Polymer Characterization with the Atomic Force Microscope (original) (raw)
Atomic force microscopy and direct surface force measurements
Pure and Applied Chemistry, 2005
Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the need for formal IUPAC permission on condition that an acknowledgment, with full reference to the source, along with use of the copyright symbol ©, the name IUPAC, and the year of publication, are prominently visible. Publication of a translation into another language is subject to the additional condition of prior approval from the relevant IUPAC National Adhering Organization.
Atomic force microscopy and direct surface force measurements (IUPAC Technical Report
Pure and Applied Chemistry, 2005
Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the need for formal IUPAC permission on condition that an acknowledgment, with full reference to the source, along with use of the copyright symbol ©, the name IUPAC, and the year of publication, are prominently visible. Publication of a translation into another language is subject to the additional condition of prior approval from the relevant IUPAC National Adhering Organization.
A Simple and Effective Method of Evaluating Atomic Force Microscopy Tip Performance
Langmuir, 2001
The morphology of a surface imaged by dynamic force mode atomic force microscopy is obtained through an interaction between the probe tip and surface features. When the tip is contaminated and the size of the contaminant is comparable to the size of the features on the sample surface, artifacts attributable to the contaminant are observed to dominate the image. To reduce the possibility of effects from such artifacts, the tip performance should be checked by scanning a reference sample of known surface morphology. We demonstrate a simple and effective method of evaluating tip performance by the imaging of a commercially available biaxially oriented polypropylene (BOPP) film, which contains nanometer-scale-sized fibers. This sample is appropriate for use as a reference because a contaminated tip will not detect the fiberlike network structure. In addition, BOPP has a soft, highly hydrophobic surface of low surface energy, thus ensuring that the tip will not be damaged or contaminated during the evaluation process.
Effect of Tip Size on Force Measurement in Atomic Force Microscopy
Langmuir, 2008
An atomic force microscope (AFM) has been used to study solvation forces at the solid-liquid interface between highly oriented pyrolytic graphite (HOPG) and the liquids octamethylcyclotetrasiloxane (OMCTS), n-hexadecane (n-C 16 H 34), and n-dodecanol (n-C 11 H 23 CH 2 OH). Oscillatory solvation forces (F) are observed for various measured tip radii (R tip) 15-100 nm). It is found that the normalized force data, F/R tip , differ between AFM tips with a clear trend of decreasing F/R tip with increasing R tip .
Study of tip–sample interaction in scanning force microscopy
Applied Surface Science, 2000
The study of the tip-sample interaction has been achieved combining the simultaneous measurement of force, resonance frequency, oscillation amplitude and quality factor vs. distance curves. From the analysis of these experiments performed in Ž . air with cantilevers of low force constant -0.75 Nrm , we propose that the tip jumps to contact due to the formation of a liquid neck between tip and sample. Besides, a few nanometers before the tip jumps to contact, a decrease in oscillation amplitude is detected. We observe that this decrease is mainly caused by a dissipative interaction. By selecting this interaction as feedback signal, the scanning force microscope can be operated in the non-contact regime. q
Atomic force microscopy is a convenient and exceptionally rich source of information about materials on the nano-scale. The instrument can be configured to operate in a large number of modes. The main task of AFM is to produce reliable and repeatable measurement of surface and intermolecular forces, which are needed for surface analysis and provide plentiful of information regarding other features of specimen. These diverse modes measure different atomic forces that are acting between apex and specimen surface and are used for producing topographical image of the sample with high molecular resolution. The force measurement is by way of cantilever deflection measures. The cantilever can be made by piezoelectric material, whereas it is a piezoelectric stage that moves the specimen with respect to the tip. The cantilever is affected by position, tip-sample separation, it’s material, and different forces. A beam of laser focused on the force sensing/imposing lever and reflected onto a sensitive detector which is position sensing photo diode PSPD. Due to high resolution and small contact areas there is no need of vacuum and problems due to contamination and roughness are minimized.
The atomic force microscope (AFM) has previously been applied to the measurement of surface forces (including adhesion and friction) and to the investigation of material properties, such as hardness. Here we describe the modification of a commercial AFM that enables the " stiffness " of interaction between surfaces to be measured concurrently with the surface forces. The stiffness is described by the rheological phase difference between the response of the AFM tip to a driving oscillation of the substrate. We present the interaction between silica surfaces bearing adsorbed polymer, however, the principles could be applied to a wide variety of materials including biological samples.
