Electrospinning Machine| Janus Electrospun Membranes

Have you ever imagined a membrane that simultaneously possesses dual properties like superhydrophobicity/superhydrophilicity or conductivity/insulation? Or clothing that can provide both warmth and cooling? In the fascinating world of materials science, Janus electrospun membranes (JEM) are revolutionizing our understanding of traditional fabrics with their "two-faced" properties. This innovative material, combining electrospinning technology with Janus asymmetric design, is driving a technological revolution in functional clothing, clean energy, and smart sensing.

Recently, Professor Yang Lumeng and Researcher Si Yifan from Sichuan University, along with Professor Hu Jinlian from City University of Hong Kong, published a cutting-edge review titled "Janus Electrospun Membranes" in the top journal Advanced Materials. The article defines the scope and classification of JEM, reviews its applications in functional clothing, clean energy, and smart sensing, and provides in-depth analysis of its construction methods, functional principles, and key mechanisms in various application scenarios. Finally, it discusses the practical challenges and technical bottlenecks JEM faces in large-scale production, performance optimization, and interdisciplinary applications, aiming to provide researchers with potential guidance and inspiration to promote technological breakthroughs and industrial upgrading of JEM technology.

Figure 1: JEM overview.

Exquisite Design: JEM Structural Construction Strategies
The fabrication of Janus electrospun membranes (JEM) hinges on achieving precise asymmetry control, with three primary design strategies currently employed (Figure 2):

Figure 2: JEM construction strategies.

Multilayer Structure DesignThe most widely adopted approach utilizes sequential electrospinning to deposit nanofiber layers with distinct properties. In laboratory settings, simply alternating spinning solutions and adjusting parameters enables multilayer JEM fabrication on a single substrate. For industrial-scale production, roll-to-roll electrospinning technology facilitates continuous manufacturing, establishing the foundation for large-scale applications.

Composite Structure DesignThis hybrid strategy combines electrospinning with complementary techniques to leverage their respective advantages. When electrospinning serves as the primary method, functional coatings can be constructed on nanofiber membranes. Conversely, when employed as a secondary process, electrospun nanofiber layers modify substrate properties—for instance, enhancing thermal insulation when applied to heat management materials. This approach represents the most practical and widely implemented solution.

Single-layer Structure DesignThe most technically demanding strategy eliminates delamination risks through monolithic construction, significantly improving JEM durability. However, achieving controlled asymmetry across scales ranging from hundreds of nanometers to micrometers presents substantial challenges. Innovative techniques like single-side plasma treatment and real-time spinning solution ratio modulation have enabled wettability gradients within unitary membranes. Nevertheless, this method generally suffers from low controllability and remains exceptionally difficult to execute.

Core Challenge: Enhancing Interlayer Bonding Strength
The biggest challenge for multilayer JEM is weak interlayer bonding, which makes it prone to delamination and fracture during use. Researchers have developed various physical and chemical strategies to address this issue (Figure 3): 

Figure 3: JEM interlayer bonding enhancement strategies.

Physical strategies include pressurization, ultrasound, and structural design. Hot pressing enhances interlayer bonding by partially melting polymers at high temperatures and then cooling, but may damage the porous structure of nanofibers. Ultrasonic welding uses frictional heat generated by high-frequency mechanical vibrations to achieve localized melting and bonding, offering advantages of low energy consumption and precise positioning. Co-spinning technology allows nanofibers from different layers to intertwine during the spinning process, forming a structure similar to "molecular entanglement," which may fundamentally prevent delamination. 

Chemical strategies mainly rely on crosslinking reactions to enhance interlayer forces. For example, heat treatment can create stronger interactions between SEBS polymer chains, or dopamine's super adhesion can be used to form coatings on fiber surfaces to promote chemical bonding between layers. These methods can significantly improve the mechanical properties of membranes but require precise control of reaction sites and conditions, presenting greater technical challenges. 

Balancing the relationship between porosity, bonding strength, and flexibility is the key to optimizing interlayer bonding design. 

Diverse Applications: From Functional Clothing to Smart Devices
The asymmetric properties of Janus electrospun membranes give them unique advantages in multiple fields: 

Unidirectional moisture transport is one of the most representative applications of JEM. Based on the asymmetric design of hydrophilic-hydrophobic porous structures, liquids can penetrate from the hydrophobic surface to the hydrophilic layer but not vice versa. This property is widely used in functional clothing to direct sweat from the body to the outer layer of the fabric and accelerate evaporation, achieving passive cooling. In wound dressings, the hydrophobic layer of JEM keeps the wound dry, while the hydrophilic layer absorbs exudate, accelerating the healing process (Figure 4).

Figure 4: Mechanism and applications of JEM with unidirectional moisture transport.

Janus-energized membranes (JEMs) also demonstrate significant applications in the energy and environmental sectors. In photocatalysis, bilayer JEMs with asymmetric wettability can effectively enhance oxygen transport to active reaction sites, thereby improving the efficiency of photocatalytic oxygen reduction for hydrogen peroxide production. For membrane distillation, JEMs address the fouling issues prevalent in conventional membranes. Furthermore, JEM technology shows great potential in fog water harvesting, metal extraction, and other emerging fields.

Smart sensing and flexible electronics represent another key application area for Janus-energized membranes (JEMs). By engineering asymmetric conductive structures, JEMs can be utilized to develop piezoelectric/triboelectric nanogenerators that efficiently convert mechanical energy into electricity. In the field of flexible conductors, the integration of liquid metals with JEMs has led to groundbreaking advancements.

In the field of thermal regulation, Janus-energized membranes (JEMs) leverage asymmetric design of physical properties—such as thermal conductivity, transmittance, and reflectivity—to achieve simultaneous heating and cooling functions within a single garment.

Figure 5: Applications of JEM based on thermal conductivity asymmetry.

Future Prospects: Challenges and Opportunities
While Janus electrospun membranes demonstrate immense potential, their development still faces multiple challenges. Critical issues requiring resolution include: industrial-scale equipment design for multilayer JEM production, further enhancement of interlayer bonding strength, and the standardization/popularization of JEM concepts. Future breakthroughs may emerge through: development of novel polymeric materials, design of porous connective interlayers, and AI-optimized fabrication processes.

The large-scale integrated production will be pivotal for the industrialization of Janus-energized membranes (JEMs). Next-generation multifunctional electrospinning production lines should encompass the entire workflow - from polymer solution preparation to final product output - featuring modular designs for flexible configuration (Fig. 6). As the technology matures, JEMs are poised to enable transformative applications across smart textiles, wearable devices, and environmental remediation, ultimately bringing disruptive innovations to our daily lives.

Paper link: https://advanced.onlinelibrary.wiley.com/doi/10.1002/adma.202507498