Polyvinylidine Fluoride Research Articles

The equation of state of supercritical HF, HCl, and reactive supercritical mixtures containing the elements H, C, F, and Cl

We develop a model of chemical equilibrium mixtures containing the elements H, C, F, and Cl. The model is based on a recently developed equation of state for the exponential-6 fluid, combined with a simple equation of state for condensed carbon. We show that the shock response of a wide variety of molecular and polymeric fluorocarbons and chlorocarbons can be modeled as a chemical equilibrium mixture of a small number of dissociation product molecules. In particular, we predict that shocked polyvinylidine fluoride (PVF2) decomposes into a fluid phase composed mostly of HF, and a phase containing condensed carbon. HF is known to strongly associate in the supercritical fluid phase. We predict that such an association also occurs under shock conditions.

Growth and chemotherapeutic response of cells in a hollow-fiber in vitro solid tumor model.

Cancer treatments that appear promising in tissue culture are often less effective in solid tumors, in part because of the proliferative and microenvironmental heterogeneity that develops in these tumors as they grow. Heterogeneous tumor models are thus needed for drug screening. Our goal was to develop and test for drug evaluation a solid tumor model based on cell growth inside biocompatible hollow fibers. Building on the experience of Hollingshead and co-workers with a sparse-cell, hollow-fiber tumor model, we tested six human tumor cell lines for in vitro growth inside 450-microns internal-diameter polyvinylidine fluoride fibers and examined them histologically. Human SW620 colon carcinoma cells grown in hollow fibers were also examined using electron microscopy, and their doxorubicin sensitivity was assessed. A colorimetric assay based on sulforhodamine B was adopted to replace the more cumbersome clonogenic cell survival assay. Five of the human tumor cell lines tested grew to confluence, forming heterogeneous in vitro tumors with subpopulations of viable and necrotic cells. For SW620 hollow-fiber tumors, maximum viable cell populations in excess of 10(8) cells/mL were obtained after 8 days of growth. This viable cell density remained roughly constant for 3-4 days, permitting dose-response experiments over this time interval. Tumor cells in hollow fibers were much more resistant to a 4-hour doxorubicin exposure than were tumor cells in monolayers: LC50 values (i.e., the drug concentrations at which the plating efficiency equals one-half the plating efficiency of untreated cells) of 3.5 microM and 0.16 microM were obtained for hollow-fiber tumors and monolayers, respectively. LC50 values decreased when drug exposure time was increased. Results from the colorimetric assay were in agreement with those from the clonogenic assay. The successful growth of tumor cells to confluence in hollow fibers and the feasibility of performing in vitro drug dose-response experiments with a relatively easy colorimetric assay demonstrate the potential of the hollow-fiber solid tumor model as a tool for experimental therapeutic research. Hollow-fiber solid tumors may prove useful for experimental drug evaluation.

AURA: A NEW RESPIRATORY MONITOR AND APNOEA ALARM FOR SPONTANEOUSLY BREATHING PATIENTS

Previous attempts to introduce non-invasive monitoring of ventilation of spontaneously breathing patients into routine practice have been unsuccessful. The Aberdeen University Respiratory Alarm (AURA) allows such monitoring by utilizing the pyroelectric property of polarized polyvinylidine fluoride sensors to detect temperature changes that occur during breathing into an oxygen delivery face mask. A quartz crystal oscillator generates pulses that allow measurement of interexpiratory time and ventilatory frequency. The system incorporates LED digital displays, a bargraph and audiovisual alarms. An analog output permits display and analysis of the sensed signals. AURA performed satisfactorily in both volunteer studies and six patients in the clinical setting. AURA may be an appropriate respiratory transducer in those patients requiring oxygen therapy.

Soliton dynamics in a microstructured lattice model

The nonlinear dynamics of localized structures of the soliton type in a lattice model involving internal degrees of freedom in rotation is presented. The physical model consists basically of a one-dimensional monoatomic chain equipped with microscopic electric dipoles associated with molecular groups. The model is particularly suitable for molecular ferroelectric crystals such as sodium nitrite exhibiting structures in ferroelectric domains and walls or for long chains of polymers such as crystalline polyethylene or polyvinylidine fluoride and others where molecular groups perform rotational motions. Two main types of motion can be distinguished in this picture: (i) the longitudinal and transverse displacements of the mass centre of the molecular group and (ii) two rigid-body rotational motions of the electric dipoles about the chain axis and perpendicular to it. The propagation of coupled solitons is investigated for two elementary configurations. A situation for which all the dipoles rotate perpendicularly to the chain axis is first studied. A second configuration is next considered when the dipole rotation takes place about the chain axis.

Noninvasive measurement of dynamic pressure inside pipes using piezoelectric strip

This paper presents the use of piezoelectric material wrapped around the outside diameter of a pipe wall for measuring the dynamic pressure inside the pipe. Recently available piezoelectric materials such as polyvinylidine fluoride (PVDF) are flexible enough to wrap around a pipe wall and provide an excellent transducer for measuring the breathing response of the pipe wall to the internal dynamic pressure. The strain induced in the piezoelectric element associated with radial deformation of the pipe wall is measured. It is shown that the sensor, since it sums the response around the entire circumference, will discriminate against strains associated with bending of the pipe for all circumferential orders which occur below the ring frequency. The relationship between the measured piezoelectric element voltage and pressure, taking into account the pipe wall characteristics, is presented. Various configurations of the device are discussed and experimental results comparing the sensor output to that of a flush mounted hydrophone are presented.

