PDMS Rupture

This work was supported by the MRSEC program of the National Science foundation (DMR-0076097) at the Materials Research Center of Northwestern University. We also thank Mark Hammersky of Proctor and Gamble for providing the TMPC used in these experiments. Much of this work was pubhshed previously in Ref [40]. 

Duchet, )., Gerard, ).F., Chapel, J.P., Chabert, B., Brisson, Journal of Applied Polymer Science, 2003, 87(2), 214— 229. 

Proceedings of the Royal Society of London Series A — Mathematical and Physical Sciences, 1971, 324(1558), 301—313. 

12 Maugis, D., Barquins, M., Journal of Physics D-Applied Physics, 1978, 13(14), 1989. 

14 Mangipudi, V. S., Huang, E., Tirrell, M., Pocius, A. V., Macromolecular Symposia, 

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Fig. 13. Shear stress t12 and first normal stress difference N1 during start-up of shear flow at constant rate, y0 = 0.5 s 1, for PDMS near the gel point [71]. The broken line with a slope of one is predicted by the gel equation for finite strain. The critical strain for network rupture is reached at the point at which the shear stress attains its maximum value...

The mechanism of movement is attributed to the rupture of oxygen bubbles creating a propulsive force driving the PDMS boat forward at the air/water interface. 

A model has been developed to describe the penetration of polydimethylsi-loxane (PDMS) into silica agglomerates [120]. The kinetics of this process depend on agglomerate size and porosity, together with fluid viscosity. Shearing experiments demonstrated that rupture and erosion break-up mechanisms occurred, and that agglomerates which were penetrated by polymer were less readily dispersed than dry clusters. This was attributed to the formation of a network between sihca aggregates and penetrated PDMS, which could deform prior to rupture, thereby inhibiting dispersion. 

In addition to the compression loading, uniaxial extension of entangled PDMS chains have been investigated by pulling a small portion of the material and measuring elastic response before the rupture happens [419]. The multiple ruptures observed in the force-distance curves (Fig. 43) have been interpreted as fractures of an entangled network of PDMS chains formed between the tip and the silica grafted surface. At small deformations, also the capillary forces were shown to contribute in the force. The elastic part of the curves was described us-... 

Even if the surface is not perfectly smooth, the initial event that must occur in the development of a nucleus is passivity breakdown, in which the protective oxide layer is ruptured to expose the underlying metal to the aqueous environment. The most highly developed theory for this process is the point defect model (PDM) [59-65]. This model postulates that the generation of cation vacancies at the film/solution interface, and their subsequent transport across the barrier layer of the passive film, is the fundamental process fiiat leads to passivity breakdown. Once a vacancy arrives at the metal/film interface, it may be annihilated by reaction (i) in Fig. 31 ... 

Undissolved oil droplets form in the surface of the film, and this can lead to film rupture. Several examples of oils may be used alkyl phosphates, diols, fatty acid esters and silicone oils (e.g., polydimethyl siloxane PDMS). 

One possible explanation of this synergetic effect is that the spreading coefficient of the PDMS oil is modified by the addition of hydrophobic particles. It has been suggested that the oil-particle mixtures form composite entities where the particles can adhere to the oil/water interface. Subsequently, the presence of particles adhering to the oil/water interface may facilitate the emergence of oil droplets into the air/water interface, so as to form lenses leading to rupture of the... 

Many of the properties of the polysiloxanes have been tabulated in handbooks of polymer science and engineering. Recent work has included the stretching of polydimethylsdoxane (PDMS) chains, in some cases to their rupture points. ... 

Self-healing is often used in a broader sense, to mean reconstruction of the entire polymer instead of just its surface. A relevant example here is a PDMS elastomer that contains microencapsulated PDMS resin and microencapsulated cross linker. If this type of PDMS is damaged, both capsules rupture and the newly formed elastomer mends the damaged area. 

A second important characteristic of an elastomeric network is the the elongation at rupture. Results on PDMS indicate that rupture occurs at approximately 80-90% of maximum chain extensibility. ... 

In the other extreme case, bonding a small number of relatively long elastomeric chains into a short-chain PDMS thermoset greatly improves both its energy of rupture and... 

Another example for microcapsule-based self-reporting materials involved the use of charge-transfer complexes (CTCs). " CTCs form between an electron donor and an electron acceptor. The transfer of charge results in the attraction between the two species and a change in colour. Poly(urea-formaldehyde) microcapsules were filled separately with a donor, hexa-methylbenzene (HMB), and with an acceptor, chloranil (CA) (Figure 11.21). Both dyes were dissolved in toluene. The capsules were embedded into a PDMS matrix. They ruptured and released the dyes upon mechanical stimulus. This resulted in the formation of CTCs which changed the colour of scratches and of deformed areas from yellow to red. 

Fig. 1.27. Typical plots of nominal stress against elongation for (unswollen) bi-modal PDMS networks consisting of relatively long chains (Me = 18 500 g mol ) and very short chains (Me = 1100 (A), 660 (o), and 220 ( )). Each curve is labeled with the mole percentage of short chains it contains, and the area under each curve represents the rupture energy (a measure of the toughness of the elastomer) [119]. (Reproduced with permission copyright 1981, John Wiley Sons, Inc.)...

Fig. 1.31. The energy required for rupture and the impact strength (as measured by the falling-dart test) shown as functions of composition for bimodal PDMS networks in the vicinity of room temperature [129].

Fig. 1.41. Mooney-Rivlin isotherms for PDMS elastomers filled with in situ-generated silica, with each curve labeled with the amount of filler precipitated into it [173]. Filled symbols are for results obtained out of sequence in order to establish the amount of elastic irreversibility, a common occurrence with reinforcing fillers. The vertical lines locate the rupture points.

Polydimethylsiloxane (PDMS) oils are frequently used as antifoam ingredients for control of the foam of both non-aqueous and aqueous liquids. Their molecular structure is depicted in Figure 3.18. In the case of aqueous foaming liquids, PDMS oils are usually mixed with hydrophobicaUy modified silica particles to facilitate rupture of the relevant pseudoanulsion films as we will describe in later chapters. However, as we will also describe in Section 3.6.3, spread films of PDMS oils can influence the rupture of pseudoemulsion films even when such particles are not present. 

Early speculations about the mode of action of PDMS-based antifoams assume that duplex film spreading from drops in foam films induces shear in the intralamellar liquid, which leads to foam film rupture. Clearly the rate of spreading would be a key aspect of that mechanism. However, as we describe in Chapter 4, this view of antifoam mechanism is now somewhat discredited. Nevertheless, other aspects of antifoam action, such as the effect of antifoam viscosity on deactivation during prolonged interaction with foam generation (see Chapter 5), could be determined by spreading rates. It is therefore appropriate to briefly review this topic here. 

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