Smart Textiles and Intelligent Textiles

Classification of Smart Textiles

Passive Smart materials

Passive smart materials can only sense environmental conditions or stimuli. The first generations of smart textiles, which can only sense the environmental conditions or stimulus, are called Passive Smart Textiles.

Active Smart materials

Active smart materials, which sense and react to the condition or stimuli. The second generation has both actuators and sensors. The actuators act upon the detected signal either directly or from a central control unit. Active smart textiles are shape memory, chameleonic, water-resistant and vapour permeable (hydrophilic/non porous), heat storage, thermo regulated, vapour absorbing, heat evolving fabric and electrically heated suits.

Very Smart materials

Very smart materials, which can sense, react and adapt themselves accordingly. Very smart textiles are the third generation of smart textiles, which can sense, react and adopt themselves to environmental conditions or stimuli. A very smart or intelligent textile essentially consists of a unit, which works like the brain, with cognition, reasoning and activating capacities. The production of very smart textiles is now a reality after a successful marriage of traditional textiles and clothing technology with other branches of science like material science, structural mechanics, sensor and actuator technology, advance processing technology, communication, artificial intelligence, biology, etc.

Intelligent materials

Intelligent materials are those capable of responding or being activated to perform a function in a manual or pre-programmed manner. New fiber and textile materials, and miniaturised electronic components make the preparation of smart textiles possible, in order to create truly usable smart clothes. These intelligent clothes are worn like ordinary clothing, providing help in various situations according to the designed applications.

Application of Smart and Intelligent Textiles

Shape Memory Materials

These are the materials which are stable at two or more states of temperature. In these different temperature states, they have the potential to assume different shapes, when their transformation temperatures have been reached. There are another type of shape memory materials which are basically composed of electro active polymers (EAPs), which can change shape in response to electrical stimuli. Shape changing fibers, yarns and fabrics are also produced with the help of suitably designed stimuli sensitive copolymers that respond quickly and reversibly to small changes in temperature and pH. These materials are capable of providing sensing functions. EAPs can provide a range of basic actuator mechanisms, force and displacement levels. Also yarns made from Shape Memory Polymers are widely used to make fabrics which possess different properties below and above the temperature at which it is activated.

Principle of shape memory materials

There are two types of Shape Memory Materials .

1. The first classes are materials stable at two or more temperature states. In these different temperature states, they have the potential to assume different shapes, when their transformation temperatures have been reached. This technology has been pioneered by the UK Defence Clothing and Textiles
2. The other types of shape memory materials are the electroactive polymers, which can change shape in response to electrical stimuli. In the last decade there have been significant developments in electroactive polymers (EAPs) to produce

substantial change in size or shape and force generation for actuation mechanisms in a wide range of applications. In contrast to many conventional actuation systems, many types of EAPs are also capable of providing sensing functions. EAPs can provide a range of basic actuator mechanisms, force and displacement levels.

Shape Memory Textiles

Chromic Materials

Other types of intelligent textiles are those, which change their colour reversibly according to external environmental conditions, for this reason they are also called chameleon fibres .Chromic materials are the general term referring to materials which radiate the colour, erase the colour or just change it because its induction caused by the external stimulus, as “Chromic” is a suffix that means colour. Therefore we can classify chromic materials depending on the stimulus affecting them.

• Photochromic: external stimulus is light.
• Thermochromic: external stimulus is heat.
• Electrochromic: external stimulus is electricity.
• Piezorochromic: external stimulus is pressure.
• Solvatechromic: external stimulus is liquid or gas.

Materials and applications in Smart Textiles

Photocromic  materials are  generally reversible unstable organic molecules that change of molecular configuration with the influence of a special radiation. The molecular arrangement also perturbs the absorption spectra of the molecule and in consequences it colour. The applications in textile are intended to the fashion area and only a few for the solar protection.

