Electrically insulating polymer dielectrics with high energy densities and excellent thermal conductivities are showing tremendous potential for dielectric energy storage. However, the practical application of polymer dielectrics often requires mutually exclusive multifunctional properties such as high dielectric constants, high breakdown strengths, and high thermal conductivities. The rational assembly of 2D nanofillers of boron nitride nanosheets (BNNS) and reduced graphene oxide (rGO) into a wellaligned micro-sandwich structure in polyimide (PI) composites is reported. The alternating stacking of rGO and BNNS synergistically exploits the large difference in their electrical conductivities to yield a high dielectric constant with a moderate breakdown strength. Moreover, the distinctively separated rGO and BNNS layers give rise to higher thermal conductivities of composites than those containing mixed fillers because of reduced phonon scattering at the interfaces between two identical fillers, as verified by molecular dynamics simulations. Consequently, the micro-sandwich nanocomposite prevails over the PI film with a simultaneously high dielectric constant of ≈579, a high energy density (43-fold higher than PI) and an excellent thermal conductivity (11-fold higher than PI) at a low hybrid filler content of only 2.5 vol%. The multifunctional nanocomposites developed in this work are promising for flexible dielectrics with excellent heat dissipation.

Realization of sensing multidirectional strains is essential to understanding the nature of complex motions. Traditional uniaxial strain sensors lack the capability to detect motions working in different directions, limiting their applications in unconventional sensing technology areas, like sophisticated human-machine interface and real-time monitoring of dynamic body movements. Herein, a stretchable multidirectional strain sensor is developed using highly aligned, anisotropic carbon nanofiber (ACNF) films via a facile, low-cost, and scalable electrospinning approach. The fabricated strain sensor exhibits semitransparency, good stretchability of over 30%, outstanding durability for over 2500 cycles, and remarkable anisotropic strain sensing performance with maximum gauge factors of 180 and 0.3 for loads applied parallel and perpendicular to fiber alignment, respectively. Cross-plied ACNF strain sensors are fabricated by orthogonally stacking two singlelayer ACNFs, which present a unique capability to distinguish the directions and magnitudes of strains with a remarkable selectivity of 3.84, highest among all stretchable multidirectional strain sensors reported so far. Their unconventional applications are demonstrated by detecting multi-degrees-offreedom synovial joint movements of the human body and monitoring wrist movements for systematic improvement of golf performance. The potential applications of novel multidirectional sensors reported here may shed new light into future development of next-generation soft, flexible electronics.To satisfy the growing interests, significant efforts have been made to improve their overall performances. Various materials and structures, [14][15][16][17][18] including nanosize metals, [19][20][21][22] conductive polymers, [23][24][25] nanocarbon materials, [26][27][28][29][30] and fiber or core-shell structure, [14,16,31] have been utilized to enhance the sensitivity, stretchability, linearity, and stability. Unfortunately, however, these strain sensors are designed to mainly detect a uniaxial strain while sensing multidirectional strains has rarely been accomplished, restricting their widespread applications. [32,33] The difficulty in achieving multidirectional strain sensing is due to the macro-or microscopically isotropic nature of conducting networks of strain sensors, which usually experience similar deformation upon stretching in any direction. To address this issue, geometrically engineered flexible strain gauge rosettes [34] and cross-shaped strain sensors [35] composed of isotropic piezoresistive materials were introduced previously. However, they showed a limited success with a small sensing range and an insufficient capability to distinguish the changes in multiaxial strain conditions because the isotropic piezoresistive materials experience significant destruction in their networks at high strains, regardless of the loading directions. To measure complex motions in 3D space with high accuracy requires rational design and use of suitable materials capable of detect...

The continuous energy-harvesting in moisture environment is attractive for the development of clean energy source. Controlling the transport of ionized mobile charge in intelligent nanoporous membrane systems is a promising strategy to develop the moisture-enabled electric generator. However, existing designs still suffer from low output power density. Moreover, these devices can only produce short-term (mostly a few seconds or a few hours, rarely for a few days) voltage and current output in the ambient environment. Here, we show an ionic diode–type hybrid membrane capable of continuously generating energy in the ambient environment. The built-in electric field of the nanofluidic diode-type PN junction helps the selective ions separation and the steady-state one-way ion charge transfer. This directional ion migration is further converted to electron transportation at the surface of electrodes via oxidation-reduction reaction and charge adsorption, thus resulting in a continuous voltage and current with high energy conversion efficiency.