We propose a strategy to realize a vertically parallel multilayered distribution of microdiamonds in a polymeric matrix by pre-constructing layers with abundantly stacked microdiamonds. Silicone-based composites with this microdiamond arrangement exhibit interesting material properties in the through-plane direction: significant increments in thermal conductivity (335% that of composites with a random structure at a similar low loading of 24.7 vol%), and excellent dielectric properties as thermal interface materials for applications such as radars. Novel numerical models focused on this design of microdiamond arrangement are proposed to further understand mechanism of thermal conductivity increment and are found to match thermal conductivity and tendency of composites with this type of microdiamond distribution. It is revealed that adjusting microstructures in pre-constructed microdiamond layers is regarded as an effective strategy to improve further thermal conductivity of composites.
Optical physical unclonable functions (PUFs) have been proven to be one of the most effective anti-counterfeiting strategies. However, optical PUFs endowed with flexibility and biocompatibility have not been developed, limiting their application scenarios. Herein, biocompatible and flexible optical PUF labels are developed by randomly embedding microdiamonds in silk fibroin films. The PUF labels can be conformally attached onto the surface of complex shaped objects, providing the desired protection against fake and interior products. In this system, silk fibroin films serve as a flexible and biocompatible substrate, while the Raman signal of the microdiamonds serves as response of the excitation. The extremely high stability and random distribution of the microdiamonds ensure the performance of PUFs, and the maximum encoding capability of 2 10000 is finally realized. The cytotoxicity analysis results also verify the biosafety of the PUF system. In addition, the as-prepared PUF labels are attached onto the surface of polyethylene material, and human skin, and even have been implanted under chicken skin tissue, promising their practical applications.
Polymeric composites with enhanced thermal conductivity are essential components for thermal management. Inspired by the stacked structure of adipose cells in the subcutis, we propose a strategy to construct a spatially interconnected thermal channel of microdiamonds (MDs) along vertical directions. In detail, a thermoplastic polyurethane (TPU)@MD core–shell structure was assembled via a microcladding method, which is utilized as reinforcement to fabricate the TPU@MD/poly(vinyl alcohol) (PVA) composite films through a doctor-blade coating technique. The resultant composite films exhibit a high through-plane thermal conductivity of 3.31 W/mK at a MD loading of 39 vol %, which is 195% higher than randomly dispersed composites. A two-step mathematical model was derived by the thermal resistance method to simultaneously analyze the mechanism of thermal conductivity enhancement. Meanwhile, the TPU@MD/PVA composites also reveal low dielectric loss. It is believed that this strategy to design and fabricate thermal interface materials with excellent properties provides effective guidance in thermal management applications.
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