Flat sheet membrane shapes

Figure 2.1 Polymeric membrane shapes and cross-sectional structures. Tubular membranes are similar to flat sheet membranes because they are cast on a macroporous tube as support. Capillary membranes are hollow fibers with larger diameter, that is, >0.5 mm.

As the name suggests, flat-sheet membranes are flat, like a sheet of paper, and can be made as thin as less than 1 pm. However, they need special holders to hold them in place. Hollow-fiber membranes are shaped like tubes (200 to 500 pm ID), allowing fluids to flow inside as well as on the outside. Hollow fibers are self-supported and offer the advantage of larger surface area per unit volume and high packing density. A large number of parallel fibers can be packed into a small volume. 

Two configurations of liquid membranes are mainly used in analytical applications flat sheet liquid membranes that give acceptable extraction efficiencies and enriched sample volumes down to 10-15 pL, and hollow fiber liquid membranes that allow smaller enriched sample volumes. Flat sheet liquid membrane devices consist of two identical blocks, rectangular or circular in shape, made of chemically inert and mechanically rigid material (PTFE, PVDF, titanium) in which channels are machined so that when... 

When discussing membrane preparation, not only must the physical structure be considered, but one must also consider the membrane form or shape. In an effort to combat concentration polarization and membrane fouling and to maximize the membrane surface area per unit module volume, membranes are produced in the form of flat sheets (used either In plate-and-frame or spiral wound modules), supported and unsupported tubes, and hollou fibers. Although much of the technology associated with membrane development and membrane production Is closely guarded as proprietary Information, some of the details are beginning to appear in the literature (6,9-13,16-20). 

Shape Bead, flat sheet or hollow fiber membrane, amorphous aggregate Crystal Ease of filtration, Control of diffusion path length and flow properties Simple preparation... 

Membrane materials are available in various shapes, such as flat sheets, tubular, hollow fiber, and monolithic. Flat sheets have typical dimensions of 1 m by 1 m by 200 pm thickness. Tubular membranes are typically 0.5 to 5.0 cm in diameter and up to 6 m in length. The thin, dense layer is on either the inside or the outside of the tube. Very small-diameter hollow fibers are typically 42 pm i.d. by 85 pm o.d. by 1.2 m long. They provide a very large surface area per unit volume. Honeycomb, monolithic elements of inorganic oxide membranes are available in hexagonal or circular cross section. The circular flow channels are typically 0.3 to 0.6 cm in diameter (Seader and Henley, 2006). 

Membrane shape. Flat sheet, hollow fiber, and hollow capsule. 

As the membrane acts as a separating medium between two flow compartments, these basic functions can be applied to liquid/liquid, gas/liquid and gas/ gas systems, respectively. The physical shape of the membrane strongly depends on the membrane material used. For polymeric systems, these can be flat sheets in a plate-and-frame configuration, spiral-wound modules, and tubular mem-... 

Membrane shape HoUow fiber Hollow fiber Hollow fiber Flat sheet... 

Disc/flat-sheet-shaped membranes are mostly applied in dense ceramic membrane reactors due to the ease of the fabrication process the ceramic material powder is pressed into discs in a stainless steel mould under an isostatic or hydraulic pressure, followed by sintering at a high temperature. Such disc-shaped membranes usually have a thickness of about 1 mm so as... 

The meaning of the elastocapillary length is well illustrated by the beautiful experiment performed recently by Py etal They used the interaction between elasticity and capillarity to produce three-dimensional [3D) structures. A liquid droplet is deposited on a thin planar sheet, and when the droplet evaporates it is spontaneously wrapped by the membrane. The final encapsulated 3D shape can be controlled by tailoring the initial geometry of the flat membrane. We now see that the critical length below which encapsulation cannot occur is the elastocapillary length Lee-... 

The complex morphology of hair essentially consists of four components of different functionality (i) The cortex that gives the hair its mechanical properties consists of elongated, spin-shaped cells aligned in the direction of the fiber axis. The keratinized protein in the form of microfibrils resides in these cells, (ii) The medulla is located in the center of some thicker fibers and it consists of a loosely packed porous cellular structure (it does not contribute to the mechanical properties of the hair), (iii) Cell membrane complex which cements the various cells of the cuticula and the cortex and it consists of several layers, (iv) Cuticle, a multilayered structure which consists of flat cuticle cells and the most outer layer, i.e. the epicuticle (which is about 2.5 nm thick) is the most important part for deposition of surfactants and polymers in the shampoo formulation. This consists of 25 % lipids and 75 % protein, the latter having an ordered possibly p-pleated sheet structure with 12% cystine. The cystine groups are acylated by fatty acids which form the hydrophobic surface region. A schematic representation of the epicuticle is shown in Fig. 1.46. 

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