MIT heat conduction path of the first Chinese research department, international leader in heat transfer academician Chen Gang

Professor Chen Gang, the US National Academy of Engineering and the American Academy of Humanities and Sciences, but also the American Society of Mechanical Engineers (ASME) Fellow, AAAS (AAAS), and Fellow of the American Physical Society (APS) Fellow. Currently serves as Head of the Department of Mechanical Engineering, Massachusetts Institute of Technology (also the first Chinese Department). Professor Chen Gang relates to heat transfer, nanotechnology and energy, including micro- and nano-scale energy conversion and transmission mechanism of energy experiments, theoretical and numerical; nano-engineered materials having a high and a low thermal conductivity; thermal radiation and electromagnetic super material; solid energy conversion system, microelectromechanical systems, heat-sensitive sensor; desalination and water treatment. In 2009, a team led by Chen Gang in \”Nano Letters\” published by radiation heat transfer experiments confirmed that the object in close proximity, can be as high as predicted by the law thousands of times, that broke the German physicist Max Planck was founded in 1900 the forecast blackbody radiation law.

Here, we review the recent years, part of the research team, Professor Chen Gang, published in Nature, Science and sub-published research on heat transfer, mainly includes the following three parts:

1. the intrinsic polymer material of high thermal conductivity
2. isotropically highly thermally conductive inorganic material
3. Research on a new phenomenon and heat conduction mechanism

(Note: due to the limited academic level, the selected article and if inappropriate expression, please criticism)

[an intrinsic high thermal conductivity polymeric material.]

1 Nature Communications:. comparable polymeric film metal thermal conductivity

crystal orientation and improve the crystallinity of the polymer can significantly increase the thermal conductivity of the polymeric material. However, the thermal conductivity in the experiments was still highly crystalline nanofiber and polyethylene high degree of orientation is much lower than the predicted value of the value of the polyethylene crystal. This is mainly due to imperfect crystalline, semi-crystalline polymer comprises a mixed crystal region and factors amorphous zones. However, the individual fibers can not solve macro-polymer body heat conduction problem, how to get a lot of material with high thermal conductivity polymer film, is still a huge problem currently facing the experimental research and industrial production! To solve this problem, the MIT professor Gang Chen team openMade a process to prepare highly stretched polyethylene film of a high thermal conductivity method, PE film coefficient of heat produced up to 62 Wm-1K-1, typical polymer than the average (about 0.1 ~ 0.2 Wm-1 K-1 ) more than two orders of magnitude, than many conventional metal and ceramic materials (e.g., 304 stainless steel is about 15Wm-1K-1, alumina is about 30 Wm-1 K-1). In this study, the authors found that the high thermal conductivity of polymerization to maximize the ordered polymer chains, reduces the entanglement of molecular chains, rather than just the pursuit of higher crystallinity. Characterization results show that the film is made of crystalline and amorphous nano-fibers through regulation of the morphology of the amorphous regions, so that the amorphous region also have a very high thermal conductivity (approximately 16 Wm-1K-1) this is an important reason for the thin film material having a high thermal conductivity. Meanwhile, the structure and phenomenological model of heat transfer is determined by high resolution synchrotron X-ray diffraction revealed the further heat transfer mechanism. \”Nanostructured polymer films with metal-likethermal conductivity\” of the paper published in the study entitled \”Nature Communications\”. Original link: https: //www.nature.com/articles/s41467-019-09697-7

2 Science Advances:. Preparation of high thermal conductivity Molecular Engineering conjugated polymer film

polymeric material low thermal conductivity (<0.2 Wm-1K-1) hindered the further development and applications of electronic devices, energy. The existing studies indicate that the interaction is a major factor of low thermal conductivity and a polymer material between the disordered molecular structure weak. Current research in this area are mainly confined to a single polymer molecule interact to enhance phonon improve transfer efficiency along the direction of the molecular chain, or to improve the interaction between a single polymer molecule to enhance the phonon transmission chains intermolecularly effectiveness. These methods require special preparation processes, and thermal anisotropy of the material exhibits, in practical application it is difficult to ensure the stability and reliability. For the preparation of a high intrinsic thermal conductivity of the polymer film material, MassachusettsGang joint team INSTITUTE Professor Karen K. Gleason Professor Molecular engineering team used to simultaneously increase the interaction between the molecules and the polymer molecules, thereby improving the thermal conductivity of the polymer. On the bottom-up chemical vapor deposition oxide (OCVD) method, using elongated along the polymer chain Fangxiang Jiang, C = C covalent bond between the molecular chains and the strong π-π stacking non-covalent interactions, the first time the conjugated polymer film [poly (3-hexyl thiophene), P3HT] high thermal conductivity. P3HT simultaneously present in the molecule and the intermolecular interaction achieve up to 2.2 W m-1 chamber was warmed conductivity of K-1, is 10 times that of traditional polymers. Analysis found, P3HT rigid conjugated π-π stacking interactions between the molecular backbone and strong. Compared with the thermal conductivity of the C-C single bond, conjugated C = C double bond strength is nearly twice as it is, it is expected to significantly improve the phonon transport direction of the polymer chain. Meanwhile, π-π stacking interactions between the molecular chains is 10 to 100 times van der Waals forces, can enhance the transmission of phonons between the polymer chains. \"Molecular engineered conjugated polymer with high thermal conductivity\" of the paper published in the study entitled \"Science Advances\". Original link: https:

