptaných kompozitních vzorků. Nanoindentační měření umožnila charakterizaci lokálních mechanických vlastností PEI a nanokompozitních folií.This Diploma thesis deals with surface analysis of nanocomposite foil – polyetherimide matrix (PEI) reinforced by exfoliated graphite nanoplatelets (xGnP). The PEI foil without reinforcement and separate xGnP particles were also analysed. Samples of the nanocomposite and the PEI foil were etched for various times by argon plasma. Scanning electron microscopy (SEM) was used to characterize xGnP agglomerates dispersed over silicon wafer and pristine/etched samples of PEI foil and nanocomposite xGnP/PEI foil. Graphite nanoplatelets were identified at surface of etched nanocomposite foil. Atomic force microscopy (AFM) was used for surface topography imaging of separate nanoplatelets and those uncovered at the surface of etched nanocomposite. Surface roughness (root mean square, peak to peak) of etched nanocomposite increased with prolonged etching time. Atomic force acoustic microscopy (AFAM) was used to characterize elastic anisotropy of etched nanocomposite. Nanoindentation measurements were employed to characterize the local mechanical properties of PEI and nanocomposite foils.

Electrospun Conjugated Polymer/Fullerene Hybrid Fibers: Photoactive Blends, Conductivity through Tunnelling-AFM, Light-Scattering, and Perspective for Their Use in Bulk-Heterojunction Organic Solar Cells

Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are prepared by electrospinning, and their properties assessed by scanning electron, atomic and lateral force, tunnelling, and confocal microscopy, as well as by attenuated total reflection Fourier transform-infrared spectroscopy, photoluminescence quantum yield and spatially-resolved fluorescence. Highlighted features include ribbon-shape of the realized fibers, and the persistence of a network serving as a template for heterogeneous active layers in solar cell devices. A set of favorable characteristics is evidenced in this way in terms of homogeneous charge transport behavior and formation of effective interfaces for diffusion and dissociation of photogenerated excitons. The interaction of the organic filaments with light, exhibiting specific light-scattering properties of the nanofibrous mat, might also contribute to spreading incident radiation across the active layers, thus potentially enhancing photovoltaic performance. This method might be applied to other electron donor-electron acceptor material systems for the fabrication of solar cell devices enhanced by nanofibrillar morphologies embedding conjugated polymers and fullerene compounds.Comment: 35 pages, 9 figure