What is spinodal decomposition?

Phase separation may occur in a way that the growth is not in extent but in amplitude. Only in the unstable region such a procedure is thermodynamically feasible. In a phase diagram the unstable region is defined by the spinodal. When a system has crossed this locus, phase separation occurs spontaneously without the presence of a nucleation step. This process is known as spinodal decomposition and commonly results to a high interconnectivity of the two phases. The Cahn-Hilliard equation describes the kinetics of the process. In this note both processes (nucleation and spinodal) are depicted schematically

H2O removal from diesel and JP8 fuels: A comparison study between synthetic and natural dehydration agents

The comparison between Thermal Polyaspartate Anion, TPA, and natural resin in their effect on the improvement of the physicochemical properties of both conventional diesel and JP8 fuels is the main scope of this work. Specifically, both studied materials were used dehydration agents in order to increase the physicochemical properties of both treated fuels. The higher amount of the removed water was obtained when used the natural resin as adsorbent material. In this case the water concentration decreased into diesel up to 68.66 % and more than 30 % in the case of jet fuel (JP8). This water removal improves the studied physicochemical properties of both studied fuels, diesel and JP8, for example up to 633 J/g (using natural resin as dehydration agent (removable additive)) and 1040 J/g (using TPA as dehydration agent) for the heat of combustion. Overall, the proposed method can be used in a simple fuel cleaning process using a metal mesh vessel of synthetic TPA polymer or natural resin. The higher water/humidity removal amount in conjunction with the very low price of the natural resin makes this material more promising for the up scaling of the proposed technique in the near future

On the formation of nanobubbles in vycor porous glass during the desorption of halogenated hydrocarbons

Vycor porous glass has long served as a model mesoporous material. During the physical adsorption of halogenated hydrocarbon vapours, such as dibromomethane, the adsorption isotherm exhibits an hysteresis loop; a gradual ascent is observed at higher pressures during adsorption, and a sharp drop is observed at lower pressures during desorption. For fully wetting fluids, an early hypothesis attributed the hysteresis to mechanistic differences between capillary condensation (adsorption) and evaporation (desorption) processes occurring in the wide bodies and narrow necks, respectively, of 'ink-bottle' pores. This was later recognized as oversimplified when the role of network percolation was included. For the first time, we present in-situ small angle x-ray scattering measurements on the hysteresis effect which indicate nanobubble formation during desorption, and support an extended picture of network percolation. The desorption pattern can indeed result from network percolation; but this can sometimes be initiated by a local cavitation process without pore blocking, which is preceded by the temporary, heterogeneous formation of nanobubbles involving a change in wetting states. The capacity of the system to sustain such metastable states is governed by the steepness of the desorption boundary

Reinforcement effects of multiwall carbon nanotubes and graphene oxide on PDMS marine coatings

Poly (dimethyl siloxane) (PDMS) is a model silicon elastomer used as marine fouling-release coating, because it meets the fouling-release zone conditions of the Baier curve. However, weak mechanical properties limit its use. In this aspect, incorporation of carbon nanoparticles into PDMS is a common method for improving its mechanical properties. Since effective dispersion of nanofillers into polymer matrices is a challenge, a major aim of this study was to examine the PDMS mechanical reinforcement by developing different dispersing methods of pristine MWCNTs into PDMS matrix. SEM images of nanocomposites prepared using dispersion methods 1 and 2 revealed the formation of aggregates which subsequently affected the overall mechanical performance of the samples. Also, the effect of p-MWCNTs content and nanoparticle type [carboxyl-functionalized-MWCNTs, graphene oxide (GO)] on the mechanical properties of the nanocomposites was evaluated. Incorporation of p-MWCNTs did not alter drastically the critical surface energy value of neat PDMS, which subsequently influenced antifouling and cleaning performance of nanoreinforced coatings. To evaluate antifouling and cleaning performance of the nanocomposite coatings, seawater immersion tests were conducted. In conclusion, MWCNTs and GO increased the mechanical strength of the matrix, whereas they contributed to a small extent to the improvement in antifouling and cleaning performance of the composites