Core-sheath Structure Research Articles

Core-Sheath Fibers via Single-Nozzle Spinneret Electrospinning of Emulsions and Homogeneous Blend Solutions.

The preparation of core-sheath fibers by electrospinning is a topic of significant interest for producing composite fibers with distinct core and sheath functionalities. Moreover, in core-sheath fibers, low-molecular-weight substances or nanosized inorganic additives can be deposited in a targeted manner within the core or the sheath. Commonly, for obtaining a core-sheath structure, coaxial electrospinning is used. It requires a coaxial spinneret and suitable immiscible solvents for the inner and outer solutions. The single-nozzle spinneret electrospinning of emulsions can address these issues, but use of a stabilizing agent is needed. A third approach-preparation of core-sheath fibers by single-nozzle spinneret electrospinning of homogeneous blend solutions of two polymers or of a polymer/low-molecular-weight substance-has been much less studied. It circumvents the difficulties associated with the coaxial and the emulsion electrospinning and is thoroughly discussed in this review. The formation of core-sheath fibers in this case is attributed to phase-separation-driven self-organization during the electrospinning process. Some possibilities for obtaining core-double sheath fibers using the same method are also indicated. The gained knowledge on potential applications of core-sheath fibers prepared by single-nozzle spinneret electrospinning of emulsions and homogeneous blend solutions is also discussed.

Excellent thermal, moisture-permeable weft-knitted fabric with core-sheath yarn structure for foot protection in cold environments

In extremely cold environments, maintaining body temperature and reducing heat dissipation is essential for maintaining human health and life safety, but the field of thermal insulation shoe upper fabric has not been deeply studied. In this paper, based on the dual-scale structure of the yarn and shoe upper fabric, a composite yarn with a core-sheath structure is designed, and a using plating stitch pattern weft-knitted whole garment thermal insulation shoe upper fabric with double-layer structure is proposed. By testing the mechanical properties and thermal and moisture performance of the shoe upper fabric and the thermal insulation performance of the whole shoe, the thermal insulation mechanism of the weft-knitted whole garment shoe upper fabric with a double-layer structure and dual-scale structure design was systematically studied. The results show that the shoes made of polyimide/hollow polyester composite yarn with core-sheath structure yarn have good thermal insulation performance. The use of core-sheath yarns can improve the thermal insulation performance of the shoe, and, with the increase of the ratio of core-sheath yarn, the thermal insulation performance of the shoe is better. Starting from the dual-scale shoe fabric structure, this article proposes a novel method for the industrial production of thermal insulation shoe upper fabrics, which is expected to provide guidance for the further development of thermal insulation shoe upper fabric in the future.

Surface engineered covalent bridging strategy to in-situ fabricate MXene-based core-sheath fiber for flexible supercapacitors with ultrahigh volumetric energy density and mechanical properties

MXene fiber-based supercapacitors (SCs) are expected to make a major contribution to the ongoing development of wearable electronics and metaverse technologies in future. However, to fabricate fiber electrodes with high energy density and strong mechanical properties remains a major challenge for their usage in SCs. Herein, we fabricated a flexible core-sheath structural Ti3C2Tx MXene@polyaniline (MX@PA) fiber electrode with ultrahigh volumetric energy density and good tensile strength through surface engineered covalent bridging strategy via wet spinning and in situ oxidant-freepolymerization processes. Benefiting from the high-order core-sheath structure and strong Ti-O-N covalent bonds between MXene and PANI, an ultrahigh tensile strength (∼168.1 MPa) and super-toughed (∼1.75 MJ cm−3) fiber electrode was achieved. The assembled SC provided much higher volumetric capacitance of 631F cm−3 (based on the SC device) at a current density of 0.5 A cm−3 and ultralong-term cycling stability with 92.6 % capacitance retention after 10000 cycles due to the rapid electron conduction of core (MXene) and large pseudocapacitive charge transfer of the sheath (PANI). As a result, the SC delivers excellent volumetric energy density of 56.1 mWh cm−3 at a power density of 204.9 mW cm−3. The integrated SC found actual application to power a 2.5 V red LED.

High Areal Capacitance and Rate Capability of 3D-Printed Thick Electrodes with Optimized Conductive Networks from the Core-Sheath Structure.

