Thermal Interference Research Articles

Scalable production of polyamide-6/graphene composites with enhanced electromagnetic shielding and thermal conductivity

Composites with thermal management (TM) capability and electromagnetic interference (EMI) shielding effect are in high demand for miniaturization and modernization of electronics. However, achieving both of these properties simultaneously by constructing a dense conductive network within the polymer matrix is a very big challenge. Herein, a fully scalable and sustainable production process for polyamide-6/few layer graphene (PA-6/FLG) with vigorous dispersion of FLG in the PA-6 matrix was demonstrated by combining mechanochemistry with supercritical CO2 (scCO2) technology. By this process, the bulk graphite was rapidly cleaved into a FLG (≈10 layers), which was completely coated onto the spherical PA-6 particles. The composite films of this coated powder with only 3 wt% FLG loading amount attained wonderful in-plane electrical conductivity (IP-σc) and through-plane electrical conductivity (TP-σc) of 4.59 S·m−1 and 29.59 S·m−1, respectively, and outstanding EMI shielding effect of 41.8 dBs. In addition, the in-plane thermal conductivity (IP- kc) and the through-plane thermal conductivity (TP- kc) were 1.78 W m−1 K−1 and 2.14 W m−1 K−1 respectively. Therefore, the films rapidly dissipate heat from an electronic LED chip. Moreover, PA-6/FLG composite filaments showed a smooth appearance and an electrical resistivity of 7.12 GΩ. This work has strong potential to improve the performance of different polymer/graphene composites and expand their applications.

Bacterial-Cellulose-Reinforced Graphite Nanoplate Films for Electromagnetic Interference Shielding, Heat Conduction, and Joule Heating

With the flourishing development of wireless communication, there is an urgent need for flexible and robust materials with excellent thermal conductivity (TC) and electromagnetic interference (EMI) shielding performance through simple and green preparation. In this work, we efficiently prepared bacterial-cellulose-reinforced graphite nanoplate (BC-GNP) composite films by the vacuum filtration of BC/GNP mixture dispersions. Compared with the pure GNP film with a loose and disordered structure, the BC-GNP composite showed a highly aligned and compact “brick-and-mortar” structure. Benefiting from the unique structure, the resultant BC-GNP with 20 wt % BC (20%BC) exhibited a high tensile strength of 47.3 ± 1.8 MPa and an electrical conductivity of 76.9 ± 3.3 S/cm. As expected, the 20%BC showed excellent EMI shielding effectiveness (EMI SE) of 36.4 dB and a specific EMI SE (SSE/t) value of 8860 ± 400 dB·cm2/g with a thickness of 38 ± 1 μm. The in-plane TC and anisotropy index could reach up to 80.2 ± 6.4 W/mK and 73 ± 3, respectively. The 20%BC also exhibited a satisfactory Joule heating performance of 139 °C at a voltage of 6 V. More importantly, the 20%BC possessed a biodegradable property, which would completely degrade after 5 days. Thus, this work provides a strategy to facilely prepare biodegradable, high-performance, and multifunctional materials for wearable devices.

A distinct structure of TiC for electromagnetic interference shielding and thermal stability of SiTiOC ceramic nanocomposites

Materials capable of thermal stability electromagnetic interference (EMI) shielding have practical significance in the fields of aerospace. In this paper, a brand-new polymer-derived SiTiOC ceramic nanocomposites with tubular carbon was designed. The titanium atoms were uniformly introduced into the polysiloxane backbone by the transesterification between tetrabutyl titanate and silanol prepolymer, leading to excellent thermal stability properties. By controlling the pyrolysis temperature, a distinct structure of TiC was formed between the amorphous SiTiOC matrix and free carbon phase for enhanced electromagnetic interference shielding performance. More conductive paths were established, and the TiC structure initiated interfacial polarization and space charge polarization, contributing to the improvement of the dielectric loss and relaxation phenomena. Simultaneously, a total electromagnetic interference shielding efficiency of 27.85 dB at the entire X-band was reported for SiTiOC ceramic nanocomposites. A maximum SET of 38.59 dB was examined at around 12 GHz, suggesting that over 99.99% of the electromagnetic waves were shielded. The SiTiOC ceramic nanocomposites exhibited outstanding prospects in thermal stability electromagnetic interference shielding application in a severe environment.

