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Dewetted structure substrates

The values of Go and y are known and for the elastomer of Young s modulus of 2.1 MPa, [/o = 8 X 10 mm-s [12]. We can then evaluate 8 at ca. 20 mn. This value is perhaps a little high but of the same order of magnitude as earlier estimated [6]. Thus, despite some necessary approximations and simplifying hypotheses, we arrive at a semiquantitative explanation of the relationship between dewetting and therefore, presumably, wetting speed and the molecular structure of the elastomeric substrate. [Pg.309]

Fig. 30. Different types of the momentary morphologies which are typically observed during wetting (a-c) and dewetting (d-f) events on a solid flat substrate, a droplet, b spherical cap with a precursor film.c thin film (eventually with a multilayer structure), d thin liquid film, e ruptured film with rims at the dewetting front,f droplets... Fig. 30. Different types of the momentary morphologies which are typically observed during wetting (a-c) and dewetting (d-f) events on a solid flat substrate, a droplet, b spherical cap with a precursor film.c thin film (eventually with a multilayer structure), d thin liquid film, e ruptured film with rims at the dewetting front,f droplets...
Modern coating technologies require increasingly thinner polymer films. This requirement is opposed by the surface pressure and the chain elasticity. Below a certain equilibrium thickness, the film is either metastable or even unstable and tends to break into droplets regardless of the chemical structure of the substrate [321, 322]. Anomalous wetting behaviour was observed for amphiphilic polymer films whose stability is controlled by the orientation of the surface active moieties [323,324]. All these phenomena belong to the dewetting problem. [Pg.117]

Fig. 4a—d. Lamellar structures in thin films that are not considered further in detail in the present article a Thin film confined between inequivalent walls, where the lower one favors the B-rich domains and the upper one the A-rich domains. Then an arrangement where the interfaces run parallel to the walls requires that thickness D and wavelength X are related as D=(n+1/2)A, n=0,l, 2... b Thin film on a substrate that favors B-rich domains undergo at the order-disorder transition (ODT) of the block copolymer melt a phase separation into a fraction x of thickness nXh and a fraction 1-x of thickness (n+1) Xh, such that D=[xn+(l-x) (n+l)] K if the air also favors B-rich domains, c If the air favors A-rich domains instead, the phase separation happens in a fraction x of thickness (n-l/2)A and a fraction 1-x of thickness (n+ 1/2)X with n= 1,2,3... d If the block copolymer film undergoes dewetting at the substrate, droplets form with a step-pyramide like structure ( Tower of Babel [30]). [Pg.6]

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. [Pg.199]

The authors distinguish between three different cases for the dewetting mechanism (Figure 9). In thin films as well as in the bulk, a regular bilayer morphology is developed. Disordering into an isotropic melt occurs in two steps. A smectic mesophase is formed before the layered structure finally breaks up at elevated temperatures. This transition is characteristically effected by the interfaces in thin films on a flat substrate and, as a consequence, a peculiar self-dewetting is observed. [Pg.169]


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