ABSTRACT
Recently, flexible wearable and implantable electronic devices have attracted enormous interest in biomedical applications. However, current bioelectronic systems have not solved the problem of mechanical mismatch of tissue-electrode interfaces. Therefore, the biomimetic hydrogel with tissue-like mechanical properties is highly desirable for flexible electronic devices. Herein, we propose a strategy to fabricate a biomimetic hydrogel with strain-stiffening property via regional chain entanglements. The strain-stiffening property of the biomimetic hydrogel is realized by embedding highly swollen poly(acrylate sodium) microgels to act as the microregions of dense entanglement in the soft polyacrylamide matrix. In addition, poly(acrylate sodium) microgels can release Na+ ions, endowing hydrogel with electrical signals to serve as strain sensors for detecting different human movements. The resultant sensors own a low Young's modulus (22.61-112.45 kPa), high nominal tensile strength (0.99 MPa), and high sensitivity with a gauge factor up to 6.77 at strain of 300%. Based on its simple manufacture process, well mechanical matching suitability, and high sensitivity, the as-prepared sensor might have great potential for a wide range of large-scale applications such as wearable and implantable electronic devices.
Subject(s)
Microgels , Wearable Electronic Devices , Humans , Hydrogels , Biomimetics , Ions , Acrylates , Sodium , Electric ConductivityABSTRACT
We synthesized PPG-terminated tetra-carbamates as a new toughening additive for epoxy thermosets through facile addition reaction of hexamethylene diisocyanate (HDI) with poly(tetra-methylene glycols) (PTMG) and poly(propylene glycols) (PPG). The effects of prepared tetra-carbamates on the rheological behavior of neat epoxy resin were studied along with the various cured properties of their modified epoxy systems. Four carbamate groups (-NHCOO-) endow the prepared additives not only with good intramolecular interactions, but also with optimal intermolecular interactions with epoxy polymers. This results in the suitable miscibility of the additives with the epoxy matrix for the formation of the typical biphasic structure of microparticles dispersed in the epoxy matrix via polymerization-induced microphase separation. The impact strength and critical stress concentration factor (KIC) of cured modified epoxy systems with the additives are significantly higher than those of unmodified epoxy systems, without sacrificing the processability (Tg) and flexural strength. The toughening mechanism is understood as a synergism combination among the phase separation mechanism, the in situ homogeneous toughening mechanism, and the particle cavitation mechanism.
ABSTRACT
In this study, we develop a novel one-step method for synthesis of nickel oxide/silicon dioxide (NiO/SiO(2)) mesoporous composites by using N-hexadecyl ethylenediamine triacetate (HED3A) as structure-directing agent. Besides playing a role in directing the mesophase formation, the anionic surfactant also functions as a chelating agent that binds nickel ions. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopic analyses were undertaken to determine the chelating ability between HED3A and nickel ions. By adjusting the molar ratio of Ni(2+)/HED3A in the template solution, a series of mesoporous composites with various NiO contents were obtained after calcination. These composites were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and nitrogen adsorption/desorption. The results showed that the generated NiO nanoparticles were aggregated into clusters with the size less than 20 nm, and the composites retained mesoporous characteristics even with high NiO contents. HRTEM images also revealed the migration and aggregation for NiO nanoparticles during the sintering process. Moreover, the energy-dispersive X-ray spectrum (EDX) results showed a close linear relationship between Ni/Si in the composites and Ni(2+)/HED3A in the templates. This chelating surfactant-assistant encapsulation route has the potential to synthesize diversiform metal oxide/silica mesoporous composites with designated compositions.
ABSTRACT
pH-sensitive micelles with hydrophilic core and hydrophilic corona were fabricated by self-assembling of triblock copolymer of poly(methylacrylic acid)-poly(ethylene glycol)-poly(methylacrylic acid) at lower solution pH. Transmission electron microscopy and laser light scattering studies showed micelles were in nano-scale with narrow size distribution. Solution pH value and the micelles concentration strongly influenced the hydrodynamic radius of the spherical micelles (48-310 nm). A possible mechanism for the formation of micelles was proposed. The obtained polymeric micelle should be useful for biomedical materials such as carrier of hydrophilic drug.
