Interaction between solid surfaces in a polymer melt studied by atomic force microscopy

Using an atomic force microscope (AFM) the interaction between an AFM tip and a planar silicon oxide surface has been measured across poly(dimethylsiloxane) (PDMS, M_W = 18 000). Due to the small radius of curvature of the AFM tip the hydrodynamic repulsion of the tip was negligible and forces could be measured in equilibrium. This is confirmed by the fact that force-versus-distance curves measured at different approaching velocities were indistinguishable. In equilibrium a repulsive force was observed which could best be described by a power law, F ∝ 1/d^2.5 where d is the distance.     

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.     

Imaging of reconstituted purple membranes by atomic force microscopy

The organization of bacteriorhodopsin (bR) within reconstituted purple membranes (RPM) was examined using atomic force microscopy (AFM). Five reconstituted species were examined: RPM 3 (bR/native polar lipids/dimyristoylphosphatidylcholine (DMPC) in a 1:9:14 molar ratio), RPM 4 (bR/native polar lipids in a 1:7 molar ratio), RPM 5 (bR/native polar lipids/1,2-di-O-phytanyl-sn-glycerol in a 1:3.5:6.1 molar ratio), RPM 6 (bR/native polar lipids/1,2-di-O-phytanyl-sn-glycero-3-phosphocholine in a 1:3.5:4.9 molar ratio), and RPM 7 (bR/native polar lipids/1,2-diphytanoyl-sn-glycero-3-[phospho-l-serine] in a 1:3.5:4.6 molar ratio). RPM 3 patches adsorbed onto mica exhibit domains of crystallized bR trimers arranged in a hexagonal packing structure, similar to those found in native purple membrane (NPM). These domains are enclosed by DMPC-rich regions. RPM 4 patches were observed to have larger domains of crystallized bR, with trimer orientation 30° different from that found in NPM. The bR-rich domains are enclosed by a large, protein-free, lipid-rich region. The topography of RPM 5 was difficult to resolve as the surface had no discernable patterns or structure. The topographies of RPM 6 and 7 were similar to that found in RPM 3 in that higher domains were formed within the patch adsorbed onto mica. They may contain protein-rich regions, but clear images of protein arrangement could not be obtained using AFM. This may be a result of imaging limitations or of the lack of organization of bR within these domains.     

Dielectrophoretic immobilization of proteins: Quantification by atomic force microscopy

The combination of alternating electric fields with nanometer‐sized electrodes allows the permanent immobilization of proteins by dielectrophoretic force. Here, atomic force microscopy is introduced as a quantification method, and results are compared with fluorescence microscopy. Experimental parameters, for example the applied voltage and duration of field application, are varied systematically, and the influence on the amount of immobilized proteins is investigated. A linear correlation to the duration of field application was found by atomic force microscopy, and both microscopical methods yield a square dependence of the amount of immobilized proteins on the applied voltage. While fluorescence microscopy allows real‐time imaging, atomic force microscopy reveals immobilized proteins obscured in fluorescence images due to low S/N. Furthermore, the higher spatial resolution of the atomic force microscope enables the visualization of the protein distribution on single nanoelectrodes. The electric field distribution is calculated and compared to experimental results with very good agreement to atomic force microscopy measurements.     

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.     

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.     

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.     

Nanomanipulation of extended single-DNA molecules on modified mica surfaces using the atomic force microscopy

The technique of nanometer scale manipulation is very important in constructing nano-structures and nano-devices. By using atomic force microscope, three kinds of controllable manipulation on single-DNA molecules were introduced in the paper. DNA molecules deposited and extended on modified mica surface were first imaged by tapping mode, then cutting, bending, and pushing were respectively performed on single-DNA molecules. The results of the manipulation depend on the interaction between tip and DNA as well as between substrate and DNA.     

Atomic force microscopy study of salivary pellicles formed on enamel and glass in vivo

This study was performed to evaluate the use of atomic force microscopy (AFM) in examining the surface of the adsorbed layer of salivary proteins (salivary pellicle) formed in vivo on dental enamel and glass surfaces. Enamel and glass test pieces were attached to the buccal surfaces of the upper first molar teeth in two adults using removable intraoral splints. The splints were carried intraorally over periods ranging from 10 min to1 h. Using the contact mode of AFM, pellicle structures could be recognised on intraorally exposed specimens compared to nonexposed enamel and glass surfaces. The surface of the adsorbed salivary pellicle was characterised by a dense globular appearance. The diameter of the globulelike protein aggregates adsorbed onto enamel and glass varied between 80 and 200 nm and 80 and 150 nm, respectively. The structure of the adsorbed protein layer was clearly visible on glass surfaces, even though minor differences in the protein layer between glass and enamel specimens were observed. This study indicates that AFM is a powerful tool for high-resolution examination of the salivary pellicle surface structure in its native (hydrated) state. AFM avoids artefacts due to fixing, dehydration and sputter-coating which occur with scanning electron microscopic analyses. Received: 29 November 2000 Accepted: 14 December 2000     

