Ice-templated Assembly Research Articles

Highly thermal conductive and flame retardant poly(vinyl alcohol) film with synergistic alignments of boron nitride nanosheets/Ti3C2Tx MXene for thermal interface materials

With the development of microelectronics and flexible wearable electronic devices, poly(vinyl alcohol) (PVA) based thermal interface materials (TIMs) have received much attention. However, poor heat dissipation and high flammability have emerged as the key issues that restrict their application. In this work, the directional alignment of phytic acid (PA) modified boron nitride nanosheets (BNNS) and Ti3C2Tx MXene in PVA matrix was achieved by ice-templated assembly, which simultaneously enhanced the flame retardancy and thermal conductivity of PVA composite films (PVA/BTx). Owing to the synergistic effect between oriented BNNS and Ti3C2Tx MXene on forming the thermally conductive network within PVA matrix, the in-plane thermal conductivity of PVA/BTx-30 composite film was increased to 8.54 W m−1 K−1, much higher than that of PVA film (0.30 W m−1 K−1). Meanwhile, the heat dissipation process of PVA films applied as TIMs was simulated, which showed that PVA/BTx-30 films exhibited excellent thermal conduction and significantly decreased the operation temperature of electronic devices. Additionally, the peak heat release rate (PHRR) and total heat release (THR) of PVA/BTx-30 films were reduced by 60.3% and 62.0%, respectively, showing good flame retardancy. Importantly, the flexible Ti3C2Tx nanosheets further enhanced the mechanical properties of PVA/BTx composite films. Therefore, this work provides an effective method for the preparation of high thermal conductivity and flame retardant composite materials, which has important potential applications in the microelectronics industry.

Bioinspired Macroporous Materials of MXene Nanosheets: Ice-Templated Assembly and Multifunctional Applications.

Biological macroporous materials, such as stems of the plants and bone of the animals, possess outstanding properties for powerful guarantee of creatures' survival through the well-aligned architecture constructed from limited components. Transition metal carbides or nitrides (MXenes), as novel 2D assemblies, have attracted numerous attentions in various applications due to their unique properties. Therefore, mimicking the bioinspired architecture with MXenes will boost the development of human-made materials with unparalleled properties. Freeze casting has been widely applied to fabricate bioinspired MXene-based materials and achieve the assembly of MXene nanosheets into 3D forms. This process solves the inherent restacking problems of MXenes, simultaneously preserving the unique properties of MXenes with a physical process. Here, the ice-templated assembly of MXene in terms of the freezing processes and their potential mechanisms is summarized. In addition, applications of MXene-based materials in electromagnetic interference shielding and absorption, energy storage and conversion, as well as piezoresistive pressure sensors are also reviewed. Finally, the current challenges and bottlenecks of ice-templated assembly of MXene are further discussed to guide the development of bioinspired MXene-based materials.

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.

Anisotropic PDMS/Alumina/Carbon Fiber Composites with a High Thermal Conductivity and an Electromagnetic Interference Shielding Performance.

The development of polymer-based composites with a high thermal conductivity and electromagnetic interference (EMI) shielding performance is crucial to the application of polymer-based composites in electronic equipment. Herein, a novel strategy combining ice-templated assembly and stress-induced orientation was proposed to prepare polydimethylsiloxane (PDMS)/alumina/carbon fiber (CF) composites. CF in the composites exhibited a highly oriented structure in the horizontal direction. Alumina was connected to the CF, promoting the formation of thermal conductive pathways in both the horizontal and vertical directions. As the CF content was 27.5 vol% and the alumina content was 14.0 vol%, the PDMS/alumina/CF composite had high thermal conductivities in the horizontal and vertical directions, which were 8.44 and 2.34 W/(m·K), respectively. The thermal conductivity in the horizontal direction was 40.2 times higher than that of PDMS and 5.0 times higher than that of the composite with a randomly distributed filler. The significant enhancement of the thermal conductivity was attributed to the oriented structure of the CF and the bridging effect of alumina. The PDMS/alumina/CF composite exhibited an excellent EMI shielding effectiveness of 40.8 dB which was 2.4 times higher than that of the composite with a randomly distributed filler. The PDMS/alumina/CF composite also exhibited a low reflectivity of the electromagnetic waves. This work could provide a guide for the research of polymer-based composites with a high thermal conductivity and an EMI shielding performance.

