Extensibility maximum

Eq. 106 describes the force as the separation between the surfaces is decreased. Let us now assume that, after reaching some minimum separation distance do, a force is applied to separate the surfaces. In this case, the force will differ slightly from that given in Eq. 106, as the asperities are extended above their original height up to a maximum extension 5s, at which point the asperity will separate from the substrate. In order to calculate the separation force Ps, one must change the lower limit of integration in Eq. 106 to... 

Random coil conformations can range from the spherical contracted state to the fully extended cylindrical or rod-like form. The conformation adopted depends on the charge on the polyion and the effect of the counterions. When the charge is low the conformation is that of a contracted random coil. As the charge increases the chains extend under the influence of mutually repulsive forces to a rod-like form (Jacobsen, 1962). Thus, as a weak polyelectrolyte acid is neutralized, its conformation changes from that of a compact random coil to an extended chain. For example poly(acrylic acid), degree of polymerization 1000, adopts a spherical form with a radius of 20 nm at low pH. As neutralization proceeds the polyion first extends spherically and then becomes rod-like with a maximum extension of 250 nm (Oosawa, 1971). These pH-dependent conformational changes are important to the chemistry of polyelectrolyte cements. 

Figure 9. The end-to-end distance per skeletal bond n for regular conformations of polydimethylsiloxane and polyethylene network chains (12). Maximum extensibility rm of this chain molecule occurs at rm/n = 1.34 A.

Figure 6.4 also illustrates a mechanism whereby 13C may be introduced into the inter-shell convection zone of a low- or intermediate-mass star. When that zone reaches its maximum extension, it covers almost the whole inter-shell region apart from a thin interval marked A. The mass of this region decreases from about... 

These responses are shown diagrammatically in Figure 6.2. A Maxwell model is an example of a material in the linear regime that is antithixo-tropic, because the resistance to deformation increases as the spring extends until the maximum extension is reached. On cessation of flow the stress is relaxed and the viscosity falls. A thixotropic material has a viscosity that increases after cessation of flow. 

These systems were referred to by Clausse t a (21) as Type U systems. On the other hand, with cofurfactants with chain length Cg to Cy (Figur 3 e-g), the Winsor IV domain is split into two disjointed areas that are separated by a composition zone over which viscous turbid and birifringent media are encountered. This second class of systems was referred as Type S systems (24). It can also be seen that the Winsor IV domain reaches its maximum extension at reducing in size below and above C. Moreover, at C, one observes a small monophasic region near the W apex (probably o/w microemulsion of the Schulman s type) which vanishes as the alcohol chain length is increased to Cg. 

Ultimate properties of toughness (energy to rupture), tensile strength, and maximum extensibility are all affected by strain-induced crystallization. In general, the higher the temperature the lower the extent of crystallization and consequently the lower these stress/strain related properties. There is also a parallel result brought about by the presence of increased amounts of diluent since this also discourages stress-related crystallization. 

Smith,T.L., Frederick, . E. Ultimate tensile properties of elastomers. IV. Dependence of the failure envelope, maximum extensibility, and equilibrium stress-strain curve on network characteristics. J. Appl. Phys. 36,2996-3005 (1965). 

---