Case Study of Polyvinylidene Fluoride Doping by Carbon Nanotubes

Modern material science often makes use of polyvinylidene fluoride thin films because of various properties, like a high thermal and chemical stability, or a ferroelectric, pyroelectric and piezoelectric activity. Fibers of this polymer material are, on the other hand, much less explored due to various issues presented by the fibrous form. By introducing carbon nanotubes via electrospinning, it is possible to affect the chemical and electrical properties of the resulting composite. In the case of this paper, the focus was on the further improvement of interesting polyvinylidene fluoride properties by incorporating carbon nanotubes, such as changing the concentration of crystalline phases and the resulting increase of the dielectric constant and conductivity. These changes in properties have been explored by several methods that focused on a structural, chemical and electrical point of view. The resulting obtained data have been documented to create a basis for further research and to increase the overall understanding of the properties and usability of polyvinylidene fluoride fiber composites.

Thermal crystallization of amorphous calcium phosphate combined with citrate and fluoride doping: a novel route to produce hydroxyapatite bioceramics

Amorphous calcium phosphate (ACP) is a material of high interest for dentistry, orthopedics, and other biomedical sectors. Being intrinsically metastable, the process of transformation of ACP into a crystalline phase...

Observation of the Reversible Ice III to Ice IX Phase Transition by Using Ammonium Fluoride as Anti-Ice II Agent

Ice III is a hydrogen-disordered phase of ice that is stable between about 0.2 and 0.35 GPa. Upon cooling, it transforms to its hydrogen-ordered counterpart ice IX within the stability region of ice II. Because of this metastability, detailed studies of the ice III to ice IX phase transition have so far not been carried out. Using ammonium fluoride doping to prevent the formation of ice II, we now present a detailed study on this phase transition using in-situ powder neutron diffraction. The <i>a</i> and <i>c</i> lattice constants are found to expand and contract, respectively, upon hydrogen ordering yielding an overall negative volume change. Interestingly, the anisotropy in the lattice constants persists when ice IX is fully formed and negative thermal expansion is observed. Analogous to the isostructural keatite and <i>b</i>-spodumenes, the negative thermal expansion can be explained through the build-up of torsional strain within in the <i>a</i>-<i>b</i> plane as the helical ‘springs’ within the structure expand upon heating. The reversibility of the phase transition was demonstrated for the first time upon heating. The ammonium fluoride doping induces additional residual hydrogen disorder in ice IX and is suggested to be a chemical way for ‘excitation’ of the ice-rules configurational manifold. Compared to ices II and VIII, the induced hydrogen disorder in ice IX is smaller which suggests a higher density of configurational states close to the ground state. This study highlights the importance of dopants for exploring water’s phase diagram and underpins the highly complex solid-state chemistry of ice.

Observation of the Reversible Ice III to Ice IX Phase Transition by Using Ammonium Fluoride as Anti-Ice II Agent

Ice III is a hydrogen-disordered phase of ice that is stable between about 0.2 and 0.35 GPa. Upon cooling, it transforms to its hydrogen-ordered counterpart ice IX within the stability region of ice II. Because of this metastability, detailed studies of the ice III to ice IX phase transition have so far not been carried out. Using ammonium fluoride doping to prevent the formation of ice II, we now present a detailed study on this phase transition using in-situ powder neutron diffraction. The <i>a</i> and <i>c</i> lattice constants are found to expand and contract, respectively, upon hydrogen ordering yielding an overall negative volume change. Interestingly, the anisotropy in the lattice constants persists when ice IX is fully formed and negative thermal expansion is observed. Analogous to the isostructural keatite and <i>b</i>-spodumenes, the negative thermal expansion can be explained through the build-up of torsional strain within in the <i>a</i>-<i>b</i> plane as the helical ‘springs’ within the structure expand upon heating. The reversibility of the phase transition was demonstrated for the first time upon heating. The ammonium fluoride doping induces additional residual hydrogen disorder in ice IX and is suggested to be a chemical way for ‘excitation’ of the ice-rules configurational manifold. Compared to ices II and VIII, the induced hydrogen disorder in ice IX is smaller which suggests a higher density of configurational states close to the ground state. This study highlights the importance of dopants for exploring water’s phase diagram and underpins the highly complex solid-state chemistry of ice.

Fluorinated Polyimide-Film Based Temperature and Humidity Sensor Utilizing Fiber Bragg Grating

We propose and demonstrate a temperature and humidity sensor based on a fluorinated polyimide film and fiber Bragg grating. Moisture-induced film expansion or contraction causes an extra strain, which is transferred to the fiber Bragg grating and leads to a humidity-dependent wavelength shift. The hydrophobic fluoride doping in the polyimide film helps to restrain its humidity hysteresis and provides a short moisture breathing time less than 2 min. Additionally, another cascaded fiber Bragg grating is used to exclude its thermal crosstalk, with a temperature accuracy of ±0.5 °C. Experimental monitoring over 9000 min revealed a considerable humidity accuracy better than ±3% relative humidity, due to the sensitized separate film-grating structure. The passive and electromagnetic immune sensor proved itself in field tests and could have sensing applications in the electro-sensitive storage of fuel, explosives, and chemicals.