Characterization of collagen fibers in Bruch’s membrane using chemical force microscopy

Bruch’s membrane is a layer composed of collagen fibers located just beneath the retina. This study validates a strategy used to map the morphological and adhesion characteristics of collagen fibers in Bruch’s membrane. Atomic force microscopy tips were functionalized with different chemical groups and used to map the hydrophilic and hydrophobic regions on the surface of the eye tissue. The largest adhesion forces were observed when tips functionalized with NH₂ groups were used. The trend in the adhesion forces was rationalized based on the distribution of different functional groups in the triple-helical structure of the collagen fibers. The results of this study can be used to design more effective strategies to treat eye diseases such as age-related macular degeneration.     

Local surface charge dissipation studied using force spectroscopy method of atomic force microscopy

We propose herein a method to study local surface charge dissipation in dielectric films using force spectroscopy technique of atomic force microscopy. By using a normalization procedure and considering an analytical expression of the tip‐sample interaction force, we could estimate the characteristic time decay of the dissipation process. This approach is completely independent of the atomic force microscopy tip geometry and considerably reduces the amount of experimental data needed for the calculation compared with other techniques. The feasibility of the method was demonstrated in a freshly cleaved mica surface, in which the local charge dissipation after cleavage followed approximately a first‐order exponential law with the characteristic time decay of approximately 7–8 min at 30% relative humidity (RH) and 2–3.5 min at 48% RH. Copyright © 2015 John Wiley & Sons, Ltd.     

Atomic force microscopy investigation of cold‐plasma‐treated poly(ethyleneterephthalate) textiles

Atomic force microscopy (AFM) has been applied to investigate the morphological and topographical surface modifications induced by radiofrequency cold plasma processing of poly(ethyleneterephthalate) textiles. Surface effects are analysed in low‐pressure air plasma for different plasma exposure times. The results show a progressive degradation of the surface with increasing roughness. The analysis suggests that modification of the surface during textile treatment may be ascribed to a plasma‐induced physical process. Copyright © 2003 John Wiley & Sons, Ltd.     

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     

Quantitative analysis of protein adsorption via atomic force microscopy and surface plasmon resonance

Surface properties have a significant influence on the performance of biomedical devices. The influence of surface chemistry on the amount and distribution of adsorbed proteins has been evaluated by a combination of atomic force microscopy (AFM) and surface plasmon resonance (SPR). Adsorption of albumin, fibrinogen, and fibronectin was analyzed under static and dynamic conditions, employing self-assembled monolayers (SAMs) as model surfaces. AFM was performed in tapping mode with antibody-modified tips. Phase-contrast images showed protein distribution on SAMs and phase-shift entity provided information on protein conformation. SPR analysis revealed substrate-specific dynamics in each system investigated. When multi-protein solutions and diluted human plasma interacted with SAMs, SPR data suggested that surface chemistry governs the equilibrium composition of the protein layer.     

Metal‐conducting polymer interface studied by Kelvin probe microscopy: Au and Al on poly(3‐octyl‐thiophene)

In this work, we report a Kelvin probe microscopy investigation on the structural and electronic properties of gold and aluminum thin films evaporated on poly(3‐octyl‐thiophene) films. Our experimental setup allows us to perform scanning force microscopy (SFM) studies of the same area even if the sample is taken out of the SFM system for different processes (Au and Al evaporation). This allows a detailed study of the effect of adsorbed metal particles on the morphology and electrical properties of polymer thin films at the nanoscale. We found different behavior for both metals in morphology and electrical properties at the interface. These results can contribute to explain what happens at the metal–polymer interface of the devices when the metal contacts are grown. Thereby the observed nanoscale structural changes can be correlated with the overall performance of the fabricated devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1083–1093     

Force microscopy analysis using chemometric tools

In this paper we report the first application of multivariate data analysis techniques to force spectrometry measurement sets to enable the physicochemical assignment of spatially ordered multi-component systems. Principal component analysis (PCA) and hierarchical clustering techniques were used to reveal hidden chemical information within force-distance curves generated by high spatial resolution force microscopy. Two experimental samples were analyzed: (i) a two-component system of cytochrome c proteins on a mica surface, and (ii) a three-component system of avidin protein islands positioned on a gold and glass surface. PCA and hierarchical clustering techniques were used to discriminate the different components of the two-component system, whereas hierarchical clustering was found to be superior for the three-component system. Results were in good agreement with the topography and prior knowledge of the surface patterns. This research represents a formative step towards the combination of force spectrometry with chemometric tools for the high resolution physicochemical investigation of complex biochemical systems.     

