Posted tagged ‘polymer’

POISSON’S RATIO

August 23, 2011

01-PoissonRatio-isotropic linearly material-youngs modulus, bulk modulus, shear modulus, auxetic materials

When an element is stretched in one direction, it tends to get thinner in the other two directions. Hence, the change in longitudinal and lateral strains are opposite in nature (generally). Poisson’s ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. Since most common materials become thinner in cross section when stretched, Poisson’s ratio for them is positive.


For a perfectly incompressible material, the Poisson’s ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. A Poisson’s ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material negative volume.


01-poissons ratio-calculate simple stress and strains-engineering mechanics

Some materials, mostly polymer foams, have a negative Poisson’s ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.Foams with negative Poisson’s ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.

An example of the practical application of a particular value of Poisson’s ratio is the cork of a wine bottle. The cork must be easily inserted and removed, yet it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, could not be used for this purpose because it would expand when compressed into the neck of the bottle and would jam. Cork, by contrast, with a Poisson’s ratio of nearly zero, is ideal in this application.

01-poissons ratio-strain changes

It is anticipated that re-entrant foams may be used in such applications as sponges, robust shock absorbing material, air filters and fasteners. Negative Poisson’s ratio effects can result from non-affine deformation, from certain chiral microstructures, on an atomic scale, or from structural hierarchy. Negative Poisson’s ratio materials can exhibit slow decay of stress according to Saint-Venant’s principle. Later writers have called such materials anti-rubber, auxetic (auxetics), or dilatational. These materials are an example of extreme materials.

POISSON'S RATIO

August 23, 2011

01-PoissonRatio-isotropic linearly material-youngs modulus, bulk modulus, shear modulus, auxetic materials

When an element is stretched in one direction, it tends to get thinner in the other two directions. Hence, the change in longitudinal and lateral strains are opposite in nature (generally). Poisson’s ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. Since most common materials become thinner in cross section when stretched, Poisson’s ratio for them is positive.


For a perfectly incompressible material, the Poisson’s ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. A Poisson’s ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material negative volume.


01-poissons ratio-calculate simple stress and strains-engineering mechanics

Some materials, mostly polymer foams, have a negative Poisson’s ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.Foams with negative Poisson’s ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.

An example of the practical application of a particular value of Poisson’s ratio is the cork of a wine bottle. The cork must be easily inserted and removed, yet it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, could not be used for this purpose because it would expand when compressed into the neck of the bottle and would jam. Cork, by contrast, with a Poisson’s ratio of nearly zero, is ideal in this application.

01-poissons ratio-strain changes

It is anticipated that re-entrant foams may be used in such applications as sponges, robust shock absorbing material, air filters and fasteners. Negative Poisson’s ratio effects can result from non-affine deformation, from certain chiral microstructures, on an atomic scale, or from structural hierarchy. Negative Poisson’s ratio materials can exhibit slow decay of stress according to Saint-Venant’s principle. Later writers have called such materials anti-rubber, auxetic (auxetics), or dilatational. These materials are an example of extreme materials.

QTC

August 23, 2011

01-3D tablet-touch screen-force sensitive touch screen-quantum tunnelling composite

QTC is a composite made from micron-sized metallic filler particles (Silicone Rubber) mixed into an elastomeric matrix. Quantum tunnelling composite is a flexible polymer that exhibits extraordinary electrical properties. In its normal state it is a perfect insulator, but when compressed it becomes a more or less perfect conductor and able to pass very high currents.

01-QTC-Graph-resistance vs force - quantum tunnelling composite

History:

First produced in 1996, QTC is a composite material made from conductive filler particles combined with an elastomeric binder, typically silicone rubber. The unique method of combining these raw materials results in a composite which exhibits significantly different electrical properties when compared with any other electrically conductive material.

01-QTC pills-variable resistor-applications of QTC using pills-touch switches

Types of QTC:

1. Elastomeric (Material: Silicone Rubber) (The particle move close together)

2. Ink / Coating Solvent or Aqueous Polymer

3. Granular Sensors

Working of Quantum tunnelling composite:

01-quantum tunnelling composite-QTC-smart flexible polymer-silicone rubber-pressure switching-sensing-metal like conductor-variable inductance principle-QTC working-QTC operation

QTC usually comes in the form of pills or sheet. QTC pills are just tiny little pieces of the material. The sheets are composed of one layer of QTC, one layer of a conductive material, and a third layer of a plastic insulator. While QTC sheets switch quickly between high and low resistances, QTC pills are pressure sensitive variable resistors.