Material extrusion 3D printing has received enormous attention to potentially overcome its limits by tailoring and designing thick electrodes. In this work, we prepared a thick reduced graphene oxide/carbon nanotube-reduced graphene oxide/carbon nanotubes/manganese oxide@carbon nanotubes (rGC-rGCMC) electrode with controlled lattice architectures, core-sheath structure, and hierarchical porosity by material coaxial extrusion 3D printing, freeze-drying, and thermal treatment. The volume ratios of core to sheath, including 100%-0%, 0%-100%, 20%-80%, 30%-70%, 40%-60%, and 50%-50%, were designed to investigate the influences of the core-sheath structure on thick electrodes. The electrodes with a core-sheath volume ratio of 30%-70% electrodes exhibited an enhanced areal specific capacitance of 588.27 mF cm-2 (39.48 F g-1) at a scan rate of 0.5 mA cm-2. All capacitance decays from core-sheath electrodes (20%-80%, 30%-70%, 40%-60%, and 50%-50%) were smaller than those from rGCMC (0%-100%) electrodes, indicating the improved rate capability from the core-sheath structure. On comparison of 30%-70% core-sheath electrodes with electrodes made of a homogeneous 30% rGC and 70% rGCMC mixture (30%+70%), lower capacitance (382.27 mF cm-2 and 25.66 F g-1 at 0.5 mA cm-2) of the 30%+70% mixture electrode without a core-sheath structure suggested less efficiency to harvest electrons from the redox reactions. Electrochemical impedance spectroscopy (EIS) data further supported and explained the resistances of thick electrodes with different volume ratios.

Flexible dual-mode pressure sensor for simultaneous dynamic-static sensing with wide-range detection and ultra-fast response speed

Flexible pressure sensors play a vital role in advancing the Internet of Things (IoT). However, piezoelectric sensors are limited in static pressure detection and suffer in achieving high flexibility and high sensitivity simultaneously, while piezoresistive sensors typically have slow response speeds and insensitive high-frequency detection ability. Here, we select a novel basalt fiber fabric (BFF) that can withstand high temperatures exceeding 1000 °C as a new substrate to enable one-step fabrication of piezoelectric layer based on coherently grown Pb(Zr0.52Ti0.48)O3 (PZT) thin films via a simple dipping method. The high piezoelectric coefficient g33 of 362.5 mV·m·N−1 and the unique core-sheath structure induced stress concentration on the PZT sheath enable the flexible piezoelectric layer (bending radius < 1.45 mm) to exhibit high sensitivity (voltage sensitivity of 2.766 V/kPa within the range of 0.11–11.11 kPa) and fast response speed (11 ms). The piezoresistive layer consisting of a three-dimensional porous elastic carbon nanotube-polyurethane sponge provides a detection range comparable to piezoelectric layer (0.11–66.67 kPa). A dual-mode flexible pressure sensor (DMFS) has been developed by integrating the piezoelectric layer with the piezoresistive layer. The DMFS exhibits an extended detection range compared to previous dual-mode pressure sensors, rapid response speed, and high sensitivity, which enables simultaneous detection of both dynamic and static pressures. The DMFS can be used for keyboard and movement posture recognition, which has significant application prospects in human-machine interaction.

Core-sheath PVDF hollow porous fibers via coaxial wet spinning for energy harvesting

Flexible piezoelectric nanogenerators (PENGs), as a promising sustainable power source in smart electronics, have attracted much attention for their potential applications in the Internet of Things. In this paper, poly(vinylidene fluoride) (PVDF) fibers with core-sheath hollow porous structure were prepared by coaxial wet spinning process, serving as the dielectric layer, which were perfused internally by liquid metal (LM) as the inner electrode layer and wrapped outside by copper-silver nanoparticles (Cu@AgNP) as the outer electrode layer, thus constructing high-performance PVDF/LM/Cu@AgNP composite fibers. The composite PVDF fibers have a layered pore structure and arbitrarily deformable LM electrodes, which can significantly reduce the effective electric constant and thus enhance the piezoelectric properties. The results reveal that PVDF/LM/Cu@AgNP-PENG yields an optimal voltage output of 410 mV, providing a clear advantage over PENG by using alternative fibers. Moreover, the PVDF/LM/Cu@AgNP-PENG shows an excellent charging capability for energy storage devices, being able to charge 1 μF capacitors to 10 V within 30 s and directly power commercial LEDs. This study demonstrates the significant potential for utilizing composite PVDF piezoelectric fibers in flexible wearable electronic devices.

