Heterogeneous polymers elasticity

Application to heterogeneous polymer solids, and elastic composites, is presented in the Section 7 (Gusev, Suter), which is followed by a summary and the outlook for the various methods reviewed here. It will be apparent to the reader that this review thus assembles several building blocks for the difficult task to bridge the gaps from the atomistic to the macroscopic scales in space and times for the simulation of polymeric materials. Integrating these building blocks into one coherent framework still is not fully solved and a matter of current research. 

This is a theoretical study on the entanglement architecture and mechanical properties of an ideal two-component interpenetrating polymer network (IPN) composed of flexible chains (Fig. la). In this system molecular interaction between different polymer species is accomplished by the simultaneous or sequential polymerization of the polymeric precursors [1 ]. Chains which are thermodynamically incompatible are permanently interlocked in a composite network due to the presence of chemical crosslinks. The network structure is thus reinforced by chain entanglements trapped between permanent junctions [2,3]. It is evident that, entanglements between identical chains lie further apart in an IPN than in a one-component network (Fig. lb) and entanglements associating heterogeneous polymers are formed in between homopolymer junctions. In the present study the density of the various interchain associations in the composite network is evaluated as a function of the properties of the pure network components. This information is used to estimate the equilibrium rubber elasticity modulus of the IPN. 

Methods of estimating the elastic properties of heterogeneous polymers... 

Quantitative and qualitative methods were developed to measure the surface mechanical properties of polymers by atomic force microscopies. They were used to study the effects of molding processes and of viscosity on the surface morphology of polypropylene / (ethylene-propylene) copolymer blends (PP/EP). On compression-molded "physical blends", EP nodules are present at the outermost surface while, on injection-molded "reactor blends", they are covered by a PP layer. Resins with high viscosity ratio between EP and PP present heterogeneous surface elastic properties corresponding to the dispersion of spherical EP nodules below the surface. The low viscosity ratio resins have homogeneous surface elastic properties comparable to those measured above EP nodules on high viscosity ratio resins. This is compatible with a fine dispersion of plate-like shaped EP nodules below the surface... 

Improvement of the mechanical properties of elastomers is usually reached by their reinforcement with fillers. Traditionally, carbon black, silica, metal oxides, some salts and rigid polymers are used. The elastic modulus, tensile strength, and swelling resistence are well increased by such reinforcement. A new approach is based on block copolymerization yielding thermoelastoplastics, i.e. block copolymers with soft (rubbery) and hard (plastic) blocks. The mutual feature of filled rubbers and the thermoelastoplastics is their heterogeneous structure u0). 

Such transformations have been extensively studied in quenched steels, but they can also be found in nonferrous alloys, ceramics, minerals, and polymers. They have been studied mainly for technical reasons, since the transformed material often has useful mechanical properties (hard, stiff, high damping (internal friction), shape memory). Martensitic transformations can occur at rather low temperature ( 100 K) where diffusional jumps of atoms are definitely frozen, but also at much higher temperature. Since they occur without transport of matter, they are not of central interest to solid state kinetics. However, in view of the crystallographic as well as the elastic and even plastic implications, diffusionless transformations may inform us about the principles involved in the structural part of heterogeneous solid state reactions, and for this reason we will discuss them. 

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