Dr. John Philip,
Head SMARTS & RTS , NDE Division
Metallurgy and Materials Group &Editor-in-Chief, Journal of nanofluids(ASP)
Kalpakkam-603 102,Tamilnadu,IndiaIndira Gandhi Centre for Atomic Reserach,
E-mail: email@example.com & firstname.lastname@example.org
doi:10.1038/nindia.2013.35; Published online 12 March 2013
Researchers have invented a novel, fast and ultrasensitive magnetic-nanofluid-based optical sensor that changes colour on exposure to extremely low concentrations of ammonia 1. The sensor will be useful in detecting minute traces of ammonia in industrial and environmental samples.
Ammonia is an important ingredient in explosives, fertilizers and industrial coolants. However, high concentrations of ammonia gas are harmful to humans and other living organisms. Existing techniques for monitoring ammonia levels in industrial and environmental samples are expensive, complex and time-consuming.
To design a portable and fast detection technique, the researchers synthesized a magnetic nanofluid by dispersing ferrimagnetic iron oxide nanoparticles in a mixture of oil, water and surfactant. This nanofluid consists of nanodroplets suspended in water.
They then placed the magnetic nanofluid in a vial, which was put inside a solenoid coil connected to a current supply. At a fixed magnetic field, a fibre-optic light source illuminated the nanofluid to which varying concentrations of ammonia were gradually added.
The colour of the nanofluid changes depending on the ammonia concentration. This color change occurs within a second after exposure to ammonia, much faster than other ammonia-sensing methods that could take several minutes. "The sensor shows a fast response because the nanodroplets in the nanofluid are suspended in water," says lead researcher John Philip. In the future, this sensor could also be used to detect other toxic ions and gases, he adds.
1. Mahendran, V. et al. An optical technique for fast and ultrasensitive detection of ammonia using magnetic nanofluids. Appl. Phys. Lett. 102, 063107 (2013)
A community website from IOP Publishing
Researchers at the Indira Gandhi Centre for Atomic Research (IGCAR) in India have made a new type of optical sensor from magnetically polarizable nanofluids and have used the device to detect tiny amounts of ammonia in solution. The sensor, which quickly changes colour in the presence of the analyte, could come in useful for many practical applications, such as monitoring pollution levels in rivers around industrial plants.
The sensor is made of an oil-in water nanoemulsion, produced by emulsifying ferrimagnetic iron oxide nanoparticles, around 10 nm in size, suspended in octane and in the presence of an anionic surfactant of sodium dodecylsulphate in water. The nanoparticle droplets align to form a 1D array when a magnetic field of around 90 Gauss is applied, and the sensor is illuminated with a fibre-optic based light source.
When ammonia is present in the surrounding solution, the lattice periodicity of the droplet array changes thanks to the fact that ammonia penetrates into the electric double layer around the emulsion droplets. This causes the wavelength of light reflected from the sensor to be significantly shifted towards the blue end of the electromagnetic spectrum – something that can be easily monitored using a digital camera.
“We plotted the reflected Bragg peak for different ammonia concentrations, and found that it blue shifts monotonically, increasing with concentrations of ammonia,” team leader John Philip told nanotechweb.org. “We can calculate the exact concentration of ammonia present from a Bragg shift calibration curve. This is a standard procedure in which the Bragg shift for a few different known concentrations of ammonia are first measured. Since the curve follows a linear trend, any unknown concentration can then be determined.”
The device can detect concentrations as low as 1ppm of ammonia and is much easier to fabricate and use than existing ammonia sensors that rely on ion-selective electrodes, infrared gas analysers, detectors based on semiconductor films such as SnO2 ad MoO3, and optical gas sensors that exploit the reaction of ammonia vapour with either a pH-dependent dye material or film. “In these techniques, the target ammonia molecules interact with the sensing element and produce changes in the light absorbance or emission spectra of the sample that are then monitored using suitable instruments,” explains team member Vellaichamy Mahendran. “Ours is a much more simple, sensitive, faster and inexpensive set up."
Ammonia is found in explosives, fertilizers and indusial coolants, among other things, and the new optical sensor could be used to continuously monitor environments in which the chemical is present - such as rivers around industrial plants, for example, says Philip.
The team, which has published its results in Applied Physics Letters, now hopes to further improve the sensitivity of its sensor and use it to detect other toxic analytes. Another important goal is to make the sensor in a reusable thin film form, adds Philip.
