Dahlquist’s criterion

FIGURE 17. Dahlquist s criterion of good PSA. (From data of Kraus. 

The first case is related to the arguments given in Section 6.1 if the interfacial gc (static, but also dynamic) is too low, once cavities are nucleated at the interface, they can easily propagate, coalesce and debonding occurs without any fibril formation. The second case is discussed in Section 6.2 and occurs when the elastic modulus of the PSA is too high (Dahlquist s criterion is not met) or when the surface is too rough for the adhesive to conform to it during the short contact time. 

To achieve a good compromise between wetting the surface (adhesion) and bearing a load (cohesion) the modulus should be in the range of 0.1 to 1 MPa in the time fi-ame of the bonding process , that is 1-100 s (Dahlquist criterion [211], p. 101). 

Dahlquist [6] noted that there seems to be a minimum value of the compliance of a PSA in order for it to exhibit tack or equivalently, a maximum value of the modulus. He analyzed data on rheological properties as a function of time (or frequency) and temperature as well as tack as a function of dwell time, separation rate and temperature. He observed that only those materials with sufficiently high compliance in the 1-s time scale at the temperature of use were tacky. This so-called Dahlquist criterion is expressed as follows for various common rheological measurements... 

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