Intelligent textiles represent the next generation of fibres, fabrics and articles produced to respond in time. It can be described as textile materials that think and act for themselves. This means, it has keep us warm in cold environments or cool in hot environments or provide us with considerable convenience in our normal day-to-day affair. Intelligent textiles are not confined to the clothing sector alone. It is used in protection, safety, added fashion and convenience. The most important intelligent materials at present in are classified as 1) Phase change materials, 2) Shape memory materials, 3) Chromic materials 4)Conductive materials and 5)Electronics incorporated textiles.
2.0 Phase Change Materials (PCM)
Every material absorbs heat during heating process and its temperature will rise constantly. The heat stored in the material is released into the environment through a reverse cooling process and the material temperature decreases continuously. A normal textile material absorbs about one kilo joule per kilogram of heat while its temperature rises by one degree Celsius. Phase Change Material (PCM) will absorb higher amount of heat when it melts. This thermo regulating effect of textiles can be obtained with the application of PCM.
Fig1: PCM Incorporated Clothing
Figure 1.describes the PCM incorporated clothing action A paraffin-PCM, absorbs approximately 200 kilojoules per kilogram of heat if it undergoes a melting process. During the complete melting process, the temperature of the PCM and its surrounding area remains constant. The paraffin's are either in solid or liquid state. In order to prevent the paraffin's dissolution in the liquid state, it is enclosed into small plastic spheres with diameters of only a few micrometers. These microscopic spheres containing PCM are called PCM-microcapsules. The microencapsulated paraffin is either permanently locked in acrylic fibres and in polyurethane foams or coated onto the surface of a textile structure.
Normal garments do not balance the heat generated and released in to the environment from the body. PCM incorporated textiles provide good thermal balance due to its thermo regulating effect. PCM controls the heat flux through the garment layers and adjusts the heat flux to the thermal circumstances, for example, if the heat generation of the body exceeds the possible heat release through the garment layers into the environment, the PCM will absorb and store this excess heat. On the other hand, if the heat release through the garment layers exceeds the body's heat generation during lighter activities, the heat flux through the garment layers is reduced by the heat emission of the PCM. The figure2 shows the thermoregulation effect of PCM incorporated clothing over the conventional clothing.
Intensity and duration of the PCM's active thermal insulation effect depend mainly on the heat storage capacity of the PCM-microcapsules and the applied quantity. Thin high-density materials support for cooling process. Thick and less dense textile structure leads to more efficient heat release. To ensure a suitable and durable active thermal insulation effect in an active-wear garment, it is necessary to apply the correct PCM in the appropriate quantity. The selected PCM is normally microencapsulated and incorporated in a textile substrate. Requirements of the textile substrate in a garment application include sufficient breath ability, high flexibility and mechanical stability. The substrate incorporated with PCM-microcapsules needs to be integrated into a suitable location of the garment design and certain design principles need to be taken into account.
3.0 Shape Memory Polymers(SMP)
These types of materials can revert from the current shape to a previously held shape, usually due to the action of heat. This technology has been extensively pioneered by the UK Defense Clothing and Textiles Agency. When these shape memory materials are activated in garments, the air gaps between adjacent layers of clothing are increased, in order to give better insulation. The incorporation of shape memory materials into garments thus confers greater versatility in the protection against extremes of heat or cold.
Shape memory alloys, such as nickel-titanium, used to provide increased protection against sources of heat, even extreme heat. A shape memory alloy possesses different properties below and above the temperature at which it is activated. Below this temperature, the alloy is easily deformed. At the activation temperature, the alloy exerts a force to return to a previously adopted shape and becomes much stiffer. The temperature of activation can be chosen by altering the ratio of nickel to titanium in the alloy.
Cuprous-zinc alloys are capable of a two-way activation and therefore can produce the reversible variation needed for protection from changeable weather conditions. They will also react to temperature changes brought about by variations in physical activity levels.
A shape memory alloy is usually in the shape of a spring. The spring is Fig3: A Shape memory polymer in action
flat below the activation temperature but becomes extended above it, which is shown in the figure 3. By incorporating these alloys between the layers of a garment, the gap between the layers can be substantially increased above the activation temperature. In consequence, considerably improved protection against external heat is provided.
