Polymers stretching

We might be tempted to equate the forces given by Eqs. (9.61) and (3.38) and solve for a from the resulting expression. However, Eq. (3.38) is not suitable for the present problem, since it was derived for a cross-linked polymer stretched in one direction with no volume change. We are concerned with a single, un-cross-linked molecule whose volume changes in a spherically symmetrical way. The precursor to Eq. (3.36) in a more general derivation than that presented in Chap. 3 is... 

Conjugated polymer stretched ITO/isotropic PTOPT/stretched 2.4 n.a. 0.1 630, 680 21... 

A polymer stretched out to its full contour length is only one of the myriad conformations possible for a polymer at temperatures above Tg, or if the polymer is entirely crystalline. The chain length is expressed statistically as the RMS distance, which is only a fraction of the contour length. 

By changing the group Ar it was possible to build into the polymer stretches of conjugated double bonds of different length, or even to build polymers with an uninterrupted conjugated chain. Several correlations were found ... 

Fig. 10.23, Force versus distance when pulling a host molecule attached via a PEC linker to the AFM-tip from a cavitant. Around a piezo displacement of 38 nm a rupture event occurs, before that the PEC polymer stretches. (Reprinted in parts from [96] with permission of Wiley, VCH, copyright 2005.)...

Figure 2. Stress vs. strain at 25 and 60°C for polyester polyurethanes. Filled symbols 25°C, unfilled symbols 60°C. Commercial polymer (stretched 1.25cm/ min) f , 0 ),unaged (A> A),aged wet. Pu 16 ( , 0),unaged ( , aged wet.

M. Chertkov. Polymer stretching by turbulence. Phys. Rev. Lett., 84 4761-4764, 2000. 

Other types of morphological changes during blending in TSE were also observed [Sundararaj et al., 1992, 1995]. The authors reported that both reactive and non-reactive blends in an extruder, internal mixer, or a miniamre cup-and-rotor mixer, show similar morphological features. Initially, during the melting, the polymers stretch into sheets and ribbons that first broke into fibers then into drops. 

The configuration of a polymer in solution depends markedly on the solvent. In a good solvent a stronger interaction occurs between solvent and polymer than between solvent and solvent, or between various segments of the polymer. The polymer stretches out in the solution (uncoils), as illustrated in Fig. 35.3(a). 

Here R and R are the rms (root mean square) end-to-end distances of the polymer chain parallel and perpendicular to the director, respectively, xr is the conformational relaxation time of the polymer, c the polymer concentration, N is the degree of polymerization, and T the temperature (K). These results are interesting, because they predict that if the dissolved polymer stretches along the director, because of an interaction with the nematic field, the increment in r]c will be much larger than that in T]b. Specifically, from Eqs. (1.82) and (1.83), the ratio of the two scales as... 

Carrington SP, Odell JA (1996) How do polymers stretch in stagnation point extensional flow-flelds J Nonnewton Fluid 67 269-283... 

In describing flowing polymeric liquids it is probably not feasible to use detailed models that describe the locations of all the atoms in the polymer molecules. Consequently, it is necessary to use some kind of mechanical models that portray the overall molecular architecture. Bead-spring models have been widely used with considerable success for relating macroscopic properties to the main features of the molecular architecture. Even the simplest of these models - the elastic dumbbell models - are capable of describing polymer orientation and polymer stretching. More complicated chain, nng, and star models reflect better the molecular structure and allow for the portrayal of the most important internal molecular motions as well. 

Non-Newtonian fluids exhibit complex flow behavior, typically because they contain additives such as polymers or particles that alter the response of the fluid. Unlike Newtonian fluids, which have constant viscosity (resistance to flow), the viscosity of a non-Newtonian fluid is not constant. The viscosity depends oti the shear rate and the amount of strain accumulated, as well as the nature of the additives, including the concentration of additives, the polymer molecular weight, and the particle size. In addition, flexible polymers stretch in a flow, leading to an elastic response. Development of microfluidic devices has centered on miniaturizing assays to analyze the biological, physical, and chemical properties of DNA, proteins, and biopolymers in solution, as well as suspensimis of cells and bioparticles. Since the analysis is typically performed in the... 

A hypothesis for the high intrinsic viscosity is that the polymers stretch when passing the porous medium. This is substantiated with a experimental procedure. Using a second porous medium downstream the first one it was found that the polymer entering the second medium gave a pressure drop that depends on the time of flight between the two porous media. 

As an indirect consequence, the polymer stretching gives rise to an increase... 

Fortunately, a similar partial crystallization effect as mentioned before could be obtained on the same polymer at lower temperatures (180°C - 1 hr) (Fig. 3.10 e, curve 3), and also at normal temperatures as a result of the polymer stretching (Fig. 3.10 e, curve 2). Evidently, in these situations the thermal degradation process could not be involved. 

---