Atomic force microscopy study of polypropylene-based self-reinforced composites

Self-reinforced composites are polymeric materials formed by a reinforcement core and a low-melting point skin, which acts as a matrix after the consolidation step. These materials are widely exploited in industrial applications for their mechanical resistance and durability, which are themselves influenced by processing conditions and polymer composition. In the present work, two similar polypropylene-based commercial fabrics were used to evaluate the surface modifications after laminate compaction and after artificial aging using atomic force microscopy. The results were correlated with the chemical and physical-chemical interactions obtained from scanning electron microscopy, transmission electron microscopy, raman and thermal analysis experiments. Single tape consolidated laminate before and after aging displayed different superficial features that can explain the differences in the macroscopic behavior of the two products.     

Atomic force microscopy studies on the dewetting of perfluorinated ionomer thin films

The surface structure and dewetting process of thin films of complex perfluorinated ion‐containing polymers have been studied with atomic force microscopy. These polymers, or ionomers, consist of hydrophilic, hydrophobic, and ionic groups, which are noncompatible with one another, and this results in the association of the polymers into supramolecular structures. These types of polymers have a broad range of technological uses, ranging from thin selective coatings to fuel cells in the form of polymer electrolyte membranes. As the technology calls for thinner films, the interfacial structure and dynamics (wetting/dewetting) of the films become critical in controlling the overall behavior of the polymers. The ionomer under consideration forms structured films consisting of bundles of micelles. These ultrathin films do not dewet above the glass‐transition temperatures of the polymers, contrary to what has been observed in thin diblock copolymers. Perturbing the system with a high‐ionic‐strength solution, however, results in a breakup of the primary aggregate and enhances the adhesion of the films and their stability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 149–158, 2003     

Atomic force microscopy characterization of β-casein nanoparticles on mica and graphite

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Atomic force microscopy imaging of ZnO nanodots deposited on quartz by sparking off different tip shapes

We have demonstrated a simple method for depositing ZnO nanodots on quartz substrates by sparking off different tip shapes at voltages of 2, 4 and 6 kV in air at atmospheric pressure. A comparison was made among the three tip shapes: the sharp tip, the conical tip and the dull tip. The surface morphology was then observed by atomic force microscopy. The mean height of the randomly distributed dots of approximately 8 nm was successfully deposited from the sharp tip at 6 kV. Characterizations by UV–vis spectroscopy and Raman spectroscopy have confirmed the presence of ZnO and the quality improvement by annealing treatments. Moreover, a nucleation mechanism of the nanodot formation is discussed. Copyright © 2006 John Wiley & Sons, Ltd.     

Atomic force microscopy of extended-chain crystals of polyethylene

Extended-chain crystals of polyethylene grown at elevated pressure and temperature were analyzed for the first time by atomic force microscopy. It was possible to compare the typical fracture surface striation features with those obtained earlier by electron microscopy. High resolution atomic force microscopy on flat surfaces enabled the recording of an atomic scale regularity that could not be fully indentified. © 1993 John Wiley & Sons, Inc.     

Atomic force microscopy observations of the structural development during the uniaxial stretching of crosslinked low-density polyethylene in partial and fully molten states

The effect of uniaxial deformation in partially and fully molten states on the morphology of crosslinked low-density polyethylene has been investigated. At low temperatures, the morphology is predominantly fibrillar, with little kebabs appearing on the fibril surfaces. As the deformation temperature is increased into the melting range, the shish density decreases, and overgrowths of kebabs on the fibrils concurrently increase in length. This gives rise to added twisting of the kebabs reflected in the orientation factor analysis. This shish/twisted lamellar kebab texture is observed only in a partially molten state. Studies in a substantially molten state indicate the absence of shish, althugh short lamellae are observed that are oriented in the transverse direction. This morphology indicates a high chain orientation factor as a result of short lamellae that exhibit small twisting similar to Matsumura's rod model. The absence of shishes in the final films stretched isothermally in a substantially molten stage agrees with Schultz's model, in which imperfectly formed shishes dissolve if they are not stabilized by rapid cooling, as is the case in these studies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2228–2237, 2004     

