Interfacial Compatibility of Core-Shell Cellulose Nanocrystals for Improving Dynamic Covalent Adaptable Networks' Fracture Resistance in Nanohybrid Vitrimer Composites.

The development of polymeric nanocomposites with dynamic covalent adaptable networks and biobased nanomaterials has been a promising approach toward sustainable advanced materials, enabling reprogramming and recycling capabilities. Herein, a core-shell nanohybrid of functionalized cellulose nanocrystals (CNCs) is explored to provide crucial interfacial compatibility for improving the covalent adaptable networks of epoxy-thiol vitrimers in fracture resistance. The poly(ε-caprolactone) (PCL) shells grafted from CNC surfaces can be cross-linked with the covalent adaptable networks via a hot-pressing transesterification process. According to the additive concentration and annealing temperature, the stress relaxation behavior of nanohybrid vitrimer composites can be effectively regulated by the core-shell PCL-grafted CNC (CNC-PCL) nanohybrids from a dispersed to cross-linked interaction. The addition of 15 wt % of the core-shell CNC-PCLs exhibits the reinforced improvement of nanohybrid vitrimer composites in the average Young's modulus of 2.5×, fracture stress of 5.4×, and fracture strain of 2.0×. The research findings might have profound implications for developing synergistic interfacial compatibility between dynamic vitrimer networks and functional nanoparticles for advanced polymeric nanocomposites.

Cellulose Nanocrystal and Silver Nanobelt Gel: Cooperative Interactions Enabling Dispersion, Colloidal Gels, and Flexible Electronics.

Using cellulose nanocrystals (CNCs) as a dispersant and cross-linker, we sought to enable the dispersion of silver nanobelts (AgNBs) in water for use in the manufacture of flexible electronics. In this work, we obtained a colloidal gel relying on contributions from both particles. When dried, particle interactions during gel collapse induced cooperative buckling of the AgNBs, obtaining a desirable spring-like conductive network that was not seen without the presence of CNCs. Thus, exploiting the collapse of bonded colloidal gels may represent a novel method to obtain desirable network buckling behavior for use in flexible electronics, which previously has only been obtained through printing on prestrained substrates.

A hybrid material that reversibly switches between two stable solid states.

Most types of solid matter have a single stable solid state for a particular set of conditions. Nonetheless, materials with distinct, interchangeable solid states would be advantageous for several technological applications. Here, we describe a material composed of a polymer impregnated with a supercooled salt solution, termed as sal-gel, that assumes two distinct but stable and reversible solid states under the same conditions for a range of temperatures (-90 to 58 °C) and pressure. On transient stimulation of nucleation, the material switches from a clear and soft solid to a white and hard state, which can be 104 times stiffer than the original (15 kPa versus 385 MPa). This hard solid becomes soft again by transient heating, demonstrating the reversibility of the transition. This concept, exploiting the robust physical metastability of a liquid state, is extended to sugar alcohols, resulting in a stimuli-responsive and non-evaporating sug-gel. These 'two-in-one' solid materials may find potential uses in soft robotics and adhesive applications.

How interface compatibility affects conductivity evolution of silver nanobelts-filled electrically conductive composites during cure and post-treatments.

Using silver nanobelts and silver microflakes in a DGEBA/TETA epoxy matrix, we sought to investigate the relationship between the evolving electrical resistivity of formulations of hybrid nanocomposites during the curing process. This was characterized using three methods: (i) in situ four-wire electrical resistance measurements; (ii) differential scanning calorimetry, and (iii) dilatometry. In a previous work we reported that the resistivity of microcomposites was strongly affected by partial vitrification during curing. In this study, the reported vitrification effect is observed again, further validating the concern of far-ranging implications on the industry practices. The addition of silver nanobelts greatly improved conductivity of the composites, though it was observed that the improvements are often lost during subsequent heating and cooling cycles. Resistivity observations indicate that the sensitivity may be due to insufficient nanobelt-nanobelt contacts in the composite, and thus further increasing the nanobelt fraction of the filler content can maximize conductivity.

How morphology and surface crystal texture affect thermal stability of a metallic nanoparticle: the case of silver nanobelts and pentagonal silver nanowires.

Thermal instability of metallic nanoparticles is typically attributed to chemical attack by contaminants. However, thermodynamic stability is independent of other affecting parameters. The importance of this will be clarified when the structural change toward a more stable thermodynamic condition may be followed by a chemical reaction with the surroundings, which may cause a wrong diagnosis. In this research, molecular dynamics simulations and experimental observations were performed to investigate the effect of crystallography and surface texture on stability at high temperature using two closely related model nanoparticles: silver nanobelts and pentagonal nanowires. Previously, the instability of silver nanowires was associated with sulfidation of the wire at high temperature. However, we found that the silver nanowires are inherently unstable at high temperature, degrading due to the high-energy nature of the nanowire's predominately (100) crystallographic surface and pentagonal geometry. In contrast, the silver nanobelts resist thermal degradation up to 500 °C because of their predominately low-energy (111) crystallographic surfaces. In this case study, we successfully demonstrate that inherent thermodynamic stability driven by morphology is significant in metallic nanoparticles, and should be investigated when selecting a nanoparticle for high temperature applications. Moreover, we identify a new one-dimensional nanoparticle, the silver nanobelt, with inherent high-temperature stability.

Unequal erasure protection technique for scalable multistreams.

This paper presents a novel unequal erasure protection (UEP) strategy for the transmission of scalable data, formed by interleaving independently decodable and scalable streams, over packet erasure networks. The technique, termed multistream UEP (M-UEP), differs from the traditional UEP strategy by: 1) placing separate streams in separate packets to establish independence and 2) using permuted systematic Reed-Solomon codes to enhance the distribution of message symbols amongst the packets. M-UEP improves upon UEP by ensuring that all received source symbols are decoded. The R-D optimal redundancy allocation problem for M-UEP is formulated and its globally optimal solution is shown to have a time complexity of O(2(N)N(L+1)(N+1)) , where N is the number of packets and L is the packet length. To address the high complexity of the globally optimal solution, an efficient suboptimal algorithm is proposed which runs in O(N(2)L(2)) time. The proposed M-UEP algorithm is applied on SPIHT coded images in conjunction with an appropriate grouping of wavelet coefficients into streams. The experimental results reveal that M-UEP consistently outperforms the traditional UEP reaching peak improvements of 0.6 dB. Moreover, our tests show that M-UEP is more robust than UEP in adverse channel conditions.