Synthesis of Liquid Gallium@Reduced Graphene Oxide Core-Shell Nanoparticles with Enhanced Photoacoustic and Photothermal Performance.

This report presents nanoparticles composed of a liquid gallium core with a reduced graphene oxide (RGO) shell (Ga@RGO) of tunable thickness. The particles are produced by a simple, one-pot nanoprobe sonication method. The high near-infrared absorption of RGO results in a photothermal energy conversion of light to heat of 42.4%. This efficient photothermal conversion, combined with the large intrinsic thermal expansion coefficient of liquid gallium, allows the particles to be used for photoacoustic imaging, that is, conversion of light into vibrations that are useful for imaging. The Ga@RGO results in fivefold and twofold enhancement in photoacoustic signals compared with bare gallium nanoparticles and gold nanorods (a commonly used photoacoustic contrast agent), respectively. A theoretical model further reveals the intrinsic factors that affect the photothermal and photoacoustic performance of Ga@RGO. These core-shell Ga@RGO nanoparticles not only can serve as photoacoustic imaging contrast agents but also pave a new way to rationally design liquid metal-based nanomaterials with specific multi-functionality for biomedical applications.

Chameleon-inspired tunable multi-layered infrared-modulating system via stretchable liquid metal microdroplets in elastomer film.

This report presents liquid metal-based infrared-modulating materials and systems with multiple modes to regulate the infrared reflection. Inspired by the brightness adjustment in chameleon skin, shape-morphing liquid metal droplets in silicone elastomer (Ecoflex) matrix are used to resemble the dispersed "melanophores". In the system, Ecoflex acts as hormone to drive the deformation of liquid metal droplets. Both total and specular reflectance-based infrared camouflage are achieved. Typically, the total and specular reflectances show change of ~44.8% and 61.2%, respectively, which are among the highest values reported for infrared camouflage. Programmable infrared encoding/decoding is explored by adjusting the concentration of liquid metal and applying areal strains. By introducing alloys with different melting points, temperature-dependent infrared painting/writing can be achieved. Furthermore, the multi-layered structure of infrared-modulating system is designed, where the liquid metal-based infrared modulating materials are integrated with an evaporated metallic film for enhanced performance of such system.

Enable Multi-Stimuli-Responsive Biomimetic Actuation with Asymmetric Design of Graphene-Conjugated Conductive Polymer Gradient Film.

In this paper, multiresponsive actuators based on asymmetric design of graphene-conjugated poly(3,4-ethylene dioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) gradient films have been developed by a simple drop casting method. The biomimetic actuation is attributed to the hygroscopic expansion property of PEDOT:PSS and the gradient distribution of graphene sheets within the film, which resembles the hierarchical swelling tissues of some plants in nature. Graphene-conjugated PEDOT:PSS (GCP) actuators exhibit reversible bending behavior under multistimuli such as moisture, organic vapor, electrothermal, and photothermal heating. Noticeably, the bending curvature reaches 2.15 cm-1 under applied voltage as low as 1.5 V owing to the high electrical conductivity of GCP actuator. To mimic the motions of nyctinastic plants, a GCP artificial flower that spreads its petals under sunlight illumination has been fabricated. GCP actuators have been also demonstrated as intelligent light-controlled switches for light-emitting diodes and smart curtains for thermal management. Not only do the GCP gradient films exhibit potential applications in flexible electronics and energy harvesting/storage devices but also the facile fabrication of multiresponsive GCP actuators may shed light on the development of soft robotics, artificial muscles, wearable electronics, and smart sensors.

Recent Advances in Thermal Interface Materials for Thermal Management of High-Power Electronics.

With the increased level of integration and miniaturization of modern electronics, high-power density electronics require efficient heat dissipation per unit area. To improve the heat dissipation capability of high-power electronic systems, advanced thermal interface materials (TIMs) with high thermal conductivity and low interfacial thermal resistance are urgently needed in the structural design of advanced electronics. Metal-, carbon- and polymer-based TIMs can reach high thermal conductivity and are promising for heat dissipation in high-power electronics. This review article introduces the heat dissipation models, classification, performances and fabrication methods of advanced TIMs, and provides a summary of the recent research status and developing trends of micro- and nanoscale TIMs used for heat dissipation in high-power electronics.

