Stretch shaping

The main chain of dendronized polymers, due to die large size of the mon-odendrons, is usually forced to take a stretched shape thus the whole molecule exists as a rigid rod architecture both in solution and in the solid state.32d Depending on the backbone stiffness, the degree of monodendron coverage, and the size of die monodendron, the architecture of these macromolecules is no longer a sphere but a cylinder this dictates die properties of the dendronized polymers. 

Figure 6.7 (Continued) shows a live normal cell in stretched shape, (d) Confocal image of FR+ cells...

Shrinkage happens when a plastic-based board, extruded and pulled from the die, cool too fast. Too fast means that stretched long polymer molecules, coming from the die, do not get enough time to settle, to come back to their thermodynamically favorable coiled form. They are trapped in the board solidihed matrix in an unsettled, stretched shape. 

To be exact, these distorted in space polymeric molecules continue to get rearranged into their energetically minimized shape, but at ambient temperature rates of this rearrangement are too slow, about 100 million times slower than those at hot melt temperature. If it would take 5 s for a polymer molecule to coil from its stretched shape at hot melt temperature, at ambient temperature it would take about 16 years. 

The strain fixity rate R describes the ability of the switching segment to fix the mechanical deformation which has been applied during the programming process. It describes how exactly the sample can be fixed in the stretched shape after a deformation to m- The resulting temporary shape u(.N) always differs from the shape achieved by deformation. 

Stretching a shape memory coil spring when it is in a martensitic (i.e. cold) state will de-twin the differently oriented martensite. The result is an almost homogenously oriented martensitic structure. Similar to a common plastic deformation the SM coil spring will stay in the stretched shape when unloaded (Fig. 6.51). 

They evaluated the shape memory performance and air and water vapor permeability, and all samples showed shape recoveries of at least 99 % and shape retentions of at least 94 %. The stretched and fixed nanowebs showed greater differences of water vapor permeability at 10 °C with 90 % relative humidity (RH) and 15 °C with 90 % RH, than the original nanowebs did, because stretched shapes of the samples could be retained by more than 70 % at 10 °C or 15 °C. The 40 mm shape memory PU nanoweb showed the best performance, maintaining high shape memory and the largest difference in water vapor permeability between when stretched and not stretched at 15 °C with 90 % RH [32],... 

Surface fraction of the polyelectrolyte in its stretched shape Specific density of pure solvent i Molar density of pure solvent i... 

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