Propagation and interference of thermal waves in turbulent thermal convection

We observe propagation and interference of two coherent thermal waves in the highly turbulent core of convective Rayleigh-B\'enard flow of cryogenic helium gas generated by top and bottom boundaries with harmonically oscillating temperatures. When the same amplitude of modulation is applied to both plates at slightly different frequencies, the resulting temperature interference pattern in the turbulent core shows a periodic increase and decrease in amplitude. If the observed time record of thermal wave interference were converted to corresponding pressure oscillations and shifted to higher frequencies, one would hear the acoustic beats often used, e.g., in tuning stringed musical instruments.

Polydopamine-assisted silver-coated spherical boron nitride as dual functional filler for thermal management and electromagnetic interference shielding

Polydopamine-assisted silver-coated spherical boron nitride as dual functional filler for thermal management and electromagnetic interference shielding

Poly(L-lactic acid)/graphene composite films with asymmetric sandwich structure for thermal management and electromagnetic interference shielding

The blowout growth of the power density and transmission efficiency of microelectronic devices makes the problems of “overheating” and electromagnetic pollution of electronic devices increasingly prominent, and it is raising an urgent demand to improve the thermal conductivity and electromagnetic interference (EMI) shielding performance of packaging materials. Additionally, the environmental damage caused by fossil-based electronic waste should not be ignored. Hence, a scalable production strategy was proposed to prepare sandwich structure poly(L-lactic acid) (PLLA) composite films with high thermal conductivity and excellent EMI shielding efficiency (SE), which was achieved via solution pouring method and stacking hot-pressing process, in which PLLA/graphene nanoplatelets (PLLA/GNPs) with different GNPs contents was the top and substrate layers, and PLLA/poly(D-lactic acid)/Fe3O4 (PLLA/PDLA/Fe3O4) with a small amount of PDLA and Fe3O4 was the middle layer. Owing to the asymmetric distribution of filler and the successful introduction of magnetic particles, when the GNPs and Fe3O4 contents of the whole film are respectively only 5.61 wt% and 4.39 wt%, and the asymmetric ratio is 1:9, the in-plane thermal conductivity (K‖) and EMI SE of the composite film reaches 7.49 W m−1 K−1 and 41.7 dB, respectively, higher than those of PLLA film with symmetric structure (3.31 W m−1 K−1 and 33.0 dB) at the same contents of fillers. Furthermore, a small amount of PDLA (4.39 wt%) promotes the formation of stereocomplex (SC) crystallites in the middle layer and further induces the interlayer SC microcrystals during the stacking hot-pressing process, enhancing the interlayer interaction to maintain the mechanical robustness of the PLLA film. This work provides a new direction for the manufacture of polymer based composite films with high thermal conductivity and directional EMI shielding, and has broad application potential in the field of large-scale production of green electronic products.

Composites of an Epoxy Resin (EP)/PVDF/NiCo-Graphene Nanosheet (GNS) for Electromagnetic Shielding

In this study, a series of three-dimensional (3D) epoxy resin/poly(vinylidene fluoride)/nickel–cobalt alloy–graphene nanosheet (EP/PVDF/NiCo-GNS) composites with high thermal conductivity and electromagnetic interference shielding effectiveness (EMI SE) were successfully prepared using a salt template-assisted strategy. X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses jointly presented the successful modification of GNS and in situ growth of NiCo alloy. The cross-sectional morphological observations on the PVDF/NiCo-GNS skeleton and epoxy-based composites clearly showed the successful construction of a honeycomb-like heat conduction network. At a NiCo-GNS loading of 15 wt %, the prepared composites’ EMI SE could reach a value of 34.62 dB. The special structures not only perfected the interconnected thermally and electrically conductive network but also facilitated the multiple internal reflections of electromagnetic waves inside the composites. The present work provides an insight into the design of multifunctional polymer-based composites for electronic 3D encapsulation applications.

