A novel method for static equation-of state-development: Equation of state of a cross-linked poly(dimethylsiloxane) (PDMS) network to 10 GPa

Photoacoustic generation of intense and broadband ultrasound pulses with functionalized carbon nanotubes

Carbon nanotubes (CNT) functionalized with siloxane groups were dissolved in polystyrene/tetrahydrofuran to produce thin films that generate broadband and intense ultrasound pulses when excited by pulsed lasers. These films absorb >99% of light in the visible and near-infrared and show no signs of fatigue after thousands of laser pulses. Picosecond laser pulses with fluences of 50 mJ cm-2 generate photoacoustic waves with exceptionally wide bandwidths (170 MHz at -6 dB) and peak pressures >1 MPa several millimeters away from the source. The ability to generate such broadband ultrasound pulses is assigned to the ultrafast dissipation of heat by CNT-siloxanes, and to the formation of very thin photoacoustic sources thanks to the high speed of sound of polystyrene. The wide bandwidths achieved allow for axial resolutions of 8 μm at depths less than 1 mm, similar to the resolution of histology but based on real-time non-invasive methods.

High-pressure Raman spectroscopy and X-ray diffraction studies of a terpolymer of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride: THV 500

High-pressure Raman spectroscopy and X-ray diffraction of THV 500, a terpolymer of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride, were performed using diamond anvil cells (DAC). Changes in the interatomic spacing as well as shifts of several of the vibrational bands as a function of pressure were measured up to approximately 10 GPa. The changes in interatomic spacing and shifts of the vibrational bands are compared to those of polytetrafluoroethylene, showing the effects of copolymerization and reduced crystallinity. The high-pressure behavior of polymers is a relatively unexplored field but is becoming increasingly important due to applications where polymers experience extreme conditions.

Brillouin-scattering determination of the acoustic properties and their pressure dependence for three polymeric elastomers

The acoustic properties of three polymer elastomers, a cross-linked poly(dimethylsiloxane) (Sylgard 184), a cross-linked terpolymer poly(ethylene-vinyl acetate-vinyl alcohol), and a segmented thermoplastic poly(ester urethane) copolymer (Estane 5703), have been measured from ambient pressure to approximately 12 GPa by using Brillouin scattering in high-pressure diamond anvil cells. The Brillouin-scattering technique is a powerful tool for aiding in the determination of equations of state for a variety of materials, but to date has not been applied to polymers at pressures exceeding a few kilobars. For the three elastomers, both transverse and longitudinal acoustic modes were observed, though the transverse modes were observed only at elevated pressures (>0.7 GPa) in all cases. From the Brillouin frequency shifts, longitudinal and transverse sound speeds were calculated, as were the C(11) and C(12) elastic constants, bulk, shear, and Young's moduli, and Poisson's ratios, and their respective pressure dependencies. P-V isotherms were then constructed, and fit to several empirical/semiempirical equations of state to extract the isothermal bulk modulus and its pressure derivative for each material. Finally, the lack of shear waves observed for any polymer at ambient pressure, and the pressure dependency of their appearance is discussed with regard to instrumental and material considerations.