In recent years, the interest in the research and development of "green energy" has increased dramatically, with
numerous research grants and investment in the areas of wind power, solar power and fuel cell technology. We present
results obtained from the evaluation of the acoustic properties of proton-exchange membranes used in hydrogen fuel
cells, which relate directly to the microelastic properties of such membranes. These properties play an important role in
the durability and applicability as well as the efficiency of such membranes. DuPont Nafion membranes are the most
commonly used polymeric membranes in hydrogen/oxygen fuel cells and are therefore used as examples in this study.
The microscope used in this non-destructive characterization study is a vector-contrast version of the scanning acoustic
microscope which yields images in magnitude- and phase contrast.
The biomaterial chitosan is used in the paper manufacturing industry, as a wound healing agent and in filtration amongst
others. In this paper the longitudinal sound velocity and acoustic impedance of thin films of chitosan of varying
thicknesses are determined by vector-contrast acoustic microscopy. The exploitation of the relative reflectivity
information from the maximum amplitude images and a comparison of the experimentally obtained V(z) curves with simulations using appropriate models are applied for the evaluation of the sound velocity. These results were compared to those previously obtained results with the same instrument.
Thin films of polystyrene (PS)/polymethylmethacrylate (PMMA) blends were made by casting from solutions with
solvents of varying vapor pressure. Solvents used were chloroform, toluene and dichloromethane. Spin coating was
carried out at varying speeds yielding films of different thickness. Atomic force microscopy and phase-sensitive acoustic
microscopy were used to investigate the effects of spin speed and solvent vapor pressure on morphology. The domains
formed due to lateral phase separation proved to be strongly influenced by vapor pressure with completely different
surface structures for the three solvents. The films cast from high vapor pressure solutions displayed an increased surface
roughness. Surface morphology is explained by the relative solubility in the different solvents, surface affinity, spin speed and viscosity.
Microscopic objects including living cells on a planar substrate are investigated in bio-medical applications of scanning
acoustic microscopy. Beside of the observation of lateral structures, the determination of sample properties such as
density, sound velocity, and attenuation is desired, from which elastic properties can be derived. This can be achieved
with the aid of the acoustic phase and magnitude contrast represented in a polar plot. For homogeneous and sufficiently
planar objects the contrast in magnitude and phase is a function of the properties of the substrate and the coupling fluid,
which both can easily be determined, and of the mechanical properties of the sample under observation. For observation
in reflection and variable thickness of the sample the signal will depend on the actual thickness. This signature of the
object can be fitted based on a conventional ray model for the sound propagating in the coupling medium and the
sample. The model includes also the refraction and reflection at all interfaces between transducer, lens material, coupling
fluid, object, and substrate. The method is demonstrated for a chitosan film deposited on a glass substrate. The scheme
presented here is capable to reach a resolution of about and even below 1% for relevant quantities in applications
involving imaging at 1.2 GHz in aqueous coupling fluids.
Soft matter acoustics is concerned with the application of acoustical techniques in the study of soft matter. In this
paper, we demonstrate the use of phase sensitive acoustic microscopy (PSAM) in synchronous mapping of threedimensional
heterogeneity of sample soft matter systems: thin film blends of polystyrene (PS) and poly
(methylmethacrylate) (PMMA). The use of acoustic phase contrast imaging for cure or health monitoring of
polymer systems is discussed.
Synchronous operation of a confocal laser scanning microscope (CLSM) and a confocal vector contrast scanning acoustic microscope (phase sensitive scanning acoustic microscopy: PSAM) has been developed. Imaging is performed on objects mounted on a cover slide with the CLSM operated in reflection through the slide with an immersion fluid and PSAM operating in water respectively aqueous solutions from the other side (half space). Examples involving living cells and soft matter samples illustrating various combinatory schemes and advantages of multi-contrast optical and acoustic contrast are demonstrated. This includes combinations with fluorescence microscopy and ultrasonic topographical imaging as well as combinatory three-dimensional imaging.
Acoustic and optical multiple contrast microscopy has been employed in order to explore characterizable parameters of
red blood cells, including cells infected by the parasite Plasmodium falciparum, in order to investigate cellular
modifications caused by the infection and to identify possible detection schemes for disease monitoring. Imaging
schemes were based on fluorescence, optical transmission, optical reflection, and amplitude and phase of ultrasound
reflected from the cells. Contrast variations observed in acoustic microscopy, but not in optical microscopy, were
tentatively ascribed to changes caused by the infection.
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