For clothing applications, the desirable temperatures for the shape memory effect to be triggered will be near body temperature. Polyurethane films, which can be incorporated between adjacent layers of clothing. With temperature of the outer layer of clothing has fallen sufficiently, then polyurethane film responds so that the air gap between the layers of clothing becomes broader. Bi-Material Film laminates rely on differing coefficients of thermal expansion to produce a reversible bending effect. Encapsulated Bi-Gels absorb liquid at differing rates according to temperature, which causes them to bend used to actuate variable insulation system. Other uses of SMPs in domestic purpose are in shower mixer valves, coffee makers, rice cookers, safety shut off valves for fuel lines in the event of fire and in air conditioning systems.
4.0 Chromic Materials
Chromic materials are the general term referring to materials which radiate the color, erase the color or just change it because its induction caused by the external stimuli, as "chromic" is a suffix that means color. It can be classified depend on the Stimuli. Out of this the first four chromic materials are important and has potential to cater the market
. Photochromic: external stimuli energy is light.
. Thermochromic: external stimuli energy is heat.
. Ionochromic: external stimuli energy is pH value
. Electrochromic: external stimuli energy is electricity.
. Piezorochromic: external stimuli energy is pressure
. Solvatechromic: external stimuli energy is liquid.
. Carsolchromic: external stimuli energy is electron beam.
4.1 Photochromic :
In this kind of chromism the color change is due to the intensity of the light(UV radiation also). The photochromic dyes interact with the electromagnetic radiation in the near UV (300-400nm),Visible(400-700nm) and near IR(700-1500nm) to produce verity of effects, which is reversible when the radiation is withdrawn. Photochromism is of Two types. Positive and Negative. In Positive Photochromism the colorless substance converted in to colored object when exposed in to the light due to Uni-molecular reaction system. Bi molecular reaction system is called Negative Photochromism i.e. from colored to colorless. the transformation is between two states that have different absorption spectra. It may be induced in one or both the direction by electromagnetic radiation. This process is a non destructive process., but side reactions may occur. Oxidation is the major cause for the degradation of the Photochromism. Main class of Photochromism is Spiropyrans. It is used in Optical switching data and Imaging system rather then the textile applications.
Thermally induced reversible color change occur in the thermochromism. A large variety of substrates such as Organic ,Inorganic Orgonomatallic and Macro molecular systems exhibit this phenomena. Mercury Iodide salts like Ag2 HgI4 shows color change from yellow to orange at 51C.This is due to the reason that each compound can under go phase change at particular temperature .Majority of thermochromic systems are unacceptable simply because of the change in the color requires large amount of energy due to involvement of inter molecular transformation. Using verity of liquid crystals ,it is possible to achive significant changes in the appearance over the narrow temperature range(5-15C) and to detect small variation in the temperature(≤1C).The thermochromic dyes used extensively in the printing of Textiles, Micro encapsulation ,coating or dope dyeing .
4.3 Ionochromic dye:
These chromic materials are sensitive to pH. Widely used these classes dyes are Phthalides, Triarylmethans and Fluorans. In analytical chemistry these dyes are used extensively. There are no commercial application of these dyes in textiles but direct thermal printing can be used. In this process substrate contain both the color former and acid co reactant in a single layer. simply by heating the surface of the paper with a thermal head causes the components to react and to produce color.
4.4 Electochromic dye:
The material that change color upon the application of Voltage are called electrochromes. This is due to oxidation and reduction process with in the electochromic material. This are of three types. First type, the coloring species remain in the solution. In the second type the reactants are in solution but the colored product is of solid. In the third type is both reactant and the color is in form of solid e.g. composite Film. Most available electochromic dyes are of inorganic oxides such as cobalt oxide, nickel oxide, molybdenum trioxide. A research is going on in MIT,USA to use thin film composite electrode material with layer by layer assembly technique, to identify whether electrochemical cell is fully charged or discharged by using color change. The most important commercial application of the electrochemic dye in the textile is of US-Military IR camouflage material (Dynam IR) .
4.5 Solvantochromic dye:
The Solvantochromism is a reversible variation of the electronic spectroscopic properties (absorption and emission)of a chemical species, induced by the solvents. It is one of the oldest chromism have been described as long as ago 1878.This is used as probes for application in polymer characterization. Where they can be used to look for localized polar features at the molecular level.
