Wrinkled surfaces

Cobalt. Without a doubt cobalt 2-ethyIhexanoate [136-52-7] is the most important and most widely used drying metal soap. Cobalt is primarily an oxidation catalyst and as such acts as a surface or top drier. Cobalt is a transition metal which can exist in two valence states. Although it has a red-violet color, when used at the proper concentration it contributes very Httie color to clear varnishes or white pigmented systems. Used alone, it may have a tendency to cause surface wrinkling therefore, to provide uniform drying, cobalt is generally used in combination with other metals, such as manganese, zirconium, lead, calcium, and combinations of these metals. 

Fig. 16 Representative data from the surface wrinkling metrology, demonstrating the unprecedented range of moduli and the precision that the methodology unlocks a modulus of a thickness gradient library of PS (reproduced with permission from [72]) b modulus as a function of composition for P(S-I-S) triblock copolymer blends c modulus as a function of thickness for ultrathin PS films (reproduced with permission from [74]). The lines are meant to guide the eye and the error bars represent one standard deviation of the data, which is taken as the experimental uncertainty of the measurement...

The mechanics of surface wrinkling necessitate that there be a reasonable modulus difference between the film of interest and the soft substrate (Es 2MPa for PDMS). In order to probe softer materials, the wrinkling metrology can be inverted, such that a sensor film of known modulus is adhered to a soft substrate of unknown modulus. Rearrangement of (1) leads to the following expression for the modulus of the soft, elastic substrate ... 

Huang H, Chung JY, Nolle AJ, Stafford CM (2007) Characterizing polymer brushes via surface wrinkling. Chem Mater 19 6555-6560... 

The concept of local distortions of space-time can be visualized in crude analogy with the impossibility of covering a curved surface with a flat sheet. It may seem to work at short range, but over an extended (closed) surface wrinkles appear in the cover and despite all efforts to smooth them away a fixed amount of misfit between surface and cover persists. Identifying space-time with a flat Euclidean cover then shows how any large-scale curvature must result in the creation of local distortions. As elementary particles of few types occur in Nature distortion of space is quantized, and like other quantum phenomena would therefore be conveniently described in wave formalism. 

FIGURE 5.33 Fiber surface wrinkles showing underlying reversal in fibrillar direction. Arrows indicate direction of fibril wrap (SEM). 

Use High-gloss varnishes, paints for metal surfaces, wrinkle finishes. 

Premixed flames may be influenced by the Darrieus-Landau hydrodynamic instability [1, 2] when the chemical heat release is sufficiently large. Hydrodynam-ically unstable premixed flames are not always observed, however, because of stabilizing influences of buoyancy and thermal diffusion. The long-wavelength flame-surface wrinkles are attenuated by buoyancy for downward propagating flames, and thermal-diffusive effects stabilize small-wavelength wrinkles when the... 

Lewis number based on the limiting reactant is sufficiently large [3]. Therefore, the Darrieus-Landau instability is expected to result in enhanced flame-surface wrinkling only when it is able to overcome stabilizing influences of buoyancy and thermal diffusion. Additionally, a flame under confinement may be influenced by acoustic waves, and coupling between the flame and acoustic-wave dynamics may result in unstable flame propagation as well. 

Surface wrinkling, creasing, and folding Mechanical stress Controlled wrinkles Down to micrometer Wrinkle, creasing or folding orientation depends on direction and magnitude of the applied stress [84, 85. 166-175]... 

Fig. 8.13 Variety of morphological patterns via swelling-induced surface wrinkling. Optical microscopy images of various wrinkling patterns produced on 500 nm thick PS films with different UVO exposure times Ifom 2-40 min [29]...

Guvendiren, M., Burdick, J.A. The control of stem cell morphology and differentiation by hydrogel surface wrinkles. Biomaterials 31(25), 6511-6518 (2010)... 

Breid, D., Crosby, A.J. Surface wrinkling behavior of finite circular plates. Soft Matter 5,... 

Years earlier, Staudinger and Hutchinson employed a homo-IPN of acrylic composition to make optically smooth surfaces. As amplified in Chapter 1, network I was swollen with more monomer of the same type to smooth out surface wrinkles by the stretching incurred on swelling. Polymerization of the new monomer yielded a homo-IPN. 

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