Drop size dependence of contact angles on two fluoropolymers

Axisymmetric Drop Shape Analysis (ADSA): An Outline

Drop shape techniques for the measurement of interfacial tension are powerful, versatile and flexible. The shape of the drop/bubble depends on the balance between surface tension and external forces, e.g. gravity. This balance is reflected mathematically in the Laplace equation of capillarity. Axisymmetric Drop Shape Analysis (ADSA) is a commonly used drop shape technique. A streamlined version of the development of ADSA over the past several decades is presented to illustrate its validity and range of utility. Several configurations of interest will be considered and presented systematically. Shape and surface tension will be linked to a shape parameter based on proper concepts of differential geometry. The resulting shape parameter will be shown to allow determination of the range of applicability of such a drop shape method.

Effect of energetic materials wettability on their outdoor effective elution rate

Energetic materials (EM) contained in military ammunitions have been found in the surface soil and water of training areas and may potentially represent a threat to human health and the environment. EM wettability is an essential physical parameter to characterize because it controls EM dissolution rate. This paper was conducted to determine the wettability of conventional and new EM formulations used in military ammunition. Wettability was estimated in the laboratory via contact angle measurements of water droplets on different EM surfaces. Results show that 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazinane (RDX), Octol and energetic thermoplastic elastomer (ETPE) 1000 are hydrophilic while Composition B, XRT, GIM, CX-85, ETPE 2000, and C4 are hydrophobic whereas HELOVA gun propellant has a mixed wettability oscillating between hydrophilic and hydrophobic. The present study demonstrates that wettability of EM formulation is generally controlled by their matrix constituents. Results indicate that hydrophobic formulations have a much slower outdoor environmental effective elution rate than hydrophilic ones, with the exception of the hydrophobic C4 formulation whose elution rate is extremely high. The addition of hydrophobic components into EM formulations is recommended to diminish the environmental impact on water, as it has already been done with XRT, GIM and CX-85 formulations.

Basic characterization and investigation of a fluorinated terpolymer in pure state and in mixtures with kaolinite at solid interphases of thin films prepared by facile solution cast and nonsolvent methods

In this work, both basic characterization and solution cast thin films of a fluorinated terpolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (VDF), known as THV, are studied. Thermal analysis of the terpolymer depicted a broad melting temperature, and thermal degradation started at 170 K above the melting temperature. Solution fluorine 19 nuclear magnetic resonance results revealed that THV 221G has higher TFE content than those of HFP and VDF. Increase in water contact angle is observed in thin films prepared from THV in pure state by the more specific nonsolvent preparation technique. By the same specific method, a similar increase is seen in thin films prepared from mixtures of polymer and kaolinite. Upon mixing the terpolymer of THV with hydrophilic kaolinite, a natural mineral, it is still possible to obtain rough and hydrophobic surfaces. The highest contact angle was obtained upon using the facile nonsolvent approach. Further, preparing the thin films with the addition of the hydrophilic mineral did not change the hydrophobic character of the films.