Discover Top Posts Tagged with #thermal properties

Machine learning helps identify 'thermal switch' for next-generation nanomaterials

Imagine being able to program materials to control heat like you can control a light with a dimmer switch. By simply squeezing or stretching the materials, you can make them hotter or colder. One of the fundamental challenges in advanced materials has been accurately predicting and controlling heat flow in complex, next-generation materials. Traditional simulation methods, which rely on simplified empirical models, fail to capture a material's intricate atomic interactions, especially under deformation. New research by Xiangyu Li, an assistant professor in the Department of Mechanical and Aerospace Engineering, and his Ph.D. student, Shaodong Zhang, helps alleviate that problem.

Thermal Diffusivity

Thermal diffusivity is defined as the ratio of a materials thermal conductivity to its density and specific heat capacity. This unit, often represented as the lowercase Greek letter alpha represents how fast heat moves through a material; the above formula gives units of length squared per time.

Sources/Further Reading: (Image source - Thermal Engineering) (Mech Content) (Wikipedia)

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Heat Capacity and Specific Heats

Heat capacity in thermodynamics is defined as the amount of heat that is needed to change the temperature of an object by a defined temperature interval. Mathematically, it is most often represented by the capital letter C and the formula for it is C equals q (heat) over the defined change in temperature (ΔT). The units for heat capacity are energy per temperature (in SI base units, J/K). Heat capacity is an extensive property and depends directly on how much of a substance there is.

The intensive version of heat capacity, which is an intrinsic property of a material and does not depend on the amount of it, is known as specific heat capacity. As with other specific values, specific heat capacity is heat capacity divided by mass. It is often represented by the lowercase letter c.

Common subscripts for both heat capacity and specific heat capacity are P and V, to indicate either heat capacity at a constant pressure (P) or constant volume (V).

Sources/Further Reading: (Image source - Gonzaga University) (NASA) (Khan Academy) (LibreTexts) (Wikipedia)

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Thermal Expansion

Most materials expand in volume when heated, a property known as thermal expansion. In the instances where this is not the case it is known as negative thermal expansion (not thermal contraction or anything similar). For solids, this can be calculated for each material using the coefficient of thermal expansion, often represented by the lowercase Greek letter alpha, and can be calculated in linear, area, or volumetric forms depending on the precision one desires (and shape of the object in question). As the shape of liquids and gases depend on the shape of their container, thermal expansion of these phases in a rigid container leads to increased pressure as well. Thermal expansion occurs primarily because an increase in temperature increases the kinetic energy of the atoms or molecules of a substance.

Sources/Further Reading: (Image source - Plumbing Supply) (Wikipedia) (LibreTexts) (Hyperphysics) (Rice University)

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AI method radically speeds predictions of materials' thermal properties

It is estimated that about 70% of the energy generated worldwide ends up as waste heat. If scientists could better predict how heat moves through semiconductors and insulators, they could design more efficient power generation systems. However, the thermal properties of materials can be exceedingly difficult to model. The trouble comes from phonons, which are subatomic particles that carry heat. Some of a material's thermal properties depend on a measurement called the phonon dispersion relation, which can be incredibly hard to obtain, let alone utilize in the design of a system.

'Countercation engineering' for thermoresponsive graphene-oxide nanosheets

Graphene-based two-dimensional materials have recently emerged as a focus of scientific exploration due to their exceptional structural, mechanical, electrical, optical, and thermal properties. Among them, nanosheets based on graphene-oxide (GO), an oxidized derivative of graphene, with ultrathin and extra wide dimensions and oxygen-rich surfaces are quite promising. Functional groups containing oxygen, such as carboxy and acidic hydroxy groups, generate dense negative charges, making GO nanosheets colloidally stable in water. As a result, they are valuable building blocks for next-generation functional soft materials. In particular, thermoresponsive GO nanosheets have garnered much attention for their wide-ranging applications, from smart membranes and surfaces and recyclable systems to hydrogel actuators and biomedical platforms. However, the prevailing synthetic strategies for generating thermoresponsive behaviors entail modifying GO nanosheet surfaces with thermoresponsive polymers such as poly (N-isopropylacrylamide). This process is complex and has potential limitations in subsequent functionalization efforts.

Researchers develop polymer that can be adapted to high and low temperature extremes

The modern world is filled with synthetic polymers, long-chained molecules designed by scientists to fill all manner of applications. Researchers at FAMU-FSU College of Engineering have developed two closely related polymers that respond differently to high and low temperature thresholds, despite their similar design. The polymer pair could be used in applications in medicine, protein synthesis, protective coatings and other fields. Their work is published in Macromolecules. "Typically, in order to have one thermal behavior, we have to prepare a polymer for that specific application, and if you want to have another extreme of polymer behavior, then you have to prepare a completely different polymer," said co-author Hoyong Chung, an associate professor in the FAMU-FSU College of Engineering. "But now, through this work, we have a single type of polymer that can be quickly adapted with minimal interference for both jobs."

The surprising thermal properties of cellulose nanofibers

Plant-derived materials such as cellulose often exhibit thermally insulating properties. A new material made from nanoscale cellulose fibers shows the reverse, high thermal conductivity. This makes it useful in areas previously dominated by synthetic polymer materials. Materials based on cellulose have environmental benefits over polymers, so research on this could lead to greener technological applications where thermal conductivity is needed.

Cellulose is a key structural component of plant cell walls and is the reason why trees can grow to such heights. But the secret of its material strength actually lies in its overlapping nanoscopic fibers. In recent years, many commercial products have used cellulose nanofiber (CNF) materials because their strength and durability make them a good replacement for polymer-based materials such as plastics that can be detrimental to the environment.

But now and for the first time, a research team led by Professor Junichiro Shiomi from the University of Tokyo's Graduate School of Engineering has investigated previously unknown thermal properties of CNF, and their findings show these materials could be even more useful still. Their research appears in Nano Letters.

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