Heterogeneous stacking strategy towards carbon aerogel for thermal management and electromagnetic interference shielding

Faced with the increasing heat dissipation and electromagnetic interference (EMI) shielding problems in electronics, carbon modified polymer-based composites with significant EMI shielding and thermal management performance are of particular interest. Herein, we proposed a carbon heterogeneous stacking strategy to construct the all carbon aerogels for the modification of epoxy resin. A hybrid 3D structure of reduced graphene oxide–carbon nanotube-vertical edge-rich graphene (rGO-CNT-VG) with covalent bonding are achieved all by chemical vapor deposition, in which the pore space of skeleton is creatively modified. Due to the elaborate design and control of microstructures, the obtained hierarchical 3D rGO-CNT-VG skeleton have plenty of seamlessly bonded heterogeneous interfaces between different components, which can create additional charge polarization, interfacial polarization and dielectric relaxation to promote significantly electromagnetic microwave attenuation and conversion and achieve ideal EMI shielding performance. Impressively, the rGO-CNT-VG/epoxy composites possess excellent thermal conductivity of 2.46 W m−1 K−1 and EMI shielding effectiveness of 56.65 dB, which are 5.1 times and 1.9 times higher than those of the rGO/epoxy composites, respectively. More importantly, the strategy of designing all carbon heterogeneous stacking skeleton in this study provides a guidance for synergistic controlling of multifunctional performance of composites.

Development of a Generalized Photothermal Measurement Model for the Layer Thickness Determination of Multi-Layered Coating Systems

In this article, a general model for 1D thermal wave interference is derived for multi-layered coating systems (with n∈N coating layers) applied on a thermally thick substrate. Such a model means the first step to building a non-contact photothermal measurement device that is able to determine the coating thickness of each layer. Test objects are to be illuminated on the surface using planar, sinusoidal excitation waves with fixed frequencies leading to the generation of thermal waves inside the object. Due to the multi-layered structure, each of these thermal waves is reflected and transmitted at layer interfaces. This process leads to infinitely many wave trains that need to be tracked to formulate the final surface temperature as a superposition of all waves. A mathematical and physical formulation of thermal wave interference is needed to model this process and relate the dependencies of the layer thicknesses, the materials, and the frequencies to the phase angle data, which then can be measured using, e.g., an infrared camera. In practice, the thermal properties of the layers might be unknown, which makes the process even more difficult. This article presents a concept to determine the thermal properties in advance. Finally, numerical experiments are presented that demonstrate the feasibility of the introduced layer thickness determination process.

Self-healable and super-stretchable conductive elastomeric nanocomposites for efficient thermal management characteristics and electromagnetic interference shielding

Due to the pressing need to mitigate current electromagnetic wave pollution (connecting to the 5 G era), lightweight, stretchable, thermally, and electrically conductive nanocomposite materials have attracted significant scientific interest. Herein, self-healable carboxylated nitrile butadiene elastomeric (XNBR) based nanocomposites were fabricated via sequential wet cum melt mixing technique utilizing multi-walled carbon nanotubes (MWCNTs). The metal-ligand complexes in the XNBR elastomer chain endow a reversible network that leads to self-healing ability. The higher aspect ratio of MWCNTs assists in constructing interconnected conductive pathways inside the XNBR matrix. The nanocomposite with MWCNTs (15 phr) provided an excellent EMI shielding effectiveness of − 27.4 dB, whereas the nanocomposite exhibited a thermal conductivity of 0.85 W.m−1. K−1. Interestingly, the interconnected networking pathway of MWCNTs in the XNBR matrix prepared a tunable analogical structure providing an absorption-dominant shielding mechanism. Under severe practical and environmental testing conditions, the nanocomposites showed a minute change in electromagnetic effectiveness, demonstrating their good performance for outdoor applications. These ultra-lightweight, self-healable, recyclable MWCNTs/ XNBR EMI shields are promising materials for next-generation super-stretchable and portable smart electronics.

