Experiments demonstrating foam

A number of rheological experiments with foams and emulsions are summarized in the reviews by Prud home and Khan " and Tadros. " These experiments demonstrate the influence of films between the droplets (or bubbles) on the shear viscosity of the dispersion as a whole. Unfortunately, there is no consistent theoretical explanation of this effect accounting for the different hydrodynamic resistance of the films between the deformed fluid particles as compared to the nondeformed... 

Film transfer experiments demonstrate that there is always a sheath of subphase associated with the monolayer. However when the mono-layer is compressed or decompressed in an enclosed area, there will be a certain degree of slippage at the monolayer/subphase interface. When the subphase water molecules are strongly bound to the monolayer, as for a protein monolayer spread on an aqueous substrate at its isoelectric point, little slippage exists, and the phenomenon in Figure 1 is observed. For monolayer systems where there is substantial slippage at the mono-layer/ subphase interface the effect will not be observed during compression or decompression experiments. This effect helps explain why proteins are used with other surfactants to stabilize emulsion and foam formulations 1,2). 

A number of rheological experiments with foams and emulsions are summarized in the reviews by Prud home and Khan [915] and Tadros [916]. These experiments demonstrate the influence... 

Our experiment demonstrated that cell collapse occurs during the cell nucleation and growth stages of the PET foaming process. PET with low intrinsic viscosity (IV) and low molecular weight were extrusion-foamed using CO2 as... 

A study was made of nucleation in PE foams produced in a counter-rotating extruder using talc powders and masterbatches as nucleating agents and CFG and HCFC blowing agents. The results indicated the importance of shear force in nucleation, as proposed in the lump cavity nucleation model and demonstrated by melt temperature effects observed in these experiments. It was shown that shear enhancement via lump break-up was not a vital mechanism in nucleation. 6 refs. 

Similarly, a Rh foam monolith with 0.56 wt.% Rh gave a lower optimal H2 selectivity than a Rh foam monolith with 9.83 wt.% Rh (75% vs. 87%). In both the Pt and the Rh experiments, the samples with the lower metal loa gs had significantly higher adiabatic reaction temperatures because of the heat generated by the formation of H2O. As demonstrated by these experiments, the formation of H2 occurs on the noble metal surface, not in the gas phase or on the catalyst support. 

Princen [57, 64, 82] and others [84] also noted the presence of wall-slip in rheological experiments on HIPEs and foams. However, instead of attempting to eliminate this phenomenon, Princen [64] employed it to examine the flow properties of the boundary layer between the bulk emulsion and the container walls, and demonstrated the existence of a wall-slip yield stress, below that of the bulk emulsion. This was attributed to roughness of the viscometer walls. Princen and Kiss [57], and others [85], have also showed that wall-slip could be eliminated, up to a certain finite stress value, by roughening the walls of the viscometer. Alternatively [82, 86], it was demonstrated that wall-slip can be corrected for and effectively removed from calculations. Thus, viscometers with smooth walls can be used. This is preferable, as the degree of roughness required to completely eradicate wall-slip is difficult to determine. 

Work at the EPA Gulf Breeze Laboratory has demonstrated the potential usefulness of encapsulation in the bioremediation of PAHs. A model system has been developed in which a pure culture capable of degrading fluoranthene (strain EPA505) has been successfully encapsulated in polyurethane foam and polyvinyl alcohol (Baker et al., 1988). The capsules can be stored for several months at 4 °C with only minimal loss of viability. Upon addition of the capsules to moist soil, fluoranthene mineralization commenced in approximately the same way as observed when fresh bacterial cells were added to the soil. These results are shown in Figure 5.7a. Since the same inoculation size was used in all flasks during this experiment, the results suggest that the immobilization process does not significantly affect microbial activity. 

This experiment is another example of a step-growth polymerization, one that produces a crosslinked polymer. Two liquids are mixed, beginning the chemical reactions that cause polymerization and foam generation. The result is a hard polyurethane foam, similar to the material commonly used for insulation, for flotation in boats and canoes, and in furniture. This activity works well either as a laboratory experiment or as a demonstration. ... 

If you have been highlighting a polymer a week, the first four experiments in Section A— Free Radical Polymerization, Synthesis of Nylon, Synthesis of Polyesters in the Melt, and Synthesis of a Polyurethane Foam —are excellent demonstrations to intersperse with the content as it is presented. If you want your students to actually perform the experiments, it might be best to wait until the end of a first-year chemistry course when the students have developed their laboratory techniques to the greatest extent. Another use for the four experiments would be to introduce a different one each quarter and discuss the polymer produced in the experiment. This is a good way to use the information on polymer chemistry if time does not permit the presentation of a Polymer of the Week. 

In conclusion it is worth to point out that the experiments with phosphatidylcholine foam bi layers demonstrate that these bi layer may exist in different phase states, corresponding to different condensed states of amphiphile monolayers constituting the foam bi layer. 

This technique was demonstrated using the bacitracin complex (BC) as a test sample because of its strong foaming capacity. The foam CCC experiment for sep-... 

To demonstrate the same effect for a foam, repeat this experiment without the oil (if you use the same container you must rinse it thoroughly first to remove any traces of the washing up liquid). Put approximately 200 ml of water in the container and shake vigorously. Bubbles form but burst very quickly when you stop shaking. When you add the washing up liquid, the surface active molecules stabilize the bubbles and a much longer lasting foam is formed. 

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