Patterned, flexible, self-supporting humidity sensor with core-sheath structure for real-time sensing of human-related humidity

Self-supported nanofiber membranes were fabricated by the rhombus-patterned collector in the electrospinning process in this work. The rhombus nanofiber networks were used to retain the mechanical flexibility of the device and stable responses such as bending and winding deformation. A resistive humidity sensor was developed by applying hydrophilic PANI with varying contents onto nanofiber surfaces through in situ polymerization, serving as electrodes. In this context, the self-supported membranes serve dual roles as both the sensing material and the substrate for the sensor. A comprehensive assessment was conducted to analyze how variations in relative humidity affect the sensing characteristics of the acquired sensors. By facilely regulating the ratio of dopant and oxidant concentration to monomer concentration in the polymerization process, the response of the sensors was increased from 49% to 83% with increasing relative humidity from 13% to 93%, good linearity (R2 = 0.97) and a short response/recovery times (33/88 s). The prepared sensors exhibited appreciable mechanical properties and showed outstanding stability after 1000 cycles of bending and the resistances only slightly increased by 2.5%. Moreover, the sensor can monitor both human respiration and non-contact skin humidity. Its exceptional performance makes it easily integrable into textiles for the creation of wearable electronics.

Core-sheath smart polymer fiber composites with high elasticity and thermal conductivity

Thermal conductive polymer fibers have broad development prospects because of its excellent thermal and mechanical properties. However, currently reported polymer fibers cannot simultaneously possess high thermal conductivity and high resilience, which greatly limits the application of thermal conductive polymer fibers. Therefore, preparing fibers with high thermal conductivity and high resilience is extremely challenging. The thermoplastic polyurethane/boron nitride liquid metal (TPU/BN-LMs) fiber with core sheath structure is prepared by coaxial wet spinning technology, the boron nitride (BN) doped in thermoplastic polyurethane elastomer (TPU) as sheath and the liquid metal (LMs) as core. The maximum tensile strength of the fiber is 3.9 MPa, and the elongation can reach 400 %. After multiple cycles of stretching, it can return to its original state. In addition, the thermal conductivity of the fiber in the horizontal direction and the vertical direction are 10.0 W m−1 K−1 and 4.6 W m−1 K−1, respectively. This work solves the current problem of high thermal conductivity and high resilience of thermally conductive polymer fibers that are difficult to be compatible. And it provides a new research idea for the design and preparation of new high thermal conductivity and high resilience polymer fiber materials.

Centrifugally spun superhydrophobic fibrous membranes with core-sheath structure assisted by hyper branched polymer and via click chemistry for high efficiency oil–water separation

Superhydrophobic fibrous membranes have been widely investigated to treat oily wastewater originated from oil spills and industrial organic pollutants. However, the applications of these membranes are usually limited by complex preparation process, high modification cost, and poor durability. In this research, we developed a cost-saving approach to construct the fiber with core-sheath structure by using centrifugal spinning, which was based on the viscosity difference of Polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), hyperbranched unsaturated polyester (HBPU). Subsequently, the hydrophobic long chain was attended on fiber surface through the mercaptan click reaction induced by ultraviolet light, which were assisted by the plenty of double bonds supplied by HBPU. Due to the coarse structure and low surface energy of the treated fibers, the fibrous membranes exhibited super hydrophobic properties for the water contact angle high as 156°. The separation capacity for water-in-oil emulsions were up to 7562.24 L·m−2·h−1 for the flux and separation efficiency were up to 99.27 %. Additionally, the flux and separation efficiency exhibited no significant changes over 50 cycles. Therefore, we provided a unique and straightforward technique for producing superhydrophobic separation fibrous membranes.