Thermochromic materials are those whose colour changes as a result of reaction to heat, especially through the application of thermochromic dyes whose colours change at particular temperatures. Two types of thermochromic systems that have been used successfully in textiles are: the liquid crystal type and the molecular rearrangement type. In both cases, the dyes are entrapped in microcapsules and applied to garment fabric like a pigment in a resin binder .

The most important types of liquid crystal for thermochromic systems are the so-called cholesteric types, where adjacent molecules are arranged so that they form helices. Thermochromism results from the selective reflection of light by the liquid crystal. The wavelength of the light reflected is governed by the refractive index of the liquid crystal and by the pitch of the helical arrangement of its molecules. Since the length of the pitch varies with temperature, the wavelength of the reflected light is also altered, and colour changes occur. An alternative means of inducing thermochromism is by means of a rearrangement of the molecular structure of a dye, as a result of a change in temperature.

The most common types of dye, which exhibit thermo chromism through molecular rearrangement, are the spirolactones, although other types have also been identified. A colourless dye precursor and a colour developer are both dissolved in an organic solvent. The solution is then microencapsulated and is solid at lower temperatures. Upon heating, the system becomes coloured or loses colour at the melting point of the mixture. The reverse change occurs at this temperature if the mixture is then cooled. However, although thermochromism through molecular rearrangement in dyes has aroused a degree of commercial interest, the overall mechanism underlying the changes in colour is far from clear-cut and is still very much open to speculation.

The Sensory Baby Vest

The sensory baby vest is equipped with sensors that enable the constant monitoring of vital functions such as heart, lungs, skin and body temperature which can be used in the early detection and monitoring of heart and circulatory illness. It is hoped to use this vest to prevent cot death and other life-threatening situations in babies. The sensors are attached in a way that they do not pinch or disturb the baby when it is sleeping.

Reflective Technology

Technology has been created to convert proprietary materials into miniature reflectors that, when embedded into fabric by the millions, reflect oncoming light, such as automobile headlights, in a way that illuminates the full silhouette of a person, bicycle, or any other object. The reflectors are smaller than a grain of sand and finer than human hair. They can be embedded into the weave of almost any fabric. The end result is a fabric that remains soft to the touch and retains its function and fashion. During the day, the treated fabrics are indistinguishable from untreated fabrics.

Thermal Performance Enhancing Fabric

Hydroweave® provides extraordinary protection against heat, actively cooling the wearer through evaporation, and helping to maintain the core body temperature in high-heat environments. It is a three-layer design that combines special hydrophilic and hydrophobic fibers into a fibrous batting core. The batting is sandwiched between a breathable outer shell fabric and a thermally conductive, inner lining.

Flash Dried Fabrics

3XDRY® finishing technology was developed to provide a treatment that retains water resistance on the face of fabric and increases wicking on the back. The two functions are truly separated within the fabric, which remains highly breathable.

3XDRY® uses a special process to apply a hydrophilic finish on the back that wicks perspiration away from the body, spreading it over the fabric, and evaporating it quickly on the face. It also has a hydrophobic finish that repels water and dirt.

The fabric dries six to eight times faster than untreated fabric. 3XDRY ® also incorporates a hygienic treatment to control odor.

Protective Flex

The new “smart response” fiber is proving to enhance passenger safety because of its unique energy-management properties. Securus™ is the first in a new category of polyester copolymer fibers being developed for managed-load applications. It combines polyethylene terephthalate (PET), which provides restraining properties, and polycaprolactone (PCL), which provides flexibility and cushioning. During a collision, Securus fiber seat belts protect the passenger in a three-step process: holding the passenger securely in place; elongating and cushioning the body as it absorbs the energy of its forward motion, and restraining and limiting that motion.

