Small-strain deformation

The properties of glassy polymers such as density, thermal expansion, and small-strain deformation are mainly determined by the van der Waals interaction of adjacent molecular segments. On the other hand, crack growth depends on the length of the molecular strands in the network as is deduced from the fracture experiments. 

Fig. 7 a and b. Scheme of the thermomechanical behaviour of a well phase-separated thermoelasto-plastic. Stress-strain (or time) curves. Plots of heat effects versus time. First loading (ABC) and unloading (CD) cycle. Second loading (AC) and unloading (CD) cycle. The yielding point occurs at B. AD indicates the residual deformation after the first cycle. AB on the dQ/dT-time curve is the endo-effect resulting from the initial small-strain deformation AB U9)... 

Thus, in brief, a successful pressure-sensitive adhesive not only has low resistance to small strain deformation in order to facilitate wetting, but also it can resist large strains without flowing apart easily. Certain neat elastomers such as acrylate-based PSAs possess these features and are intrinsically tacky without additives. Other PSAs are formulated by diluting high molecular weight rubbers with special resins called tackifiers. 

Now consider a small strain deformation of unit volume of an elastic solid occurring under adiabatic conditions. The first law of thermodynamics gives... 

Thus, the requirements for a successful pressure sensitive adhesive formulation are that it must possess little resistance to small strain deformation, so that rapid wetting takes place, and yet it must also be able to support large strains without flowing apart easily. These features are obtained by a loose network of high-molecular-weight entangled molecules, diluted with special resins (tackifiers). 

I. Small-Strain Deformation and Fracture of Highly Oriented Polymers.174... 

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