Group performance of multiple series-connected energy piles under thermal loading

Thermomechanical behaviors of energy piles in rows, which are connected by a branch or branches, are investigated through a series of in-situ field tests. Thermally induced group effect influenced by thermal interference was measured and discussed. The interaction factor was extended to reflect the group effect of the pile branches which had differential head displacements. Results indicated that the heat exchange efficiency and thermal expansion coefficients were reduced, while the degree of freedom and pile head displacement were enlarged with the thermal interference. The pile temperatures, thermally induced stresses, and head displacement are decreased linearly with the direction of the flowing water. The heat exchange efficiency of the thermally affected branch was 93.6% and 91.8% of that of the isolated branch (1 × 3) as the thermal interference was on one side (2 × 3) and both sides (3 × 3), respectively. Additionally, the thermal interference of one adding pile branch caused the maximum thermally induced stress of the pile in the adjacent branch to increase by 49.0%, which is −1.46 MPa. The interaction factor on the branch effected by both-side thermal interference is 52.7%, which is about five times that of the branch effected by one-side thermal interference (10.6%).

Ice-templated assembly strategy to construct oriented porous Ti3SiC2 ceramics for thermal management and electromagnetic interference shielding in harsh thermal environments

Given the electromagnetic interference (EMI) and heat aggregation issue faced by electronic components, an urgent need exists to integrate EMI shielding and thermal conductivity in one material. Herein, a novel lightweight porous Ti3SiC2 ceramic with ordered structural arrangement was fabricated by using budget-friendly raw materials through ice template design and in-situ reaction synthesis. Leveraging the excellent conductivity and thermal conductivity of Ti3SiC2, a dual-functional advanced material with efficient EMI shielding and thermal management capabilities was obtained. At room temperature, porous Ti3SiC2 ceramics can achieve a shielding effectiveness of 35.44 dB and a thermal conductivity of 12.17 W/mK, with performance that can be tuned by porosity. In further, the porous Ti3SiC2 ceramic can work stably in thermal environments from room temperature to 700 °C or in corrosive environments rich in acid, alkali, and salts due to its excellent high temperature oxidation resistance and corrosion resistance. In view of the dual-functional characteristics and the stability of operation in harsh thermal environments, ordered porous Ti3SiC2 ceramics are promising for modern maritime and aerospace applications.

Laminated MXene Foam/Cellulose@LDH Composite Membrane with Efficient EMI Shielding Property for Asymmetric Personal Thermal Management.

Facing the increasingly complex and deteriorated environment, people's thermal comfort and health requirements are expanding. Therefore, wearable materials with integrated functions have progressed rapidly due to the fair compatibility for various functions and precise regulation. In this work, a laminated MXene foam/cellulose@LDH composite membrane was fabricated via a facile process consisting of in situ growth, vacuum filtration, and foaming for asymmetrical personal thermal management and electromagnetic interference shielding. In detail, the Zn-Al LDH side shows a high solar reflectance of 0.89 and an infrared emissivity of 0.97 in the atmospheric window, demonstrating the superior radiative cooling property. In contrast, the outstanding radiative warming performance is revealed by the high solar absorption (0.72) and infrared reflectivity (0.55) of the MXene foam. As a result, prominent temperature differences were achieved during the validation test. Compared to the control group, an 18 °C reduction of the Zn-Al LDH side and a 9.6 °C increment of the MXene foam side were observed, bringing out the excellent optical properties and radiative thermal management performances. What is more, due to the outstanding electrical conductivity of MXene, a rapid and prominent temperature rise to 44.2 °C could be expected by applying a low voltage of 1 V to provide active joule warmth. In addition, hydrophobization and the associated stain resistance were explained by the high water contact angles of obtained membranes. The excellent electromagnetic interference shielding performance (43.9 dB) given by the introduction of MXene provides a prospective candidate to replace the common shielding materials. The results, in general, provide a promising strategy for meeting the updating requirements for comfortable living in a world full of potential thermal and health threats.

