Cohesion within

Visually, the failed specimens appeared as shown in Fig. 34. Failure was mostly cohesive within the adhesive. However, there was a small region of apparent interfacial failure at one end of each substrate that was referred to as the metal... 

All failures were cohesive within the adhesive. Adhesive E610 nylon epoxy (Asulab SA). 

Eqs. 1-5 hold whether failure is interfacial or cohesive within the adhesive. Furthermore, Eq. 5 shows that the reversible work of adhesion directly controls the fracture energy of an adhesive joint, even if failure occurs far from the interface. This is demonstrated in Table 5, which shows the static toughness of a series of wedge test specimens with a range of adherend surface treatments. All of these samples failed cohesively within the resin, yet show a range of static toughness values of over 600%. 

Optimized grit blast/silane treatments can provide wedge test durability as good as PAA with failure entirely cohesive within the adhesive (Fig. 21) [89]. Maintaining the process parameters within acceptable tolerances is critical with the heat drying of the silane on the treated surface being the most sensitive process parameter. 

CRS which had been phosphated prior to bonding exhibited a significant enhancement of durability and corrosion resistance under the same accelerated conditions (Figure 4). The crystalline barrier layer restricted the exposure of the metal oxide to moisture by reducing the rate of water penetration at the interface. Even samples exposed to the cycle test were able to maintain failure within the adhesive for up to 10 days, after which varying amounts of interfacial failure were noted. Again, room temperature control samples maintained initial joint strength and failure remained cohesive within the adhesive. 

Samples constructed from adherends which had been alkaline cleaned, lubricated or left untreated exhibited similar joint strength values and durability trends (Figure 10). Adhesive joints placed in the room temperature control environment or the 23 C water bath retained lOOZ and 92% of initial joint strength, respectively. Failure remained cohesive within the adhesive for all of the control samples and for the first 20 days of exposure in the 23 C water bath. After 20 days, some failure began to initiate at both the primer/steel and primer/topcoat interfaces. The adhesive/topcoat interface proved to be more durable than those found between the substrate/primer/topcoat layers. Samples exposed to the more severe salt fog, 60 C water bath and cycle tests were able to retain 70% to 50% of their initial strength over a 60-day exposure period. 

Adhesives based on hydrolysis resistant chemistry (i.e., adhesives D and E) show a high retention of initial properties after exposure to an aggressive corrosion environment and the failure occurs cohesively within the adhesive. The cure reactions of these adhesives involve the formation of hydrolysis resistant carbon-nitrogen bonds in reactions involving the free N-H functionality of the Versamid or Genamid hardener with the oxirane functionality of the epoxy resin that is present in the adhesive formulation ... 

Person 1 Calculate the work of cohesion within the epoxy adhesive. This is the work required to separate epoxy bonds from one another. 

This indicates a lack of dynamic cohesion within the adducts i.e. the substrate has considerable freedom for reorientation within the receptor. The apparent reason for an absence of mechanical coupling is the nearly cylindrical symmetry of cucurbituril, which allows the guest an axis of rotational freedom when held within the cavity. Hence, the bound substrates show only a moderate increase in tc relative to that exhibited in solution. No relationship exists between values and the thermodynamic stability of the complexes as gauged by K (or K, cf. Tables 1 and 2). It must be concluded that the interior of cucurbituril is notably nonsticky . This reinforces previous conclusions that the thermodynamic affinity within adducts is chiefly governed by hydrophobic interactions affecting the solvated hydrocarbon components, plus electrostatic ion-dipole attractions between the carbonyls of the receptor and the ammonium cation of the ligands. 

In purification filters for purifying liquids or gases, sometimes a loose bed of grains of an adsorbent material, such as activated carbon, is located between two porous walls which confine the grains. Since there is no cohesion within the granular material, the flow and filter use period are difficult to control. 

Tape stripping can be further used to investigate intercorneocyte cohesion within the SC by quantifying the amount of SC removed.11 When using standardized tape stripping conditions, the more SC removed, the smaller the SC cohesion. For instance, tape stripping in combination with a protein assay to accurately quantify SC removal proved to be a sensitive method in detecting keratolytic efficacy of salicylic acid preparations within hours of application.27 This method may also be useful to measure the influence of moisturizers or other skin care preparations on SC cohesion. 

A comparison of experimentally determined failure times for different stress levels and those predicted by the above equation for epoxy-aluminum lap shear joints aged at 60°C and 95 percent RH is presented in Table 15.3. These results indicate that the reaction rate method is satisfactory for predicting the effects of temperature and stress on the lifetime of adhesive bonds, provided that failure is cohesive within the adhesive. This, of course, should be validated by prototype testing. 

Certain adhesive systems are more resistant to interfacial degradation by moist environments than are other adhesives. Table 15.16 illustrates that a nitrile-phenolic adhesive does not succumb to failure through the mechanism of preferential displacement at the interface. Failures occurred cohesively within the adhesive even when tested after 24 months of immersion in water. A nylon-epoxy adhesive bond, however, degraded rapidly under the same conditioning owing to its permeability and preferential displacement by moisture. 

The cohesion within water that results from these transitory hydrogen bonds allows water to move upward in plants against the force of gravity. Where water and another, less dense, substance meet, the bonds between water molecules contribute to surface tension. 

Tenacity is the force of cohesion within a substance. These words describe how a material holds together under stress or pressure. Some of these, like ductility and malleability, refer only to metals. The words flexibility and elasticity are often used interchangeably and incorrectly they really are two very different properties ... 

Hydrogen bonding also influences the viscosity of water. Viscosity indicates the resistance to flow, reflecting the cohesion within a fluid as well as transfer of molecular momentum between layers of the fluid. It is thus a... 

For many pairs the adhesion is weakened because of poor lattice matching between the transferred material and the substrate, or major differences in their mechanical properties, or by poor cohesion within the transferred material. Conversely, it follows that smooth, effective transfer is more likely to take place when... 

Mathematical Theory of Reactions in Films Among the variables which affect these surface reactions are (i) the surface pressure, (ii) the concentration in the surface of accessible groups, and (iii) the cohesion within the film. 

To represent the interests of a majority of pharmacists and to create cohesiveness within the profession on matters of practice, principle, and policy. 

Coulomb interactions between ions are responsible for the cohesion within some condensed phases such as ionic solids. These interactions are also operative in liquid solutions. Although such interactions are usually regarded as versions of chemical valence forces between atoms in the molecules, they also act as a physical force between molecules. The physical Coulomb force between two ionic molecules is by far the strongest force we see, stronger even than most chemical bonds. However, physical Coulomb force is long range up to 70 nm distance compared with the extremely short range chemical covalent bonds (0.1-0.2 nm)... 

---