Macromolecules slip

Shear stress results as the flowing layers of macromolecules slip past one another. The shear rate is the difference in the rates of flow or the shear gradient-that is, the change in the rates of the flowing layers across the radius of the cross section. The viscosity decreases with increasing shear rate. 

In their first step towards building dendritic rotaxanes Stoddart et al. [140] reported the construction of such materials via a so-called slipping method (Fig. 24). Thus, treatment of bisparaphenylene-34-crown-10 (BPP34C10) with tris(bipyridinium) compound 54 at 50 °C in acetonitrile for 10 days afforded mono-, di-, and tris-rotaxanes 55, 56, and 57, respectively. ES-MS was used to determine the molar masses of these macromolecules while upfield shifts in the... 

A second line of evidence Is provided by an experiment In which the degree of crosslinking of photopolymerlzed specimens was progressively Increased by exposure to Y-rays. The expectation was that crosslinking should reduce plastic deformation by preventing macromolecules from slipping past one another. 

Comparison of the non-affine slip-tube model [Eq. (7.65) using Gx and as adjustable parameters] with experiments, see M. Rubinstein and S. Panyukov, Macromolecules 35, 6670... 

Figure 7.10 Illustration of Stick Boundary Condition. Solute biological macromolecule shown as single grey sphere moves with an average velocity through water (shown as light blue spheres). Water molecules in immediate hydration layer move at the same average velocity due to tight hydration interactions. Under Slip Boundary Conditions, water molecules do not possess hydration interactions and therefore do not move with the biological macromolecule at all.

As opposed to copolymers, polyblends may unmix during processing. On the other hand, production of the blends is often more economical and can be realized right on the processor s premises. In many cases, the long-term properties (creep) of polyblends are less desirable (slipping of macromolecules) than those of copolymers. 

Macromolecules (state) Chain slipping Mechanical damping internal friction ... 

The primary forming of plastics is generally a flow process. The individual macromolecules of thermoplastics, duroplastics, and elastomers must be mobile and capable of chain slipping. The duroplastics and elastomers do not crosslink or vulcanize until after forming, when they develop their characteristic crosslinked structure. 

Fig. I. Chain tilt and slip (a) in a crystal lamella leading to the formation of a crack, (b) bridged by the partially unfolding macromolecules (Peterlirfi).

Once the glass transition temperature (7 ) has been exceeded, the intermolecular forces have become so weak that the influence of external forces can cause the macromolecules to slip apart from one another. The strength declines steeply, while the elongation leaps upward. In this temperature range, the plastic exists in a rubber-elastic or thermoelastic state. 

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