Ice-templated assembly strategy to construct three-dimensional thermally conductive networks of BN nanosheets and silver nanowires in polymer composites

Polymer composites have been widely employed as electronic packaging materials, due to their low cost, flexibility, chemical stability, and high malleability, etc. However, the thermal conductivity of polymer composites becomes increasingly requirement, with the rapid growth of electronics toward miniaturization and high-power density. Conventional method to enhance the thermal conductivity of polymer is addition of high-content thermally conductive fillers, but it will deteriorate other significant properties of polymers, such as optical, electrical, and mechanical performance. Herein, we report an ice-templated assembly strategy to construct three-dimensional thermally conductive networks of BN nanosheets (BNNS) and silver nanowires (AgNWs) in epoxy resin composites. The thermal-conduction pathway can be easily built by the synergistic effects between two-dimensional BNNS and one-dimensional AgNW. Furthermore, the welding of the adjacent AgNWs through low-temperature sintering process enlarges the total contact area per unit filler volume. The resulted polymer composite thus exhibits a through-plane thermal conductivity of 1.10 Wm−1K−1 at only about 5.0 vol% fillers content, which is six times higher than that of the pure epoxy resin. This work shows great potential in advanced packaging materials, such as substrate materials and printed circuit board materials.

Vertically aligned silicon carbide nanowires/reduced graphene oxide networks for enhancing the thermal conductivity of silicone rubber composites

Ice-templated assembly strategy is an effective method to construct filler networks. The filler networks can be used to increase the thermal conductivity of polymer composites. Herein, silicon carbide nanowires, reduced graphene oxide and cellulose nanofiber were used as assembly units to construct vertically aligned filler networks by ice-templated assembly strategy. Polydimethylsiloxane grafted with poly(ethylene glycol) could enhance the interfacial interaction and improve the wettability between silicone rubber and the filler networks. Silicon carbide/reduced graphene oxide/silicone rubber composites were prepared by infiltrating the filler networks with silicone rubber. The thermal conductivity of the composites increased with increasing the contents of silicon carbide and reduced graphene oxide. The thermal conductivity of the composite with 1.84 vol% filler network was as high as 2.74 W/(m·K), exhibiting significant enhancement of thermal conductivity of 16 times compared with silicone rubber. This work provides an insight for preparing highly thermally conductive silicone rubber composites.

Influence of pore architectures of silk fibroin/collagen composite scaffolds on the regeneration of osteochondral defects in vivo.

The regeneration of osteochondral defects faces great challenges because of the limited self-regenerative capabilities of cartilage tissues. In situ inductive regeneration can be realized using bioactive scaffolds combined with endogenous reparative cells. Cell migration could be significantly facilitated by scaffolds with oriented channels. For this purpose, silk fibroin (SF) was composited with collagen (Col) to fabricate extracellular matrix (ECM)-mimetic SF/Col composite scaffolds with random pores, radially aligned pores or axially aligned pores by ice-templated assembly and temperature gradient-guided thermally-induced phase separation. Scanning electron microscopy (SEM) observation confirmed the random and aligned architectures in the respective scaffolds. The three kinds of SF/Col composite scaffolds exhibited a porous structure with a porosity of ∼85%, an appropriate elastic modulus with mechanical anisotropy in the aligned scaffolds, and good biocompatibility. The oriented channels could improve in vivo cell migration and infiltration. During the tissue remodeling processes, the regeneration of osteochondral tissues particularly cartilage was obviously faster in the radially aligned scaffold group than in the other two groups. Nevertheless, satisfactory regeneration was achieved in the two aligned scaffold groups with hyaline cartilage formation at 18 weeks post-surgery, while a hybrid of hyaline cartilage and fibrocartilage was formed in the random scaffold group.

