Smart polymers are turning with huge importance in the universe of today. The utilizations gained from smart polymers are of all time turning and with new progresss in scientific discipline and engineering smart polymers have cemented themselves as a basis in polymer scientific discipline.
Smart polymers have been an country of research for many old ages. Though it is hard to depict precisely what a smart polymer is, a general definition for them can be that they are a type of polymer that react to a alteration in its environment [ 1-3 ] . The environmental factors which can implement these alterations can be temperature, pH, electric field, light, force per unit area etc. The alteration in the environment must do a outstanding and fast response from the polymer for it to be classed as a smart polymer [ 4,5 ] .
Smart polymers are hard to group but for the intent of this reappraisal they will be grouped by how the behavior of the smart polymer is driven. This can be slackly grouped into chemically driven, electrically driven and physically driven. The applications of smart polymers are of all time turning and in this reappraisal a scope of them will be investigated and explained. The association to industrial relevancy will besides be examined and a glimpse of the recent and future developments of research in smart polymers and possible applications will be explored excessively.
In chemically goaded systems of smart polymers, chemical alterations at the molecular degree drive the behavior at the macroscopic degree. Chemically goaded systems can be seen in ph Responsive and temperature antiphonal polymers.
pH Responsive polymers
These polymers have a physical alteration in response to the alteration in pH in their environment. Usually these are polyelectrolytes, which are, supermolecules that dissociate to give polymeric ions after fade outing in H2O or dissolver ( polymers with ionisable groups ) [ 6 ] . These polyelectrolytes contain a polyacid or polybase that accept/donate protons as a response to alter in pH fig 1. [ 7 ]
Fig. 1. pH dependent ionisation of polyelectrolytes. ( a ) Poly ( acrylic acid ) ( polyacid ) , and ( B ) Poly ( N, Naˆ?-diethylaminoethyl methacrylate ) ( polybase ) from Qiu and Park ( 2001 ) , reprinted with permission of Elsevier Science
The macromolecular alteration of the polymer is due to the electrostatic repulsive force coercing the polymer to spread out or swell. The construction alteration of the polymer besides depends on the combination of the hydrophobic / hydrophilic surface energy [ 8 ] .
pH antiphonal polymers allow the synthesis of tailorable smart functional stuffs and have found themselves used in several different applications such as pH antiphonal coppices [ 9 ] , controlled drug bringing [ 10 ] , biological and membrane scientific discipline [ 11 ] , ph antiphonal cysts [ 12 ] .
Temp antiphonal polymers
Temperature antiphonal polymers are the most studied in the field of smart polymers [ 6, 13-14 ] . These smart polymers have a sudden and disconnected physical alteration in response to alter in temperature and therefore are classed every bit smart as they show a non additive response to external stimulation. The polymer ironss have a sudden alteration in solubility at a critical temperature [ 6 ] .
In general chemical science the solubility of solids in a solution usually increases as temperature additions but temperature antiphonal polymers show different chemical science. In temperature antiphonal systems the solubility decreases as the temperature increases [ 15 ]
A popular illustration of a temperature antiphonal polymer system can be explored with Poly ( N-isopropyl acrylamide ) ( poly- ( NIAPAAm ) fig. 2 [ 15 ] .
Fig 2. Structural expression of N-isopropylacrylamide ( NIPAAm ) . LCST = lower
critical solution temperature rhenium, from Maharajan ( 2008 ) reprinted with permission from Elsevier Sciecne
Poly NIAPAAm contains hydrophilic and hydrophobic groups. At lower temperatures which are below the ‘lower critical solution temperature ‘ ( LCST ) – the critical temperature at which polymer solution undergoes phase separation ( one stage to two stages ) [ 16 ] the H2O molecules bond to amide groups, organizing H adhering which cause solubilisation of the polymer concatenation. When the temperature is above the LCST the H2O molecules do non bond to the amide groups and the consequence of the hydrophobic groups dominate and the polymer concatenation prostration and come in a ball-shaped province fig. 3 [ 15 ]
Fig. 3 Coil to globule passage and subsequent solution turbidness alteration when poly-NIPAAm is heated above the lower critical solution temperature ( LCST )
The LCST of these polymers can be changed by the add-on of hydrophobic or hydrophilic functional groups into the construction Fig. 4 [ 17 ] . An illustration of this can be the co-polymerisation of NIPAA monomers with acrylamide ( hydrophilic monomer ) which leads to an addition in the hydrophilic of the polymer and in bend a higher LCST of the co-polymer. The antonym of this can be achieved by adding n-butyl acrylamide ( hydrophobic monomer ) it will increase the hydrophobicity and lower the LCST of the co-polymer [ 17 ] .