Hydrophone measurements in diagnostic ultrasound fields

Some of the methods, calculations, and problems associated with making hydrophone measurements in diagnostic ultrasound fields are considered. Several organizations have proposed definitions of various peak and average intensities that need to be specified when characterizing medical ultrasound fields. All of these can be determined from hydrophone measurements, but the bandwidths encountered (>50 MHz), along with the small focal diameters achievable ( approximately 1 mm), can place great demands on hydrophone performance. Two general types of hydrophones are available-the spot-poled membrane and needle types. Both employ the piezopolymer polyvinylidine fluoride (PVDF), and for the most part they have effective dimensions in the 0.5-1.0-mm range. Hydrophones can be made with useful bandwidths extending beyond 50 MHz. However, above approximately 15 MHz the nature of the response becomes highly dependent on the method of construction and PVDF film thickness used, as well as the characteristics of any associated preamplifier circuitry. Other factors that can affect measurement accuracy are discussed.

Wide-band piezoelectric polymer acoustic sources

The design of a wideband acoustic source made of the piezoelectric polymer polyvinylidine fluoride (PVDF) is described. The source was developed for the characterization and absolute calibration of ultrasonic hydrophone probes. Construction details are described and performance characteristics of the wideband PVDF transmitter, including its transmitting voltage response and directivity patterns, are compared with theoretical predictions in the frequency range up to 40 MHz. The Krimholtz-Leedom-Mattaei (KLM) model was used to examine the influence of the PVDF polymer film thickness, the backing acoustic impedance, the cable length, and the electrical source resistance on overall transmit transfer characteristics. A comparison is made with traditional piezoelectric ceramic acoustic sources, and it is shown that piezopolymer transmitters exhibit some improved properties and are well suited for certain ultrasound dosimetry applications. In particular, the polymer sources have been found useful in measurements based on swept-frequency excitation. Those measurements allow characterization of transmitters and receivers to be performed as a virtually continuous function of frequency.

Magnetic Properties of Iron Implanted Polymers and Graphite

ABSTRACTWe have measured the magnetic properties of highly oriented pyrolytic graphite (HOPG), polyethylene (PE), and polyvinylidine fluoride (PVF2), implanted with fluences of 25 keV iron atoms ranging from 1016 to 1017 atoms/cm2 . The lowest fluence specimens were paramagnetic down to 2 K, with evidence for clusters of only a few spins, while the highest fluence specimens were clearly ferromagnetic, with magnetization curves resembling those of a set of randomly oriented soft magnetic planes. The critical fluence for formation of a ferromagnetic state appears to be between 1 and 3 × 1016 atoms/cm2 at 25 keV. Theseresults can be qualitatively understood based on the critical density for percolation of near neighbor exchange interactions.

Nonlinear acoustic off-axis imaging

Nonlinear imaging, in which object acoustic illumination is at a frequency ω and the output is detected at 2ω, has been complicated by competing nonlinear generation from the propagation medium between the object and the output lens. However, recent results with a nonspecular oblique incidence acoustic reflection microscope show interesting object nonlinear generation from polyvinylidine fluoride (PVF)2 and mica in granite. These micrographs will be presented and discussed.

Studies of PVF2 transducers

Thin film polyvinylidine fluoride (PVF2) polymer transducers are being used for various applications over the frequency range 0.2 to 30 MHz. Operated in the thickness mode, they have been employed as sources and detectors of longitudinal and surface waves. Wideband impulses are easily generated and detected with these elements, so that a transducer's performance can easily be evaluated by examining its direct and Fourier transformed response. Detailed data are presented on the sensitivity, frequency response, and other characteristics of various PVF2 transducer configurations. [Work was partially performed at Stanford University and supported by ONR.]

Experimental studies of ultrasonic radiation from cylindrical shells in water

Studies are being made of ultrasonic waves radiated into water from air‐filled cylindrical metal shells. A shell is directly excited by polyvinylidine fluoride thin film transducers mounted on its inside surface. By using arrays of such transducers it has been possible to excite various normal modes of the cylinder. Both schlieren and acoustic probe techniques are being used to examine the radiated acoustic fields. Data are presented to indicate the applicability of this new technique. [Work supported in part by ONR.]

PVF2 dual mode sensor technology

In continuation of papers presented to the Society in the area of automatic vehicle ranging and target classification, the current effort is to prove the viability of using a polyvinylidine fluoride (PVF2) thin‐film detector to detect both airborne acoustic‐ and infrared‐emitted vehicle signatures. In brief, vehicle detection and discrimination have been performed using a single‐point detector to sample both information spectra. Infrared detectors of PVF2 material have been known for some time. Our work in combining these effects to form a viable dual‐mode sensor has led to some novel and interesting potential applications. Using a single detection element in this manner leads to intrusion techniques that can classify and locate intruders, sort out nonalarms, such as animals and spurious events, and open up the possibility of triple‐mode operation (where the third sensor input could be seismic in nature). Vehicle signature separation is accomplished by noting that the PVF2 detector has a frequency respons...

On the Nature of Poling by Corona Charging and the Pyroelectric Effect in PVF2

The effect of corona charging (at 12.5 kV) of polyvinylidine fluoride (PVF <L xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</L> ) is studied by infrared spectroscopy and X-ray diffraction techniques. The results show that changes in molecular conformation occur with such a poling process that is in agreement with Southgate. The pyroelectric coefficient was observed to increase significantly after such a poling, reaching a maximum value of ~3 nC/cm2K at ~343 K. It is suggested that the pyroelectricity in PVF2 at this temperature is due to dipolar orientation.