About the author
Belle Dumé is contributing editor at nanotechweb.org
Special Arrangement Test specimens with two circular defects – one big and one small (right) and a rectangular and a circular defect (left) imaged using nanofluid optical sensor developed by Dr. John Philip, IGCAR, Kalapakkam
Defective regions produce magnetic resistance, which in turn leads to leakage of magnetic flux
Detecting and imaging structural defects like cracks, holes etc, present in components made of ferromagnetic materials like pipelines, railway tracks and tubes has now become easy with optical sensors. These sensors were developed by Dr. John Philip and his team at the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam near Chennai. The results of their work were published recently in the Applied Physics Letters journal.
The work provides a “methodology for extracting defect feature information from optical images,” notes the paper.
The optical sensor has oil droplets (about 200 nanometres in diameter) containing a few nanoparticles of magnetic materials, about 6.5 nanometres in size. The oil droplets are present as an emulsion with water.
Since the sensor contains magnetic particles, it responds to magnetic fields. “The sensor is magnetically polarizable,” said Dr. Philip, Head of SMART Section at IGCAR. He is the senior author of the paper.
The sensor works on the principle that defective regions in a material produce magnetic resistance, and this in turn leads to leakage of magnetic flux (field lines). “The leakage of magnetic flux will be right outside the point where the defect in the material is present,” Dr. Philip explained. “The nanofluid-based optical sensor can detect such leakages.”
The material whose structural integrity is to be evaluated has to be first magnetised. This can be done by using two strong magnets kept on either ends of the material to be tested. The sensor, which is sandwiched between two glass plates, is kept on top of the magnetised material. The sensor is then illuminated with white light.
Magnetic flux passes through the material the moment it is magnetised. The magnetic flux leaks if the material has any structural defects, and the nanofluid inside the optical sensor immediately forms an one dimensional array or chain along the direction of the magnetic field. “When it forms an one dimensional array, the spacing between the droplets satisfies the criterion to diffract one particular colour in white light,” he said.
The colour that is diffracted or reflected depends on the inter-droplet spacing. “When the defect is large, the magnetic flux leakage is more, and the spacing between the droplets is smaller. The reflected colour is violet,” he explained. Alternatively, if the defect is small, the spacing between the droplets is more and the reflected light is red or orange.
While the optical sensor can provide the result immediately, the dimension of the defect can be found using certain modelling. “We can map different shapes (geometry) of the defects,” Dr. Philip said.
“Future perspectives include the fabrication of large flexible films for the inspection of large components and development of suitable pattern recognition software for rapid inspection of components,” the paper notes.
The sensor has several advantages over existing techniques. For instance, the optical sensor can be repeatedly used as the one-dimensional array formed in the nanofluid is “perfectly reversible.”
“It takes less time to detect flaws in the material, allows direct visual inspection of the defects, and does not destroy the material being tested,” he explained. “The sensors are very cheap — a one inch by one inch sensor would cost just a few hundred rupees.”
doi:10.1038/nindia.2012.21; Published online 15 February 2012
Sensor detects cracks in magnetic matter
Researchers have developed a new kind of optical sensor from an emulsion of magnetic nanofluid containing droplets of iron oxide nanoparticles1. The sensor could be used to image defects such as cracks, corrosion and erosion buried in rail tracks, pipelines and tubes.
External magnetic fields generate magnetic flux leakage signals near defects in magnetic materials. This signal can be used in a device such as a hall probe sensor to provide information on the defect. However, scientists have yet to develop a visual and non-contact sensor for this purpose.
To design such a sensor, the researchers first employed a simple emulsification process to prepare a magnetic nanofluid from oil-based ferric oxide in the presence of water and sodium dodecyl sulphate, a surface-active molecule. They then made a thin-film sensor by placing the nanofluid between two microscopic glass plates. The nanofluid droplets contained ferric oxide nanoparticles of around 6.5 nm in size. The researchers placed the head of the sensor near the rear surface of mild steel plates containing artificial defects.
They magnetized the steel plate and sensor using a horseshoe-sized bar magnet. Applying an external magnetic field generated magnetic flux lines around the defective region of steel plate, which led to the formation of one-dimensional nanodroplet arrays in the direction of the field. The droplets generated bright colours when irradiated with white light, thus providing a signature of the defects buried in the material.
Violet light was produced where the magnetic flux leakage signal was at a maximum. "The most important aspect of this technique is the reusability of the flux sensor due to perfectly reversible one-dimensional arrays of droplets formed in the fluid," says lead researcher John Philip.
Mahendran, V. & John Philip,Nanofluid based optical sensor for rapid visual inspection of defects in ferromagnetic materials. Appl. Phys. Lett. 100, 073104 (2012)
IOP A community website from IOP publishing, UK
Feb 27, 2012
The sensor will be able to locate defects and discontinuities such as fatigue, cracks, corrosion pits, metallic inclusions and abrasion in ferromagnetic components and structures, says team leader John Philip of the Indira Gandhi Centre for Atomic Research (IGCAR) in Tamilnada. It might also be used to inspect magnetic materials used in the aircraft industry, such as those used to make turbines, for example.