3 Nature Nanotechnology //advances.sciencemag.org/content/4/3/eaar3031:. Thermal conductivity up to 104 W m-1 K-1 polymer nanofibers [123 polymeric materials commonly used in thermal conductivity method] experimental research and industrial production are added to improve the high thermal conductivity fillers, such as MCNT, graphene. However, this method has a greater difficulty is that a large thermal resistance between the heat conductive filler to the polymer matrix, the polymer and thus thermal conductivity of the composite is always limited to within one order of magnitude. Low thermal conductivity of the polymer material is mainly due to random microstructure and macroscopic defects macromolecular chains. For materials such as polyethylene, polyethylene theoretically predicted value of the value of the single crystal up to 237 Wm-1 K-1, however, the industrial production of high molecular weight microLevel meter (10 ~ 25um) thermal conductivity of polyethylene fibers is only 30 ~ 40 Wm-1 K-1 in order to further enhance the thermal conductivity of polyethylene fibers and establish a relationship between thermal conductivity and molecular chain structure, Massachusetts Professor Gang team INSTITUTE polyethylene nanofibers between 50 ~ 500 nm in diameter were prepared by the super drawing method between exhibits a more superior micrometer polyethylene fiber thermal conductivity. Polyethylene was found nanofibers thermal conductivity increases with increasing stretch ratio and the stretch ratio of the thermal conductivity of the sample corresponding to 160,270 and 410 respectively 53.3,80.4 and 104 Wm-1 K-1, the maximum value which is not specially treated polyethylene material 300 times 0.35 Wm-1 K-1, while more than half of platinum, iron and nickel, the thermal conductivity of the pure metal material. The authors found that study, compared to the micron fibers, nanofibers having a higher thermal conductivity because of the lower defect density nanofibers, larger defects (such as voids and impurities) or greater entanglement zone unlikely appears; and smaller defects (e.g., smaller and entanglement zone chain ends) may still be present as part of the amorphous regions, partially converted to crystals during stretching. I.e. nanofibers contributes recombinant nanoscale polymer chains during drawing, the fiber mass is closer to an ideal single crystal fibers. However, experimental results show that the thermal conductivity of polyethylene nanofibers is still lower than the theoretical value of the thermal conductivity of the single crystal of polyethylene, because the nanofibers are made from a number of interacting chains, Van der Waals interactions between each of these chains will internal evoked chain phonon scattering, thereby reducing the thermal conductivity. The study, entitled \”Polyethylene nanofibres with very high thermal conductivities\” published in \”Nature Nanotechnology\”.

Original link: https: //www.nature.com/articles/nnano.2010.27 [II] isotropically highly thermally conductive inorganic material

1.Science: high thermal conductivity arsenide boron crystal

at room temperature, both diamond and graphite carbon value of the thermal conductivity of the same ferrite crystal reached a record of about 2000 W m-1 K-1. However, the thermal expansion coefficient between the diamond are expensive and do not match with the ordinary semiconductor shortcomings and further limit their large-scale application. The thermal conductivity of the graphite has a high anisotropy, an outer surface of the thermal conductivity than the thermal conductivity of the surface of about two orders of magnitude. Further, the semi-metallic nature of graphite also hampered their use as the active electronic material. Therefore, the development of high thermal conductivity material isotropic for the development of future high-density integrated circuits and electronic fields is important. To solve this problem, MIT professor Gang Chen, Boston College Professor David Broido, Professor Zhifeng Ren University of Houston and University of Texas at Austin Li Shi joint preparation of an isotropic, local thermal conductivity as high as 1000 W m-1 K-1, the average thermal conductivity of 900 W m-1 high boron arsenide crystalline material is K-1, the study of cognitive break traditional theory. According to the conventional theory, ultra-lattice thermal conductivity can occur by the strongly bound in the crystal elements of light, and is limited by three anharmonic phonon process. However, the authors found are boron arsenide block of light elements and heavy elements (BAs) crystal may also be implemented in an extremely high thermal conductivity of boron and arsenic. The study of solid thermal conductivity so that people have a better understanding of the physics and show that BAs are the only known semiconductor material with ultra-high thermal conductivity. The study, entitled \”Unusual high thermal conductivity in boron arsenide bulk crystals\” published in \”Science\”.

