3. Content
•History
•Microgels: structure, nature and composition
•Classification
•Difference between cationic and anionic microgels
•Structure and composition
•Synthesis
•Application
•Conclusion
4. History
Baker was the first who designated
microgel particles as ‘new
molecules’and suggested
emulsion copolymerization (ECP) for
localizing gelation to small dimensions.
5. INTRODUCTION
Microgels : Structure and Nature
Definition
Polymer microgels are crosslinked colloidal particles with
a network structure that are swollen in a suitable solvent.
Aqueous colloidal microgels (where the solvent is water)
are referred to as hydrogels.
8. The applications of microgels are suitable due to
their stimulus-responsive nature, that is, their
ability to undergo reversible volume phase
transitions in response to external stimuli such as
• Change in pH
• Temperature
• Ionic strength of the surrounding medium
• The action of an external electromagnetic field
• Quality of solvent
9. Classifications of microgels
Microgels are best classified in two ways
Classes based on nature of the cross-links
Physically-crosslinked microgels
Chemically cross-linked microgels
Classification based on response
Non-responsive microgels
Stimulus-responsive microgels
10. •a) Collapse of linear free chains
•b) Swelling or shrinking of a gel
•c) Swelling or collapsing on surface
11. Synthesis
Microgels can be synthesized by a variety of techniques: precipitation polymerization and
microemulsion polymerization.
Precipitation polymerization
13. Polyelectrolyte (PE) microgels/Cationic and anionic
microgels
Microgels functionalized with ionic groups
Particles are often be anionic and/or cationic
Polyampholyte (PA) microgels
Both cationic and anionic groups are present along the
polymer chain
14. Difference between cationic and anionic
microgels
Anionic microgels composed of weak acidic
polymers such as e.g. poly(meth)acrylic acid. Cationic
microgels based on polymers containing weak basic
groups such as e.g. amino moieties.
As polyelectrolytes are charged their properties will
change with pH and ionic strength of the solution.
An anionic polymer exhibiting a strong polyelectrolyte
effect shows a large change in ionisation on going from
a pH value below the pKa to a value above the pKa and
the reverse case holds for a cationic polymer.
15.
16. Synthesis
All microgels were synthesized using fixed concentrations of initiator
and a cross-linker.
The initiator solution was heated in flask to 70 °C, with constant
stirring, using a feedback hotplate stirrer. The flask was silanated
before use by rinsing the flask. A water-cooled condenser and a nitrogen
gas line were connected to the flask.
In a separate beaker distilled water, monomer and co-monomer and the
cross-linking agent were added together and stirred for 30 min. This
mixture was then added to the reaction vessel containing the initiator
solution. The reaction was allowed to proceed with continuous stirring
(∼ 400 rpm). After the completion of the reaction, the final product was
cooled to room temperature and any unreacted components were
removed by filtration through glass wool, followed by extensive dialysis
against distilled water for several days.
17. Amphoteric, poly(N-isopropylacrylamide)-based microgels are
functionalized with aminophenylboronic acid (PBA) functional groups to
produce colloidally stable, glucose-responsive gel nanoparticles that
exhibit glucose-dependent swelling responses at physiological
temperature, pH, and ionic strength
18. Applications of Microgels
Components of binders for organic coatings
Carriers of dyes
Pharmaceuticals and biochemical compounds
Fillers and materials for reinforcing plastics
19. CONCLUSION:
By choosing suitable monomer combinations the
composition , size and structure of microgels can be
widely varied, thus adjusting these macromolecules
to special applications.
Responsive microgels are of utmost importance in
almost every sector of technological advancement
such as
Chemistry
Biology
