Probe tack tests

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 another tack test, a steel ball of specified diameter is rolled down a grooved incline onto a conditioned surface area of pressure sensitive adhesive (ASTM D 3121, PSTC-6). The length of travel before it stops is the rolling ball tack (Fig. 2d) reported in millimeters. It is relatively inexpensive and simple to set up. Similar test variables to the probe tack test apply. 

The recorded force first increases, then decreases the maximum value, called the tack force is a measure of the adherence in this experimental condition the area under the curve, called the tack energy, is equal to the work GdA of the singular stress at the crack tip. Tackiness refers to the ability of an elastomer to adhere instantaneously to a solid surface, or to itself, after a brief time of contact under low pressure. Probe tack testing procedure can be analyzed by Eq. 14 and tack curves obtained by computer integration closely coincide with experimental ones (25). ... 

Polyken Probe Tack Test, ASTM D2979. 

A probe tack test may be regarded as a mechanical thumb in which a disc or hemisphere of standard material (e.g. brass) is brought into contact with the adhesive surface under a fixed load for a specified dwell time (e.g. 1 s) and then removed at a specified rate. The maximum force of removal is usually taken as the tack value, although sometimes the work or energy of separation is reported. In such a test, it is important to control accurately the variables probe material and finish, probe diameter and shape, load on probe, thickness of adhesive, dwell time, rate of debonding of probe from adhesive, and... 

Several variations of the test exist. Historically, the first referenced probe test is the Polyken probe tack test developed by Hammond [6]. In this case, the probe has a flat tip and is upside down. The compressive force is controlled by lifting a... 

Starting from a flat probe tack test such as that described in Fig. 2, the sequence of events can be broken down into four main events [8] ... 

Fig. 3. Schematic of the deformation mechanisms taking place during a probe tack test and corresponding images of the stages of debonding. Images from [70].

Fig, 9. Debonding energy, W, as a function of temperature for probe tack tests of different acrylic polymers. , Poly(2-ethylhexyl acrylate) o. poly(n-butyl acrylate) , polyfisobutyl acrylate) a, poly(ethyl acrylate) , poly(methyl acrylate). Contact time 0.02 s. Data from [34. ... 

Fig. 15. Elastic modulus, , in a relaxation experiment (o) and adhesion energy, W, in a probe tack test on steel ( ) as a function of resin content for a natural rubber/glycerol ester of hydrogenated resin blend. Data from [34].

The strain rate of an adhesive sample in a probe-tack test is related to the debonding velocity of the probe, however not in a straightforward way. Indeed, the separation stage induces very heterogeneous shear and elongation flows in the sample [31]. A common approximation, bypassing all these considerations, is, however, to consider that, at the beginning of the separation process at least, the... 

Most of the results which are discussed in this review were obtained with flat probe tack tests on thin adhesive films (typically, 20-100 p,m). While this geometry has several advantages for the analysis of fundamental properties of PSA, it is by no means the only one that can be used and one should be careful to understand clearly what features of a lack curve are due to the material and which ones are due to the specific experimental geometry. 

Primary tack measurement techniques include probe tack tests, loop tack, quick stick, and rolling ball techniques. These techniques are illustrated schematically in Fig. 22.12. 

Illustration offeree vs time trace for a probe tack test of a pressure-sensitive adhesive as the probe is compressed to make contact, held for a fixed dwell time, then removed... 

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