Thermal Sensitivity

SmartSkin™ hydrogel is a new technology involving a hydrophilic/hydrophobic copolymer, which is embedded in an open-cell foam layer bonded to the inside of a closed-cell neoprene layer in a composite wet suit fabric with nylon or nylon/Lycra® outer and inner layers. SmartSkin absorbs cold water that has flushed into the suit and expands to close openings at the hands, feet, and neck, preventing more water from entering. Water trapped inside the suit heats up upon body contact. If the water warms up past a transition temperature determined by the proportion of hydrophilic to hydrophobic components, the hydrogel releases water and contracts, allowing more water to flush through the suit. This passive system constantly regulates the internal temperature — no batteries or mechanical action are needed.

Phase Change Materials

Outlast® temperature-regulating technology effectively recycles body heat, keeping the wearer’s skin temperature within a comfortable range. Outlast was first developed for use in astronaut uniforms and as a protection for instruments against the severe temperature changes in outer space. The technology is now used in apparel, footwear, equipment, and linens. Outlast is a paraffin wax compound that is micro-encapsulated into thousands of minuscule, impenetrable, hard shells. It recycles body heat by absorbing, storing, distributing, and releasing heat on a continuous basis, keeping the wearer’s skin temperature within a comfortable range.

Wearable Technology

Clothing is currently supposed to have more functions than just certain climatic protection and a good look. These functions can be referred to as wearing and durability properties. A revolutionary new property of clothing is to exchange information. Clothing is now capable of recording, analyzing, storing, sending, and displaying data, which is a new dimension of intelligent systems. Clothing can extend the user’s senses, augment the view of reality and provide useful information anytime and anywhere the user goes.

Application fields are:

• Working: displaying helpful data, connecting to the internet or to other people
• Medicine: monitoring health parameters
• Security: detecting danger, calling for help

Wearable Technology

Bio-mimics

Fibers have been developed that can quickly change their color, hue, depth of shade or optical transparency by application of an electrical or magnetic field could have applications in coatings, additives, or stand-alone fibers. Varying the electrical or magnetic field changes the optical properties of certain oligomeric and molecular moieties by altering their absorption coefficients in the visible spectrum as a result of changes in their molecular structure.

The change in color is due to the absence of specific wavelengths of light; it varies due to structural changes with the application of an electromagnetic field.

Tissue Engineering

Tissue engineering uses living cells and their extracellular components with textile-based biomaterial scaffolds to develop biological tissues for human body repair. The scaffolds provide support for cellular attachment and subsequent controlled proliferation into predefined tissue shapes. Such an engineering approach would solve the severe shortage problem associated with organ transplants. Textile-based scaffolds have been used for such tissue engineering purposes. The most frequently used textile-based scaffolds are non-woven structures, preferably of biodegradable materials, because then there is no permanent foreign-body tissue reaction toward the scaffolds and, over time, there is more volume space into which the engineered tissue can grow.

Detection of Vital Signals

Sensatex is developing a SmartShirt™ System specifically for the protection of public safety personnel, namely firefighters, police officers, and rescue teams. Used in conjunction with a wireless-enabled radio system, the SmartShirt™ can monitor the health and safety of public safety personnel/victims trapped in a building or underneath rubble with the ability to detect the exact location of victims through positioning capability. In addition to monitoring vital signs, the system can detect the extent of falls, and the presence of hazardous gases; it also offers two-way voice communication.

Global Positioning System (GPS)

Textiles integrated with sensory devices driven by a GPS can detect a user’s exact location anytime and in any weather. Interactive electronic textiles with integrated GPS enhance safety by quickly locating the wearer and allowing the suit to be heated. GPS can provide added safety for firefighters and emergency personnel by facilitating offsite monitoring of vitals. It is wireless, hands-free communication. Fabric area networks (FANs) enable electronic devices to exchange digital information, power, and control signals within the user’s personal space and remote locations. FANs use wireless RF communication links using currents measuring one nanoamp; these currents can transmit data at a speed equivalent to a 2400-baud modem.

