Coating phase inversion technique

Effect of Evaporation Condition Previous studies on more traditional applications have investigated the effect of increased air velocity, that is, forced-convection conditions for a combination of dry/wet phase inversion techniques to produce defect-free, ultrahigh flux asymmetric membranes with ultrathin skin layers [115-117]. To investigate the effect of evaporation condition on the release rate of drug, tablets were dip coated with CA solution containing 10% CA, 80% acetone, and 10% water and allowed to dry by blowing air across the surface with a blower (forced convection). As a comparison, tablets coated with the same solution were air dried under natural free-convection conditions. 

The fastest growing desalination process is a membrane separation process called reverse osmosis (RO). The most remarkable advantage of RO is that it consumes little energy since no phase change is involved in the process. RO employs hydraulic pressure to overcome the osmotic pressure of the salt solution, causing water-selective permeation from the saline side of a membrane to the freshwater side as the membrane barrier rejects salts [1-4], Polymeric membranes are usually fabricated from materials such as cellulose acetate (CA), cellulose triacetate (CTA), and polyamide (PA) by the dry-wet phase inversion technique or by coating aromatic PA via interfacial polymerization (IFP) [5]. 

Wang et al. [51] studied the separation of a water/acidic mixture by pervapora-tion using a plasma-treated asymmetric poly(4-methyl-l-pentene) (TPX) membrane, which was further dip-coated with polyacryUc acid (PAA). The asymmetric TPX membrane was prepared by the wet phase inversion technique. Membranes were treated with residual air plasma in a tubular-type reactor. The modification of the... 

GFCSS, a German company, developed a composite membrane on the basis of the above principle, a composite membrane that is illustrated schematically in Figure 10.27 [328]. The membrane consists of three layers. The first layer is a non woven polyester backing material. A porous membrane of polyetherimide (Ultem, General Electric) material is cast on the backing material by the phase-inversion technique. The porous membrane is further coated with... 

Polymers are the most used materials in membrane separation units. This is mainly due to their relatively easy processing by coating or phase inversion techniques and to a good reproducibihty in membrane preparation, which are coupled with reduced costs with respect to inorganic materials. Among the few polymers industrially used, silicones have a prominent role for different applications related to gas, vapor and liquid sepcffations. 

The spiral wound membranes tested for extraction of impurity-free NaSCN from aqueous process solution were polyamide (PA-300), CTA-700, PERMA-400, and PERMA-250. PA-300 was prepared by interfacial polymerization technique, while the PERMA membranes were prepared by coating a novel proprietary copolymer onto a microporous polysulfone substrate followed by cross-linking of the top layer. Thus, the morphology of these membranes was TFC. CTA-700 was asymmetric in nature and was prepared by solution casting and phase inversion method. 

Symmetric membranes and asymmetric membranes are two basic types of membrane based on their structure. Symmetric membranes include non-porous (dense) symmetric membranes and porous symmetric membranes, while asymmetric membranes include integrally skinned asymmetric membranes, coated asymmetric membranes, and composite membranes. A number of different methods are used to prepare these membranes. The most important techniques are sintering, stretching, track-etching, template leaching, phase inversion, and coating (13,33). 

The majority of the commereial gas separation membranes are made by wet phase inversion method whieh results in an integrally skinned asymmetrie membrane. This method was first used by Loeb and Sourirajan to produee cellulose acetate membranes for desalination of sea water. An alternative method for making gas separation membranes uses an ultra-porous skinned asymmetric membrane over which a thin polymer film is deposited by either coating or by interfacial polymerization. This method was developed by Cadotte for the creation of in situ dense skin thin film composite membranes for water desalination. These membrane fabrication techniques were made commercially successful for gas separation membranes by a brilliant empirical discovery for in situ sealing of the tiny pinhole defects on the skin of the membrane. 

Microfiltration and ultrafiltration membranes can be made from organic polymers or inorganic materials such as ceramic, glass, or metal or organic polymers. Materials used in MF and UF membrane fabrication are shown in Table 6.1. A number of different techniques are employed to prepare synthetic MF/UF membranes the most important are phase inversion, coating, sintering, and track etching. 

The amount of enzyme immobilized on the solid phase is inversely proportional to the amount of free antigen present in the incubation mixture. This approach has been used both in the equilibrium and sequential technique (Tijssen and Kurstak, 1981). The technical procedures are similar to those in Table 14.7 and its quasi-equilibrium variant with the modifications that Ag is coated on the solid phase and Ab E is used. 

The column is the most important part of the system, as its function is to encourage repetitive partitioning of each solute molecule between the gas and the liquid or solid phase. Packed columns are commonly used with the polymer or blend to be analysed coated on to a non-reactive substrate (Chromasorb W) which is then packed into the stainless-steel GC column. More recently capillary columns have been employed. Here the polymer is dynamically or statically coated as a uniform film on to the walls of the fused silica capillary. Inverse gas chromatography is a very flexible analytical technique however, full commercialisation of the technique has yet to be realised. 

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