In-field performance of continuous flight auger (CFA) energy piles with different configurations

In order to face the national energy crisis in Brazil, the use of geothermal energy piles (GEP) integrated with heat pumps is an attractive and cost-effective solution for the building cooling demand. On the other hand, there are very few field studies on the thermal performance of GEP systems in Brazilian soils and climate conditions, and for this reason, the implementation of this technology is still a challenge. Motivated by this need, continuous flight auger (CFA) energy piles were constructed to support a building in São Paulo city, and an experimental study, described in this paper, was carried out to provide useful data for the design of these GEPs. This work examined two key aspects of the design of GEP systems: (1) the influence of the heat exchange pipe configuration, and (2) the thermal response of GEPs and their effect on nearby piles installed in multi-layered ground. For this study, thermal response tests (TRTs) were conducted on four GEPs constructed with different pipe configurations, installed in a saturated sandy deposit intercalated by soft organic clay layers. The results obtained showed that: (i) the influence of pipe configuration on the GEP heat transfer is more significant during the first hours of pile heating process, and decreases with time due to the thermal interference between the pipe loops; (ii) the GEP temperature profile is impacted by the presence of soil layers of highly different thermal conductivities and groundwater flow velocities; and (iii) the temperature variation of nearby piles was also affected by the thermal characteristics of the soil layers, and therefore it should be considered for the structural design of GEPs.

Experimental and numerical simulation research on heat transfer performance of coaxial casing heat exchanger in 3500m-deep geothermal well in Weihe Basin

The deep coaxial borehole heat exchanger (DCBHE), as an important part of the deep-seated ground heat exchanger system, undertakes the important task of heat exchange with the underground geotechnical body to provide heating for the building. In this paper, through field test, numerical simulation and sensitivity analysis, the influence of thermal insulation performance of inner tube, heat preservation method of inner tube and diameter ratio of inner tube to outer tube on heat extraction capacity of deep coaxial borehole heat exchanger is studied. Field tests in intermittent operation mode (9.5 h operation and 14.5 h shutdown) show that the short-term single-well heat extraction capacity of the deep coaxial borehole heat exchanger using the vacuum gel steel tube with a thermal conductivity of 0.002 W/(m·K) as the inner tube is 574.96 W/m. The simulation results show that the diameter ratio of the inner and outer tubes has little effect on the heat extraction capacity, and the diameter ratio of the inner and outer tubes of 0.65 has the smallest resistance loss along the way. For heat exchanger with depth of 3500 m, the location of severe thermal interference between the inner and outer tubes is mainly located in the upper part of the heat exchanger near the surface, especially in the 1400 m to 2100 m section. The research results can provide a reference for the optimization design of medium-deep coaxial heat exchange buried pipe system and the promotion of medium-deep geothermal energy utilization.

Polypyrrole nanotube derived flame-retardant substrate of cellulose nanofiber composites with thermal conductive and electromagnetic interference shielding effect

In this work, the substrate of cellulose nanofiber (CNF) with polypyrrole (PPy) nanotube (PNT) composite (named as SF/PNT) membranes were prepared using vacuum filtration, which provided effective network for conducting electron and heat, simultaneously endowing the membranes with excellent thermal conductive performance and electromagnetic interference shielding effectiveness (EMI SE, 34.2 dB). Meanwhile, the SF/PNT composite membranes showed the electrical conductivity around 613 S/m, which also presented certain mechanical properties, with the latent heat of 155.2 J/g. In particular, the presence of Mg(OH)2 and PNT network contributed remarkable anti-dripping performance and flame-retardant properties to the membranes during combustion. The provided novel SF/PNT composites indicated promise for a wide variety of applications in thermal energy storage, battery thermal management system, microelectronic packaging and smart buildings.

Composite phase change materials embedded into cellulose/polyacrylamide/graphene nanosheets/silver nanowire hybrid aerogels simultaneously with effective thermal management and anisotropic electromagnetic interference shielding