 

Global Positioning System (GPS)

Cooling – Warming System

A new high-tech vest has been developed to help keep soldiers, firefighters, etc. alive in the searing temperatures of deserts, mines, and major fires. The vest uses a personal cooling system (PCS), which is based on heat pipe technology which works by collecting body heat through vapor-filled cavities in a vest worn on the body. The heat is then transferred via a flexible heat pipe to the atmosphere with the help of an evaporative cooling heat exchanger. The heat exchanger is similar in principle to a bush fridge where a cold cloth is put over a container and the temperature drop caused by evaporation keeps the food cool. It is designed to be worn by personnel underneath NBC (nuclear, biological, and chemical) clothing, body armor, and other protective clothing.

Warning Signaling

A combination of sensors and small flexible light-emitting displays (FLED) can receive and respond to stimuli from the body, enabling a warning signal to be displayed or sent. The sensors can monitor EKG, heart rate, respiration, temperature, and pulse oximetry readings. If vital signals were below critical values, a FLED would automatically display, for example, a flashing red light, and a wireless communication system could send a distress signal to a remote location.

Self Cleaning Fabrics

Far from being a dream, nanotechnology has proved successful in many of the emerging businesses during this time including textiles and fashion industries. Out of some of the most exciting areas of challenges and opportunities in this field such as the development of carbon nano tube-based “super carbon fiber”, solar cells to store energy for electro textiles, Quantum dots to create the shades which are not achievable by normal techniques, etc., self-cleaning fabric is of major interest for garment and fashion-related industries

 

Nanosize particles of Titanium Dioxide, Zinc Oxide, etc, possess photocatalytic and oxidizing ability which is exploited in making self-cleaning fabrics. The fabric is coated with a thin layer of titanium dioxide particles that measure only 20 nanometers in diameter. When this semi-conductive layer is exposed to light photons with energy equal to or greater than the bandgap of the titanium dioxide excites electrons up to the conduction band.

The excited electrons within the crystal structure react with oxygen atoms in the air, creating free-radical oxygen. These oxygen atoms are powerful oxidizing agents, which can break down most carbon-based compounds through oxidation-reduction reactions. In these reactions, the organic compounds (i.e. dirt, pollutants, and microorganisms) are broken down into substances such as carbon dioxide and water. Since the titanium dioxide only acts as a catalyst to the reactions, it is never used up. This allows the coating to continue breaking down stains over and over.

Electrical conductive fabrics

Electrical conductive fabrics are manufactured by using metals and polymers. However, the same materials can be used for both conductivity (thermal and electric). Fabrics are manufactured by direct use of conductive yarns in order to provide a versatile combination of physical and electrical properties for a variety of demanding applications. The yarn could constitute metal such as silver, copper, etc… or conductive polymers such as polythiophene, polyaniline, and their derivatives. These conductive fabrics satisfy very well all the important properties that a garment should have. They are lightweight, durable, flexible, and cost-competitive and they are able to be crimped and soldered, and subjected to textile processing without any problems.

Smart Bra

One of the best examples of conductive polymer-coated fabric for improving the comfort properties of women is the Smart Bra, an Australian invention. Wallace et. al at the University of Wollongong has developed a bra that will change its properties in response to breast movement. This bra will provide better support to active women when they are in action. The smart bra will tighten and loosen its straps, or stiffen and relax its cups to restrict breast motion, preventing breast pain and sag. The fabrics can alter their elasticity in response to information about how much strain they are under.

 

The smart bra will be capable of instantly tightening and loosening its straps or stiffening cups when it detects excessive movement These conductive fabrics have also found wide application in the field of making sports garments. Also, these conductive textile materials can be used as heated clothes for extreme winter conditions or heated diving suits to resist very cold water. Other main applications of conductive textile materials are their uses for the power supply of electronic devices used in the garments called “SMART SHIRT” which is manufactured for use in combat conditions, for fire-fighters where the sensor that monitors oxygen or hazardous gas levels and other sensors monitor respiration rate and body temperature, etc.