Stretched polymer surfaces: Atomic force microscopy measurement of the surface deformation and surface elastic properties of stretched polyethylene

The surface structure and surface mechanical properties of low‐ and high‐density polyethylene were characterized by atomic force microscopy (AFM) as the polymers were stretched. The surfaces of both materials roughened as they were stretched. The roughening effect is attributed to deformation of nodular structures, related to bulk spherulites, at the surface. The surface‐roughening effect is completely reversible at tensile strains in the elastic regime and partially reversible at tensile strains in the plastic regime until the polymers are irreversibly drawn into fibers. AFM force versus distance interaction curves, used to measure changes in the stiffness of the surface and the surface elastic modulus as a function of elongation, show that the surfaces become softer as the polymers are drawn into fibers at high strains. At low elastic strains, however, the surface elastic modulus of HDPE increases—attributed to elastic energy stored by the amorphous regions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2263–2274, 2001     

Direct observation of uncoated spectrin with atomic force microscope

Spectrin molecules extracted from human blood ceil membrane have been examined by atomic force microscopy (AFM) without using shadowing or staining procedures. A drop of the solution containing spectrin molecules was deposited on the freshly deaved mica substrate. After about 1 min, the residual solution was removed with a piece of filter paper. Afterwards the sample was imaged with a home-made atomic force microscope (AFM) in air in a constant force mode. The obtained AFM images revealed that the spectrin molecules prepared from the above procedures exhibit several kinds of structures as follows: (i) the compact rod-like spectrin heterodimers with a length of around 100 nm; (ii) bent or curved linear tetramers with a length of around 200 nm; (iii) somewhat curved spectrin hexamers, octomers or decamers with lengths of about 300, 400, or 500 nm; and (iv) high oligomers with a length above 1 000 nm.     

Atomic force microscopy of the three-dimensional crystal of membrane protein, OmpC porin

Three-dimensional microcrystals of OmpC osmoporin were air-dried slowly and imaged in air with an atomic force microscope (AFM). The overall structural features in AFM images are in good agreement with the X-ray diffraction data of these OmpC osmoporin crystals: monoclinic P2₁ with the unit cell constants a=117.6 Å, b=110 Å, c=298.4 Å, β=97°. Such a good correspondence between X-ray diffraction and AFM data suggests that the slow and mild air-drying of these crystals did not induce any significant alterations in the crystal lattices as expected upon crystal dehydration. At the (100) crystal face, individual trimeric protein–detergent complexes were resolved. These results show the potential for studying the molecular structure of microcrystals of integral membrane proteins. This study also suggests that the crystal grew in a fashion of rapid two-dimensional expansion along the bc plane followed by a slow deposition along the a axis, perhaps as a rate-limiting nucleation process. Thus, AFM imaging of air-dried crystals would also be of considerable use in the early stages of a project to grow large three-dimensional crystals of membrane proteins suitable for high-resolution X-ray diffraction studies.     

Adsorption behavior of hexadecyltrimethylammonium bromide (CTAB) to mica substrates as observed by atomic force microscopy

The study of the adsorption behavior of surfac-which makes people further study the adsorptiontants to interfaces is very important in colloid and in-mechanism at the molecular level.terface science[1]owing to the important applications In situ AFM measur…     

Application of atomic force microscopy to the study of blown polyethylene films

Atomic force microscopy (AFM) has been used for the characterization of the surface topography and microstructure of polyethylene (PE) films with thickness of about 50 μm. Different compositions of the films were tested, including mixtures of LDPE fabricated with metallocene polyethylene (mPE). The characteristics of the fibrils and spherulites of the films have been observed by means of AFM without any preparation of the samples, allowing also differentiation of the amorphous and crystalline zones. A method is proposed for the quantification of the proportion of crystallinity based on the roughness of the films.     