Exploiting an advanced material simultaneously with effective thermal management (TM) and electromagnetic interference (EMI) shielding capacity is ungently demanded yet challenging for the miniaturized and integrated electronics. Anisotropic networks can be impregnated with phase change materials (PCMs) to fabricate multifunctional shape-stable PCMs (ss-CPCMs) simultaneously with excellent TM and EMI shielding, which is rarely reported. Herein, the anisotropic cellulose/polyacrylamide/graphene nanosheet/silver nanowire (CPGxAy) hybrid aerogels were successfully prepared using directional freeze-drying method, and then utilized as supporting skeletons to embed polyethylene glycol (PEG) via vacuum-assistant impregnation. Profited by the synergistic effect of graphene nanosheets (GNPs) and silver nanowires (AgNWs), the resultant polyethylene glycol@cellulose/polyacrylamide/graphene nanosheet/silver nanowire hybrid aerogel (PEG@CPGxAy) ss-CPCMs exhibit fascinating thermal conductivity (TC) of 0.84 W/m·K (200% increase in comparison with that of pure PEG) and anisotropic average EMI shielding effectiveness (SE) of 71.08 dB along the transverse direction and 35.21 dB along the longitudinal direction, while remaining high melting and crystallization enthalpy efficiency of 93.47% and 93.08%, respectively. In addition, PEG@CPGxAy ss-CPCMs also display great shape stability, thermal stability, and cyclic reusability in the storing/releasing latent heat processes. This investigation sheds new light on designing and fabricating ss-CPCMs with pretty comprehensive properties for TM and EMI shielding of modern electronics.Graphical Abstract

An Investigation of the Effects of Thermal Interference between Adjacent Nitinol Spring Actuators in a Tactile Display

Over the years, there has been increased research interest in the application of Nitinol as an actuator, due to its shape memory behaviour, simplicity, high power-to-weight ratio, compactness, and extreme high fatigue resistance to cyclic motion, and noiseless operation. Nitinol has found application in tactile displays which reproduce tactile parameters such as texture and shape, depending on the application. This paper presents the effects of thermal interference between adjacent Nitinol spring actuators in a tactile display. The tactile display is made of a 3 by 3 pin array whose spatial resolution was varied from 4 mm to 6 mm in steps of 1 mm while a current of 1.5 A was used to actuate 8 of the springs, and the centre spring was left unactivated to observe the thermal effects on it due to the heat gradient formed. A Finite Element (FE) model was developed using COMSOL Multiphysics and the results were further verified through experimentation. In both cases, there was visible thermal interference between actuators. The increase in spatial resolution saw a decrease in thermal interference by 12.7%. Using a fan to introduce forced convection, reduced the thermal interference in the simulation by 20% and during experimentation by 11%. The results of this research indicate a spatial resolution of 6 mm reduced the thermal inference to a negligible rate. However, thermal interference could not be eliminated with these two methods.

Melamine foam-induced isotropic graphite foam for effective thermal management and electromagnetic interference shielding

A series of isotropic graphite foams (GFs) were synthesized using a melamine foam (MF) template-assisted strategy for effective thermal management and EMI SE.

Exploiting Tunable Q-Factor Wavelet Transform Domain Sparsity to Denoise Wrist PPG Signals

Wearable health monitoring devices based on photoplethysmogram (PPG) can estimate valuable physiological parameters and are often regarded as a touchstone for indicating the cardiovascular status of a person. Severe motion artifacts are generally observed in the acquired PPG signals from the biosensors in the wearables when the PPG acquisition is performed during different physical activities. Classical filters can remove thermal noise and electromagnetic interference from the raw PPG signals, but they fail to handle the motion artifacts that cover a wider range of signal frequencies. This work introduces a new motion artifact removal scheme that exploits the sparsity of PPG signals in the tunable-Q factor wavelet transform (TQWT) domain using the basis pursuit denoising (BPDN) scheme. The proposed scheme deftly removes noise while preserving the original morphology of the PPG signal without using any reference accelerometer sensor data. In particular, a regularized SALSA-based BPDN algorithm is employed for sparse recovery, which utilizes a soft thresholding approach to denoise the noisy PPG signals. TQWT can be tuned according to the oscillatory behavior of the raw PPG signal. At the same time, BPDN exploits the sparsity of the wavelet coefficients to yield an artifact-free reconstruction of PPG. Further, heart rate estimation is performed using the denoised PPG signal with support vector regression to demonstrate the clinical information preservation during the proposed denoising process. The proposed denoising scheme is evaluated on two publicly available databases, and an overall minimum mean absolute error (MAE) of 1.03 and 0.76 beats per minute (bpm) is achieved. The suggested denoising approach has demonstrated better performance with the lowest MAE compared to the previously reported methods.