Probing surfaces with single-polymer atomic force microscope experiments
Biointerphases, 2006
In the past 15 years atomic force microscope ͑AFM͒ based force spectroscopy has become a versatile tool to study inter-and intramolecular interactions of single polymer molecules. Irreversible coupling of polymer molecules between the tip of an AFM cantilever and the substrate allows one to study the stretching response up to the high force regime of several nN. For polymers that glide or slip laterally over the surface with negligible friction, on the other hand, the measured force profiles exhibit plateaus which allow one to extract the polymer adsorption energies. Long-term stable polymer coatings of the AFM tips allow for the possibility of repeating desorption experiments from solid supports with individual molecules many times, yielding good sampling statistics and thus reliable estimates for adsorption energies. In combination with recent advances in theoretical modeling, a detailed picture of the conformational statistics, backbone elasticity, and the adsorption characteristics of single polymer molecules is obtained.
Tip-Sample Forces in Atomic Force Microscopy: Interplay between Theory and Experiment
MRS Proceedings, 2013
ABSTRACTSeveral examples of Atomic Force Microscopy imaging in the oscillatory resonant and non-resonant modes are analyzed with a theoretical description of tip-sample force interactions. The problems of high-resolution imaging and compositional mapping of heterogeneous polymers are considered. The interplay with theory helps the experiment optimization and rational understanding of the image contrast.
Atomic Force Microscopy as a Tool Applied to Nano/Biosensors
Sensors, 2012
This review article discusses and documents the basic concepts and principles of nano/biosensors. More specifically, we comment on the use of Chemical Force Microscopy (CFM) to study various aspects of architectural and chemical design details of specific molecules and polymers and its influence on the control of chemical interactions between the Atomic Force Microscopy (AFM) tip and the sample. This technique is based on the fabrication of nanomechanical cantilever sensors (NCS) and microcantilever-based biosensors (MC-B), which can provide, depending on the application, rapid, sensitive, simple and low-cost in situ detection. Besides, it can provide high repeatability and reproducibility. Here, we review the applications of CFM through some application examples which should function as methodological questions to understand and transform this tool into a reliable source of data. This section is followed by a description of the theoretical principle and usage of the functionalized NCS and MC-B technique in several fields, such as agriculture, biotechnology and immunoassay. Finally, we hope this review will help the reader to appreciate how important the tools CFM, NCS and MC-B are for characterization and understanding of systems on the atomic scale.
An atomic force microscope tip designed to measure time-varying nanomechanical forces
Nature Nanotechnology, 2007
Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.
Langmuir, 1997
Measurements are made of the forces acting on the tip of an atomic force microscope when the sample and cantilever are in air and also immersed in polar solvents like water and DMSO. For large tip/substrate separations (>1000 nm) the liquid drag force can be modeled using a classical hydrodynamic drag force expression. For separations between the tip and substrate smaller than around 100 nm in a water medium, the force due to the effective viscosity increase of the compressed films for high tip/substrate relative velocity is comparable to the contribution of the double-layer repulsion and the van der Waals attraction. After tip/substrate contact these compressed films produce an attractive force that is a function of the liquid medium. In the DMSO medium the attractive force between tip and substrate shows an adhesive force that has at least two components indicating a multilayered structure between the tip and substrate during the tip/substrate separation. The scanning of a surface immersed in water and DMSO with a tip "in contact" produces distinct AFM images which depend on the liquid. These images show diverse symmetries and spacings between features which presumably correspond to the solvated atomic structure and are only obtained with atomic resolution for a scanning speed of ∼2 nm/s. It is possible to estimate the viscous relaxation time of the compressed layer value to be ∼250 ms from the observed resolution of substrate structures as a function of scanning speed.
Functionalization of Afm Tips for Use in Force Spectroscopy between Polymers and Model Surfaces
Materiali in Tehnologije
The following work presents the use of two different methods for the attachment of different functional groups onto the AFM tip surface. Such functionalized tips then allow for further binding of molecules with different origins and natures, thus allowing for use when measuring forces, and the extent of interactions appearing between two model surfaces and in real systems. Force spectroscopy, in combination with chemical force microscopy (CFM), as used in this study, exhibits great potential for chemical sensing in the field of polymer sciences. In modern wound treatment, it is very important to know the type and ranges of interactions between different polymer materials, which are mostly crucial components of the dressings. Precise measurement of these interactions would help to choose those materials that fit together without the use of additional chemical modifications on their surfaces. Such modifications are often the cause of unpredictable complications during the course of wo...
Experimental Mechanics, 2018
The bottom substrate effect is one of the major sources of error in force map studies of adherent cells and thin soft samples in an atomic force microscope (AFM)-based force spectroscopy. Because of this, samples appear stiffer than the natural. The popular Sneddon's contact model, which assumes the sample as infinitely thick, fails to correct this error. In the present work, a simple asymptotically correct analytical correction to the bottom substrate effect is derived through contact mechanics approach and later the model is experimentally validated on a wide range of thickness of soft polyacrylamide gel and on adherent cells.