Original link: https: //science.sciencemag.org/content/361/6402/582 2.Science: Cubic Boron Nitride Crystal – super-heat-conducting material

All known materials at room temperature are located in the thermal conductivity of about 0.01 ~ 1000 1 m-1K-this range W, the preferred thermal conductivity such as silicon and the thermal conductivity of copper is 100 W m-1K-1 of this order of magnitude. However, with the interior of the heat flux advanced microelectronic chip increasing, in order to ensure effective heat dissipation, the material having the ultra-high heat conductivity requirements have become more urgent. Diamond thermal conductivity at room temperatureAbout 2000 W m-1K-1, from 1953 to now, has been recognized as the highest thermal conductivity of the bulk material. However, high-quality diamond that is rare and expensive, not widely used for heat dissipation. In 2018, researchers found that the thermal conductivity of high quality boron arsenide may be up to about 1200 W m-1K-1, an isotropic thermal conductivity becomes highest non-carbon material. Recently, MIT professor Gang Chen, Boston College Professor David Broido and Peking University Professor Song Bo joint team found that after boron isotope enrichment, including the heat cubic boron nitride crystals about 99% of the boron-10 or B-11 conductivity of more than 1600 W m-1K-1. This value is much higher than the boron arsenide, which means isotopically enriched boron crystal cubic boron nitride, boron arsenide has been substituted, and the carbon to be the best non-isotropic thermal conductivity material. Common thermal conductivity of cubic boron nitride is approximately 850 W m-1K-1, and after lifting mainly cubic boron nitride, the thermal conductivity of the element after elimination of enrichment natural abundance cubic boron nitride crystal, for resistance to heat flow due to the boron and boron -11 -10 produced by mixing the two isotopes. The research paper entitled \”Ultrahigh thermal conductivity in isotope-enriched cubic boron nitride\” published in \”Science\”.

Original link: https: //science.sciencemag.org/content/367/6477/555 [Three studies of heat conduction mechanism and a new phenomenon]

1.Nature Communications: sub-nano interface establishing a thermal conduction model

thermal conduction and thermal radiation heat transfer are two basic ways. Planck\’s law of black body radiation, when the surface temperature approaches 300K, the far field limit heat radiation thermal conductivity of about 6 Wm-1 K-1. Recent results suggest that, in the near field of the two surfaces apart if only tens of nanometers, the thermal conductivity between the interface may be too high law of blackbody radiation prediction value of 3 to 4 orders of magnitude. And this result is also consistent with the theory of electrodynamics fluctuations and macro-Maxwell equations established. However, when twoAfter the interface direct contact with the heat transfer mainly depends on the conduction mechanism; for solid crystals, is described with the phonon transport, and thermal conductivity by the transmission mechanism is generally between 107 ~ 109 Wm-1 K-1 . Thus, two pitches of tens of nanometers from the interface direct contact with the conductivity of heat generated during a four to five orders of magnitude of the increase, the intermediate transition phase there is no suitable theoretical model to describe. To solve this problem, the MIT professor Gang Chen to develop a team to describe the two interfaces are constantly approaching the process, heat conduction transition from near-field radiation phonon thermal conductivity to microscopic atomistic model equations and lattice dynamics theory based on Maxwell thermal conductivity of evolution. The results show that under the conditions of the interface pitch of 1nm>, the results of model predictions to establish the kinetics consistent with the fluctuations of the results of the continuum theory. However, when the clearance reaches the interface sub-nanometer, the authors found that the thermal conductivity four times higher than the theoretical value of the continuous medium. This indicates that when approaching atomic layer spacing, the continuum theory based on the local permittivity fail. Enhancement Based on observations of the model is dissipated because of the low frequency phonon coupling to an electric field through the vacuum gap, to provide additional channels for the energy transfer. When two surfaces are in or near contact, a major phonons heat carrier. The study, entitled \”Transition from near-field thermal radiation to phonon heat conduction at sub-nanometre gaps\” of papers published in \”Nature Communications\”.

