Adhesion measurements from contact

The effect of corona discharge treatment on the surface physico-chemistry of PP and PET films has been investigated using surface energy measurements from contact angles, XPS and AFM. The information gathered from these techniques, in addition to practical adhesion measurements, has enabled identification of the dominant mechanisms of adhesion of silicones to these plastic films. The physisorption mechanism and the mechanism of mechanical interlocking are not the cause of... 

W. Duncan-Hewitt and R. Nisman. Investigation of the surface free energies of pharmaceutical materials from contact angle, sedimentations, and adhesion measurements. In Contact Angle, Wettability and Adhesion, edited by K. L. Mittal. Utrecht, The Netherlands VSP, 1993, 791-811. 

Fig. 14. Measurement of adhesion between PDMS and PS, and PDMS and PMMA. It can be seen that there was no adhesion hysteresis. The contact radius at a given load, during loading and unloading was the same. From these data, we get WpoMs-ps = 49 3 mJ/m-, and Tfdm.s-fm.ma = 57 1 mJ/m-.

An example of interaction stiffness and force curves for a Si surface with a native oxide at 60% relative humidity (RH) is shown in Fig. 12 [104]. The stiffness and force data show an adhesive interaction between the tip and substrate. The hysteresis on retraction is due to a real change in contact area from surface oxide deformation and is not an experimental artifact. The adhesive force observed during retraction was consistent with capillary condensation and the surface energy measured from the adhesive force was close to that of water. 

As shown in Fig. 2.31, a contact angle can be experimentally measured by looking at two adhesive droplets. However, a direct determination from side views is rather difficult unless the contact angle is large enough, as in Fig. 2.31. A more convenient way to achieve measurements of contact angles consists of measuring the radius of two adhesive droplets, a and d2, and the radius of the adhesive film between the droplets, r (Fig. 2.32) [104-107]. One has ... 

EDWARDS, M. c. (1996) The use of FT-Raman Spectroscopy to measure transfer of adhesives from sticky labels to the surface of fruits. MAFF Project No. 22244. PETERSEN, J.-H. in Adhesives in food contact materials and articles, Proceedings from a Nordic seminar June 2001 by Kettil Svensson, Mona-Lise Binderup, Cato Brede, Bente Fabech, Anja Hallikainene, Turid Hellstrom, Jens Hpjslev Petersen and Sesselja Maria Sveinsdottir. 

Results. This experiment demonstrates that metal ions are etched from metal substrates by acidified monomers. This experiment is a little more than assessment of the degree of surface etching and mobility of the metal ions throughout the adhesive joint. The results obtained are only apparent when compared with the same monomer/acid mixture measured before contact with the lapshears (Table 6.13). 

There is no direct way by which /gy /sL be measured, but the difference between /jy and can be obtained from contact angle measurements (= /lv COS0). This difference is referred to as the wetting tension or adhesion tension [5-7]... 

Table 3 lists some ionization properties of functionalized gold-thiol monolayers and relevant alkylsiloxane monolayers together with the appropriate bulk values. Monolayers with carboxylate terminal groups show abnormal wetting behaviour, which makes it difficult to determine accurately their surface pKa values308. Apart from contact angle titration, other methods were also used to study proton transfer equilibria at the mono-layer surfaces, such as quartz crystal microbalance (Table 3, line 1), measurements of the adhesion force between the monolayer deposited at the surface of an AFM tip and the same monolayer deposited on the substrate (chemical force microscopy, Table 3, lines 3, 4, 15), FT-IR spectroscopy (Table 3, line 7), adsorption of polyelectrolytes (Table 3, line 5) and differential capacitance measurements (Table 3, lines 12, 13). 

These considerations lead to the conclusion that a rational approach to.problems of the adhesion of cells to solid surfaces can be developed from knowledge of the surface properties of both the substrate and the cell. Solid surface energies can be obtained by measurements of contact angles and use of Neumann s equation (Eq. 6), thus allowing calculations of free energy charges associated with adhesion. Zeta potentials and resultant electrostatic contributions to adhesion can also be obtained experimentally. This type of approach should provide insight into microbial adhesion problems in the marine and aquatic environments, disease and infection and in the industrial immobilization of whole cells. 

In the first part of this section, wetting criteria as well as surface and interface free energies are defined quantitatively. The estimation of a reversible work of adhesion W from the surface properties of materials in contact is therefore considered. Next, various models relating the measured adhesion strength G to the free energy of adhesion W are examined. 

Interdiffusion between a pair of polymers is a demonstration of their thermodynamic miscibility. The adhesion between contacted rubber sheets parallels the extent of any interdiffusion of the polymer chains (Roland and Bohm, 1985). If the contacted sheets are comprised of immiscible rubbers, no interdiffusion occurs. Natural rubber (NR) and 1,2-polybutadiene (1,2-BR) are miscible even at high molecular weights (Roland, 1988a Roland, 1987). When NR is brought into contact with 1,2-BR, they interdiffuse spontaneously. When some form of scattering contrast exists between the materials, interdiffusion will enhance the scattering intensity (either X-ray or neutron) measured from the plied sheets. A variety of spectroscopic methods (Klein, 1981 ... 

Kunz W, BeUoni L, Bernard O, Ninham BW (2004) Osmotic coefficients and surface tensions of aqueous electrolyte solutions role of dispersion forces. J Phys Chem B 108 2398-2404 Lee L-H (2000) The gap between the measured and calculated liquid-liquid interfacial tensions derived from contact angles. J Adhesion Sci Technol 14 167-185 Li ZX, Lu JR, Styrkas SA, Thomas RK, Rennie AR, Penfold L (1993) The structure of the surface of ethanol/water mixtures. Mol Phys 80 925-939 LoNostro P, Fratoni L, Ninham BW, Baglioni P (2002) Water absorbency by wool fibers hofmeiter effect. Biomacromol 3 1217-1224... 

The surface properties of polymers are important in technology of plastics, coatings, textiles, films, and adhesives through their role in processes of wetting, adsorption, and adhesion. We will discuss only surface tensions of polymer melts that can be measured directly by reversible deformation or can be inferred from drop shapes. Those inferred from contact angles of liquids on solid polymers ( critical surface tension of wetting ) are excluded, as their relations to surface tensions are uncertain. 

It is evident from these results that two of the adhesion proeesses (making contact and breaking contact) can be observed in the atomie force microscope. The size of the contact spot can also be deteeted if some additional technique for sensing contact spot size is used, for example, eleetrieal contact or thermal contact. Thus the three stages of adhesion can be found in the AFM. It has become clear from sueh measurements that all materials adhere in this test, verifying the first law of adhesion. These results will be considered in more detail in Chapter 4. 

To check this law out more rigorously, Chaudhury and Whitesides made 11 different mixtures of methanol and water, ranging from 5% methanol to 100%, and used them to verify Young s equation. First they measured the surface tension Ylv of each mixture, then they measured the contact angle 6 of each mixture on a flat surface of the PDMS rubber. This enabled them to calculate the term2yLv cos in the equation of Fig. 6.7. Plotting this as the vertical axis in Fig. 6.8 allowed a comparison with the work of adhesion of the rubber ITsi. measured in the 11 methanol/water mixtures. 

The experiment was conducted as before, measuring the contact spot size d both making and breaking the contact, then calculating the adhesive energy T and crack speed v from the TV record using the equation derived from equation 9.7... 

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