Effect of alkaline treatment on cellulose supramolecular structure studied with combined confocal Raman spectroscopy and atomic force microscopy

The aim of this work was to investigate the morphological and structural changes associated with mercerization of cellulose fibres with combined confocal Raman and atomic force microscopy (AFM). During mercerization the alkali induces a change in polymorphic lattice from cellulose I to II. This was observed by confocal Raman spectroscopy from cellulose samples treated with 10, 15 and 25% aqueous sodium hydroxide solution. AFM images from the same samples illustrated that microfibrils were swollen and more granular in cellulose II than in cellulose I. Raman spectral images in plane and depth directions showed that the polymorphous cellulose structure was uniform throughout the cell wall, whereas the microfibril orientation varied between fibre cell wall layers. The changes in microfibril orientation on the sample surfaces were confirmed by AFM images measured from the same sample position.     

Characterization of human cells exposed to deltamethrin by means of Raman microspectroscopy and atomic force microscopy

Raman spectroscopy is a powerful technique for studying cellular biochemistry. In fact, each toxic chemical induces biochemical changes related to the own action mechanism. In this investigation Raman microspectroscopy has been used, in correlation with atomic force microscopy images, to detect biochemical and structural damages occurring in cultured human cells as a consequence of deltamethrin exposure. Cultured human keratinocyte cells have been exposed at increasing concentrations of deltamethrin from 10⁻³ M to 10⁻⁶ M for 24 h. A viability test indicated that the cytotoxic dose corresponds to exposure at deltamethrin solution for 24 h with the chemical concentration between 10⁻⁴ M and 2.5 10⁻⁴ M. The compared analysis of Raman spectra and AFM images allows to state that an evident damage occurs in the plasmatic membrane and it is already detectable after exposure of keratinocytes at the lowest investigated deltamethrin concentration (10⁻⁶ M). The most important modifications are related to the breakdown of CH₂ bonds of lipidic chains, whereas proteineous bonds are less involved in the deltamethrin action. On the whole, cellular damage starts after exposure to deltamethrin doses well lower than that established as cytotoxic.     

Surface morphology of polypyrrole core/polyacrolein shell latex by atomic force microscopy (AFM)

 Polypyrrole latex (P(P)), synthesized in Redox polymerization of pyrrole, was used as seed for radical polymerization of acrolein initiated with K₂S₂O₈. In this process the polypyrrole core/polyacrolein shell latex (P(P–A)) was obtained. Morphology of the surface of P(P–A) particles was investigated by atomic force microscopy (AFM). It was found that macromolecules of polyacrolein are not randomly distributed on the surface of polypyrrole but form patches. Apparently, attraction between macromolecules of poly-acrolein in the surface layer is high and the enthalpy of formation of polyacrolein macromolecule clusters is sufficient to compensate, at least, the negative entropy change due to ordering of these macromolecules. Thickness of the polyacrolein layer on the surface of polypyrrole particles, which were covered only partially with polyacrolein, was equal to only 1.6 nm (standard deviation σ= 0.2 nm) and thus, it was reasonable to assume that it corresponded to the monolayer coverage. Received: 30 April 1997 Accepted: 25 August 1997     

An atomic force microscopy study of asphaltenes on mica surfaces. Influence of added resins and demulsifiers

 Monolayers of asphaltene and resins on the water surface have been transferred at a surface pressure of 10 mN/m onto mica substrates using the Langmuir–Blodgett technique. Atomic force microscopy (AFM) has been used to examine the topography of these layers. Monolayers consisting of pure asphaltene fractions provide a rigid film with a close-packed structure, while the resins build up a continuous open network. Mixed films of these two fractions show that a gradual increase in resin concentration leads to an opening of the rigid asphaltene structure towards a more resin like configuration. Increased aggregation when the two heavy functions are present in one film is seen as larger individual units in the AFM pictures. Addition of high-molecular-weight demulsifiers/inhibitors results in the same kind of influence on the asphaltene film as seen with the resins. Received: 30 April 1999 Accepted: 29 November 1999     

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…     

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.     