2007
Atomic force microscopy (AFM) has been useful to investigate materials performance, processes, physical and surface properties at the nanometer scale. In addition to the standard AFM, which measures surface topography, many accessories have been developed to obtain specific additional information. In this chapter, we shall concentrate on atomic force spectroscopy (AFS), which derived from AFM and is used to measure surface forces through force curves. The latter curves have become an important tool to study materials properties, such as elasticity, surface charge densities and wettability. With AFS one probes interactions at the nanometer scale, especially van der Waals interactions and double-layer forces. A brief theoretical background is included, and we comment on the large variety of measurements involving AFS. phone: +55 1633742477. Modern Research and Educational Topics in Microscopy. A. Méndez-Vilas and J. Díaz (Eds.) ©FORMATEX 2007 747 _______________________________________________________________________________________________ ©FORMATEX 2007 Modern Research and Educational Topics in Microscopy. A. Méndez-Vilas and J. Díaz (Eds.) ©FORMATEX 2007 Modern Research and Educational Topics in Microscopy. A. Méndez-Vilas and J. Díaz (Eds.) 750 _______________________________________________________________________________________________ ©FORMATEX 2007 Modern Research and Educational Topics in Microscopy. A. Méndez-Vilas and J. Díaz (Eds.) ©FORMATEX 2007 Modern Research and Educational Topics in Microscopy. A. Méndez-Vilas and J. Díaz (Eds.) Modern Research and Educational Topics in Microscopy. A. Méndez-Vilas and J. Díaz (Eds.) ©FORMATEX 2007 755 _______________________________________________________________________________________________
Determination of solid surface tension at the nanoscale using atomic force microscopy
2006
Engineered surfaces, such as thin inorganic or organic films, self-assembled organic monolayers and chemically-modified polymeric surfaces, cannot be melted, dissolved, or fractured; therefore, their surface-interfacial tension (γ ) cannot be determined using conventional surface tension measurement techniques. New surface tension characterization methods need to be developed. Atomic force microscopy (AFM) is capable of solid surface characterization at the microscopic and sub-microscopic scales. As demonstrated in several laboratories in recent years, and reviewed in this paper, it can also be used for the determination of surface tension of solids from pull-off force measurements. Although a majority of the literature γ results were obtained using either Johnson-Kendall-Roberts (JKR) or Derjaguin-Muller-Toporov (DMT) models, a re-analysis of the published experimental data presented in this paper indicates that these models are often misused and/or should be replaced with the Maugis-Dugdale (MD) model. Additionally, surface imperfections in terms of roughness and heterogeneity that influence the pull-off force are analyzed based on contact mechanics models. Simple correlations are proposed that could guide in the selection and preparation of AFM probes and substrates for γ determination. Finally, the possibility of AFM measurements of solid surface tension using real-world materials is discussed.
Surface chemistry and tip-sample interactions in atomic force microscopy
Colloids and Surfaces A-physicochemical and Engineering Aspects, 1995
Microfabricated silicon nitride cantilevers with integral tips are commonly employed in atomic force microscopy. The link between surface chemistry, including surface group acid-base dissociation and counterion complexation, and tip-sample interaction in aqueous electrolyte solution is examined. Silicon nitride tip interaction with "flat plate" samples of both muscovite mica and silicon nitride as a function of aqueous solution pH and electrolyte concentration is investigated. The long-range component of the interaction is normalized with respect to an effective tip radius, and as a result electrical double layer and van der Waals interactions can be discussed quantitatively. Microfracture and tribochemical tip wear is also discussed with reference to atomic force microscope contact mode imaging. Nonretarded Hamaker constants are reported for a range of silicon nitride, silica, silicon and muscovite mica systems.
Indian Journal of Engineering and Materials Sciences
Atomic force microscopy (AFM) is a relatively new technique used for the surface characterization of polymers. It is capable of producing images of a non-conducting polymer surface without any chemical etching or staining. The unique fea-ture of this technique as compared to other microscopy techniques is that we can study the mechanical properties of the polymer surface and it also does not involve the use of electron beam radiation that damages the polymer surface. This paper describes the various applications of atomic force microscopy like evaluation of mechanical properties, determining the chemical composition, studying photo-oxidative degradation of polymers, measuring the surface adhesion forces, studying the thermal phase transitions in polymers and determining the molecular weight and polydispersity index of polymer brushes. These applications have been elucidated with suitable examples. IPC Code: G01N13/16 The chemical properties and topography of polymer surfaces determi...