Original link: https: //www.nature.com/articles/ncomms7755 2.Nature Nanotechnology: measuring the thermal conductivity of the quasi-ballistic transport in nanoscale based spectrum

In recent years, as new appears nanofabrication methods, techniques and sophisticated manufacturing equipment, design structures on the nanoscale to control the thermal conductivity of the material has already done a lot of research and has achieved very significant results. But clearly the relationship between structure and thermal properties of nano size remains to be further studied and established, the main challenge at present is to transfer heat spectrum typically it involves heat carrier pointsCloth, and this distribution in most of the solid is unknown. In most semiconductor and dielectric materials, these are mainly the heat carrier phonon thermal conductivity of the material and the macro is the sum of all the different modes phonon contributions, but they are distributed in the range of Brillouin zone is very wide. Therefore, to quantify the different modes of the phonon contribution to the thermal conductivity is critical to adjust the thermal conductivity of the material using nano-structured method, but this information is still difficult for most materials come through effective methods statistics. To solve this problem, Chen Gang, professor at MIT team used ultrafast spectroscopy techniques, quasi-ballistic transport in the vicinity of the nano-probe heat source (depth of 30nm) by, for the first time experimentally measured distribution of this spectrum. This method can quantify all phonon modes silicon-germanium alloy 95% contribution to the overall spectrum of the thermal conductivity of the material, and the measurement results and simulation results coherency Multiscale first principles and higher, while this method It can also be applied to gallium arsenide, gallium nitride, sapphire, and other materials. This study provides a general approach to the spectrum of different phonon MFP contribution to heat transfer, the measurement result of the thermal properties superior design nanostructured material having a promoting effect throughout the experiment quantization phonons, while miniaturization thermal management of electronic devices is also important. The study, entitled \”Spectral mapping of thermal conductivity through nanoscale ballistic transport\” papers published in \”Nature Nanotechnology\”.

Original link: https: //www.nature.com/articles/nnano.2015.109 3.Nature Communications: the use of liquid – solid phase transition on the thermal conductivity of the material temperature adjustment reversible

thermally conductive material adjusting the temperature of the reversible in many applications makes sense, including seasonal adjustment of the temperature of the building, heat storage and sensors. The method of adjusting the thermal conductivity of the solid phase by the temperature change is a great potential of – due to the phase transition temperature of the material of the wide range, so the liquid. Meanwhile, since the liquid – solid phase transition occurs usually do not cause metal material – insulator transition, the liquid can beAdding nanoparticles body controlling properties between the liquid and solid phases. In particular crystallization solution crystals containing nanoparticles, the nanoparticles upon cooling will be squeezed into the grain boundaries; and the internal stress generated during cooling and crystallization can adjust the state of contact between the nanoparticles, so that the composite material can improve the thermal conductivity. Theoretically, by adjusting the concentration of the nanoparticles, can be further optimized phase transition effect on the thermal conductivity. Based on this design, MIT Professor Gang Chen developed a team of adding a liquid to form a stable suspension of nanoparticles, and between the liquid and crystalline solid utilized effectively adjust a phase change of the thermal conductivity method. OF graphene / octadecyl system as an example of systems studied in the graphene / octadecyl phase change composite material (≈18 ℃) process, the internal stress reducing the thermal resistance threshold infiltration graphene network, lead to large changes in thermal conductivity – containing composites graphene 1wt%, the thermal conductivity of the phase change before <0.4 Wm-1 K-1, nearly 1.2 Wm-1 K-1 after phase change, enhance the rate of 3.2 times. Meanwhile, this method may also increase the conductivity of the composite material, to enhance the maximum amplitude of up to 2 orders of magnitude. The study, entitled \"Reversible temperature regulation of electrical and thermal conductivity using liquid-solid phase transitions\" papers published in \"Nature Communications\".

Original link: https: //www.nature.com/articles/ncomms1288 4 Nature Communications:. Phonon transmission fluid dynamics graphene

