Poly , longitudinal-mode

The acoustic properties of polymers are just as for many properties strongly dependent on temperature around the glass-rubber transition the sound speed decreases rapidly from a relatively high value at T < Tg to a relatively low value at T > Tg. During this transition the absorption shows a maximum value. An example is given in Fig. 14.4, where data for a poly(metacarborane siloxane) are displayed. The measurements were made in the longitudinal mode as a function of temperature at a frequency... 

Low-frequency Raman spectroscopy (LFRS) has been used to measure the longitudinal acoustic mode (LAM) of semicrystalline diblocks containing poly(ethylene oxide) (Mai et at. 1996 Viras et at. 1988 Yang et at. 1995), The LAM mode frequency is inversely proportional to the crystal stem length, and indicates whether chains are folded or extended. 

Figure 1. Velocity of longitudinal acoustic mode of poly(dG)-poly (dC) as a function of nonbonded strength parameter f3. Various curves as listed in text.

Figure 2. Absorption cross section per base pair vj. frequency for the longitudinal, torsional, and bending acoustic modes for chains of poly(dG) poly(dC) B conformation of lengths 51 and 451 base pairs. The absorption of a similar mass of water...

Raman spectral-band frequencies for poly (thietane) as a crystallized melt annealed at 62° satisfy the rules for a longitudinal acoustic-mode frequency for deducing thickness. The morphology and physical properties of isoprene thietane block copolymers have been studied. Potential energies have been calculated for helical- and glide-type conformations of poly (thietane), and the conformations of the homopolymer have been calculated. ... 

The longitudinal acoustic mode (LAM), measured by Raman spectroscopy, continues to be a powerful means of measuring the average stem length in crystalline polymers. Its application has been extended to polyethers, poly-thioether," and also polytetrafluorethylene and its oligomers. ... 

---