Chenglong Li

Bio: Chenglong Li is an academic researcher from Qilu University of Technology. The author has contributed to research in topics: Materials science & Piezoresistive effect. The author has an hindex of 1, co-authored 3 publications receiving 20 citations.

Development of Conductive Hydrogels for Fabricating Flexible Strain Sensors.

Abstract: Conductive hydrogels can be prepared by incorporating various conductive materials into polymeric network hydrogels. In recent years, conductive hydrogels have been developed and applied in the field of strain sensors owing to their unique properties, such as electrical conductivity, mechanical properties, self-healing, and anti-freezing properties. These remarkable properties allow conductive hydrogel-based strain sensors to show excellent performance for identifying external stimuli and detecting human body movement, even at subzero temperatures. This review summarizes the properties of conductive hydrogels and their application in the fabrication of strain sensors working in different modes. Finally, a brief prospectus for the development of conductive hydrogels in the future is provided.

Engineered Microstructure Derived Hierarchical Deformation of Flexible Pressure Sensor Induces a Supersensitive Piezoresistive Property in Broad Pressure Range.

Abstract: Fabricating flexible pressure sensors with high sensitivity in a broad pressure range is still a challenge. Herein, a flexible pressure sensor with engineered microstructures on polydimethylsiloxane (PDMS) film is designed. The high performance of the sensor derives from its unique pyramid-wall-grid microstructure (PWGM). A square array of dome-topped pyramids and crossed strengthening walls on the film forms a multiheight hierarchical microstructure. Two pieces of PWGM flexible PDMS film, stacked face-to-face, form a piezoresistive sensor endowed with ultrahigh sensitivity across a very broad pressure range. The sensitivity of the device is as high as 383 665.9 and 269 662.9 kPa-1 in the pressure ranges 0-1.6 and 1.6-6 kPa, respectively. In the higher pressure range of 6.1-11 kPa, the sensitivity is 48 689.1 kPa-1, and even in the very high pressure range of 11-56 kPa, it stays at 1266.8 kPa-1. The pressure sensor possesses excellent bending and torsional strain detection properties, is mechanically durable, and has potential applications in wearable biosensing for healthcare. In addition, 2 × 2 and 4 × 4 sensor arrays are prepared and characterized, suggesting the possibility of manufacturing a flexible tactile sensor.

Mold Flow Simulation Analysis of Molded Underfill in an Ultra-thin High-Density Package

Abstract: The consumer electronics devices continue to develop towards ultra-thin, high-density and miniaturization. Advanced mold flow simulation analysis before the actual experiment will help to predict and understand the potential risks of Epoxy Molding Compound (EMC) filling and then effectively promote mold design and material selection. However, the contribution of mold flow simulation to EMC material evaluation is still insufficient. One of the main reasons is that mold flow simulation requires a large number of material parameters, so it is difficult to analyze the material by traditional design of experiment (DOE) methods. In this paper, we investigate a structure for an ultra-thin and fine-pitch package, and uses one commercial EMC material to study its mold flow filling process in Modex3D software. The changing of temperature, shear rate, curing degree and viscosity during the filling process are analyzed in detail. In addition, based on detailed analysis of the viscosity equations and curve, the influences of temperature, filling time, viscosity, gel point and curing kinetics parameters on filling state are discussed in depth. This research is expected to provide theoretical guidance for improving the filling state in ultra-thin fine-pitch devices in terms of material design and process control.

Comparative Analysis of Flow Capability of Epoxy Molding Compound between Spiral Structure and Actual Mold by Mold Flow Simulation

Abstract: Plastic package usually requires the epoxy molding compound (EMC) to be filled in mold by transfer molding method. In order to achieve better filling results, the selected EMC needs to have good flow capability at molding temperature to avoid insufficient filling or voids during molding process. At present, a commonly used method for evaluating flow capability of EMC is spiral flow test, and the spiral flow length, i.e., the length that EMC could fill in the spiral structure at molding temperature, is regarded as the key index of flow capability. However, due to the significant difference in structure, whether the spiral flow length can fully reflect the filling results of EMC in real mold is worth paying attention. In this paper, we use mold flow simulation to simulate the EMC with similar physical properties to fill in the spiral pattern and actual mold structure respectively, to verify the differences in flow capability. The key material properties of EMC and the influence of the main process parameters on the filling results of these two structures are further studied. For material properties, we mainly focus on the zero shear viscosity, gel point and curing kinetics of EMC, while for process conditions, we focus on molding temperature and filling time. It shows that the spiral flow length is much more sensitive than the filling results in actual mold structure, so the spiral flow length could not fully represent the flow capacity in actual mold. The mechanism of flow results of EMC in spiral flow mold and actual mold is analyzed in detail based on the principles of fluid mechanics and material properties of EMC.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

Abstract: A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling effect is considered to be the principal mechanism of the sensor under small strains.

Development of Conductive Hydrogels for Fabricating Flexible Strain Sensors.

Abstract: Conductive hydrogels can be prepared by incorporating various conductive materials into polymeric network hydrogels. In recent years, conductive hydrogels have been developed and applied in the field of strain sensors owing to their unique properties, such as electrical conductivity, mechanical properties, self-healing, and anti-freezing properties. These remarkable properties allow conductive hydrogel-based strain sensors to show excellent performance for identifying external stimuli and detecting human body movement, even at subzero temperatures. This review summarizes the properties of conductive hydrogels and their application in the fabrication of strain sensors working in different modes. Finally, a brief prospectus for the development of conductive hydrogels in the future is provided.

Ultra‐Sensitive, Deformable, and Transparent Triboelectric Tactile Sensor Based on Micro‐Pyramid Patterned Ionic Hydrogel for Interactive Human–Machine Interfaces

Abstract: Rapid advances in wearable electronics and mechno‐sensational human–machine interfaces impose great challenges in developing flexible and deformable tactile sensors with high efficiency, ultra‐sensitivity, environment‐tolerance, and self‐sustainability. Herein, a tactile hydrogel sensor (THS) based on micro‐pyramid‐patterned double‐network (DN) ionic organohydrogels to detect subtle pressure changes by measuring the variations of triboelectric output signal without an external power supply is reported. By the first time of pyramidal‐patterned hydrogel fabrication method and laminated polydimethylsiloxane (PDMS) encapsulation process, the self‐powered THS shows the advantages of remarkable flexibility, good transparency (≈85%), and excellent sensing performance, including extraordinary sensitivity (45.97 mV Pa−1), fast response (≈20 ms), very low limit of detection (50 Pa) as well as good stability (36 000 cycles). Moreover, with the LiBr immersion treatment method, the THS possesses excellent long‐term hyper anti‐freezing and anti‐dehydrating properties, broad environmental tolerance (−20 to 60 °C), and instantaneous peak power density of 20 µW cm−2, providing reliable contact outputs with different materials and detecting very slight human motions. By integrating the signal acquisition/process circuit, the THS with excellent self‐power sensing ability is utilized as a switching button to control electric appliances and robotic hands by simulating human finger gestures, offering its great potentials for wearable and multi‐functional electronic applications.