phonon is nonmetallic solids primary heat carrier. Fourier heat conduction model to describe the diffusion phonon transport laws, but later found to Fourier\’s law has certain limitations in the bulk material, such as ballistic transport and fluid dynamic phonons. Because of these phenomena only in very low temperatures and a narrow temperature range can be observed, therefore less people to its attention. However, recent studies have found that low-dimensional materials sound of bullets Road transportPractical and important potential in applications such as electronic devices and thermoelectric material, and therefore the study of the hydrodynamic low dimensional phonon transport material is imminent. MIT Professor Gang Chen team first-principles calculation result of the prediction, phonon power transmission fluid may occur in suspension in the graphene, and its temperature significantly higher than the bulk material, while a wider temperature range. We found phonon fluid power transmission suspension graphene with ordinary diffusion or ballistic phonon transport a significant difference, which is mainly due to the characteristics of two-dimensional graphene, such as conservation of momentum N during maximum scattering rate and the long wavelength high density of phonon states ZA. By drift motion of phonons, phonon Poiseuille flow stream and to focus on the second phonon-phonon fluid power transmission sub-ambient temperatures range suspended graphene, and the prospect of its future real important application: for example unimpeded rapid thermal conduction characteristics can Nigeria graphene used in thermal or thermal interconnect signal transmitter. The study, entitled \”Hydrodynamic phonon transport in suspended graphene\” papers published in \”Nature Communications\”.

Original link: https: //www.nature.com/articles/ncomms7290 5. Nature Materials: electrochemically induced phase change of the thermal conductivity SrCoOx way adjustment

The traditional view, with a wide dynamic control of different electrical conductivity, thermal conductivity of the material can not be adjusted by the potential. This is because the dopant atoms into the lattice material is purely scattering source of the heat carrier, which will reduce the rate of heat transfer material. However, MIT Professor Gang Chen joint team of Prof. Bilge Yildiz team found that by controlling the electrochemical doping of oxygen and hydrogen doping may be adjusted bidirectional SrCoO thermal conductivity of the oxide. In the study, the authors use the interaction between the ions and the defects in the atomic structure of electrochemically different kinds of ions are inserted into SrCoO film, and initiate the phase change, resulting in a greater change in the thermal conductivity at room temperature. The results show that after celite SrCoO2.5 oxygen doping into perovskite SrCoO3-δ, thermal conductivity can be increased 2.5 times the maximum;And after doping hydrogen into hydride SrCoO2.5, the maximum thermal conductivity can be reduced four times. On the study found that the thermal conductivity due to variations of different doping elements is defect, the lattice parameter changes caused by concentration and lattice symmetry of the internal SrCoO. For example, hydrogen ion doped changed SCoO chemical and physical structure, acts phonon scattering source, resulting in a decrease in thermal conductivity. This study showed that the defect or by various types of ions, atomic and electronic structures of electrochemically controlled simultaneously, can be adjusted on the thermal conductivity of the material over a wide range (in this study, the thermal conductivity is adjustable from 0.44 ~ 4.33 W m -1 K -1). And compared with traditional approaches, this method can be adjusted on a larger thermal conductivity of oxide, is designed for smart windows, thermal management and energy harvesting oxide functionality provides a new way. The study, entitled \”Bi-directional tuning of thermal transport in SrCoOx with electrochemically induced phase transitions\” papers published in \”Nature Materials\”.

Original link: https: //www.nature.com/articles/s41563-020-0612-0 6.Science Advances: phonon thermal conductivity of the positioning

in the heat transfer area of ​​research, nanostructures non-phonon diffusion thermal transfer widely observed often attributed to the classical size effect, while ignoring Potter of phonons. Recent previous simulation and experimental results show that, in the superlattice material (SLs is), since the short-wavelength phonons are strongly scattered out mixing at the atomic interface, and therefore responsible for the majority of the phonon thermal conductivity have relatively long wavelength. These long wavelength phonon through a plurality of cycles in the whole process even thickness SL are kept in their phases, theoretically, if the phonon scattering can be effectively, then SL is the thermal conductivity will be further reduced, so that in accordance with decrease of thermal conductivity, it can be positioned inside the phonon transport. To verify this, Chen Gang, professor at Massachusetts Institute of Technology team through the GaAs / AlErAs nanodots disposed on the inner interface type SLs As the ability to control the transmission of long-wavelength phonons to study the behavior of the positioning of the phonon thermal conductivity. The results showed that the introduction of nanodots can ErAs SLs 2-fold decrease thermal conductivity. Meanwhile, at low temperature, experimental results show that the variation of the thermal conductivity increases and then decreases the occurrence of these SLs (phonon consistent with the orientation effect) with increasing number of cycles SL. Simulation based on Green function, the authors confirmed this shift from ballistic to local transport. While at higher temperatures, the thermal conductivity of these SLs with variation of the number of cycles SL exhibits a transition from a ballistic behavior to diffusion. These observations have important guiding significance for the use of wave effect to design the thermal conductivity of phonons. The study, entitled \”Phonon localization in heat conduction\” of papers published in the \”Science Advances\”.

Original link: https: //advances.sciencemag.org/content/4/12/eaat9460