RESUMEN
Ferroelectric materials exhibit a phase transition to a paraelectric state driven by temperature - called the Curie transition. In conventional ferroelectrics, the Curie transition is caused by a change in crystal symmetry, while the material itself remains a continuous three-dimensional solid crystal. However, ferroelectric polymers behave differently. Polymeric materials are typically of semi-crystalline nature, meaning that they are an intermixture of crystalline and amorphous regions. Here, we demonstrate that the semi-crystalline morphology of the ferroelectric copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) strongly affects its Curie transition, as not only a change in crystal symmetry but also in morphology occurs. We demonstrate, by high-resolution nanomechanical measurements, that the semi-crystalline microstructure in the paraelectric state is formed by crystalline domains embedded into a softer amorphous phase. Using in situ X-ray diffraction measurements, we show that the local electromechanical response of the crystalline domains is counterbalanced by the amorphous phase, effectively masking its macroscopic effect. Our quantitative multi-scale characterisations unite the nano- and macroscopic material properties of the ferroelectric polymer P(VDF-TrFE) through its semi-crystalline nature.
RESUMEN
Considerable changes have been occurring in the original concepts of drinking water quality, and at present the principles of water treatment are more generally accepted, especially those concerning the elimination of harmful matter and fluoridation programs that improve dental health by maintaining a low and accurate level of fluoride in the water
Current engineering advances in materials, supplies, equipment, and processes are so effective that the accurate and safe fluoridation of all water systems is possible. The acceptance of the addition to water of such substances as aluminum, phosphorus, calcium and chlorine compounds, which have helped improve water systems, has made acceptable also the addition of flourides which not only improve the system but also increase the effectiveness of drinking water in protecting users against dental caries
The problem of obtaining competent personnel responsible for drinking water systems in small communities with little economic resources, has been solved by contracting a single expert to operate and maintain the equipment, including fluoridation equipment, used by several communities at the same time. For this purpose, education and training courses for such operators have also been established
Other important contributions of engineering to fluoridation include uniformity in the quality of the fluoride compounds; use of fluorite, a compound which ...(AU)