Evaporative casting

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

The distinguishing features of these sensors are the simplicity of their preparation and simple instrumentation. Typically, they are implemented as interdigitated electrodes (Fig. 8.4), which are patterned on an insulating substrate, and the signal is at zero frequency, that is, dc. The purpose of interdigitation is to increase the contact area. The selective layer is then deposited by solvent casting, evaporation sublimation, and so on, over the pattern of these electrodes. In most cases, the contact area for the positive and the negative terminal is the same. This fact does not aid the interpretation of the results. 

Figure 8.19. Phase diagram of PVC/NBR/THF and optical micrograph of the solution cast fdm. Spinodal and binodal curves are shown by the broken and solid lines, respectively. The arrow indicates the casting (evaporation) process [Inoue et al., 1985],...

Fig. 3.26 Casting-evaporating procedures for preparation of polymer/CW nanocomposites...

FIGURE 11.9 Schematic illustration of solution blending and subsequent casting-evaporation process for the preparation of CN-filled nanocomposites. See insert for color representation of the figure.)... 

In most publications, authors have opted for a simple casting-evaporation method in the preparation of starch-based nanocomposites. The general method consists in dispersing the nanocrystals in aqueous solution and adds this suspension to the mixtore of starch and other components which will be then gelatinized. Other authors prefer to add the suspension after the gelatinized starch. This was already discussed in section casting of nanocomposites. 

Alloin F, D Aprea A, Dufresne A, El Kissi N, Bossard F. Poly(oxyethylene) and ramie whiskers based nanocomposites influence of processing extrusion and casting/evaporation. Cellulose 2011 18 957-73. 

CNs have also been incorporated into poly(ethylene-co-vinyl acetate) (EVA) to make EVA/CN composite membranes. Elanthikkal et al. [59] investigated the effect of CN on barrier properties of EVA membranes. Cellulose from banana waste was exposed to alkali treatment, bleaching, and acid hydrolysis to obtain CNs. The resulting CNs were approximately 300 nm long with an average fiber diameter of 30 nm. Tetrahydrofuran was used as solvent to dissolve EVA and to disperse aqueous suspension of CNs. Membranes were obtained by casting-evaporation method. Cellulose fibers were exposed to alkali treatment and bleaching followed by acid hydrolysis. An aqueous suspension obtained after dialysis and ultrasonication was... 

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