Application:

01-QTC touch Screen-pills-force or pressure sensors-quantum tunneling composite screen-pressure sensitive variable resistors

– Touch switches (sheet)
– Force/pressure sensors (pills)
– Motor speed control using force (pills)

Benefits:

  • QTC is a pressure/force sensing material. It can be easily integrated into existing products to enable force sensing opportunities and solutions.
  • Product surfaces can be incorporated, coated or impregnated with QTC to impart the properties of force sensing into or onto the host surface.
  • QTC material can be formed or moulded into virtually any size, thickness or shape, permitting redesign of product interfaces and providing improved ergonomics, aesthetics and user comfort.
  • QTC is an enabling technology which is simple and reliable to use.
  • QTC material is durable – it has no moving parts to wear out.
  • QTC material is mechanically strong.
  • QTC material can be made to withstand extreme temperatures limits.
  • QTC material is versatile, both electrically and physically e.g. Its range and sensitivity can be altered. QTC material is also intrinsically safe – the material is a contactless switch, ideal for sparkless operation.
  • QTC material can be directly interfaced to standard electronic and electrical devices.
  • QTC material and/or technology can be customized for customer requirements, applications and products.

NANO GENERATOR

August 23, 2011

01-cellphone-charger-nanogenerator

After six years of intensive effort, scientists are reporting development of the first commercially viable Nano generator, a flexible chip that can use body movements — a finger pinch now en route to a pulse beat in the future — to generate electricity.

This development represents a milestone toward producing portable electronics that can be powered by body movements without the use of batteries or electrical outlets.

The latest improvements have resulted in a Nano generator powerful enough to drive commercial liquid-crystal displays, light-emitting diodes and laser diodes. By storing the generated charges using a capacitor, the output power is capable to periodically drive a sensor and transmit the signal wirelessly.

01-nanogenerator-energize LED light and LCD display-future power generaration technologies-power production by body movement

If we can sustain the rate of improvement, the Nano generator may find a broad range of other applications that require more power.


Example:

  • Personal electronic devices powered by footsteps activating Nano generators inside the sole of a shoe;
  • Implanted insulin pumps powered by a heart beat; and
  • Environmental sensors powered by Nano generators flapping in the breeze.

01-heart-powered-pacemaker-insulin pumping by nano generator

Preparation:

The key to the technology is zinc oxide (ZnO) nanowires. ZnO nanowires are piezoelectric — they can generate an electric current when strained or flexed. That movement can be virtually any body movement, such as walking, a heartbeat, or blood flowing through the body. The nanowires can also generate electricity in response to wind, rolling tires, or many other kinds of movement.

01-concept-NanoGenerator-Zinc oxide Nano wires

The diameter of a ZnO nanowire is so small that 500 of the wires can fit inside the width of a single human hair. Scientist found a way to capture and combine the electrical charges from millions of the Nano scale zinc oxide wires. They also developed an efficient way to deposit the nanowires onto flexible polymer chips, each about a quarter the size of a postage stamp. Five Nano generators stacked together produce about 1 micro Ampere output current at 3 volts — about the same voltage generated by two regular AA batteries (about 1.5 volts each).

While a few volts may not seem like much, it has grown by leaps and bounds over previous versions of the Nano generator. “Additional nanowires and more Nano generators, stacked together, could produce enough energy for powering larger electronics, such as an iPod or charging a cell phone.”

NANO GENERATOR

August 23, 2011

01-cellphone-charger-nanogenerator

After six years of intensive effort, scientists are reporting development of the first commercially viable Nano generator, a flexible chip that can use body movements — a finger pinch now en route to a pulse beat in the future — to generate electricity.

This development represents a milestone toward producing portable electronics that can be powered by body movements without the use of batteries or electrical outlets.

The latest improvements have resulted in a Nano generator powerful enough to drive commercial liquid-crystal displays, light-emitting diodes and laser diodes. By storing the generated charges using a capacitor, the output power is capable to periodically drive a sensor and transmit the signal wirelessly.