A facile method for continuous production of temperature-adaptive hyperthermal management core-sheath polyurethane nanofiber yarns based on vanadium dioxide toward commercialization

As a facile method for producing nanofiber materials, electrospinning is widely used in various fields. However, it is generally adopted for fabricating nonwoven nanofiber membranes, which limited its applications. In this study, we propose a new facile mechanism for continuous production of high-strength electrospinning nanofiber-covered yarns, which can be directly used for fabric weaving toward commercialization. After doping of vanadium dioxide(VO2), a solid–solid phase change material (PCM) with a phase change temperature close to room temperature, a smart nanofiber-covered yarn with hyperthermal management capability is obtained. Benefiting from the delicate core-sheath structure and rigorous adjustment of spinning solution composition as well as spinning parameters (including spinning voltage, solution flow rate, and spinning distance), it achieved optimal nanofiber diameter at 510 nm, and patterns sewn on polyester fabric can be lowered by up to 19 °C compared to polyester fabric. The nanofiber-covered yarn can be used for textiles such as garments and curtains, which helps reduce the tremendous energy consumed for thermal regulation.

Hydrophilic and hydrophobic drug release from core (polyvinylpyrrolidone)-sheath (ethyl cellulose) pressure-spun fibers

A core-sheath structure is one of the methods developed to overcome the challenges often faced when using monolithic fibers for drug delivery. In this study, fibers based on polyvinylpyrrolidone (core) and ethyl cellulose (sheath) were successfully produced using a novel core-sheath pressure-spinning process. For comparison, these two polymers were also processed into as blend fibers. All samples were then investigated for their performances in releasing water-soluble ampicillin (AMP) and poorly water-soluble ibuprofen (IBU) model drugs. Scanning electron,digital and confocal microscopy confirmed that fibers with a core-sheath structure were successfully made. Fourier transform infrared spectroscopy showed the success of the pressure-spinning technique in encapsulating AMP/IBU in all fiber samples. Compared to blend fibers, the core-sheath fibers had better performance in encapsulating both water-soluble and poorly water-soluble drugs. Moreover, the core-sheath structure was able to reduce the initial burst release and provided a better sustained release profile than the blend fiber analog. In conclusion, the pressure-spinning method was capable of producing core-sheath and blend fibers that could be used for the loading of either hydrophilic or hydrophobic drugs for controlled drug delivery systems.

PVDF-based nanofiber membrane decorated with Z-scheme TiO2/MIL-100(Fe) heterojunction for efficient oil/water emulsion separation and dye photocatalytic degradation

Membrane separation is one of the most widely used methods for water purification, but membrane fouling is a stumbling block that must be overcome for its further promotion and application. In this work, a self-cleaning PVDF-based hybrid nanofiber membrane with core-sheath structure were constructed via electrospinning and in-situ synthesis, using polyvinylidene fluoride/polyvinyl pyrrolidone (PVDF-PVP) electrospun nanofibers as skeleton cores and in-situ synthesis of Z-scheme TiO2/MIL-100(Fe) heterojunctions as photocatalytic sheaths. The hybrid membrane exhibited excellent superhydrophilicity (water contact angle of 0°) and underwater superoleophobicity (underwater oil contact angle of 161.4°) with high permeate fluxes and superior separation efficiencies (more than 99.5%) for various oil/water emulsions. Furthermore, the Z-scheme TiO2/MIL-100(Fe) heterojunctions anchored on the nanofibers possessed robust photocatalytic activity with the removal efficiency of dyes up to 99.9% under simulated sunlight. More importantly, the membrane has excellent recyclability due to its outstanding anti-fouling and self-cleaning properties. Therefore, the hybrid membrane has attractive potential application in wastewater purification.

Application of Electrospun Drug-Loaded Nanofibers in Cancer Therapy.

In the 21st century, chemotherapy stands as a primary treatment method for prevalent diseases, yet drug resistance remains a pressing challenge. Utilizing electrospinning to support chemotherapy drugs offers sustained and controlled release methods in contrast to oral and implantable drug delivery modes, which enable localized treatment of distinct tumor types. Moreover, the core-sheath structure in electrospinning bears advantages in dual-drug loading: the core and sheath layers can carry different drugs, facilitating collaborative treatment to counter chemotherapy drug resistance. This approach minimizes patient discomfort associated with multiple-drug administration. Electrospun fibers not only transport drugs but can also integrate metal particles and targeted compounds, enabling combinations of chemotherapy with magnetic and heat therapies for comprehensive cancer treatment. This review delves into electrospinning preparation techniques and drug delivery methods tailored to various cancers, foreseeing their promising roles in cancer treatment.