Achieving Significant Thermal Conductivity Enhancement via an Ice-Templated and Sintered BN-SiC Skeleton.

Conventional polymer composites normally suffer from undesired thermal conductivity enhancement which has hampered the development of modern electronics as they face a stricter heat dissipating requirement. It is still challenging to achieve satisfactory thermal conductivity enhancement with reasonable mechanical properties. Herein, we present a three-dimensional (3D), lightweight, and mechanically strong boron nitride (BN)-silicon carbide (SiC) skeleton with aligned thermal pathways via the combination of ice-templated assembly and high-temperature sintering. The sintering has introduced atomic-level coupling at the BN-SiC junction which contributes to efficient phonon transport via the newly formed borosilicate glass BCxN3-x (0 ≤ x ≤ 3) and SiCxN4-x (0 ≤ x ≤ 4) phases, leading to much lower interfacial thermal resistance. Thus, the obtained BN-SiC skeleton shows satisfactory thermal performance. The prepared 3D BN-SiC/polydimethylsiloxane (PDMS) composites exhibit a maximum through-plane thermal conductivity of 3.87 W·m-1·K-1 at a filler loading of only 8.35 vol %. The thermal conductivity enhancement efficiency reaches 220% per 1 vol % filler when compared to pure PDMS matrix, superior to other reported BN skeleton-based composites. The feature of our strategy is to allow the oriented three-dimensional skeleton to be strongly bonded by a sintered ceramic phase instead of polymer-like adhesive, namely, to improve the intrinsic thermal conductivity of the skeleton to the greatest extent. This strategy can be applied to develop novel thermal management materials that are lightweight and mechanically tough that rapidly transfer heat. It represents a new avenue to addressing the heat challenges in traditional electronic products.

Epoxy Nanocomposites with Reduced Graphene Oxide-Constructed Three-Dimensional Networks of Single Wall Carbon Nanotube for Enhanced Thermal Management Capability with Low Filler Loading.

Thermal management materials are solutions to heat dissipation issues in electronic devices, which are key to the device reliability and lifetime. Epoxy-based materials have been widely used but suffer from their intrinsically low thermal conductivity. In this work, we employ the combined hydrothermal reduction, ice-templated assembly, and vacuum-assisted infiltration methods to construct well-aligned rigid three-dimensional (3D) networks of reduced graphene oxide (RGO) walls bridged by (functional) single wall carbon nanotubes ((f)SWCNTs) in the epoxy resin. The 3D RGO/(f)SWCNT aerogel notably enhances thermal conductivity, reduces the coefficient of thermal expansion (CTE), and increases the glass-transition temperature (Tg) without deteriorating the electrical insulating property. Remarkably, the (RGO/fSWCNT)1:2.5 epoxy nanocomposite reaches a thermal conductivity of 0.63 to 0.69 W m-1 K-1 from 300 to 390 K at a very low filler loading of 3.65 vol %, which is more than four times enhancement over the pure epoxy resin. The CTE decreases by 11.2 ppm K-1 and Tg increases by 20 K. We also show that the functional groups associated with the 3D RGO/fSWCNT aerogel are beneficial for improvement in thermal conductivity, dimensional stability, and thermal stability. The epoxy nanocomposites reported by this work demonstrate strong potential for thermal management application in electronic packaging.

Liquid nitrogen driven assembly of nanomaterials into spongy millispheres for various applications

We report a facile strategy suitable for common nanomaterials, in which ice-templated assembly and liquid nitrogen-assisted rotation are coupled, for fast processing of uniform spongy millispheres. Such spheres possess a hierarchical structure with an interpenetrating network and abundant external voids, exhibiting great potentials in energy & environmental field.