Spectral force analysis using atomic force microscopy reveals the importance of surface heterogeneity in bacterial and colloid adhesion to engineered surfaces

Coatings developed to reduce biofouling of engineered surfaces do not always perform as expected based on their native properties. One reason is that a relatively small number of highly adhesive sites, or the heterogeneity of the coated surface, may control the overall response of the system to initial bacterial deposition. It is shown here using an approach we call spectral force analysis (SFA), based on force volume imaging of the surface with atomic force microscopy, that the behavior of surfaces and coatings can be better understood relative to bacterial adhesion. The application of vapor deposited TiO₂ metal oxide increased bacterial and colloid adhesion, but coating the surface with silica oxide reduced adhesion in a manner consistent with SFA based on analysis of the “stickiest” sites. Application of a TiO₂-based paint to a surface produced a relatively non-fouling surface. Addition of a hydrophilic layer coating to this surface should have decreased fouling. However, it was observed that this coating actually increased fouling. Using SFA it was shown that the reason for the increased adhesion of bacteria and particles to the hydrophilic layer was that the surface produced by this coating was highly heterogeneous, resulting in a small number of sites that created a stickier surface. These results show that while it is important to manufacture surfaces with coatings that are relatively non-adhesive to bacteria, it is also essential that these coatings have a highly uniform surface chemistry.     

Interpreting the conductive atomic force microscopy measured inhomogeneous nanoscale surface electrical properties of Al‐doped ZnO films

In this work, conductive atomic force microscopy is used to study the inhomogeneous surface electrical conductivity of Al‐doped ZnO thin films at a nanoscale dimension. To this end, Al‐doped ZnO films were deposited onto the soda lime glass substrates at substrate temperature (T_s) varying from 303 to 673 K in radio frequency magnetron sputtering. The obtained local surface electrical conductivity values are found to be influenced by their bulk electrical resistivity, surface topography and tip geometry. Further, the average (local) surface conductivity from the film surface is found to increase with increasing T_s from 303 to 623 K, beyond which they decrease until 673 K. Copyright © 2016 John Wiley & Sons, Ltd.     

Quantitative determination of surface energy using atomic force microscopy: the case of hydrophobic/hydrophobic contact and hydrophilic/hydrophilic contact

Atomic force microscopy (AFM) has been used to determine the surface energy of chemically modified surfaces at a local scale. In order to achieve this aim, it was necessary to graft both the AFM tip and the substrate with the same chemical functional groups. Two different organothiols terminated either by hydrophilic or hydrophobic chemical functionalities were used. Grafting process classically reported shows that after UV/ozone treatment for 30 min, the tip is coated by thermal deposition with 4‐5‐nm‐thick titanium layer followed by a 30‐nm‐thick gold layer. Finally, the tip is grafted by organothiols. The thickness of the layer deposited on the tip is of the same order of magnitude as the tip radius. To avoid the use of Ti and to decrease the thickness of the gold layer, we have developed a new way of grafting by using organic molecules like (3‐mercaptopropyl)triethoxysilane (MPS) as a linkage agent. Then this way of grafting was checked. Finally, AFM force‐distance curves, between grafted tips and chemically modified surface, were carried out in contact mode. Calibration of the various parts of the apparatus and especially of the cantilever (spring constant and tip radius) is of major importance to reach quantitative data. Finally, by applying a suitable theory of contact, we were able to determine the surface energy of our system. Copyright © 2005 John Wiley & Sons, Ltd.     

Single polymer molecules adsorbed to mica and the oppositely charged polymer/surfactant complexes formed at the air–water interface visualized by atomic force microscopy

In the present study, the structure and morphology of single sodium poly(styrenesulfonate) (PSS) molecules adsorbed to mica surface from the natural aqueous solution is investigated using atomic force microscopy technique. Results show that single PSS molecules are observed which show a morphology of wormlike coils. Meanwhile, single sodium poly(styrenesulfonate) (PSS)/Hexadecyltrimethylammonium bromide (CTAB) complexes deposited on mica from the air–water interface are also observed. However, the PSS/CTA⁺ complexes show different conformations by appearing in the morphology of circular patches. Experimental data are in fair agreement with the theoretical analysis.     

