Wetting/adhesion angle

They affect contact angles and thereby capillary phenomena such as wetting, adhesion of particles, capillary displacement, and dispersion of powders in a liquid. 

In view of the foregoing discussion, it is clear that good wetting (contact angle of adhesive against adherend, 6 O ") is a requirement (but not necessarily a... 

Contact angle between liquid and solid Yes (many goniometers and other methods) Yes (combination of Young equation with a theory for solid-liquid interfaces) Wetting, adhesion, characterization and modification of surfaces... 

In the pendular state, shown in Figure la, particles ate held together by discrete lens-shaped rings at the points of contact or near-contact. For two uniformly sized spherical particles, the adhesive force in the pendular state for a wetting Hquid (contact angle zero degree) can be calculated (19,23) and substituted for H. in equation 1 to yield the foUowing, where y is the Hquid surface tension in N/m. 

In seeking to minimize the contact angle or to promote wetting of the adherend by the adhesive, one must consider the effects both of the chemistry of the components and of the morphology of the adherend surface on the observed contact angle. Finally, comment must be made on the dynamics of the wetting process and the factors upon which it depends. 

The effect of the chemical makeup of the adhesive/adherend system on contact angle and wetting is manifest through the influence of such chemistry on the surface free energies of the adhesive-air (or other fluid medium), adherend-air... 

Good wetting is of course not a sufficient criterion for good contact adhesion because it takes no account of the factors that influence the mechanical loss factor, C, in Eq. 8, nor does it account for residual stress development during cure. But aside from these factors, one might inquire into the validity of the correlation between practical contact adhesion and VEa beyond 0° contact angle , i.e. can any distinction be made based on VEa between different adhesives, all of which perfectly wet the adherend ... 

If the contact angle is known, insight into the extent of wetting to be expected at equilibrium can be obtained from calculations for idealised rough surfaces. The conclusions may require modification when kinetic effects, such as setting of the adhesive, are taken into account. 

Functional adhesives provide the bonded product with a new or enhanced attribute. For example, adhesives now exist which promote the penetration of fluids into bonded non-woven products by virtue of their low contact angle with water [82]. These materials have been used successfully in both diapers and sanitary napkins for bonding the non-woven cover sheet to the absorbent core. Other examples are water absorbing adhesives that can act as wetness indicators by changing color [69] or can be bonded once moistened ]99]. Additional functionalities are currently underdevelopment. 

The contact angles of water and adhesive resin on wood are higher in the case of freshly harvested wood compared to stored chips. This means that the surface of particles from this fresh wood is more hydrophobic. This influences the wetting and the penetration negatively and with this the gluability. Reason for this lower wettability of freshly harvested wood is a higher content of some wood chemical components, or wood extractives, as has been determined by water extraction. This result, however, must not be confused with the better wettability of a freshly cut surface, independently if it is freshly harvested or stored wood. 

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