Chromic dyes contain highly specialized components that require extraordinary careful manufacturing technique and has great potential for both fashion and higher end market.
5.0 Conductive materials
Exploration of human/machine interaction and wholly new types of interface sensor technology has resulted in the development of sensory fabric. These materials also afford designers new opportunities in developing for product markets. The ability to dispense with fixed casings, rigid mountings and inflexible substrates facilitates new radical possibilities in flexible, user-friendly interfacing textiles. By using conductive plastics, pressure sensitive inks and piezo films the above application succeeded in textiles. The main emphasis is currently on X-Y position sensing and pressure sensors.
5.1 X-Y position sensing
The structures of these materials offer the capability of reading the location, within a fabric sheet (Pad), of a point of pressure (such as a finger press). It is possible to incorporate this function into an elastic sheet structure, allowing the sheet to conform to many 3-D shapes, including compound curves, while still accurately measuring an X-Y position. The Fabric structures that provides an X-Y position function can also be used to provide accurate 'switch matrix' functionality. Interpreting electronics are used to identify the location of switch areas in any configuration to suit product requirements. Since this is done in software, an endless array of configurations can be addressed at the touch of a piece of fabric.
5.2 Pressure sensors
Readings can be obtained from smart fabrics according to force and area. This allows the user to differentiate between separately identified inputs ranging from high-speed impact to gentle stroking. The force/area reading is versatile, as fabrics can be constructed to be more sensitive to either force or area.
There are other applications for conductive materials such as heated clothes for extreme winter conditions or heated diving suits to resist very cold water. In these cases a heat or energy source is needed as the conductive material is not able to generate energy, it is only capable of conduction, to distribute the heat throughout the entire garment or suit.
The advantages and benefits that conductive materials over the existing wire system are uniform temperature distribution, pliability, strength (resistance to flex and stress), non-corrosive nature, and cost effectiveness.
6.0 Other Intelligent textiles
Patterned new cold protection apparel. Cell foam materials such as neoprene and polyethylene can be used in the construction of garments. Stomatex NE is ideal for close contour fitting apparel for unhindered body movement. Stomatex PE is a lightweight apparel and has a significant cost advantage over neoprene. Stomatex PE is suitable for use in multi-layered clothing systems and footwear where weight may be an important factor.
Patterned product is meant for comfortably in extreme cold and wet condition. Super water-absorbing polymer fibre blended into fibrous matting, this matting is positioned between a breathable exterior shell and a conductive, waterproof inner lining. The breathable outer shell can be made from a variety of woven or knitted fabrics to deliver the performance needed for a wide range of applications. The inner lining is a thermally conductive micro-porous membrane. This special material allows perspiration to escape, and keeping the wearer cool and dry. The advantages are
. Evenly distributes cooling effect over the entire fabric.
. Wearer will feel good comfort.
6.3 Photonic fibres:
Dielectric mirror alternative layers of two materials with different refractive indices produce Photonic band gap. It reflects light in a certain range of wavelength and absorb light out side this range this fibres can be woven in to a fabric to form shields and filters in military operations. Bar codes made with this fibre are authentic.
6.4 Electronic systems incorporated in Textiles
There have been some very exciting developments recently regarding clothing with electronic systems incorporated into the constituent fibres and fabrics. Some examples of this are:
1.Music t-shirts- they allow to the wearer listen his/her favorite music stored on a chip, or to tune into the favorite radio station. They can also have moving images on the back.
2.Businessman garments-, which has a microphone, incorporated in the collar, a display, and a personal digital assistant in the sleeve.
3.Solar energy re-charge jacket- it includes some tools for creative playing and communication, such as a camera, display and microphone attachments.
4.Massage kits- It gives a soothing massage to the wearer that can be regulated depending on the level of relaxation desired by the user by applying vibration and pressure.
In the coming years, clothing products will increasingly assume intelligent functions. Clothing will combine the functions of medium, carrier and interface for an extremely wide range of micro system applications. This new generation of "intelligent textiles" places considerable new demands on innovative ability within the clothing industry, demands which also offer huge potential for future business sectors.