Atomic force microscopy study of the polymer growth in a polymer stabilized liquid crystal

The growth of a cholesteric polymer network in a polymer stabilized cholesteric texture (PSCT) was studied by atomic force microscopy (AFM). The liquid crystal is removed by dipping the samples into a solvent bath and the polymer network remaining on each strip is analyzed. Several aspects of the polymer growth were studied: irradiation time, use of an orientation layer and application of an electric field during polymerization. AFM has proved to be an accurate means to study polymer networks thanks to its high resolution. The pitch of the cholesteric polymer is observable under special conditions of polymerization. Copyright © 2002 John Wiley & Sons, Ltd.     

A correlation between the virulence and the adhesion of Listeria monocytogenes to silicon nitride: An atomic force microscopy study

Listeria monocytogenes is a facultative intracellular Gram-positive bacterium that is widely distributed in the environment. Despite being pathogenic at the species level, L. monocytogenes in fact comprises a diversity of strains from pathogenic ones that can result in disease and/or mortality to others that are relatively avirulent. The main goal of the current study was to answer the question on whether enhanced binding or attachment of L. monocytogenes to inert surfaces bears any relationship to pathogenicity in food-borne isolates. To answer this question, the nanoscale adhesion forces of eight L. monocytogenes strains that vary in their pathogenicity levels to a model surface of silicon nitride were quantified using atomic force microscopy. The strains used were the highly pathogenic (EGDe, 874, 1002, ATCC 19115), the intermediate pathogenic (ATCC 19112, ATCC 19118), and the non pathogenic (ATCC 15313 and HCC25). Our results indicate that the average nanoscale adhesion (in nN) and the 50% lethal dose (LD50) of strain virulence quantified in mice are logarithmically correlated according to: (nN) = −0.032 ln (LD50) + 1.040, r² = 0.96. Such correlation indicates that nanoscale adhesion could potentially be used as a design criterion to distinguish between virulent and avirulent L. monocytogenes strains. Finally, stronger adhesion of virulent strains to inert surfaces modeled by silicon nitride might be a way for pathogenic strains to survive better in the environment and thus increase their likelihood of infecting animals or humans.     

The influence of molten fraction on the uniaxial deformation behavior of polypropylene: Real time mechano‐optical and atomic force microscopy observations

In this study, we have coupled the real time mechano‐optical measurements with the off‐line structural characterization techniques including AFM, WAXS, and DSC to establish the quantitative relationships between the “true mechano‐optical behavior and developed morphology” as influenced by the fraction of molten phase present in the polypropylene films. Stretching PP in the solid state invariably leads to formation of fibrillar texture. The evolution of surface morphology in partially molten state was found to depend on the fraction of the molten phase present at the start of the deformation. If the samples are strained past the yielding in partially molten state, the birefringence begins a rapid rise. Concurrent with this, the equatorial zones of the spherulites begin to crack while meridional regions remaining intact. This leads to temporary reduction of crystallinity because of destruction of some of the crystals. If held in this strained state, the crystallite thickening was observed while the birefringence increases while the lost crystallinity is recovered. If the films are strained past the strain hardening point, the microfibrillar structure was found to dominate the surface morphology. When the films are stretched in the melting temperature range, they exhibit substantial nodular surface topology. These nodules that were absent in the solid state deformed samples are hard lamellae buried inside amorphous “soft matter”. The tangential lamellae increasingly become dominant as the processing temperature approaches substantially molten state leading to the observation of a* oriented crystallites in the X‐ray analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 925–941, 2006     

A Study of the Probe Effect on the Apparent Image of Biological Atomic Force Microscopy

The atomic force microscopy (AFM) possesses high spatial resolution and it is compatible with liquid environments. AFM can provide possibility to study a wide range of biological problems at the molecular level and acquire topological information at nanometre resolution under physiological conditions1,2. However, a major problem for image reconstruction of biological specimens is that structures of most biological molecules are very soft and delicate, which could be easily deformed and dama…