Bubble-stretching

Cai LF, Huang XB, Rong MZ, Ruan WH, Zhang MQ (2006) Fabrication of nanoparticle/ polymer composites by in situ bubble-stretching and reactive compatibilization. Macromol Chem Phys 207(22) 2093-2102... 

When the centrifugal force is larger than the surface tension force, the bubble would be stretched in the x-direction. During the stretching, the aspect ratio, a, becomes smaller while d, and M), can be assumed to remain constant. As a result, the centrifugal force increases, the surface tension force decreases, and the bubble stretching becomes an irreversible process. Using the Davies-Taylor equation (Davies and Taylor, 1950) for the bubble rise velocity, the maximum stable bubble size is expressed by... 

Refer to Fig. 4-26. After the plastic sheet is heated and sealed across the female cavity (A), air is introduced into the mold cavity and blows the sheet upward into a bubble stretching it evenly (B). Normally an electric photocell is used to control the height of the bubble. A plug, shaped roughly to the contour of the cavity, plunges into the plastic sheet (C). When the plug has reached its lowest position, a vacuum is drawn on the cavity to complete formation of the sheet (D). In some instances pressure forming air is also used in this process. 

In pneumatic prestretching or bubble stretching, the hot sheet is clamped over a hollow shape that acts as a blow box. TTie sheet is then inflated with air pressure of up to 70 KPa with the height of the bubble monitored and controlled with a photoelectric eye or a microswitch. For male or positive molds, the sheet is drawn with vacuum into a draw box. The mold is then immersed into the prestretched sheet. Again, the extent of prestretching is monitored and controlled. The shape of the prestretched bubble is determined by the variation in temperature across the sheet surface. 

In consideration of the fact that stretching is superior to shearing in separating aggregated granules, Wu and co-workers proposed an in situ bubble-stretching... 

Bubble-stretching induced dispersion of Si02 nanopaiticles in PI matrix... 

Figure 3.16. Schematic drawing of the proposed bubble-stretching effect realized via graft itiacroiiiolecular foaming agent onto silica naiiopai ticles [37]...

There are a number of relatively simple experiments with soap films that illustrate beautifully some of the implications of the Young-Laplace equation. Two of these have already been mentioned. Neglecting gravitational effects, a film stretched across a frame as in Fig. II-1 will be planar because the pressure is the same as both sides of the film. The experiment depicted in Fig. II-2 illustrates the relation between the pressure inside a spherical soap bubble and its radius of curvature by attaching a manometer, AP could be measured directly. 

Both high bulk and surface shear viscosity delay film thinning and stretching deformations that precede bubble bursting. The development of ordered stmctures in the surface region can also have a stabilizing effect. Liquid crystalline phases in foam films enhance stabiUty (18). In water-surfactant-fatty alcohol systems the alcohol components may serve as a foam stabilizer or a foam breaker depending on concentration (18). 

Bubbles are formed instantaneously. This conclusion made in [33] is based on estimates taken from earlier works [37]. As seen from the above cited works by S. E. Sosin et al., this is not always true viscoelastic liquids under triaxial stretching stress are not destroyed instantly. The existence of an induction period may produce a considerable effect on foam growth kinetics upon free foaming, when pressure is lowered instantaneously from P > Pcr to P < Pcr in a melt with dissolved gas. However, it would appear that microfaults in polymer melts, which are caused by factors... 

In quiescent liquids and in bubble columns, buoyancy-driven coalescence is more important. Large fluid particles with a freely moving surface will also have a low-pressure region at the edge of the particle where the velocity is maximum. This low-pressure region will not only allow the bubble to stretch out and form a spherical cap but also allow other bubbles to move into that area and coalesce. Figure 15.14 shows an example of this phenomenon. 

Stretching a polymer in two perpendicular directions, either successively or by blowing a bubble of molten material, leads to its biaxial orientation, which strongly improves mechanical properties in the stretching directions and/or gas permeability (e.g., biaxial orientation of polypropylene leads to BOPP (for biaxially oriented polypropylene) or biaxial orientation of poly(ethylene terephthalate) gives CC>2-impermeable bottles for carbonated beverages.) (Characterisation methods for determining molecular orientation are considered in Chapter 8.)... 

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