Fig. 4. Consequence of co-polymerization of poly-NIPAAm with hydrophilic acrylamide ( AAm ) or hydrophobic N-tert-butylacrylamide ( N-tBAAm ) on the lower critical solution temperature ( LCST ) ( from Hoffman et Al. ( 2000 ) , reprinted with permission from John Wiley & A ; Sons, Inc. ) .
Temperature antiphonal polymer systems have found many applications, some of which are drug bringing [ 18 ] , chemical valves [ 19 ] , thermo antiphonal surfaces [ 20 ] . These will be discussed subsequently in the reappraisal.
In electrically driven systems the behavior is determined by the charges in the system. Electrically goaded systems can be seen in Electrorheological fluids and in Electroactive Polymers ( EAP )
Electrorehological fluids are stuffs with dielectric belongingss [ 21 ] . The size of the dielectric atoms are in the scope of 0.1-100Aµm.The term rheological is the survey of viscousness of a liquid.
The features of a electrorheological fluids i.e. viscousness, output emphasis and shear modulus can alter in the different media [ 22 ] .
They change in viscousness as a rapid response when an electric field is applied [ 23 ] . They can travel from a liquid stage to solid stage or frailty versa. The passage occurs when the electric field is applied and so taken off [ 24 ] As seen in Fig. 5. The response clip is so speedy it can be within a affair of msecs [ 25 ] .
Fig 5. of The structural development of dielectric microspheres under an increasing electric field, from ( a ) no field, to ( B ) a moderate field of 500 V mm21, to ( c ) a strong field of 900 V mm21. Ref Weijia Wen [ 25 ] reprinted with permission from Royal Society of Chemistry
Winslow ( 1949 ) [ 26 ] Discovered the electrorehological consequence decennaries ago, it was in the 80 ‘s when new research was undertaken and the apprehension of ER mechanisms was clear.
Typical flow curves for an ERF are shown in fig 6. The greater addition as the electric field strength is increased
Fig.6. Shear emphasis is plotted against shear rate for an ERF consisting of silicon oxide atoms in silicone oil ( volume fraction 0.2 ) . Each curve corresponds to a changeless District of Columbia electric field strength, as follows ( units of kV/mm, from top to bottom ) : 2.5, 2.0, 1.5, 1.0 and 0. [ 27 ] Howard See ( 2006 ) reprinted with permission
Desired belongingss of ER fluids consist of ; High shear emphasis at low electric Fieldss, low zero field viscousness, low conduction, stable recreation, low cost, low conduction [ 28 ] .
ER fluids due to their alone belongingss are ideal stuffs to electronically command gesture and to reassign energy. ER fluids can be sub divided into two groups ; homogeneous and heterogenous [ 28 ] . ER fluids have found applications in assorted field, such as ; daze absorbers, human musculus simulators and other control systems [ 29 ] .
Electroactive Polymers ( EAP )
Electroactive polymers have emerged since the 90 ‘s [ 30 ] . Electroactive polymers respond to external electrical stimulation and alteration in form in or size [ 31 ] . They can be subdivided into two groups by the manner they are activated ; 1 ) ionic systems ( polymer Ionics ) 2 ) electronic systems ( carry oning polymers ) [ 32 ]
Some Common EAP ‘s subdivided into the two groups are show in table 1
Table 1 shows some common EAPs, subdivided into Ionic or Electronic. Ref [ 30 ]
Ionic Polymer Gel ( IPG )
Conductive Polymers ( CP )
Carbon Nanotubes ( CP )
Some advantages of Ionic EAPs are ; need low electromotive force and can hold big flexing supplantings. However they have a slow response clip [ 32 ] .
Ionic Polymer Gels ( IPG )
When these are activated they respond by bending, due to the mobility of cations and fixed anions. For the polymer to flex they require low electromotive forces and low frequences. The charged electrodes attract the cations to the negative electrode coercing it to flex.
Conductive Polymers ( CP )
These are activated through the procedures of redox chemical science. The polymer can alter in volume, through oxidization and decrease chemical science. The exchanges of ions occur at electrodes [ 33 ] .
Some advantages of Electronic EAPs are ; they have rapid response times, map in room conditions for long periods of clip. However they require high electromotive forces, consist of comprises of emphasis and strain [ 32 ] .