Current techniques, such as "magnetic flux leakage" (MFL), that detect defects in ferromagnetic materials work by measuring stray fields near cracks using a sensor. However, such methods require sophisticated instrumentation and complex signal processing to correlate the MFL signal with the defect signature. Moreover, sophisticated algorithms are then needed to recreate a 2D or 3D image of the defect. Alternative techniques that employ magnetic particles to visualize flux lines around an inclusion, for example, are messy because the magnetic particles must adhere to the component being tested and are difficult to remove afterwards.
"Our new sensor overcomes all of these challenges because it does not come into contact with a sample – it is placed a few millimetres above – and does not involve any complex signal collection or analysis," said Philip. "It is a simple visual test for relatively large defects (a few millimetres in size) buried inside a sample."
Philip's team developed a special nano-emulsion to make its sensor that consists of a colloidal suspension of single-domain superparamagnetic Fe3O4 nanoparticles around 6.5 nm in size that are magnetically polarizable – that is, they respond to a weak magnetic field. The particles are capped with a monolayer of anionic surfactant (sodium dodecyl sulphate) so that they do not agglomerate.
In the absence of a magnetic field, the nanodroplets are randomly oriented but when the nanofluid comes into contact with a magnetic defect, the droplets align in a chain-like fashion along the field created by the defective region. This chain of particles diffracts incident white light to produce bright colours and the colours obtained depend on the defect features. "This approach allows us to directly visualize the defect, with a violet colour being seen at the point where the magnetic flux leakage reaches its maximum – that is at the edge of the defect," explained Philip.
Rectangular and cylindrical defects
The researchers tested their technique on steel plate specimens containing artificially fabricated rectangular and cylindrical defects. The samples were magnetized prior to the experiments. The images obtained clearly show a colour spectrum on both sides of the defects that follows their shape – straight lines are seen for the rectangular defects and curved lines for the cylindrical ones.
Spurred on by these results, the team now plans to make a large-area flexible-film-based sensor using its nanofluid and develop the appropriate pattern recognition software. Such a device could be used by non-specialists to rapidly analyse defective regions in a wide variety of ferromagnetic materials, says Philip.
The current work is detailed in Applied Physics Letters.
About the author
Belle Dumé is contributing editor at nanotechweb.org
doi:10.1038/nindia.2011.136; Published online 26 September 2011
NATURE (India) 2011
Researchers have produced a new viscous nanofluid containing magnetic nanoparticles that conducts heat efficiently when under an intense magnetic field1. This magnetic nanofluid could be useful as a super-coolant or for damping unwanted vibrations in optoelectronic devices.
Magnetic nanofluids exhibit both liquid and magnetic properties. Such fluids can be easily tailored using external magnetic fields for applications such as optical switches and drug-delivery devices. However, existing magnetic nanofluids exhibit low thermal conductivity.
The researchers produced their magnetic nanofluid by first capping magnetite nanoparticles with oleic acid and then dispersing the resulting nanoparticles in kerosene and hexadecane. They studied the thermal conductivity and viscosity of their nanofluid by varying the strength of the external magnetic field while also changing the size and concentration of the nanoparticles.
Nanofluids with a higher concentration of nanoparticles exhibited larger thermal conductivity when under a strong magnetic field. Applying the magnetic field parallel to the nanofluid aligned them along the direction of the field, forming chain-like structures with lengths ranging from tens of nanometres to several micrometres.
Increasing the magnetic field strength increased the chain length, resulting in the formation of evenly spaced single-nanoparticle chains throughout the nanofluid volume. This reduced the space between the nanoparticle chains, thus allowing for efficient heat flow.
Increasing the magnetic field strength also caused the viscosity of the nanofluid to rise. The nanofluid with the largest nanoparticle size (9.5 nm) exhibited the largest enhancement in thermal conductivity.
"This magnetic nanofluid could be used to design multifunctional smart materials for cooling-cum-damping applications," says lead researcher John Philip. Such fluids can also be used to improve the heat transfer of solar collectors used to harness solar energy, he adds.· References
- Shima, P. D. & J.Philip Tuning of thermal conductivity and rheology of nanofluids using an external stimulus. J. Phys. Chem. C doi: 10.1021/jp204827q (2011)
Sep 30, 2011
Certain nanofluids can be made to conduct heat extremely well when a magnetic field is applied to them, says a duo of researchers at the Indira Gandhi Centre for Atomic Research in Tamilnadi, India. The phenomenon may be used to cool down miniature devices like micro- and nano-electromechanical systems, and computer chips.