Pulp cellulose-based core–sheath structure based on hyperbranched grafting strategy for development of reinforced soybean adhesive

Formaldehyde adhesive is the primary source of indoor formaldehyde pollution, posing a serious threat to human health. Soybean meal (SM), as an abundant biomacromolecule and co-product of soybean oil industry, emerges as a promising alternative to formaldehyde adhesive. However, the SM adhesive exhibits inferior water resistance and unsatisfactory bonding strength. In this study, a novel core–sheath structure with an inexpensive pulp cellulose core and a hyperbranched polymer sheath is synthesized and introduced into SM to develop a robust bio-based adhesive. Specifically, aldehyde-functionalized pulp cellulose is grafted with hyperbranched polyamide, which is terminated via epoxy groups, to synthesize a core–sheath hybrid (APC@HBPA-EP). The core–sheath APC@HBPA-EP serves as both a crosslinker and an enhancer. The results show that the wet shear strength of the modified SM adhesive exhibits a remarkable 520 % increase to 0.93 MPa, and its dry shear strength reaches 2.10 MPa, meeting the established indoor use standards. The Young's modulus of the modified SM adhesive shows a significant 282 % increase to 19.27 GPa. Additionally, the modified SM adhesive exhibited superior impact toughness (7.48 KJ/m2), which increased by 24 times compared with pure SM adhesive. This study provides a versatile strategy for developing robust protein adhesives, hydrogel patch, and composite coatings.

Interfacial polymerization of PEDOT sheath on V2O5 nanowires for stable aqueous zinc ion storage

Interfacial polymerization of 3,4-ethylenedioxythiophene (EDOT) on V2O5 nanowires generates the V2O5@PEDOT core-sheath structure, which enhances conductivity, suppresses electrode dissolution, and stabilizes V2O5 nanowires for zinc ion storage.

Thermoregulatory elasticity braided fibers designed with core–sheath structure for wearable personal thermal management

The thermoregulatory elasticity fiber was designed and fabricated using coaxial wet spinning, which combines solar-thermal and phase-change energy. This exploration presents a strategy to develop smart fabrics for personal thermal management.

Friction spun spandex/rGO/Ag/polyester core-sheath yarn with antibacterial activity for wearable sensors

Wearable sensors, which feature textile substrates integrated with conductive layers, have received increasing attention from researchers due to their huge potential in health management. However, the inevitable damage of conductive layer caused by friction and bacterial growth on the textile substrate during its direct contact with bare skin are still the issues that hinder the long-term service of wearable sensors. Herein, a core-sheath yarn was prepared by wrapping polyester (PET) fibers coated with reduced graphene oxide (rGO)/silver nanoparticles (Ag NPs) around the spandex filaments via friction spinning. The core-sheath structure guarantees good prevention of the interface composed of rGO and Ag NPs in between from friction, while the introduction of Ag NPs ensures antibacterial activity of the yarn. The morphology and chemical composition of the nanomaterials deposited on the surface of PET fibers was investigated to reveal the sensing mechanism of the yarn. Meanwhile, its sensing performance was comprehensively evaluated from the perspectives of sensitivity, durability and comparison of commercial ECG. Despite the fact that inevitable damage of the rGO/Ag layer occurred during the friction spinning process, the core-sheath yarn still featured a gauge factor of 8.11 and a threshold of sensing range up to 68.57 %. Apart from being able to detect respiratory signals, cardio signals with the frequency of 70 beat per min (bpm) was also recorded. Compared to signals with the frequency of 73 bpm recorded by a commercial ECG sensor simultaneously, the core-sheath yarn exhibited satisfying precision. Moreover, the existence of Ag NPs in the conductive interface endowed the yarn with ability to yield 13-mm and 15-mm wide growth inhibition zones of E. coli and S. aureus, respectively. The cardiorespiratory sensing ability coupled with antibacterial activity of the yarn suggested its satisfying sensitivity and prolonged service time, making it a promising wearable sensor subjected to direct skin contact for long-time cardiorespiratory monitoring.

