Adherence energy

Dissipation phenomena generally occur during measurement of the adherence of polymer materials, leading to an adherence energy function of both the number and nature of interfacial interactions (adhesion) and dissipative properties, mainly due to viscoelastic behavior [1-5]. Friction properties of polymers are also governed by interfacial interactions and dissipation mechanisms. Common phenomena (interfacial interaction and dissipation) therefore control adherence and friction behaviors. However, the relationship between the two phenomena is still vague or undefined. The first objective of this experimental work is then to compare adherence and friction of polydimethylsiloxane (PDMS) networks in order to establish relationships between these two properties. 

Table 5.1 Adherence energy E [J m ] of PDMS 5 and 17 (before extraction) and PDMS 6 and 17 (after extraction) measured for a normal force of 1 N and for an initial contact time of 300 s and two separation speeds V (A =0.02 J m ).

Tack results indicated a higher adherence energy for PDMS 17 than for PDMS 6. Separation speed also greatly affected the adherence value, with an increase of the separation energy with the separation speed [6]. 

The influence of speed is significant, as shown by the increase of adherence energy. It is explained by the viscous behavior of large-scale chain motion during separation. This large-scale motion, which affects adsorbed chains (free and pendant) preferentially, is rate-sensitive, due this viscous behavior. Movements and pull-out of longer chains are more difficult and more sensitive to the separation speed. 

If the contact angle is zero, as in Fig. XIII-8e, there should be no tendency to adhere to a flat surface. Leja and Poling [63] point out, however, that, as shown in Fig. XIII-8/, if the surface is formed in a hemispherical cup of the same radius as the bubble, then for step la, the free energy change of attachment is... 

Resilient Diners. Resilient liners reduce the impact of the hard denture bases on soft oral tissues. They are designed to absorb some of the energy produced by masticatory forces that would otherwise be transmitted through the denture to the soft basal tissue. The liners should adhere to but not impair the denture base. Other critical properties include total recovery from deformation, retention of mechanical properties, good wettability, minimal absorption of... 

While polymeric surfaces with relatively high surface energies (e.g. polyimides, ABS, polycarbonate, polyamides) can be adhered to readily without surface treatment, low surface energy polymers such as olefins, silicones, and fluoropolymers require surface treatments to increase the surface energy. Various oxidation techniques (such as flame, corona, plasma treatment, or chromic acid etching) allow strong bonds to be obtained to such polymers. 

When properly formulated, they will adhere well to low surface energy substrates. 

---