Study uses electrospun nanofibers to improve flexible piezoelectric sensors

Flexible piezoelectric sensors are essential to monitor the motions of both humans and humanoid robots. However, existing designs are either costly or have limited sensitivity.

In a recent study, researchers from Japan tackled these issues by developing a novel piezoelectric composite material made from electrospun polyvinylidene fluoride nanofibers combined with dopamine. Sensors made from this material showed significant performance and stability improvements at a low cost, promising advancements in medicine, health care, and robotics.

Their study, which was led by Distinguished Professor Ick Soo Kim in association with Junpeng Xiong, Ling Wang, Mayakrishnan Gopiraman, and Jian Shi, is published in Advanced Fiber Materials.

The world is accelerating rapidly towards the intelligent era—a stage in history marked by increased automation and interconnectivity by leveraging technologies such as artificial intelligence and robotics. As a sometimes-overlooked foundational requirement in this transformation, sensors represent an essential interface between humans, machines, and their environment.

However, now that robots are becoming more agile and wearable electronics are no longer confined to science fiction, traditional silicon-based sensors won't make the cut in many applications. Thus, flexible sensors, which provide better comfort and higher versatility, have become a very active area of study.

Piezoelectric sensors are particularly important in this regard, as they can convert mechanical stress and stretching into an electrical signal. Despite numerous promising approaches, there remains a lack of environmentally sustainable methods for mass-producing flexible, high-performance piezoelectric sensors at a low cost.

Against this backdrop, a research team from Shinshu University, Japan, decided to step up to the challenge and improve flexible piezoelectric sensor design using a well-established manufacturing technique: electrospinning.

The proposed flexible sensor design involves the stepwise electrospinning of a composite 2D nanofiber membrane. First, polyvinylidene fluoride (PVDF) nanofibers with diameters on the order of 200 nm are spun, forming a strong uniform network that acts as the base for the piezoelectric sensor.

Then, ultrafine PVDF nanofibers with diameters smaller than 35 nm are spun onto the preexisting base. These fibers become automatically interweaved between the gaps of the base network, creating a particular 2D topology.

After characterization via experiments, simulations, and theoretical analyses, the researchers found that the resulting composite PVDF network had enhanced beta crystal orientation.

By enhancing this polar phase, which is responsible for the piezoelectric effect observed in PVDF materials, the piezoelectric performance of the sensors was significantly improved. To increase the stability of the material further, the researchers introduced dopamine (DA) during the electrospinning process, which created a protective core–shell structure.