Spinning thin liquid film

When a thin liquid film with a thickness of approximately 2 pm prepared by spin coating of a 15% benzene solution of polymer 1 was irradiated with a 500-W Xe-Hg lamp for 300 s in air, a transparent solid film was obtained. The UV spectrum of this solid film shows that an absorption at 235 nm due to phenyldisilanyl units vanishes after UV-irradiation (Figure 1). This clearly indicates that photolytic cleavage of silicon-silicon bonds leading to the cross-linking occurred. Similar photolysis of the thin liquid films under a nitrogen atmosphere again afforded transparent solid films whose UV spectra show no absorption at 235 nm due to phenyldisilanyl units. 

A number of dielectric films are deposited by the spin-on technique. In this case the film s constituent molecules are dissolved in a solvent to form a liquid. After spinning the liquid over a semiconductor surface the solvent is driven off with a baking step, leaving behind the thin dielectric film. Common films include polyimide and benzocyclobutene (BCB). The deposition process for these films is simple, making it attractive for a manufacturing process. 

Summarizing, two conditions must be fulfilled in order to obtain from the simulations a confinement-induced and thickness-dependent distribution of the end-to-end distance for terminal subchains. First, a chain should be in contact with both interfaces. This happens only when the film thickness becomes comparable to the size of the chains and, obviously, explains why the confinement-induced mode does not exist in the bulk. Second, the interactions at the interfaces should be asymmetric One interface should immobilize the polymer chains, while the second one should only reflect them. This asymmetry could be induced by the nonequivalent preparation of the electrodes in the experiment While one interface is prepared by spin-coating, the other one is prepared by evaporation of aluminium on top of the polymer film (see Section II for details). A similar picture of asymmetry was found in studies on thin PS films, with a preparation procedure identical with ours. For thin PS films capped between two aluminum electrodes a three-layer model was proposed, in which, in addition to a middle-layer having bulk properties, a dead (immobilized) layer and a liquid-like layer were assumed to be present at the interfaces. 

Fig. 2 A schematic for spin coating thin films. The coating solution is either (A) dripped on the substrate while it is at rest or (B) dripped on while the substrate is spinning (C) spin-off stage, forming a thin liquid coating on the substrate (D) solvent evaporation results in self-assembly and thin film formation.

With respect to the interfacial structure of ionic liquids with solids, the molecular layering and local order in thin liquid crystalline films of [RMIM][PFis] ionic liquids with long alkyl chains (e.g., R = dodecyl and octadecyl) on solid silicon supports have been studied using X-ray reflectivity [45]. Here, thin films of the crystalline ionic liquids with a thickness of 100-210 A were deposited on polished and cleaned silicon wafers by initial spin-coating of a solution of the ionic liquids in methanol followed by heating the samples into the isotropic liquid state and crystallization. 

The brushes were covered by spin-coating with thin PDMS films of various molecular weights (Mw ranging from 3 to 308 kg/mol, corresponding to viscosities ranging from 10 to 1,000 Pa.s) of variable thickness (/i < 200 nm). Ellipsometry was used to measure the thickness of the PDMS film. In order to initiate the instability, the surrounding air was replaced by some liquid. Mainly, the PDMS films were embedded in water or an aqueous surfactant solution. This system is a suitable candidate to study the self-destruction of thin polymer films as it provides excellent control over kinetics and intermolecular interactions. ... 

The spontaneous spreading of thin microdroplets on solid substrates is slow and can be conveniently monitored using spatially resolved ellipsometry. On the other hand, extended thin wetting films can be spin-coated on solids or deposited on liquid substrates and thereafter studied under a polarized microscope for nanometric thicknesses or a Brewster angle microscope for molecular ones. X-ray reflectometry provides complementary information. 

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