Adhesion imaging

Fig. 3.66 Pulsed force mode AFM images of carbon black filled rubber (a) height, (b) stiffness, (c) adhesion image. Reproduced with permission from [142], Copyright 1998 American Chemical Society. The image contrast in the images (a. height, b. stiffness, c. pull-off force) have been scaled from dark (low values of property) to bright (high values of property) contrast...

Fig. 4.10 Histograms of the pull-off forces and corresponding adhesion images of (a) unexposed PDMS and oxidized PDMS after (b) 0.1 day after exposure to 60 min of UV/ ozone. In the adhesion images, the color scales are individually scaled from dark (low pull-off) to bright (high pull-off). Reproduced with permission from [28]. Copyright 2004. American Chemical Society...

Fig. 4.12 Pulsed force mode measurement on a thin film of a blend of P2VP and PtBMA. The pulsed force mode AFM adhesion image (5x5 pm) clearly distinguishes the PtBMA islands from the surrounding P2VP. (Reprinted with permission from [30]. Copyright 2000. American Institute of Physics.)...

The first example for the study of polymer surfaces by adhesion force mapping known to us is the report by Mizes et al., who studied polycarbonate with a conventional Si3N4 tip [173]. On the polycarbonate film depicted in Fig. 22, a clear contrast in the adhesion image is seen. 

The contrast in friction and adhesion images can be increased by chemically modifying the SFM probe with the functional group or biomacromolecule of choice and by changing the environment in which the measurement is carried out. At this point, it is important to differentiate between various probe modification methods such as pure chemical modification, thin film deposition, and modification of the probes with biological elements like biomacromolecules or cells. In addition, the distiction is made between functionalization of the cantilevers by gluing spheres to the lever or by direct derivatization of silicon tips. 

Figure 8. Adhesion image of the lamellar PE crystal shown in Figure 6. Bright tones corresponds to low adhesion (50 nN), dark tones to high adhesion (80 nN). The contrast in the adhesion images is defined on the basis of the convention that attractive forces are negative.

High performance wound dressings can be heid secureiy in piace on the skin using a pressure sensitive adhesive (image copyright by Smith Nephew April 2010)... 

Berger C E FI, van der Werf K O, Kooyman R P FI, de Grooth B G and Greve J 1995 Funotional group imaging by adhesion AFM applied to lipid monolayers Langmuir 4188... 

Photocurable materials for photographic films contain pentaerythritol and dialkylamino and/or nitrile compounds, which have good adhesion and peelabihty of the layers, and produce clear transfer images (97,98). 

A triangular shaped wheel cover with the center cut out to provide hub access was then applied to a wheel. The cover was constructed from a heat shrinkable poly- 10 olefin ftlm. Tape was attached to the apex points of the triangle. The tape liner was removed and the three adhesive sites were fastened to the spokes. As an identical complementary cover was then applied to the opposite face of the wheel in a mirror image fashion. The 1 adhesive contact points were positioned to encapsulate the spoke on either side within the adhesive contact point. Heat was then used to shrink the covers and achieve a wrinkle-free condition. This example demonstrates that design can play a part in providing a stylish wheel cover that is capable of individualizing the bicycle to meet a wide variety of consumer tastes. 

Thermal imaging is sensitive to iafrared radiation that detects temperature changes over the surface of a part when heat has been appHed. Thermal diffusion ia a soHd is affected by variatioa ia composition or by the preseace of cracks, voids, delamiaatioas, etc the effects are detected by surface temperature changes. Defects cannot be detected if their depth below the surface is more than two to three times their diameter. Nondestmctive testing has been primarily used for composites and analysis of adhesive bonds or welds. Several studies are documented ia the Hterature (322—327). 

The dry-processed, peel-apart system (Fig. 8b) used for negative surprint apphcations (39,44) is analogous to the peel-apart system described for the oveday proofing apphcation (see Fig. 7) except that the photopolymer layer does not contain added colorant. The same steps ate requited to produce the image. The peel-apart system rehes on the adhesion balance that results after each exposure and coversheet removal of the sequentially laminated layer. Each peel step is followed by the apphcation of the appropriate process-colored toners on a tacky adhesive to produce the image from the negative separations. The mechanism of the peel-apart process has been described in a viscoelastic model (45—51) and is shown in Figure 8c. 

Numerous AFM imaging techniques have been developed and commercialized to monitor topography, friction, mechanical response, capacitance, magnetic properties, etc. However, adhesion measurements require the tip to come into, and out of, contact to measure attractive and adhesion forces. Therefore, other than to select an analysis region, most imaging techniques are not useful for adhesion studies. Instead, measurements are necessarily based on force-displacement curve approaches. 

Depth-sensing nanoindentation is one of the primary tools for nanomechanical mechanical properties measurements. Major advantages to this technique over AFM include (1) simultaneous measurement of force and displacement (2) perpendicular tip-sample approach and (3) well-modeled mechanics for dynamic measurements. Also, the ability to quantitatively infer contact area during force-displacement measurements provides a very useful approach to explore adhesion mechanics and models. Disadvantages relative to AFM include lower force resolution, as well as far lower spatial resolution, both from the larger tip radii employed and a lack of sample positioning and imaging capabilities provided by piezoelectric scanners. 

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