Cuttlebone-like V2O5 Nanofibre Scaffolds \u2013 Advances in Structuring Cellular Solids

The synthesis of ceramic materials combining high porosity and permeability with good mechanical stability is challenging, as optimising the latter requires compromises regarding the first two properties. Nonetheless, significant progress can be made in this direction by taking advantage of the structural design principles evolved by nature. Natural cellular solids achieve good mechanical stability via a defined hierarchical organisation of the building blocks they are composed of. Here, we report the first synthetic, ceramic-based scaffold whose architecture closely mimics that of cuttlebone –a structural biomaterial whose porosity exceeds that of most other natural cellular solids, whilst preserving an excellent mechanical strength. The nanostructured, single-component scaffold, obtained by ice-templated assembly of V2O5 nanofibres, features a highly sophisticated and elaborate architecture of equally spaced lamellas, which are regularly connected by pillars as lamella support. It displays an unprecedented porosity of 99.8 %, complemented by an enhanced mechanical stability. This novel bioinspired, functional material not only displays mechanical characteristics similar to natural cuttlebone, but the multifunctionality of the V2O5 nanofibres also renders possible applications, including catalysts, sensors and electrodes for energy storage.

Highly compressible graphene/polyurethane sponge with linear and dynamic piezoresistive behavior

A high-elastic graphene/polyurethane (PU) nanocomposite with excellent electromechanical properties was fabricated by a facile ice-templated assembly strategy.

An ice-templated assembly strategy to construct graphene oxide/boron nitride hybrid porous scaffolds in phase change materials with enhanced thermal conductivity and shape stability for light–thermal–electric energy conversion

Multifunctional phase change materials for light-thermal-electric energy conversion are fabricated by an ice-templated assembly strategy.

Ice-templated three dimensional nitrogen doped graphene for enhanced supercapacitor performance

The three-dimensional (3D), nitrogen doped reduced graphene oxide (N-RGO) monoliths have been synthesized using graphene oxide and melamine through an ice-templated assembly. The self-assembled monoliths are accompanied with the considerable reduction of graphene oxide after annealing and specific surface area of 190 m2 g−1. The blue shift of approximately 22 cm−1 and 4 cm−1 in D and G bands for N-RGO is notified in Raman analysis, confirming the incorporation of nitrogen onto the graphene sheet. In addition, an extra peak at 1251 cm−1 appears possibly due to the stretching vibration of C–N bonds. The detailed doping configurations analyzed by x-ray photoemission spectroscopy indicate the nitrogen content of around 6.2 at% in the N-RGO with predominant pyridinic N-type configuration. The specific capacitance is enhanced up to 217 F g−1 at a scan rate of 5 mV s−1, which is approximately three times higher than that of the pristine 3D RGO owing to the pseudocapacitive behavior of N-RGO. The high electronic conductivity of the N-RGO electrode with low charge transfer resistance as confirmed by electrochemical impedance spectroscopy is associated with good rate capability. Furthermore, the N-RGO sample exhibits an excellent cyclic stability with no decay in capacitance even after 5000 cycles at scan rate of 100 mV s−1.

Thermoresponsive Composite Hydrogels with Aligned Macroporous Structure by Ice-Templated Assembly

Natural tissues, such as bone, tendon, and muscle, have well defined hierarchical structures, which are crucial for their biological and mechanical functions. However, mimicking these structural features still remains a great challenge. In this study, we use ice-templated assembly and UV-initiated cryo-polymerization to fabricate a novel kind of composite hydrogel which have both aligned macroporous structure at micrometer scale and a nacre-like layered structure at nanoscale. Such hydrogels are macroporous, thermoresponsive, and exhibit excellent mechanical performance (tough and high stretchable), attractive properties that are of significant impact on the wide applications of composite hydrogels, especially as tissue-engineering scaffolds. The fabrication method in this study including freeze-casting and cryo-polymerization can also be applied to other materials, which makes it promising for designing and developing smart and multifunctional composite hydrogels with hierar chical structures.