"Nanofluids could be ideal coolants for future electronic devices but for such applications, the fluids need to have large thermal conductivities," explained team leader John Philip. "This is why we need to develop novel nanofluids." The materials studied by the researchers are a colloidal suspension of single-domain superparamagnetic Fe3O4 nanoparticles between 3 and 10 nm in size that are magnetically polarizable – that is, they respond to a weak magnetic field. The particles are capped with a monolayer of surfactant molecules so that they do not agglomerate – something that is crucial for the experiments subsequently performed.
In the absence of a magnetic field, the magnetic moments of the particles are oriented in random directions. When a field is applied, the particles align in the direction of the field when the magnetic dipolar interaction energy between the particles overcomes the thermal energy of the particles. The dipolar interaction energy depends on the distance between neighbouring particles and their mutual orientation.
As soon as the dipolar interaction becomes sufficiently strong, the magnetic particles form a chain-like structure as they line up in the direction of the applied field. The thermal conductivity of the nanofluid then increases because heat can then flow very efficiently along the chain, says Philip.
The increase in the thermal conductivity in these fluids is extremely high – several hundred times that of traditional nanofluids. What is more, the increase is perfectly reversible and can be tuned from high to low values by applying the magnetic field either parallel to the direction of particle chains or perpendicular to them. These properties mean that the nanofluids could be ideal for use as "intelligent" coolants, states Philip.
Programming the magnetic field strength
"Depending on the heat load of the fluid, you can simply programme the magnetic field strength to achieve higher cooling," he told nanotechweb.org. "All you need is a feedback control circuit in a device that automatically senses and varies the magnetic field strength depending on the amount of cooling needed." The set-up could be used to cool computer chips, for instance, or cool down MEMS and NEMS devices.
The team now plans to further develop and test these fluids through microchannels to test the cooling efficiencies under flow. "We are also working on developing a new class of nanofluid that can work at very high temperatures and react quickly," revealed team member P D Shima.
The current work is reported in The Journal of Physical Chemistry C.
About the author
Belle Dumé is contributing editor at nanotechweb.org
Nature Nanotechnology (2008)
Published online: 8 February 2008 | doi:10.1038/nnano.2008.38
Subject Category: Nanofluidics
Magnetic nanofluids: Chain reaction
Fluids containing magnetic nanoparticles can display potentially useful thermal properties
Colloid suspensions containing magnetic nanoparticles are known to exhibit higher thermal conductivities than liquids with larger particles or no particles at all. The enhanced thermal conductivity of these magnetic nanofluids could have applications in controlling the flow of heat in various devices if it can be controlled in a reversible manner.
Now, John Philip and colleagues1 of the Indira Gandhi Center for Atomic Research have demonstrated such control over a suspension of hexadecane containing 6.7-nm superparamagnetic particles. When a magnetic field of 101 Gauss is applied to a nanofluid that contains 4.5% nanoparticles by volume, the thermal conductivity was enhanced by 216%. The magnetic field caused the nanoparticles to form chains in the direction of the magnetic field, with the chains falling apart when the field was switched off.
Evidence that this mechanism is indeed responsible for the enhanced thermal conductivity was provided by measurements showing that the efficiency of heat flow along the chains increased in the presence of the magnetic field.
1. Philip, J., Shima, P. D. & Raj, B. Nanofluid with tunable thermal properties. Appl. Phys. Lett. 92, 043108 (2008). | Article |
Apr 4, 2008
Nanofluid could cool tiny electronic devices
Researchers in India have shown that the thermal properties of a magnetic nanofluid can be tuned by applying a magnetic field. The effect comes thanks to the magnetic particles lining up in chains when the field is applied. The nanofluid, which is made from a colloidal suspension of magnetite nanoparticles, could find use in a variety of technology applications, including "smart" cooling devices.
Magnetic nanofluids are unique materials that can be used in applications such as optical modulators, optical fibre filters, optical switches and gratings. Many of the physical properties of these materials can be tuned by simply varying the applied magnetic field. Now, John Philip, PD Shima and Baldev Raj of the Indira Gandhi Centre for Atomic Research in Tamilnadu have shown that the nanofluid's thermal properties can be tuned in this way as well. This new result could be useful because nanofluids are often touted as being ideal coolants for future electronic devices and engines.
Philip and co-workers developed a stable colloidal suspension of Fe3O4 nanoparticles, with an average diameter of 6.7 nm. "The observed reversibly tunable thermal property of our nanofluid may find many technological applications in nanoelectromechanical and microelectromechanical-based devices," Raj told nanotechweb.org. "For example, depending on the cooling requirement, the magnetic field can be precisely programmed to obtain the desired level of thermal conductivity enhancement or cooling," added Philip.
The work was published in Applied Physics Letters.
About the author
Belle Dumé is contributing editor at nanotechweb.org