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     

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     

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…     

Morphology of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) assemblies in diluted aqueous solution and gel studied by atomic force microscopy

Morphologies of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) triblock copolymer self‐assemblies in the diluted solution and in gel were studied by atomic force microscopy (AFM). The copolymer self‐assembled into wormlike aggregates, of uniform diameter, in water. The wormlike aggregates arranged in order to form separate clusters in the diluted copolymer solution; at a higher copolymer concentration, the clusters became bigger and bigger, and packed together to form gel. Copyright © 2008 John Wiley & Sons, Ltd.     

Melting behavior of lamellae of isotactic polypropylene studied using hot-stage atomic force microscopy

The α- and β-form lamellae of isotactic polypropylene were developed at different temperatures. The melting behaviors of the lamellae were observed in real time at elevated temperatures using a hot-stage atomic force microscopy. The melting behavior of the α-form lamellae was determined by the lamellar defects. For the α-form lamellae developed at different undercoolings, the larger the undercoolings, the relatively higher amount of defect in the lamellae was observed. The lamellae with defects were melted into lamellar segments, and recrystallization took place during the heating process. The β-form lamellae had lower thermal stability, and they melted firstly and separately from that of α-form.     

Observation of adhesive force and energy of adsorbents on rubber substrates by atomic force microscopy

We observed the surface morphology and adhesive interaction of adsorbents on rubber substrates by atomic force microscopy (AFM). The detachment of adsorbents from rubber substrates is an important issue for various machines like home appliances and laundry machine. Since a clean surface of the functioning parts is required, a frequent cleaning process must be developed. In particular, dust and lint have a tendency to bind to the rubber surface of a laundry machine. Several practical methods have been attempted to remove these particles from the surface. Pure water, detergent, sodium hypochlorite (65 °C), and cold water (18 °C) are treated onto artificial dust and lint mixtures on rubber with water fluid by rapid rpm. The dust‐and‐lint adsorbents are investigated by AFM after the treatment, and topographic images and force–distance (F–D) curves were generated for the samples. The roughness, measured as the root mean square, is a key factor to judge the cleaning quality. From the F–D curves, we are able to obtain adhesive energy in addition to adhesive force which will yield qualitative measures of the interactions between the remaining adsorbents and the rubber surface. Considering the values that were measured, hot water with water fluid by rapid rpm offers the best performance when cleaning the surface. The chemical like sodium hypochlorite is good for thinning the materials, but it solidifies them, which is eventually detrimental to proper functioning. Copyright © 2014 John Wiley & Sons, Ltd.     

Delamination of organic coating on carbon steel studied by scanning Kelvin probe force microscopy

Corrosion‐induced delamination of an epoxy coating on the AISI/SAE 1045 carbon steel was studied under a humid atmospheric condition (temperature of 25 °C, 1 standard atmospheric pressure, relative humidity of 90%) by the technique of scanning Kelvin probe force microscopy (SKPFM). Surface‐polished 1045 samples were first cold‐coated with the epoxy and then subject to the atmospheric corrosion under the specified condition. At predetermined time intervals, surface Volta potential differences of the samples were measured using the SKPFM over the dry surface of epoxy coating. The map of Volta potential differences demonstrated high contrasts among three characteristic zones: intact steel‐epoxy interface, delaminated interface, and interface with active corrosion, which was then linked to the actual corrosion potential of the steel (measured using a potentiostat with respect to a saturated calomel electrode) based on a rigorous calibration procedure. It was found that the SKPFM was able to provide direct and nondestructive detection of early active corrosion and coating delamination on steels at a submicroscopic resolution, which outperformed the conventional electrochemical techniques for the same purposes. Copyright © 2012 John Wiley & Sons, Ltd.     