Developing Thermal Regulating and Electromagnetic Shielding Nacre-Inspired Graphene-Conjugated Conducting Polymer Film via Apparent Wiedemann-Franz Law.

In this work, we observed size-dependent behavior of filler on both the thermal and electrical conductivities of nacre-like graphene-conjugated conducting polymer films and demonstrated the display of apparent Wiedemann-Franz law and tunability of Lorenz constant in such films. The maximum thermal and electrical conductivities of as-fabricated films can reach over 73 W·m-1·K-1 and 1200 S·cm-1, respectively. Furthermore, the maximum value of electromagnetic interference shielding reaches 54 dB with SSE/t over 16000 dB·cm2·g-1. These films can not only show high-quality electromagnetic interference shielding performance with small thickness and low filler ratio but also achieve simultaneous thermal management during electromagnetic shielding. The findings in this work offer new insight into designing flexible graphene-conjugated polymers with customizable thermal and electrical properties in the broad fields of thermal management systems, electromagnetic defense systems, and flexible electronic systems.

Facile Approach to Enhance Electrical and Thermal Performance of Conducting Polymer PEDOT:PSS Films via Hot Pressing.

This paper studies the impact of hot pressing on the electrical and thermal performance of thick (thickness >5 µm) conducting polymer poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films after acid treatment. Thick conducting polymer films usually exhibit low electrical and thermal conductivities similar to bulk polymer because charge and heat carriers are easily scattered by the irregular arrangement of crystalline domains inside the polymer. In this work, the in-plane electrical conductivity of thick hot-pressed PEDOT:PSS film exceeded 1500 S/cm, and 50% enhancement was obtained in comparison with its non-hot-pressed counterparts. Its in-plane thermal conductivity reached as high as 1.11 W/mK (improved by almost 100% compared to acid-treated PEDOT:PSS films), which is comparable to that of some commercial thermal pads. Such electrical and thermal enhancement via the hot-pressing process is attributed to the optimized morphology and microstructures, which provide short paths for thermal and electrical transportation. We have also demonstrated that the hot-pressed PEDOT:PSS films could be potentially utilized as a flexible conductor and heat spreader for application in flexible electronics and thermal management, respectively. This study not only offers a new insight into the process-property relationship for conducting polymers but also further enables the use of PEDOT:PSS films with simultaneously improved electrical and thermal performance in practical applications, such as thermal management for organic electrodes in batteries, flexible electronics, soft robotics, and bioelectronics.

Liquid Metal Composites with Enhanced Thermal Conductivity and Stability Using Molecular Thermal Linker.

Gallium-based liquid metal (LM) composite with metallic fillers is an emerging class of thermal interface materials (TIMs), which are widely applied in electronics and power systems to improve their performance. In situ alloying between gallium and many metallic fillers like copper and silver, however, leads to a deteriorated composite stability. This paper presents an interfacial engineering approach using 3-chloropropyltriethoxysilane (CPTES) to serve as effective thermal linkers and diffusion barriers at the copper-gallium oxide interfaces in the LM matrix, achieving an enhancement in both thermal conductivity and stability of the composite. By mixing LM with copper particles modified by CPTES, a thermal conductivity (κ) as high as 65.9 W m-1 K-1 is achieved. In addition, κ can be tuned by altering the terminal groups of silane molecules, demonstrating the flexibility of this approach. The potential use of such composite as a TIM is also shown in the heat dissipation of a computer central processing unit. While most studies on LM-based composites enhance the material performance via direct mixing of various fillers, this work provides a different approach to fabricate high-performance LM-based composites and may further advance their applications in various areas including thermal management systems, flexible electronics, consumer electronics, and biomedical systems.