These expand or contract when an electric field is applied, or bring forth an electrical charge when force per unit area is applied [ 34 ] . Research in this field is dominated by Poly ( vinylidene fluoride ) or PVDF ( semi crystalline polymer ) . PVDF consists of a C concatenation, H ‘s and fluorides and when poled, the H have a positive charge and the fluorides have a negative charge. When the electric field is applied they either contract or acquire thicker dependent on the manner the electric field is applied Fig 7.
Fig 7, Schematic representation of the difference of consequence when the electric field is applied in two ways. [ 34 ]
7a ) Where the electric field is in the opposite way of the poled way and the sheet is stretched. 7b ) shows the electric field being applied in the same way as the poled and the sheet length contracts.
In physically driven systems the behavior is determined by the microstructure of the stuff. The behavior of physically driven systems can be seen in Auxetic stuffs and Shape Memory Polymers ( SMP ) .
Auxetic stuffs have a negative Poisson ‘s ratio. Poisson ‘s ratio is the measuring of
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Conventionally most stuffs have a positive poisson ‘s ratio, and hence when different forces are applied, the stuff has a decrease in length perpendicular to the loading way [ 35 ] . However, auxetic stuffs have the opposite characteristic when different forces are applied to it. The auxetic stuff gets thicker when it is stretched [ 36 ] . As shown in fig 8, 8a ) shows the behavior of a non auxetic stuff, when force is applied in the longitudinal ( x ) way the stuff responds from the dotted lineation to the solid lineation. It stretches in the longitudinal way and contracts in the sidelong ( y ) way. 8b ) shows the opposite feature of 8a ) . The auxetic stuff stretches in the longitudinal and sidelong way when forced is applied along the longitudinal way.
Fig 8 Behaviour of stuff with positive and negative poisson ‘s ratio
8a ) Non auxetic stuff. When force applied in longitudinal ( x ) way stuff transforms from dashed lineation to solid lineation
8b ) Auxetic stuff. When forced applied in longitudinal ( x ) way stuff transforms from dashed lineation to solid lineation. Material stretches in both waies. [ 37 ] Kenneth E. Evans ( 2000 ) reprinted with permission from Adv. Matter
Auxetic stuffs have been theoretically known for approx 150 year [ 38 ] with illustrations seen in nature e.g. some stones and minerals [ 39- 41 ] and in some signifiers of tegument like cattles teat [ 42 ] . It was non until the late 80 ‘s, when the existent possibilities of auxetic stuffs were recognised when the first synthesis of auxetic froth was manufactured [ 38 ] . It was Lakes [ 43 ] in 1987, that was foremost to detect a negative poisson ‘s ratio in polyurethane ( PU ) froth with reentrant constructions.
The physical construction of auxetic stuffs is the ground for its behavior and holding negative Poisson ratio value when tensile force per unit area is applied upon it [ 44 ] . Fig 9 shows constructions of a ) non auxetic and B ) auxetic stuffs when force per unit area is applied in the sidelong ( y ) way. In 9a we can see the conventional response, the cells stretch along the y-axis and fuse together in the x axis giving a positive passion value. 9b ) is known as a reentrant honeycomb construction and when force is applied, the stuff stretches in both waies ( along ten and y axis ) .
Fig. 9. a ) Conventional honeycomb web deforming by hinging of the cell walls in response to a tensile burden applied in the y way, taking to a positive Poisson ‘s ratio ( non-auxetic ) . B ) Re-entrant honeycomb web holding a negative Poisson ‘s ratio ( auxetic ) for the same distortion mechanism and lading status as for ( a ) . [ 44 ] Kenneth E. Evans reprinted with permission from Wiley
Auxetic stuffs have found applications in several different Fieldss. For illustration they are used as robust daze absorbers, aircraft and land vehicles [ 45 ] , through scaling up procedures of auxetic froth [ 46 ] , new applications were found in place shock absorbers, as they performed better so conventional froth samples due to their lower upper limit seating force per unit area [ 47 ] .
Wang and Lakes ( 2002 ) [ 48 ] found an analytical probe that found axuetic shock absorbers gave better public presentations to those who suffered from force per unit area induced uncomfortableness when seated. More normally they are used as blast stuffs and fibre complexs [ 49 ] .
Another illustration is personal protective vesture such as slug cogent evidence waistcoats and helmets. When the force is applied to the stuff, it responds to compact in all waies doing the stuff denser and therefore more impact immune [ 50 ] .
