Dewetting effect

Adicoff, Dynamic Mechanical Behavior of Highly Filled Polymers Dewetting Effect , Rept No NWC-TP-5486 (1971) 11) H. Yasu-... 

One method of overcoming the detrimental solvent dewetting effects is to use liquid C02 as the solvent for nanoparticle dispersions [52], since C02 does not experience the dewetting instabilities due to its extremely low surface tension [53]. In this case, nanoparticles must be stabilized with fluorinated ligands [30, 33, 54—65] or other C02-philic ligands [60,66-76], such that they will disperse in the C02 prior to dropcasting. These fluorinated ligands tend be toxic and environmentally persistent and, typically, only very small nanoparticles can be dispersed at low concentrations. 

Moving into the interfacial region, other interesting effects are observed. First, there is a distinct minimum in the total system density for system WAT, but this minimum disappears as acetonitrile cOTicentration is increased. This dewetting effect for water near extended hydrophobic surfaces has been predicted by Lum, Chandler, and Weeks and is attributed to a disruption of the solvent s hydrogen bonding network [58]. Also present in the interfacial region is an enrichment in the acetonitrile concentratiOTi for the binary solvent systems. This effect is most dramatic for system 33A, where a distinct density maximum for acetonitrile is observed at around z = 17 A. 

The two basic deformation mechanisms in a polymer are by shear yielding and crazing. In a composite system, such as the MIM feedstock, an additional mechanism, dewetting, is observed [75]. The yield point is actually due to crazing effect or a dewetting effect in which the particle-matrix interface is destroyed and resulting in a dramatic drop in the modulus of the material [59]. 

The experimental results achieved so far for semiconductors demonstrate that the structural perfection of the crystals can be improved when the dewetting effect is used [17]. However, there remains still a lot of research to be done until this technology can be transferred into an industrial production. 

G. Henn, D. J. Bucknall, M. Stamm, P. Vanhoorne, R. Jerome. Chain end effects and dewetting of thin polymer films. Macromolecules 29 4305 313, 1996. 

An important consideration is the effect of filler and its degree of interaction with the polymer matrix. Under strain, a weak bond at the binder-filler interface often leads to dewetting of the binder from the solid particles to formation of voids and deterioration of mechanical properties. The primary objective is, therefore, to enhance the particle-matrix interaction or increase debond fracture energy. A most desirable property is a narrow gap between the maximum (e ) and ultimate elongation ch) on the stress-strain curve. The ratio, e , eh, may be considered as the interface efficiency, a ratio of unity implying perfect efficiency at the interfacial Junction. 

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... 

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. 

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