The study, published in the journal Advanced Composites and Hybrid Materials, was led by Ki-Hyun Ryu and Sungju Lee of the Korea Institute of Science and Technology, together with colleagues across several KIST research centers. Their central insight is deceptively simple: instead of trying to push ions into a densely packed nanotube fiber after the fact, why not build molecular-scale breathing room into the material from the very beginning? The answer they arrived at relies on a thermodynamically driven co-assembly process borrowed from the world of liquid crystals, a field more often associated with display screens than with supercapacitors.

To understand why the problem matters, it helps to picture what happens inside a conventional carbon nanotube fiber. Individual nanotubes, each essentially a rolled-up sheet of graphene a few nanometers wide, are drawn together into bundles, and those bundles are packed into a fiber with inter-bundle spacing measured at the molecular scale. This ultra-dense arrangement maximizes the contact between tubes, which is exactly what you want for load transfer and for electrons hopping from one tube to the next. But for electrochemical applications, the picture inverts. Ions from an electrolyte can only access the outermost surfaces of the fiber; the deep internal channels between bundles remain inaccessible, so the enormous theoretical surface area of the nanotubes goes largely unused. Materials scientists have long described this as a packing-accessibility trade-off, and it has been a persistent bottleneck in translating the extraordinary properties of individual nanotubes into practical devices.

The Korean team’s strategy attacks the problem at the molecular level using soft poly(vinyl alcohol), or PVA, chains. PVA is a hydrophilic, water-soluble polymer, and the researchers exploited its strong non-covalent adsorption onto carbon nanotube surfaces to intercalate the polymer chains directly into the nanotube bundles during fiber formation. Because the process occurs during a lyotropic liquid crystalline co-assembly stage, the rigid nanotubes retain the high axial alignment that is essential for efficient electron transport along the fiber, while the flexible polymer chains wedge themselves between the bundles and hold the channels open. The researchers describe the resulting architecture as unlocked, in the sense that the interstitial channels that would normally collapse into dense packing are instead molecularly secured at a controlled spacing.

The thermodynamics of this intercalation are worth appreciating. When long, flexible polymer chains are confined between rigid nanotubes, they lose some conformational entropy, but the strong adsorption energy between the polymer and the carbon surface compensates for that loss, driving the hybrid structure to self-assemble spontaneously. Once in place, the entropic relaxation of the soft chains, their tendency to coil and spread, effectively props open the interstitial channels without any external scaffolding, template, or post-processing step. This bottom-up approach stands in contrast to more common strategies that graft bulky functional groups onto nanotube walls or hybridize the fibers with additional active materials, both of which can disrupt the intrinsic structure of the nanotubes or add complexity and cost to manufacturing.

The benefits of the unlocked architecture extend beyond simple spacing. Carbon nanotube surfaces are inherently hydrophobic, which impedes wetting by aqueous electrolytes and further limits ion access. The intercalated PVA chains, being hydrophilic, impart wettability to the composite fiber, so electrolyte ions are not only given physical pathways into the interior but are also chemically encouraged to penetrate. In effect, the polymer performs double duty: it acts as a molecular spacer that maintains the channels, and it converts the fiber’s internal environment from one that repels electrolytes to one that welcomes them. The dormant internal volume of the fiber, previously inaccessible, becomes an active participant in electrochemical processes.

The quantitative evidence for this internal activation is striking. When the researchers measured the electrochemical performance of their composite fibers, they found an 11.2-fold enhancement in specific capacitance compared with pristine carbon nanotube fibers. Specific capacitance is a direct measure of how much charge a material can store per unit mass, and an improvement of more than an order of magnitude indicates that ions are genuinely reaching the deep core of the fiber rather than merely decorating its surface. The composite fibers also showed superior rate performance, meaning they retained much of their charge-storage capability even when charged and discharged rapidly. Rate capability is a sensitive probe of ion diffusion resistance: if ions had to fight their way through dense packing, performance would collapse at high rates. The fact that it did not confirms that the engineered channels substantially mitigate diffusion resistance throughout the fiber’s cross-section.

What makes this work particularly significant is its generality. The authors frame their methodology as a universal design paradigm for next-generation composite materials that require dynamic ion transport. Dense assemblies of one-dimensional nanomaterials are not limited to carbon nanotubes; nanowires, nanofibers, and other elongated building blocks face the same packing-accessibility dilemma whenever they are assembled into macroscopic forms. A spacing strategy that works during co-assembly, requires no complex active-material hybrids, and preserves the intrinsic structure of the constituent nanomaterials could therefore be applied far beyond the supercapacitor context in which it was demonstrated here. The approach also avoids covalent modification of the nanotubes, which is important because covalent chemistry on carbon surfaces introduces defects that degrade the electrical conductivity that makes nanotubes valuable in the first place.

