PH-sensitive polymers
Encyclopedia
pH sensitive or pH responsive polymers are materials which will respond to the changes in the pH
of the surrounding medium by varying their dimensions. Such materials swell or collapse depending on the pH of their environment. This behaviour is exhibited due to the presence of certain functional groups in the polymer chain.
There are two kinds of pH sensitive materials: one which have acidic group (-COOH, -SO3H) and swell in basic pH, and others which have basic groups (-NH2) and swell in acidic pH. Polyacrylic acid
is an example of the former and Chitosan
is an example of the latter. The mechanism of response is same for both, just the stimuli vary.
The response is triggered due to the presence of ionisable functional groups (like -COOH, -NH2) which get ionized and acquire a charge (+/-) in a certain pH. The polymer chains now have many similarly charged groups which causes repulsion and hence the material expands in dimensions. The opposite happens when pH changes and the functional groups lose their charge hence the repulsion is gone and the material collapses back. These materials are being extensively used in controlled drug delivery systems, biomimetics
and responsive plasmonics.
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of the surrounding medium by varying their dimensions. Such materials swell or collapse depending on the pH of their environment. This behaviour is exhibited due to the presence of certain functional groups in the polymer chain.
There are two kinds of pH sensitive materials: one which have acidic group (-COOH, -SO3H) and swell in basic pH, and others which have basic groups (-NH2) and swell in acidic pH. Polyacrylic acid
Polyacrylic acid
Poly or PAA or Carbomer is a type of anionic polymer. The monomer of poly is acrylic acid. In a water solution at neutral pH, many of the side chains of PAA will lose their protons and acquire a negative charge. This makes PAA a polyelectrolyte.Dry PAA is a white solid...
is an example of the former and Chitosan
Chitosan
Chitosan is a linear polysaccharide composed of randomly distributed β--linked D-glucosamine and N-acetyl-D-glucosamine...
is an example of the latter. The mechanism of response is same for both, just the stimuli vary.
The response is triggered due to the presence of ionisable functional groups (like -COOH, -NH2) which get ionized and acquire a charge (+/-) in a certain pH. The polymer chains now have many similarly charged groups which causes repulsion and hence the material expands in dimensions. The opposite happens when pH changes and the functional groups lose their charge hence the repulsion is gone and the material collapses back. These materials are being extensively used in controlled drug delivery systems, biomimetics
Biomimetics
Biomimetics is the study of the structure and function of biological systems as models for the design and engineering of materials and machines. It is widely regarded as being synonymous with biomimicry, biomimesis, biognosis and similar to biologically inspired design.-History:The term biomimetics...
and responsive plasmonics.