Polymers bubbles

It has been known for a long time that gas is formed during irradiation of PMMA. When the internal pressure of the gas formed in the reaction is sufficient to overcome the viscosity of the irradiated polymer, bubbling occurs. By suitable control of the irradiation dose and subsequent heating of the polymer, this bubbling effect can transform PMMA into a foamed material. Data on the volatile products formed at room temperature has been given by many workers [392—396]. The results are shown in Table 29. The yields seem to depend on the purity of the polymer sample. This problem will be discussed below in relation to the yield of chain scission. 

The possibility of preparing colloidal particles of Pt between 50 - 60 A in diameter by photoreduction of K2PtCl4 inserted into polymer bubbles [49] was demonstrated. It was, moreover, found that the catalyst activity in during C2H4 hydrogenation increases with a decrease in Pt particle size. The dispersity of colloidal particles size depended on the concentration of the solvent used for K2PtCl4. 

Microcapsules are small polymer bubbles in which a thin pol5mier wall surrounds a core of active solute. These microcapsules are often used to deliver special ingredients as part of a product. For example, in a hand soap, microcapsules could release perfume while one is washing their hands. 

A recent design of the maximum bubble pressure instrument for measurement of dynamic surface tension allows resolution in the millisecond time frame [119, 120]. This was accomplished by increasing the system volume relative to that of the bubble and by using electric and acoustic sensors to track the bubble formation frequency. Miller and co-workers also assessed the hydrodynamic effects arising at short bubble formation times with experiments on very viscous liquids [121]. They proposed a correction procedure to improve reliability at short times. This technique is applicable to the study of surfactant and polymer adsorption from solution [101, 120]. 

The film tube is collapsed within a V-shaped frame of rollers and is nipped at the end of the frame to trap the air within the bubble. The nip roUs also draw the film away from the die. The draw rate is controlled to balance the physical properties with the transverse properties achieved by the blow draw ratio. The tube may be wound as such or may be sHt and wound as a single-film layer onto one or more roUs. The tube may also be direcdy processed into bags. The blown film method is used principally to produce polyethylene film. It has occasionally been used for polypropylene, poly(ethylene terephthalate), vinyls, nylon, and other polymers. 

Writing by Bubble Forming. Bubble formation occurs under thin metal layers on polymeric substrate films, caused by local evaporation when hit by a focused laser beam (see Fig. 3c). Bubble formation occurs as in the DIP concept in dye-in-polymer films which are covered by a thin metal (mostiy gold) or ceramic layer (6) (see Fig. 3d). 

The mechanism of hole- or bubble-forrning in metal or dye polymer layers continues to be a subject of intensive investigation (7). 

Reversible Rubble Generation. In a two-layered pigmented polymeric layer system with ceramic coating, a bubble forms beneath the ceramic coating when heated locally (write process). For erasure, the bubble is closed again by heating the polymer close to its melting poiat (119). This development is also hampered by extensive erase times (>5 ms). 

Foam Inhibitors. Methyl sihcone polymers of 300-1000 mm /s(= cSt)) at 40°C are effective additives at only 3—150 ppm for defoaming oils in internal combustion engines, turbines, gears, and aircraft appHcations. Without these additives, severe churning and mixing of oil with air may sometimes cause foam to overflow from the lubrication system or interfere with normal oil circulation. Because sihcone oil is not completely soluble in oil, it forms a dispersion of minute droplets of low surface tension that aid in breaking foam bubbles. 

Pure amorphous polymers, being homogeneous materials, are transparent. Atactic polystyrene is a good example. The crystalline syndiotactic form is not transparent. Alack of transparency does not necessarily indicate crystallinity, however. It can also be caused by inorganic fillers, pigments, gas bubbles (as in a foam), a second polymer phase, etc. 

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