Controlling the Hierarchical Structuring of Conductive PEBA in Ternary and Quaternary Blends

Flexible Sensors with a Multilayer Interlaced Tunnel Architecture for Distinguishing Different Strains

The diversity of body joints and the complexity of joint motions cause flexible strain sensors to undergo complex strains such as stretching, compression, bending, and extrusion, which results in sensors that do not recognize different strains, facing great challenges in detecting the true motion characteristics of joints. Here, the monitoring of body joints' real motion characteristics has been realized by the sensor that can output response signals with different resistance trends for different strains. The sensor prepared by the sacrificial template method is characterized by a multilayered interlaced tunnel architecture and carbon black embedded in the inner wall of the tunnel. Stretching, compressive, and bending strains result in increasing, decreasing, and increasing resistance, followed by a decrease in resistance of the sensor, respectively. The sensor can still output distinguishable response signals, even in the presence of complex strains induced by squeezing. Low strain detection limits (0.03%) and wide detection ranges (>600%) are achieved due to the localized strain enhancement caused by the unique structure. The sensor can detect the motion characteristics of different joints in flexion-extension, abduction-adduction, and internal-external rotation, which, in turn, can be used for real-time monitoring of complex joint motions involved in limb rehabilitation. In addition, the sensor recognizes the 26 letters of the alphabet represented by sign language gestures. The above studies demonstrate the potential application of our prepared sensors in flexible, wearable devices.

Closely Packed Conductive Droplets with Polygon-Like Patterns Confined at the Interface in Ternary Polymer Blends

This work reports on the formation of closely packed conductive droplets demonstrating polygon-like patterns at the interface in partially wetted ternary polymer systems prepared by melt blending and annealing treatment. The low-density polyethylene/poly(ether-block-amide)/poly(butylene-adipate-co-terephthalate) (LDPE/PEBA/PBAT) blend showed an intermediate partial wetting tendency where the interfacially localized conductive PEBA phase developed connected structure after blending but transformed into dispersed droplets upon annealing. The coalescence of the PEBA droplets appeared to be initiated by the Rayleigh-type instability in the thin PBAT film separating PEBA. However, the intrinsic coalescence rate of the PEBA droplets was very low due to the low interfacial tension of PEBA/PBAT. This slow coalescence of PEBA combined with the fast reduction in the interfacial area during annealing and the intermediate partial wetting state of the LDPE/PEBA/PBAT system resulted in a unique morphology of closely packed PEBA droplets with polygon-like patterns at a volume fraction of 50/10/40. Two other representative ternary polymer blends, LDPE/PEBA/polypropylene (PP) and compatibilized LDPE/PEBA/polystyrene (PS), with strong and weak partial wetting morphologies were also examined to highlight the mechanism for the morphology development in the LDPE/PEBA/PBAT blend.

Structures and properties of newly synthesized semi-aromatic polyamide thermoplastic elastomers

Novel semi-aromatic polyamide based thermoplastic elastomers containing both strong and weak H-bond units were fabricated via a facile “two-step” melt polycondensation method. The structures and properties of a series of TPAEs are discussed.

Nucleation of Poly(lactide) Partially Wet Droplets in Ternary Blends with Poly(butylene succinate) and Poly(ε-caprolactone)

This work presents the first investigation on the crystallization behavior of partially wet droplets in immiscible ternary blends. Poly(lactide), poly(ε-caprolactone), and poly(butylene succinate) (PLA, PCL, and PBS, respectively) were melt blended in a 10/45/45 weight ratio to produce a "partial wetting" morphology with droplets of the PLA minor phase located at the interface between the other two major components. The crystallization process of the higher melting PLA droplets was studied by polarized light optical microscopy, while the other components remain in the molten state. We found that neighboring partially wet droplets nucleate in close sequence. This is unexpected since partially wet droplets display points of three-phase contact and, hence, should not touch each other. Moreover, the onset of poly(lactide) crystallization is frequently observed at the interface with molten PCL or PBS, with a significant preference for the former polymer. The observed sequential droplet-to-droplet crystallization is attributed to the weak partial wetting behavior of the PCL/PLA/PBS ternary system. In fact, the contact between the interfacially confined droplets during crystallization due to their mobility can lead to a transition from a partial to a completely wet state, with the formation of thin continuous layers bridging larger partially wet droplets. This allows crystallization to spread sequentially between neighboring domains. Using a simple heterogeneous nucleation model, it is shown that the nucleation of PLA on either PCL or PBS melts is energetically feasible. This study establishes a clear relationship between the unique partial wetting morphology of ternary blends and the nucleation of the minor component, paving the way to the understanding and control of crystallization in multiphasic polymer blends for advanced applications.