Adsorption of polyelectrolyte multilayers and complexes on silica and cellulose surfaces studied by QCM-D

The adsorption of polyelectrolyte (PE) multilayers and complexes, obtained from both high- and low-charge polyelectrolytes, was studied on silica and on cellulose model surfaces by quartz crystal microbalance with dissipation (QCM-D). The film properties acquired with the different strategies were compared. When polyelectrolytes were added on an oppositely charged surface in sequence to form multilayers both the change in frequency and dissipation increased. The changes in frequency and dissipation were clearly higher if low-charge PEs were used in the multilayer formation. The substrate, silica or cellulose, did not affect the adsorption behaviour of low-charge PEs and only minor differences were seen in the adsorbed amounts and changes in dissipation of high-charge PEs between SiO₂ and cellulose. The complexes formed by low-charge PEs had higher changes in frequency and dissipation at low ionic strength on both surfaces, while the complexes formed from high-charge polyelectrolytes adsorbed more at high salt concentration. The complexes of low-charge polyelectrolytes adsorbed more on silica, while the complexes formed by high-charge PEs formed thicker layers on cellulose. The charge ratio had a significant effect on the adsorption and the highest changes in frequency and dissipation were obtained in the anionic/cationic charge ratio of 0.5–0.6. Generally, the multilayers and complexes formed by low-charge polyacrylamides adsorbed highly and formed rather thick layers on both surfaces, unlike the high-charge PEs which formed thin layers using either one of the addition techniques.     

Size fractionation of aquatic colloids and particles by cross-flow filtration: analysis by scanning electron and atomic force microscopy

The suitability of the combined application of environmental scanning electron microscopy (ESEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) for the evaluation of the ability of cross-flow filtration (CFF) to perform adequate size fractionation of freshwater colloids and particles was examined. ESEM and SEM imaging provided reference images of the CFF-generated fractions and, in estimating the experimental cut-off diameter of the membrane, provided evidence that separation was not consistent with nominal pore sizes of the membranes. However, analysis of the images showed that size distribution of CFF-generated fractions and the estimated cut-off diameter of the membranes were dependent on the advantages and limitations of the two imaging techniques. With both ESEM and SEM, best estimates of size cut-offs were lower than the nominal pore size of the membrane in the case of 0.45 μm membranes, but roughly accurate in the case of 0.1 μm pore size membranes. The results also suggested that the effectiveness of CFF may benefit from a pre-separation step using a minimally perturbing technique such as split thin-flow fractionation. AFM demonstrated the presence of colloids smaller than 50 nm in all fractions including the retentates, showing that CFF fractionation is not fully quantitative and not based on size alone. The results indicate that previous studies investigating trace element partitioning using CFF may need re-evaluation as the importance of particles and large colloids may be over-estimated.     

Features of the hedritic morphology of β‐isotactic polypropylene studied by atomic force microscopy

The lamellar organization of melt‐crystallized β‐isotactic polypropylene was studied by atomic force microscopy (AFM) after permanganic etching. Hedritic objects grown at a high crystallization temperature (140–143 °C) were investigated. Essential features of the hedritic development were revealed by the characteristic projections exposed at the sample surface. A three‐dimensional view of the morphology was obtained by AFM. Hedritic growth proceeded mainly by branching around screw dislocations resulting in new lamellae that further developed. Successive lamellar layers often diverged. Deviation from the planar lamellar habit was observed, varying with the position within the hedrite. Twisting of the lamellae also was observed occasionally in the vicinity of the screw dislocations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 672–681, 2000     

Observation of banded spherulites and lamellar structures by atomic force microscopy

Spherulites are common structures of semi-crystalline polymers. It has been known that semi-crystalline polymers can form spherulites when crystallized from solution or from melt. A dark Maltese cross of a spherulite could be easily observed under the polarized optical microscopy (POM). Moreover, some spherulites show an additional alternating dark and bright concentric ring structure that is attributed to the regular twisting of the radial crystallite ribbons as they grow from the spherulit…     

Dissolution of the barite (001) surface by the chelating agent DTPA as studied with non-contact atomic force microscopy

DTPA (diethylenetriaminepentaacetic acid) is a chelating agent widely used for removal of barium sulfate (barite) scale in the petroleum industry. In this paper we report ex-situ investigations of barite dissolution in deionized water and in 0.18 M DTPA aqueous solutions. Non-contact atomic force microscopy (NC-AFM) was used to observe dissolution on the BaSO₄ (001) cleavage surface. Dissolution was carried out at room temperature in a 10 ml reactor. Each sample was first etched in solution and dried before examination by NC-AFM. Dissolution on the BaSO₄ (001) surface took place via development of etch pits. In deionized water, triangular etch pits were observed on the (001) terraces at room temperature. And, zigzag shaped etch pits were found at the edges of steps. In DTPA solutions, etch pits on the (001) terraces were observed and these became deeper and longer with increasing time. The geometry of these etch pits was trapezoidal, and/or trapezohedral. To explain this characteristic morphology caused by dissolution we suggest that the active sites of one DTPA molecule bind to two or three Ba²⁺ cations exposed on the (001) surface.