Polymer chain stretching

The grafting of polymers to substrates has been studied for over fifty years and remains an important goal in polymer science. Recent work has focused on the synthesis of so-called polymer brushes whereby the polymer chains stretch out away from the substrate or interface [1-5]. This contemporary topic is a direct descendent of earlier work on organic graft copolymers in industry and academia. Research in this area is driven by the need to control the interfacial properties of films and the compatibility of blends. 

F. 5a. A schematic of a single polymer chain stretched along the crown of the void surface, b Imaginary tube surrounding this chain its intersection with the plane of separation at a distance x from one of the chain ends represents a stagnation point, c Plot of the force on the chain as a function of x... 

The advantages of the Durham route are (1) contaminating catalyst residues can be removed because the precursor polymers are soluble and can be purified by dissolution and reprecipitation and (2) the precursors can be cast as films or drawn and oriented prior to conversion to the all-trans form of polyacetylene. This allows a degree of control over the morphology of the final product which in the pristine state appears to be fibrous and disordered. Because conductivity increases by alignment of the polymer chains, stretching the film or fiber assists this process and this can be performed using the prepolymer. 

When a polymer chain stretches, entropy tends to return the coil to its equilibrium configuration, leading to an elastic restoring force. Thus, elastic stresses are generated as the polymer chain stretches and relaxes in response to flow. A liquid exhibiting both elastic and viscous stresses is viscoelastic. We note that the ratio of a viscosity r/ to an elastic modulus G yields a characteristic relaxation time X rj/G characterizing the memory of a fluid of its past deformation history or the timescale for a stretched polymer chain to relax toward equilibrium. 

Anionic charges repel each other) polymer chains stretch and dissolve... 

Fig. 7.13 Schematic representation of the Herman s orientation factor, related to polymer chain stretching direction.

Finally, in order to compare the relative states of polymer chain stretch in the immediate interface vicinity, while accounting for the difference in molecular weights of the respective resins, a Viscosity Normalized Nonlinearity Ratio was defined as shown below. 

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