Membrane sponge-like structure

Membrane simulations were performed with 2, = 4,9, and 15. The mesoscopic structure of the hydrated membrane is visualized in Figure 6.7, revealing a sponge-like structure similar to structures obtained by other mesoscale simulations.ii Together with hydrophilic beads of side chains, water beads... 

Phase-inversion membranes frequently show a sponge-like structure. The volume flux through these membranes is described by the Hagen-Poiseulle or the Kozeny-Carman relation, although the morphology is completely different. 

Skin Type Membranes With "Sponge"- and "Finger"-Like Structures. In skin-type membranes, the two characteristic structures shown in Figure 1.14 are obtained. One is a sponge-like structure and the other is a finger-like substructure underneath the skin. 

With the increase of the concentration of PPESK in the casting solution, the viscosity strongly increases and becomes shear-rate dependent. Then the morphology of the hollow fiber membranes changes from a finger-like structure to sponge-like structure. 

Weaker nonsolvents with a lower solubility parameter other than water, such as ethanol, are sometimes used. These weaker nonsolvents lead to the formation of a denser membrane (Albrecht et al. 2001 Young and Chen 1995). Systems with a rapid phase inversion rate (strong nonsolvent) tend to form macrovoids with finger-like structures, whereas systems with a slow phase inversion rate yield sponge-like structures (Young and Chen 1995). In addition, polymer crystallinity can be affected by the choice of nonsolvent, as reported by Buonomenna et al. (2007b) for the (DMA/ water and DMA/C1-C8 alcohols) system. 

Morphology D No viscous lingering takes place with a fully sponge-like structure throughout the membrane. 

FIGURE 10.11 Porosity of sponge-like structure of normally sintered membrane and controlled sintered membranes with various pretreatment temperatures. (Data from Wu, Z.T. et al., Journal of Membrane Science, 446, 286-293, 2013.)... 

Efforts to overcome the limitations of the fragile membranes (as delicate as soap bubbles) have evolved with the use of membrane supports, such as polycarbonate filters (straight-through pores) [543] or other more porous microfilters (sponge-like pore structure) [545-548]. 

This so-called "active" layer has characteristics similar to those of cellulose acetate films but with a thickness of the order of 0.1 micrometer (jjm) or less, whereas the total membrane thickness may range from approximately 75 to 125 ym (see Figure 1). The major portion of the membrane is an open-pore sponge-like support structure through which the gases flow without restriction. The permeability and selectivity characteristics of these asymmetric membranes are functions of casting solution composition, film casting conditions and post-treatment, and are relatively independent of total membrane thickness. 

As an example of hybridization of zeolites with cellulose derivatives, self-supporting zeolite membranes with a sponge-like architecture and zeolite microtubes were prepared by using CA filter membranes as a template [154]. The hierarchical structure with sub-nanometer- to micrometer-sized pores is a characteristic of great promise for a wide range of applications such as catalysis, adsorption, and separation. There was also an attempt to prepare alginate membranes incorporated with zeolites, e.g., for pervaporation separation of water/acetic acid mixtures [155]. 

Stucky11751 developed a procedure for the synthesis of sponge-like silica membranes with 3-D meso-macrostructures. The process utilizes multiphase media composed of a mesoscopically ordered block copolymer-silica phase that macroscopically separates from an electrolyte phase. The different characteristic lengthscales in hierarchically organized composite structures can be independently adjusted. 

Skin Type Membranes With "Sponge"- and "Finger -Like Structures. In... 

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