Superhydrophobic and breathable polydimethylsiloxane/nano-SiO2@polylactic acid electrospun membrane with core-sheath fiber structure

Polylactic acid (PLA) has great potential to replace traditional petroleum-based polymers, especially in membrane production, due to its biocompatibility, degradability, and renewability. However, there are rare reports of superhydrophobic and breathable PLA membranes. In this work, a multifunctional PDMS/SiO2@PLA membrane with superhydrophobicity and breathability was prepared by coaxial electrospinning method to coat the surface of PLA fiber with a thin layer of biocompatible polydimethylsiloxane (PDMS) and nano-silica particles. The prepared membrane has a water contact angle (WCA) of 151.8 ± 1.3° and a water sliding angle (WSA) of 5.7 ± 0.3°. Thanks to its superhydrophobicity, it can support a water column of 195 cm. The membrane has excellent breathability that its water vapor transmission rate is ~14.7 kg·m−2·24 h−1. Moreover, the freezing time of the membrane is 2.25 times longer than that of the original PLA membrane. In addition, it has an oil-water separation efficiency of 99.9 % and a flux of ~12,300 L·m−2·h−1. The overall performance of this multi-functional PDMS/SiO2@PLA membrane is one of the best among the fluorine-free electrospun membranes.

Liquid Crystal Elastomer Artificial Tendrils with Asymmetric Core-Sheath Structure Showing Evolutionary Biomimetic Locomotion.

The sophisticated and complex haptonastic movements in response to environmental-stimuli of living organisms have always fascinated scientists. However, how to fundamentally mimic the sophisticated hierarchical architectures of living organisms to provide the artificial counterparts with similar or even beyond-natural functions based on the underlying mechanism remains a major scientific challenge. Here, liquid crystal elastomer (LCE) artificial tendrils showing evolutionary biomimetic locomotion are developed following the structure-function principle that is used in nature to grow climbing plants. These elaborately designed tendril-like LCE actuators possess an asymmetric core-sheath architecture which shows a higher-to-lower transition in the degree of LC orientation from the sheath-to-core layer across the semi-ellipse cross-section. Upon heating and cooling, the LCE artificial tendril can undergo reversible tendril-like shape-morphing behaviors, such as helical coiling/winding, and perversion. The fundamental mechanism of the helical shape-morphing of the artificial tendril is revealed by using theoretical models and finite element simulations. Besides, the incorporation of metal-ligand coordination into the LCE network provides the artificial tendril with reconfigurable shape-morphing performances such as helical transitions and rotational deformations. Finally, the abilities of helical and rotational deformations are integrated into a new reprogrammed flagellum-like architecture to perform evolutionary locomotion mimicking the haptonastic movements of the natural flagellum.

Heterostructure design of one-dimensional ZnO@CoNi/C multilayered nanorods for high-efficiency microwave absorption

Dimensional design and heterogeneous interface engineering are promising approaches for the fabrication of superior absorbers with high loss performance and a wide effective bandwidth. Therein, ZnO nanorods were successfully synthesized and combined with CoNi nanosheets by hydrothermal method, and PDA was then encapsulated on the surface of the material to form a unique one dimensional (1D) core-sheath structure. The extensive defects and residual functional groups are present in the calcined material, as well as the multiple heterogeneous interfaces enhance the dielectric loss induced by polarization. Simultaneously, the 1D structure wrapped with PDA offers an efficient pathway for electron transfer, hence facilitating the enhancement of conductive loss. In addition, the CoNi-LDHs sheet layer stacked on the surface not only causes multiple scattering and reflections of electromagnetic waves, but also provides magnetic losses to optimize the impedance matching. Finally, radar cross section (RCS) simulations further reveal that the composite can dissipate electromagnetic energy in practical applications. Consequently, the 1D multilayer ZnO@CoNi/C composite exhibits an optimal reflection loss of −55 dB with a thickness of 2.3 mm and an effective absorption bandwidth (EAB) value of 6.8 GHz when the filling ratio is only 20 wt%. In summary, this paper provides a new direction for the fabrication of 1D multilayer nonhomogeneous interfacial absorbers with excellent performance.