Synthetic membrane
Synthetic membranes have been successfully used for small and large-scale industrial processes since the middle of the twentieth century.
Even though ceramic membranes have a high weight and substantial production costs, they are ecologically friendly and have long working life.
[6] The polymer sometimes has to offer a low binding affinity for separated molecules (as in the case of biotechnology applications), and has to withstand the harsh cleaning conditions.
[6] The polymers can range form amorphous and semicrystalline structures (can also have different glass transition temperatures), affecting the membrane performance characteristics.
The polymer has to be obtainable and reasonably priced to comply with the low cost criteria of membrane separation process.
[6] The most common polymers in membrane synthesis are cellulose acetate, Nitrocellulose, and cellulose esters (CA, CN, and CE), polysulfone (PS), polyether sulfone(PES), polyacrilonitrile (PAN), polyamide, polyimide, polyethylene and polypropylene (PE and PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylchloride (PVC).
Applications within energy storage include rechargeable metal-air electrochemical cells and various types of flow battery.
By contrast with polymeric membranes, they can be used in separations where aggressive media (acids, strong solvents) are present.
Synthetic membrane chemistry usually refers to the chemical nature and composition of the surface in contact with a separation process stream.
This difference can result from material partitioning at some stage of the membrane's fabrication, or from an intended surface postformation modification.
Membrane surface chemistry creates very important properties such as hydrophilicity or hydrophobicity (related to surface free energy), presence of ionic charge, membrane chemical or thermal resistance, binding affinity for particles in a solution, and biocompatibility (in case of bioseparations).
[6] The consequence of the contact angle's magnitudes is known as wetting phenomena, which is important to characterize the capillary (pore) intrusion behavior.
The membrane surface may develop an electrokinetic potential and induce the formation of layers of solution particles which tend to neutralize the charge.
Polymeric dense membranes such as polytetrafluoroethylene and cellulose esters are usually fabricated by compression molding, solvent casting, and spraying of a polymer solution.
[2] Porous membranes are intended on separation of larger molecules such as solid colloidal particles, large biomolecules (proteins, DNA, RNA) and cells from the filtering media.
The structure of porous membrane is related to the characteristics of the interacting polymer and solvent, components concentration, molecular weight, temperature, and storing time in solution.
