Thin-film multilayer process steps

A bioadhesive hot-melt extruded film for intraoral drug delivery and the processing thereof has been patented.f Applications of these films may be utilized in transmucosal drug delivery or even transder-mal systems. The films may be produced separately and layered after extrusion, or in some cases, a multilayered system may be extruded in one continuous process. Currently on the market is an extruded film device that is utilized as a denture adhesive. This system includes thermoplastic polymers that have a bioadhesive quality when the film is wetted. Before application and wetting, however, this thin film may be held in one s hand and shaped or cut. This device is again produced by a one-step, continuous process using hot-melt extrusion technology. 

The same methods to introduce grain boundaries, i.e. bi-crystal substrates, step-edges and bi-epitaxial techniques, also apply to the other superconductors [14.52, 14.107-14.109], The details of the interfacial interactions between the substrates and the thin films need to be investigated in order to find the optimum conditions and geometries for each individual system. The chemical interactions must also be considered when integrating the superconductors into multilayer structures. Intermediate non-superconducting layers that are inert to the YBCO may react chemically with the other superconductors. It is also necessary to carefully consider the ex situ processes of the Tl- and Hg-based superconductors producing multilayer structures. 

A thin film composite reverse osmosis membrane can be defined as a multilayer membrane in which an ultrathin semipermeable membrane layer is deposited on a preformed, finely microporous support structure. This contrasts with asymmetric reverse osmosis membranes in which both the barrier layer and the porous substructure are formed in a single-step phase inversion process and are integrally bonded. 

The first decision in choosing a synthetic method for a PPV material is the way in which the material will be processed (Scheme 7.8). The precursor routes will enable the preparation of solvent-resistant and more durable thin films of PPV. This is particularly desirable if a multilayer device structure is required for the application. When choosing different precursor methods, it is important to assess the criteria of the application. Most precursor methods involve a thermal elimination step to convert the precursor polymer to the PPV material. Sul-fonium precursors require higher-temperature elimination compared to sulfinyl precursors. This makes the sulfinyl route compatible with deposition on plastic substrates. Another factor to consider in precursor methods is the nature of the elimination byproducts. Sulfonium precursors convert to PPV with elimination of acids, such as HCl or HBr, which has been shown to be detrimental to device performance. Xanthate and dithiocarbamate routes involve the elimination of amine and CO2 and CS2, respectively. 

The most widely used chemically modified PPO in the development of thin film composite membranes is sulfonated polyphenylene oxide (SPPO). The polymer in the acid form as well as salt form has been used by Bikson to produce multilayer composite membranes. These types of membranes have been described to have at least two chemically distinct layers deposited on a porous substrate in a single coating step process. The outer layer forms a protective defect-sealing surface whereas the inner layer is the selective SPPO layer. This layer is adjacent to the porous support membrane. The two top layers are formed simultaneously on top of porous polysulfone support hollow fibers. A coating solution of SPPO in the lithium salt form (SPPO-Li ) and amine functional silicone fluid was coated on top of the polysulfone fibers. These coated fibers were used to construct a hollow fiber separator permeator. 

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