Peculiarity of polymer gel mechanism
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Fig. 1 Extreme diversity in physical property widens the function of the gel. |
Polymer gels dissent in numerous
ways that from laborious solid polymer materials. The polymer chains among the
gel are sometimes thought-about to be with chemicals or physically cross-linked
and to create a three-dimensional network structure. as an example, polymer gel
is typically a matter swollen with its smart solvent, and also the
characteristics are diversified from virtually|a virtually} solid compound
almost to an answer with terribly low polymer content however still maintaining
its form by itself. This extreme diversity in physical properties widens the
operate of the gel (see Fig. 1).
Fig. 2 Various actuating modes of polymer gels: (a) swelling and de-swelling,(b) asymmetric swelling or de-swelling. |
From the point of view of the
mechanism, the gel behaves sort of a typical solid mechanism or biological
muscle, or sort of a shapeless amoeba. The gels even have numerous causative
modes, bilaterally symmetrical volume modification with swelling and
de-swelling, uneven swelling behavior, bilaterally symmetrical deformation and
uneven deformation (see Fig. 2). The strain iatrogenic within the gel can even
be very massive, reckoning on the cross-link structure within the gel.
Triggers for causative compound
gels
As {may be|could also be|is also}
expected from the diversified physical characteristics of the gel and also the
wide selection of the causative modes, there ar numerous triggers for the
causative polymer gels.
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Fig. 3 Triggers for polymer and/or gel actuation can be classified into twocategories: chemical and physical. |
The triggers may be classified
into 2 classes, chemical triggers and physical triggers (see Fig. 3).
As
chemical triggers, solvent exchange includes jumps in solvent polarity (e.g.
from smart solvent into poor solvent), in pH (e.g. in weak electrolyte gel from
a unconnected condition into associate degree associated condition) and in
ionic strength (utilizing salting-out or coagulation). These 2 varieties
accompany swelling and de-swelling of the solvent, and also the deformation is
typically bilaterally symmetrical as way because the gel incorporates
ahomogenised structure (see Fig. 4).
Fig. 5 Temperature jump as a physical trigger: (a) poly(vinyl methyl ether)and (b) poly(N-isopropyl acrylonide). |
Temperature jump, that could be a physical
trigger, can even induce bilaterally symmetrical deformation above all polymer
gels wherever the solubility incorporates a vital transition temperature.
Typical examples ar the gels of poly (vinyl alkyl ether) and poly (N-isopropyl
acrylamide). These gels have high water absorption at low temperatures and
de-swell at the characteristic vital temperature around 30—40 °C (see Fig. 5).
Fig. 6 Chemical trigger can induce swelling and de-swelling of gel, e.g.substrate of urease, urea, is changed into ammonia and the ammoniainduces swelling and de-swelling by varying pH. |
The transition temperature may be controlled by dynamical chemical structure.
within the case of enzyme immobilized gel, the addition of organic compound, a
substrate of enzyme, induces swelling and deswelling by utilizing the hydrogen
ion concentration modification iatrogenic by the accelerator reaction (see Fig.
6).
Fig. 7 Light-induced deformation of polymer film. Example shown is thecase of PVC film containing spyrobenzopyrane. |
A physical trigger like
lightweight irradiation is beneficial for causative a gel among which the
light-induced reversible transition happens and also the transition accompanies
physical strain. during this case, the modification is typically uneven and
also the gel bends toward or against the direction of the irradiation,
reckoning on the image iatrogenic reaction (see Fig. 7).
In the case of electrical field
application, the gels sometimes bend, as a result of the sector application
induces uneven charge distribution and therefore the uneven strain within the
gel. uneven charge distribution will simply be iatrogenic in electrolyte gels,
and this can be why electrolyte gel has principally been investigated as on
electro active polymer material (see Fig. 8).
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Fig. 9 Magnetic field active gel utilizing super paramagnetic property of aferro-fluid-immobilized gel. , ferrofluid 75wt%; , ferrofluid 50wt %; ,ferrofluid 25 wt %. |
Magnetic field application can
even induce a strain during a gel once a structure or species sensitive to the
field is contained in it.
we tend to initial planned the thought of applying an
excellent magnet fluid to a gel. The gel was found to be sensitive to the field
gradient and to induce strain terribly sensitively, and also the structure
modification within the gel was investigated (see Fig. 9).
Fig. 10 Magnetic field induced large deformation. By turning the magneticfield (H) on and off, the gel deforms instantly. |
Zryhni
and his coworkers investigated constant materials and located discontinuous
deformation of the gel by dominant the field (see Fig. 10).
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