The research was carried out at the Advanced Conductive Materials Research Center, the Carbon Composite Materials Research Center, and the Functional Composite Materials Research Center of the Korea Institute of Science and Technology in Wanju, Republic of Korea. It was supported by the Nano and Material Technology Development Programs through the National Research Foundation of Korea, funded by the Ministry of Science and ICT, as well as by a KIST Institutional Program. The work was published as an open-access article on 10 September 2026, making the full technical details freely available to researchers worldwide.

For a field that has spent decades chasing ways to make carbon nanotube assemblies live up to their nanoscale promise, the message of this study is refreshingly constructive. Rather than treating dense packing as an unavoidable compromise, the researchers showed that molecular-level design, using nothing more exotic than a soft polymer and the thermodynamics of liquid crystalline assembly, can unlock the hidden interior of a nanotube fiber while keeping its celebrated strength and conductivity intact. If the strategy proves as transferable as the authors suggest, the dense-but-dead interiors of one-dimensional nanomaterial assemblies may soon become some of the most valuable real estate in materials science.

Subject of Research: Liquid crystalline co-assembly of carbon nanotube and poly(vinyl alcohol) hybrid fibers to open interstitial channels for enhanced interfacial ion transport

Article Title: Bottom-up co-assembly of carbon nanotube and soft polymer hybrids: unlocking interstitial channels for enhanced interfacial ion kinetics

Article References: Ryu, K.-H., Lee, S., Lim, S.-I., Kim, S. G., Kim, S. M., Kim, N. D., Hwang, J. Y., Moon, S. Y., Yu, H., Jeong, H. S., & Kim, D.-Y. (2026). Bottom-up co-assembly of carbon nanotube and soft polymer hybrids: unlocking interstitial channels for enhanced interfacial ion kinetics. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02076-z

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02076-z

Keywords: carbon nanotubes, poly(vinyl alcohol), liquid crystals, co-assembly, nanocomposites, composite fibers, interstitial channels, ion diffusion, specific capacitance, supercapacitors, soft matter, Korea Institute of Science and Technology

Polyvinylidene difluoride, or PVDF, has long been a favorite of flexible electronics engineers because it combines the mechanical resilience of a plastic with genuine piezoelectric behavior. The catch is that piezoelectricity in PVDF depends entirely on which of its several crystal phases dominates. The nonpolar alpha phase, which forms under ordinary processing conditions, contributes essentially nothing to energy conversion. The polar beta phase, in which the fluorine and hydrogen atoms on the polymer chain are arranged so that each unit cell carries a permanent dipole moment, is the phase that actually generates charge when the material is stretched or compressed. In untreated electrospun PVDF fibers, the beta-phase fraction typically hovers around two-thirds of the crystalline content, leaving considerable room for improvement.

The Pakistani-led team attacked this problem by dispersing BST particles throughout the polymer solution before electrospinning it into fibers. Electrospinning itself already helps: the intense electric field applied as the polymer jet is drawn toward the collector stretches the chains and encourages them to fold into the polar beta configuration. The researchers found that the ceramic particles act as nucleation sites that amplify this effect. Their negatively charged surfaces attract the positively polarized CH2 groups of the PVDF chains, locking the polymer into the all-trans beta conformation as the fiber solidifies. The result, confirmed by both X-ray diffraction and Fourier transform infrared spectroscopy, was an increase in beta-phase content from roughly 65.7 percent in pristine PVDF fibers to about 87.4 percent at the optimal filler loading.

That optimum turned out to be 30 weight percent BST. The team systematically tested loadings of 10, 20, 30, 40, and 50 weight percent, and the structural measurements showed the polar fraction rising steadily up to the 30 percent mark before declining again at higher concentrations. The decline at high loadings is a familiar pattern in composite piezoelectrics: once too much ceramic is packed into the matrix, the particles begin to agglomerate, disrupting the polymer chains instead of aligning them and simultaneously making the fibers stiffer and more brittle. The sweet spot balances nucleation benefits against these aggregation penalties, and the spectroscopic data pinpointed it precisely.

The electrical payoff was substantial. Piezoelectric nanogenerators built from the optimized 30 percent BST/PVDF composite fibers delivered an open-circuit voltage of about 23.3 volts and a short-circuit current density of roughly 0.194 milliamperes per square meter, with a maximum power density of approximately 4.52 milliwatts per square meter measured at a load resistance of 60 megaohms. By comparison, devices made from the pristine PVDF fibers produced an open-circuit voltage of only about 11.8 volts, a current density of about 0.118 milliamperes per square meter, and a peak power density near 1.39 milliwatts per square meter at 50 megaohms. In other words, the ceramic additive roughly doubled the voltage and more than tripled the power output, a leap that stems directly from the higher density of aligned dipoles available to respond to mechanical strain.

