Smart materials responsiveness

Key words smart material, responsive polymer, lower critical solution temperature (LCST), upper critical solution temperature (UCST),phase transition. 

Smart materials have active responses to external stimuh and can serve as sensors and actuators... 

Many kinds of nonbiodegradable vinyl-type hydrophilic polymers were also used in combination with aliphatic polyesters to prepare amphiphilic block copolymers. Two typical examples of the vinyl-polymers used are poly(/V-isopropylacrylamide) (PNIPAAm) [149-152] and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) [153]. PNIPAAm is well known as a temperature-responsive polymer and has been used in biomedicine to provide smart materials. Temperature-responsive nanoparticles or polymer micelles could be prepared using PNIPAAm-6-PLA block copolymers [149-152]. PMPC is also a well-known biocompatible polymer that suppresses protein adsorption and platelet adhesion, and has been used as the hydrophilic outer shell of polymer micelles consisting of a block copolymer of PMPC -co-PLA [153]. Many other vinyl-type polymers used for PLA-based amphiphilic block copolymers were also introduced in a recent review [16]. 

Supermolecular interlocked macromolecules have been paid much attention as candidates of smart materials. Polyrotaxane (PRX) is a typical example. PEG/ cyclodextrin (CD)-based polyrotaxane was firstly reported by Harada and coworkers by attachment of stoppers to pseudopolyrotaxane (pPRX) consisting of a PEG and CDs [263]. Subsequently, many CD-based PRXs have been designed and prepared as smart materials such as biomaterials, light-harvesting antennae, insulating polymers, stimuli-responsive molecular shuttles etc. [264—268]. 

Shape-memory polymers (SMPs) are a class of smart materials with the ability to change shape on demand in response to an environmental stimuli [322-325]. So far, the most commonly investigated SMPs are temperature-induced SMPs, whose shape-recovery behavior is triggered by thermal stimuli. Such SMPs have one shape at certain temperature and are converted to another shape at a different temperature (Fig. 22). Temperature-responsive SMPs usually require the combination... 

Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain polymers, such as synthetic polypeptides, are known to change shape on application of electric current, temperature, and chemical environment. For instance, selected bioelastic smart materials expand in salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent adhesion growth between surgically operated tissues, and in controlled drug release, where the material is designed to behave in a predetermined matter according to a specific chemical environment. 

Smart materials are extremely efficient, performing a variety of jobs that would otherwise require researchers and engineers to spend a lot of time and money to develop and design a number of different substances. Materials capable of multitasking are one of the most interesting and promising frontiers of chemistry and materials science. This chapter describes research on a variety of materials and systems that exhibit some degree of responsiveness to their environment. 

Materials that respond to electricity or magnetism were some of the earliest smart materials to be discovered. The British researcher James Joule (1818-89) found in 1842 that iron changes length in response to a magnetic field, a process called magnetostriction. Since electric and magnetic fields are easy to produce and control with precision, these smart materials can be extremely useful. 

Chemical engineers can sometimes increase the size or alter the nature of the response of a smart material by a process known as doping. 

Y. Zhao, Smart Light-Responsive Materials, Wiley-Blackwell, Indianapolis 2009 Ch. Dugave (ed.), cis-trans Isomerisation in Biochemistry, Wiley-VCH, Weinheim 2006 For photomobile polymer materials and light driven plastic motors, see M. Yamada, Y. Yu, M. Kinoshita, C.J. Barret,... 

But the day of dumb buildings is on its way out, just as is the day of dumb cars, dumb airplanes, dumb weapons, dumb satellites, and just about any other kind of dumb structure you can imagine. The day of smart structures built with smart materials has just about arrived in the developed world. Smart materials have been defined as materials that respond to environmental stimuli by making some change in their physical characteristics, such as their size, shape, electrical or magnetic conductivity, or optical properties. Because they respond to change in the surrounding environment, smart materials are also sometimes called responsive materials. 

In the broadest sense, all materials are smart materials because they all change in at least some way when exposed to changes in their environment. For example, the volume of any material changes when the temperature around it changes. In the vast majority of cases, the volume of the material increases as the temperature increases. This principle lies at the basis of at least one familiar appliance in your home that uses responsive materials a thermostat. A thermostat is a metal strip consisting of two metals bonded to each other. The two metals expand at different rates when they are heated. Since they expand at different rates, the strip bends in one direction or another as the temperature changes. As it bends, the strip either comes into contact with a metal electrode and closes a circuit, or it moves away from that contact and stops the flow of current through the circuit. 

As exciting as nanomaterials may he for many researchers, smart materials may present an even more promising future. With the ability to sense changes in the environment around them, analyze those changes, and then develop appropriate responses, smart materials have some of the fundamental qualities that people associate with "life. Will smart materials someday act so much like living materials that the difference between "life and "nonlife becomes unclear As smart materials become smarter, people wonder. 

Responsive (Smart) Materials Available online. URL http //www. 

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