Shape Memory Polymers
These category of polymers quickly change form on response to external stimulations [ 51 ] . They can be deformed and fixed into a impermanent form and retrieve their original form when desired when exposed to the appropriate stimulation [ 52 ]
Appropite stimulation that would force a SMP to quickly alter could be ; temperature, visible radiation, electric field, magnetic field, pH, specific ions or enzyme [ 52 ]
SMPs are going more appealing to research because of their scientific and technological significance [ 53-55 ] . Properties that SMPs have that make it so appealing are its ability of high form deformability and recoverability. It is besides lightweight, good processability and have low costs [ 56-60 ] .
In a SMP, the polymer ironss are able to repair a given construction by chilling below a certain passage temperature ( Ts ) . When the polymer ironss are reheated above the passage temperature ( Ts ) the original form is recovered. A macroscopic conventional representation is shown in fig. 10
SMP systems consist of two stages ; one being a fixed stage and the other a impermanent stage
Fig 10. representation of macroscopic form memory consequence [ 61 ] Debdatta Ratna ( 2008 ) reprinted with permission from Springer
The passage temperature can either be glass passage temperature ( Tg ) or runing temperature ( Tm ) ( ref a reappraisal of smp complexs ) . SMPs can keep its lasting form by either physical or chemical crosslinks fig. 11
Fig 11 micromechanism of form memory consequence of polymers [ 61 ] Debdatta Ratna ( 2008 ) reprinted with permission from Springer
For a polymer to be classed as an SMP they must besides hold some of import belongingss. Such as strain recovery rate ( Rr ) which is the ability of the polymer to retrieve its original form and strive fastness rate ( Rf ) which is the ability of the polymer for it to be able to repair its mechanical distortion [ 61 ] .
SMPs were foremost developed by a Gallic company in 1984 called CDF under the trade name Polynorbornene Since so SMPs have found themselves in a broad usage of applications in ; smart fabrics [ 62 ] intelligent medical devices [ 63-65 ] detectors and actuators [ 66-67 ] micro-systems [ 68 ] and in other industrial countries [ 69-71 ]
A figure of blends are now in the procedure of being made excessively. Qinghao Meng ( 2009 ) [ 51 ] described grounds for why complexs and blends of SMPs are being processed ; to better form recovery emphasis, lessening form recovery initiation clip and better the mechanical belongingss among some of the grounds.
Presently working on
Applications of Smart Polymers
Main application is in Biotechnology and med
Image of utilizations from journal spider diagram
Biotechnology and medical specialty
Drug bringing – responsive gels, antiphonal vehicles, antiphonal polymer coated stuffs
Future Direction of smart polymers
Maharajan P. Et all have discussed the relationship between smart polymers and the nutrient industry. Ref [ 15 ]
They discuss the development of selective and cost effectual isolation techniques that can reply to the increasing demand of functional nutrient ingredients. They focus on Chromatography as a technique to bring forth these nutrient ingredients utilizing smart polymers. Smart polymers are being associated with this industry because of their behavior to alter stages dependent on their environment and have potential to offer a cheaper path to bring forthing the coveted functional nutrient ingredients. However there are gray countries in this technique such as the efficiency of separation and capacity of media. Ref Food industy ( Pankoj M, Louise e white avens )
Smart polymer to textile
Ref Application of smart polymers to textile
By: S. Ariharasudhan and Mr. R. P.Sundaram
The application of smart polymers to fabrics are slightly a turning importance in the industrial universe. Smart polymers can be used in this industry by transplant copolymerization onto the surface of cloths. Ref 1- G.H. Chen, A.S. Hoffman, Graft copolymers that exhibit temperature induced stage passages
over a broad scope of pH, Nature 373 ( 1995 ) 49-52.
Ref 2- Y. Kaneko, S. Nakamura, K. Sakai, A. Kikuchi, T. Aoyagi, Y.Sakurai, T. Okano, Deswelling
mechanism for comb-type grafted poly ( N-isopropylacrylamide ) hydrogels with rapid temperature
responses, Polym. Gels Network 6 ( 1998 ) 333-345.
An illustration of a smart polymer used in this industry is temperature-senstiive polyurethane ( TS-PU ) This polymer grafted on to a cloth would let it to be rainproof ( due to its H2O vapor permeableness of its membrane ) and adaptable breathability in response to alter in the clime temperature. Ref Graham-Rowe, D. , Going Commando, New Scientist, March ( 31 ) , 22 ( 2001 )
Smart polymers could be modified to orient our demands of certain cloths due to their ability of reacting to external stimulations. They would let us to maintain warm or cool in a cold or hot environment severally.