The mechanism behind this enhancement involves more than simple nucleation. Barium titanate is itself a classic ferroelectric perovskite, and substituting a small fraction of strontium for barium modifies its lattice in ways that previous studies have linked to improved piezoelectric and dielectric response. When the BST particles are embedded in the polar polymer matrix, local electric fields around the ceramic inclusions interact with the dipoles of the surrounding PVDF chains, and the electrospinning process ensures that both components are oriented along the fiber axis. The composite therefore benefits from the flexibility and processability of the polymer alongside the strong polarization of the ceramic, with the interface between the two phases acting as the critical region where charge transfer and dipole coupling take place.

To demonstrate that the devices could do real work, the researchers connected their nanogenerators to practical loads. The BST/PVDF fiber devices were able to illuminate multiple light-emitting diodes and to power a digital multimeter and a hygrometer, the kind of low-power electronics that define the growing internet of things. This demonstration matters because many piezoelectric energy harvesters reported in the literature produce impressive voltage numbers on an oscilloscope but deliver too little current or power to drive anything tangible. Showing that the composite fibers can sustain multiple LEDs and run measurement instruments places the material firmly in the category of functional, application-ready energy harvesters rather than laboratory curiosities.

The broader context is the surging demand for sustainable power sources in flexible and wearable devices. Sensors for health monitoring, motion tracking, and environmental measurement are proliferating, but batteries impose weight, rigidity, charging requirements, and eventual disposal problems. Piezoelectric nanogenerators offer an alternative: they scavenge energy from the very motions that the devices experience, whether that is a footstep, a heartbeat, a breeze, or the flexing of a fabric. PVDF-based systems are particularly attractive for these roles because they are lead-free, unlike the widely used lead zirconate titanate ceramics, and because electrospinning can produce them as soft fiber mats that integrate naturally into textiles and conformal coatings. The challenge has always been output, and the BST strategy reported here represents a straightforward, scalable route to closing that gap.

The choice of strontium doping level also reflects a deliberate design decision grounded in the ceramics literature. Prior work on Ba1-xSrxTiO3 systems has shown that modest strontium substitution can tune the ferroelectric transition temperature and enhance piezoelectric coefficients in the resulting ceramics, while higher substitution levels shift the material toward different structural regimes. By fixing the composition at Ba0.96Sr0.04TiO3, the team selected a formulation with favorable polarization characteristics and then focused their optimization effort on the parameter that mattered most for the composite: the filler concentration. This two-stage design logic, tuning the ceramic first and the composite second, offers a template that other groups working on related systems, from KNN/PVDF to PZT/PVDF composites, can readily adapt.

Funded in part by the Higher Education Department of Khyber Pakhtunkhwa through its Higher Education Research Endowment Fund, and carried out in the Nano Physics Laboratory at Abdul Wali Khan University Mardan, the study adds to a rapidly expanding body of work on PVDF composite fibers for energy harvesting. The authors suggest that their BST/PVDF composite fibers could serve as high-efficiency piezoelectric materials for sustainable energy sources in flexible electronic devices, and the numbers support that claim. With beta-phase content near 87 percent, voltages above 23 volts, and power densities exceeding 4.5 milliwatts per square meter from a lead-free, textile-compatible platform, the material brings self-powered wearables a practical step closer to reality, and it does so using processing techniques that are already compatible with large-scale fiber manufacturing.

Subject of Research: Strontium-doped barium titanate enhancement of beta-phase PVDF composite fibers for flexible piezoelectric energy harvesting

Article Title: Barium strontium titanate induced β-phase enhancement in electrospun polyvinylidene difluoride composite fibers for high-efficiency flexible piezoelectric nanogenerators

Article References: Khan, S., Din, J. U., Shah, S. K., Ali, N., Saleem, S., Yousaf, J., Rauf, M., & Hayat, K. (2026). Barium strontium titanate induced β-phase enhancement in electrospun polyvinylidene difluoride composite fibers for high-efficiency flexible piezoelectric nanogenerators. Polymer Bulletin, 83(12), Article 655. https://doi.org/10.1007/s00289-026-06719-5

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06719-5

Keywords: PVDF, barium strontium titanate, BST, piezoelectric nanogenerator, electrospinning, beta-phase, energy harvesting, flexible electronics, composite fibers, wearable devices, lead-free piezoelectrics, power density