Everything about Semipermeable Membrane totally explained
A
semipermeable membrane, also termed a
selectively-permeable membrane, a
partially-permeable membrane or a
differentially-permeable membrane, is a membrane that will allow certain
molecules or
ions to pass through it by
diffusion and occasionally specialized "
facilitated diffusion." The rate of passage depends on the
pressure,
concentration, and
temperature of the molecules or
solutes on either side, as well as the permeability of the membrane to each solute. Depending on the membrane and the solute, permeability may depend on solute size,
solubility, properties, or chemistry. An example of a semi-permeable membrane is a
lipid bilayer, on which is based the
plasma membrane that surrounds all
biological cells. Many natural and synthetic materials thicker than a membrane are also semipermeable. An example of this is the thin film on the inside of an
egg.
One example of a semipermeable membrane is a
phospholipid bilayer, a group of
phospholipids (consisting of a phosphate head and 2 fatty-acid tails) arranged into a double-layer, with the hydrophilic phosphate heads exposed to the water content outside and within the cell and the hydrophobic fatty-acid tails hidden in the inside. The phospholipid bilayer is the most permeable to small, uncharged solutes. Protein channels float through the phospholipids, and, collectively, this model is known as the
fluid mosaic model.
In the process of
reverse osmosis,
Thin film composite membranes (TFC or TFM) are used. Thin film composite membranes are semipermeable membranes manufactured principally for use in
water purification or
desalination systems. They also have use in chemical applications such as batteries and fuel cells. In essence, a TFC material is a molecular sieve constructed in the form of a film from two or more layered materials.
Membranes used in reverse osmosis are, in general, made out of
polyimide, chosen primarily for its permeability to water and relative impermeability to various dissolved impurities including salt ions and other small molecules that can't be filtered. Another example of a semipermeable membrane is
dialysis tubing.
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