End‐grafting copolymers of styrene and 4‐vinylpyridine on an interacting solid surface

Copolymers of styrene and 4‐vinylpyridine with a styrene fraction f varying from 1 to 0 were grafted onto a silicon substrate in the melt. The grafting reaction and the stability of the grafted chains were investigated by Fourier transform infrared and X‐ray photoelectron spectroscopy. The thickness and surface morphology of the grafted copolymer layers were characterized with ellipsometry and atomic force microscopy (AFM). The copolymer chains were successfully grafted to the surface of the silicon substrate by a reaction between the hydroxyl groups of the nitroxide moiety at the end of the copolymers and the silanol groups on the surface of the silicon wafer. A measurement of the thickness of the grafted copolymer layers showed that the ratio of grafted‐layer thickness to the unperturbed chain radius of gyration decreased with the increasing fraction of 4‐vinylpyridine in the copolymer; this indicated that the grafted layer was strongly attracted to the substrate. In addition, an accelerated grafting process was observed at grafting times ranging from 48 to 72 h for pure poly(4‐vinylpyridine) and copolymers with f values of 0.3 and 0.5. AFM observation revealed that the grafted layers densely and homogeneously covered the silicon substrate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1332‐1343, 2005     

Chemical force microscopy: applications in surface characterisation of natural hydroxyapatite

Detailed mapping of surface chemistry with nanometer resolution has application throughout the physical and life sciences. The atomic force microscope (AFM) has provided a tool that, when using functionalised probes, is capable of providing chemical information with this level of spatial resolution. Here, we describe the technique of chemical force microscopy (CFM) and demonstrate the sensitivity of the technique using chemical force titrations against pH. We describe in detail the specific application of mapping the surface charge on natural hydroxyapatite from skeletal tissue and show that this new information leads to a better understanding of the binding of matrix proteins to the mineral surface.     

Kinetics of latex formation of PBMA latex in the presence of alkali soluble resin using atomic force microscopy

 The effect of alkali-soluble resin (ASR), poly(ethylene-co-acrylic acid), EAA, postadded to emulsifier-free monodisperse poly(butyl methacrylate) (PBMA) latexes on the kinetics of film formation was investigated using atomic force microscopy (AFM). Corrugation height of latex particles in films was monitored at various annealing temperatures as a function of annealing time. Enhanced polymer diffusion was found in a latex film containing ASR regardless of anneal-ing temperature. With increasing annealing temperature, a much higher rate of polymer diffusion was found in latex films containing ASR. These results can be interpreted that the low molecular weight and low Tg EAA resin adsorbed at the particle surface is more susceptible to diffusion than that of the PBMA in the film formation stage, thus it enhances the mobility of PBMA polymer. Received: 30 October 1997 Accepted: 20 March 1998     

A study of the surface morphology of poly(p-phenylene terephthalamide) chars using scanning probe microscopy

The objective of this work was to investigate the changes in surface morphology associated with thermal degradation of poly(p-phenylene terephthalamide) (PPTA) into chars. To this end, PPTA samples decomposed at several temperatures up to 800 °C were studied on a local scale using atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). Domains with a diameter of 40-50 nm started appearing among PPTA nanofibrils at about 500 °C. At this temperature and above, a film coating the fibre developed. This layer was much less rigid than PPTA, and remained deposited on the fibres, even at high temperatures. At 800 °C, the STM images showed a surface distribution typical of a carbonaceous material, isotropic although somewhat heterogeneous. When an intermediate isothermal step (500 °C, 200 min) was introduced along with heat treatment of PPTA under a constant rate, the material obtained at the end of this step was conductive enough to be studied by STM. Although the coating over the fibres also remained after the isothermal step, it was less homogeneous than in the absence of isothermal treatment. On further heating, the residue exhibited a surface morphology typical of a carbonaceous material, but much more homogeneous and isotropic than in the absence of the isothermal step.     

Atomic force microscopy study on blend morphology and clay dispersion in polyamide‐6/polypropylene/organoclay systems

The phase structure and clay dispersion in polyamide‐6(PA6)/polypropylene(PP)/organoclay (70/30/4) systems with and without an additional 5 parts of maleated polypropylene (MAH‐g‐PP) as a compatibilizer were studied with atomic force microscopy (AFM). AFM scans were taken from the polished surface of specimens that were chemically and physically etched with formic acid and argon ion bombardment, respectively. The latter technique proved to be very sensitive to the blend morphology, as PP was far more resistant to ion bombardment than PA6. In the absence of the MAH‐g‐PP compatibilizer, the organoclay is located in the PA6 phase; this finding is in line with transmission electron microscopic results. Further, the PP is coarsely dispersed in PA6 and the adhesion between PA6 and PP is poor. The addition of MAH‐g‐PP resulted in a markedly finer PP dispersion and good interfacial bonding between PA6 and PP. In this blend, the organoclay was likely dispersed in the PA6‐grafted PP phase. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43:1198–1204, 2005