Recent Developments and Future of Smart Polymers
Use of smart stuffs to move as detectors to observe biological stuffs and pollutants
Smart polymer to be used in protection of ID Chips
Smart polymer helps sawboness
December 27, 2005
A German research worker has created a “ smart ” polymer sawboness can utilize to shut stitches from inside the organic structure of a patient.
Professor Andreas Lendlein, a chemist at the GKSS Research Center in Teltow, near Berlin, said the polymer can be placed into the organic structure in tight signifier, so alter back to its original form, make its occupation and dissolve, Deutsche Welle reported Monday.
“ Therefore you can present a bulky implant in a tight signifier into the organic structure through a little cut, such as in keyhole surgery, ” Lendlein said. “ By warming the room temperature to organic structure temperature the implant unfurls and so the whole thing disintegrates after a certain ( sum of ) clip. It dissolves so that you do n’t hold to transport out a 2nd operation to take the implant. ”
Lendlein has besides created a particular yarn for sawboness that makes itself into a cringle one time inside the organic structure.
Copyright 2005 by United Press InternationalA
Scientists in India and germany developing a smart polymer for radioactive waste decrease
Instantaneous penetration: Polymers move cleverly
04 December 2008
Hans-Jorg Schneider and Kazuaki Kato, University of Saarlandes, Germany, introduce polymers that respond to chemical and biological stimulations through motion
Chemomechanical polymers are a new type of smart polymer with specific acknowledgment sites that can react selectively to chemical and biological stimulations through big motions. They have the alone characteristic of uniting a detector and an actuator ( a mechanical device for traveling or commanding a mechanism or system ) within one individual unit, without the demand of external devices such as a transducer or a power supply.A
When exposed to chemical or biological stimulations – such as bases, aminic acids or peptides – in the local environment these polymers produce big and reversible enlargements and contractions. They can besides be downsized to thin movies or microparticles, with enhanced speed and sensitiveness of response.A
Enantioselective contraction of a chitosan hydrogel atom can be induced byA L- orD- dibenzoyl-tartaric acid
Until late, chemomechanical polymers were merely known for reacting to instead broad alterations in pH, salts and dissolvers. In the last few old ages the Schneider group has applied known rules of supramolecular chemical science to do hydrogels with suited acknowledgment sites, taking to stuffs that respond selectively to external organic stimulations by non-covalent interactions.A
A big assortment of flexible hydrogels have now been made incorporating these supramolecular binding sites that can selectively place specific organic molecule signals being transmitted from the environing aqueous environment.A
“ A peculiar high spot of these polymers is an ability to separate between optical isomers ”
A peculiar high spot of these polymers is an ability to separate between optical isomers. Recently the interaction of chitosan gels and tartaric acid derived functions was for the first clip shown to straight interpret chiral acknowledgment into big shrinkings of the hydrogel atom. It was shown that exposing a chitosan hydrogel atom to D- dibenzoyl-tartraric acid caused it to shrivel by 94 per cent, but when the same hydrogel was exposed to the L-enantiomer merely 20 per cent shrinking was seen.
The gestures of these smart hydrogels are besides strongly dependent on the pH of the environing environment. And scientists have now taken advantage of this to do hydrogels that can move as simple logic Gatess, where the gesture depends on both the presence of a trigger ( such as a base ) and the right pH.
“ In polymers with both ester and amine functional groups the gesture induced by aminoacids and peptides is merely triggered when Cu or Zn ions are besides present ”
A related logic gate consequence is besides seen in polymers with both ester and amine functional groups. A instead dramatic illustration is a polymethyl ( methyl ) acrylate-based gel incorporating ethylenediamine-type binding sites – where the gesture induced by aminoacids and peptides is merely triggered when Cu or Zn ions are besides present.A
It is hoped that these smart stuffs will happen multiple future utilizations including in systems for controlled drug bringing, in the consumption of toxic compounds, in commanding flow in medical devices and even in microfluidic machineries. Besides of involvement is seting these smart hydrogels into tubings or onto flexible sheets to do unreal musculuss that can interpret the energy produced by non-covalent binding of a trigger molecule into mechanical motion.A A
The hereafter for this research is bright, and it is hoped that the execution of more sophisticated acknowledgment elements into chemomechanical polymers and a better apprehension of the underlying mechanism will take to even smarter materials.A