Adhesion and mechanical properties

As is true for macroscopic adhesion and mechanical testing experiments, nanoscale measurements do not a priori sense the intrinsic properties of surfaces or adhesive junctions. Instead, the measurements reflect a combination of interfacial chemistry (surface energy, covalent bonding), mechanics (elastic modulus, Poisson s ratio), and contact geometry (probe shape, radius). Furthermore, the probe/sample interaction may not only consist of elastic deformations, but may also include energy dissipation at the surface and/or in the bulk of the sample (or even within the measurement apparatus). Study of rate-dependent adhesion and mechanical properties is possible with both nanoindentation and... 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

In this chapter, we overview basic techniques for making nanoscale adhesion and mechanical property measurements. Both quasi-static and dynamic measurements are addressed. In Section 2 of this chapter, we overview basic AFM instrumentation and techniques, while depth-sensing nanoindentation is overviewed in Section 3. Section 4 addresses recent advances in instrumentation and techniques... 

The above measurements all rely on force and displacement data to evaluate adhesion and mechanical properties. As mentioned in the introduction, a very useful piece of information to have about a nanoscale contact would be its area (or radius). Since the scale of the contacts is below the optical limit, the techniques available are somewhat limited. Electrical resistance has been used in early contact studies on clean metal surfaces [62], but is limited to conducting interfaces. Recently, Enachescu et al. [63] used conductance measurements to examine adhesion in an ideally hard contact (diamond vs. tungsten carbide). In the limit of contact size below the electronic mean free path, but above that of quantized conductance, the contact area scales linearly with contact conductance. They used these measurements to demonstrate that friction was proportional to contact area, and the area vs. load data were best-fit to a DMT model. 

Overall, the AFM is a powerful tool that can provide very high force and spatial resolution measurements of adhesion and mechanical properties. The reader is... 

We have recently been exploring this technique to evaluate the adhesive and mechanical properties of compliant polymers in the form of a nanoscale JKR test. The force and stiffness data from a force-displacement curve can be plotted simultaneously (Fig. 13). For these contacts, the stiffness response appears to follow the true contact stiffness, and the curve was fit (see [70]) to a JKR model. Both the surface energy and modulus can be determined from the curve. Using JKR analyses, the maximum pull off force, surface energy and tip radius are... 

Scholtens, B. J. R. and Brackman, J. C., Influence of the film former on fibre-matrix adhesion and mechanical properties of glass-fibre reinforced thermoplastics, J. Adhes., 52, 115 (1995). 

Polymers used as dental materials must meet several stringent requirements. Dental restorative materials must be nontoxic, have aesthetic appearance, and good adhesive and mechanical properties. In addition, these materials must exhibit long term stability in the presence of water, enzymes, and various oral fluids, and withstand thermal and load cycles. Finally, a desirable dental restorative materia] should be convenient to work with at the time of application. 

Felton, L.A. Baca, M.L. Influence of curing on the adhesive and mechanical properties of an apphed acrylic poljmer. Pharm. Dev. Technol. 2001, 6 (1), 1-9. 

PPE, with SAN, SMMA, SAA or SMA Miscibility of copolymers with PPE when the amount of comonomer is small. The interfacial energy between the blend components was significantly reduced by adding either a PS-b-PMMA, or PS-b-PEB-b-PMMA. The copolymers had a profound influence on morphology, phase adhesion and mechanical properties of the blend. Gottschalk et al., 1994... 

The atomic force microscope (AFM) is a promising device for the investigation of materials surface properties at the nanoscale. Precise analysis of adhesive and mechanical properties, and particularly of model polymer surfaces, can be achieved with a nanometer probe. This study distinguishes the different contributions (chemical and mechanical) included in an AFM force-distance curve in order to estabhsh relationships between interfacial tip-polymer interactions and the surface viscoelastic properties of the polymer. 

In order to obtain good interfacial adhesion and mechanical properties, the hydrophilie elay needs to be modified prior to its introduction in most polymer matriees, which are organophilie. When nanometric dispersion of primary clay platelets is obtained, the aspect ratio of the filler particle is increased and the reinforcement effect is improved [75-25],... 

Yoo Yoon, T. H., Liptak, S. C., Priddy Jr., D. B., McGrath, J. E. Adhesive and mechanical properties of reactive polysulfone modified epoxy resins, J. Adhesion 45 (1994) 191-203. 

Many practical benefits can be obtained by blending polymers. Blending allows for the beneficial properties of two polymers to be combined in one material while shielding their mutual drawbacks. Deviations in the mle of mixing can lead to properties of the blend over and above those of its components. Thus, processibility, chemical and environmental resistance, adhesion, and mechanical properties of polymer blends are superior to those of their homopolymers. 

Vohnsky, A. A., VeUa, J. B. Gerberich, W. W. Fracture toughness, adhesion and mechanical properties of low-k dielectric thin films measured by nanoindentation. Thin Solid Films 429, 201-210 (2003). 

Polymeric binders like waterborne PETs and polyurethanes are often used to improve the film s adhesive and mechanical properties. Especially, in cases where plastic substrates are coated by PEDT PSS and subsequently mechanically treated after coating, such as by thermoforming, the PEDT PSS needs a binder to maintain the overall conductivity. Choice of binder varies with the targeted properties of the final film. If, for example, an end-user desires a final film that is resistant to a particular solvent and well adherent to PC, then a binder designed for solvent-resistant coatings on PC should be chosen. 

Louis H. Sharpe received his Ph.D. degree in Physical Chemistry from Michigan State University in 1957. He is the Supervisor of Adhesive Engineering and Development at Bell Laboratories. Dr. Sharpe is the Editor-in-Chief of the Journal of Adhesion. His research interests have been adhesion, adhesives and mechanical properties of polymers. 

BK Larson, LT Drzal. Glass fibre sizing/malrix interphase formation in liquid composite moulding effects on fibre/malrix adhesion and mechanical properties. Composites 25 711-721, 1994. 

Polymeric binders such as waterborne polyesters and polyurethanes are often used to improve the adhesive and mechanical properties of films. 

Adhesion and mechanical properties of thin films examples... 

Over the years, the use of coatings such as HAp for implants and prostheses has gone from being a rarity to being an absolute necessity. A number of excellent studies on adhesion and mechanical properties have been carried out on a range of coatings major ones include HAp, diamond-like carbon (DLC), titanium nitride, titanium oxide, and nickel-titanium (Ben-Nissan et al., 2013). Listed below are some studies carried out on pure HAp and DLC thin films. 

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