01-nanogenerator-energize LED light and LCD display-future power generaration technologies-power production by body movement

If we can sustain the rate of improvement, the Nano generator may find a broad range of other applications that require more power.


Example:

  • Personal electronic devices powered by footsteps activating Nano generators inside the sole of a shoe;
  • Implanted insulin pumps powered by a heart beat; and
  • Environmental sensors powered by Nano generators flapping in the breeze.

01-heart-powered-pacemaker-insulin pumping by nano generator

Preparation:

The key to the technology is zinc oxide (ZnO) nanowires. ZnO nanowires are piezoelectric — they can generate an electric current when strained or flexed. That movement can be virtually any body movement, such as walking, a heartbeat, or blood flowing through the body. The nanowires can also generate electricity in response to wind, rolling tires, or many other kinds of movement.

01-concept-NanoGenerator-Zinc oxide Nano wires

The diameter of a ZnO nanowire is so small that 500 of the wires can fit inside the width of a single human hair. Scientist found a way to capture and combine the electrical charges from millions of the Nano scale zinc oxide wires. They also developed an efficient way to deposit the nanowires onto flexible polymer chips, each about a quarter the size of a postage stamp. Five Nano generators stacked together produce about 1 micro Ampere output current at 3 volts — about the same voltage generated by two regular AA batteries (about 1.5 volts each).

While a few volts may not seem like much, it has grown by leaps and bounds over previous versions of the Nano generator. “Additional nanowires and more Nano generators, stacked together, could produce enough energy for powering larger electronics, such as an iPod or charging a cell phone.”

PEM FUEL CELLS

August 23, 2011

01-fuel_cell_technology-polymer electrolyte membrane fuel cell-ethanol to hydrogen onboard reformer

Polymer electrolyte membrane (PEM) fuel cells—also called proton exchange membrane fuel cells—deliver high-power density and offer the advantages of low weight and volume, compared with other fuel cells. PEM fuel cells use a solid polymer as an electrolyte and porous carbon electrodes containing a platinum catalyst. They need only hydrogen, oxygen from the air, and water to operate and do not require corrosive fluids like some fuel cells. They are typically fueled with pure hydrogen supplied from storage tanks or on-board reformers.

PEM Technology:

01-PEM-Proton exchange membrane-fuel cell-polymer elctrolyte membrane fuel cell-PEFC-carbon diffusion layer-catalyst layer-platinum nano particles-hydrogen fuel cell production

Polymer electrolyte membrane fuel cells operate at relatively low temperatures, around 80°C (176°F). Low-temperature operation allows them to start quickly (less warm-up time) and results in less wear on system components, resulting in better durability. However, it requires that a noble-metal catalyst (typically platinum) be used to separate the hydrogen’s electrons and protons, adding to system cost. The platinum catalyst is also extremely sensitive to CO poisoning, making it necessary to employ an additional reactor to reduce CO in the fuel gas if the hydrogen is derived from an alcohol or hydrocarbon fuel. This also adds cost. Developers are currently exploring platinum/ruthenium catalysts that are more resistant to CO.

PEM Fuel Cell Applications:

PEM fuel cells are used primarily for transportation applications and some stationary applications. Due to their fast startup time, low sensitivity to orientation, and favorable power-to-weight ratio, PEM fuel cells are particularly suitable for use in passenger vehicles, such as cars and buses.

Disadvantages of Fuel Cell:

01-PEM Fuel cell with methanol reformer-CO resistant proton exchange membrane fuel cell system-onboard fuel cell processor-higher density liquid fuels

A significant barrier to using these fuel cells in vehicles is hydrogen storage. Most fuel cell vehicles (FCVs) powered by pure hydrogen must store the hydrogen on-board as a compressed gas in pressurized tanks. Due to the low-energy density of hydrogen, it is difficult to store enough hydrogen on-board to allow vehicles to travel the same distance as gasoline-powered vehicles before refueling, typically 300–400 miles. Higher-density liquid fuels, such as methanol, ethanol, natural gas, liquefied petroleum gas, and gasoline, can be used for fuel, but the vehicles must have an on-board fuel processor to reform the methanol to hydrogen. This requirement increases costs and maintenance. The reformer also releases carbon dioxide (a greenhouse gas), though less than that emitted from current gasoline-powered engines.