Dewetting process

G. Reiter. Unstable thin polymer films rupture and dewetting process. Langmuir 9 1344-1351, 1993. 

The dependence on film thickness is attributed to the dewetting nucleation, which occurs in the 2.5-4.5 nm thickness range via the formation of randomly distributed droplets rather than the formation of holes. When the initial film thickness exceeds 4.5 nm, dewetting is trigged via nucleation of holes instead of droplets, and for film thickness above 10 nm, dewetting develops slowly via hole nucleation at defects. The different dewetting processes observed for different initial film thicknesses can be explained in terms of the variation of disjoining pressure and the inability of the polymer to spread on its own monolayer. 

Recently, we explored the effect of molecular weight on the pattern and employed post-dewetting processes to alter the shape of the dewetted polymer droplets. Since the viscosity of a polymer solution is nonlinear with respect to concentration and also strongly dependent on polymer weight, we expected a drastic effect. Figure 11.4... 

Reiter, G. (1993) Unstable thin polymer films Rupture and dewetting processes. Langmuir, 9, 1344-1351. 

The above statements are adequate for liquid defoamers that are insoluble in the bulk. Experience has proven, however, that certain dispersed hydrophobic solids can greatly enhance the effectiveness of defoaming. A strong correlation between the effectiveness of a defoamer and the contact angle for silicone-treated silica in hydrocarbons has been established [300]. It is believed that the dewetting process of the hydrophobic silica causes the collapse of a foam by the direct mechanical shock occurring by this process. 

The migration of clay from EPDM to CR phase can also be explained as a wetting/dewetting process between polymers and filler. Hereby, the driving force of filler particle migration is the difference of the interfacial tensions between the rubbers and clay ... 

From examination of the dewetting process, the requirement for the wettable (by water) or hydrophilic surface could be defined that the contact angle of water should be below ti/2. By the same principle, a contact angle above n could be set as the requirement for the nonwettable or hydrophobic surface. The surface whose contact angle is between n and ti/2 could be viewed as the surface having amphoteric wettability or amphoteric hydrophilicity/hydrophobicity. 

The crazing process does not induce large-scale energy dissipation in pure Polypropylene so the cavitation / dewetting process is the main toughening mechanism in CaC03 filled Polypropylene. The basic micro-mechanisms depend on the material properties and on the loading conditions. 

In general, if a substrate has a lower surface tension than a fluid, this fluid will not form a stable film when deposited onto such a substrate. Consequently, such an unstable fluid film will retract from this substrate by a dewetting process [108-111]. This process is the result of driving forces that try to remove the fluid and of dissipative processes that reflect the resistance of the fluid to its removal. 

We anticipate that the entanglement density in the dry spin-coated films is lower than in an equilibrated bulk system. Such a departure fi om equilibrium most likely generates residual stresses. As one consequence, we tentatively attribute the observed hole nucleation, which initiated the dewetting process of holes, to the presence of such residual stresses within the film [165]. In this way, rupture can be related to the spin-coating process used to prepare thin polymer films. 

Example 2 GBs in AIN can reduce the thermal conductivity if they are not clean. Because AIN is difficult to sinter to high density without the use of a liquid phase (the bonding is mainly covalent), the GBs often contain a second phase, which always has a lower thermal conductivity (Chapter 34). Yttria may be added to react with oxide in the GBs to form YAG at the triple junctions a GB-dewetting process. 

The first interpretation of this newly identified short-time breakup of thin nematic films was put forward by van Effenterre et al. [73] and is rooted in basic thermodjmamics, i.e., in the biphase coexistence of the two (meta)stable phases taking part in the discontinuous transition. However, as pointed out in detail by Ziherl and Zumer [74], the explanation misses two critical points First, that the isotropic-nematic coexistence can only exist in the temperature range where both phases are thermodynamically metastable or stable, and second, that the nematic director is only distorted in thick enough films (i.e., above the critical thickness dc = [Ai — A2I). Therefore, the dewetting process in thin LC films is still an open question for both theoretical and experimental studies. 

A typical example of dissipative structure-assisted self-assembly of nanoparticles is shown in Figure S. The dark dots and lines are aggregates of organopassivated Cu nanoparticles, and the light surroundings are polystyrene matrices. The dewetting process determines first the wavelength of spatial pattern (frozen dissipative structure) of polymer matrices that are isolated one... 

By using a dewetting process micrometer-sized domes of polymers were formed on solid substrates, and it was found that the aggregation state and ftius the photophysical properties of incoiporated d e molecules depend on the dome size. During dewetting two processes compete, the formation of polymer dorr s and the aggr lion of the dye. Thus, due to the namics of the process self-organized mesoscopic and hierarchic structures can be formed. 

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