Electrical Conductivity and In Situ SAXS Probing of Block Copolymer Nanocomposites Under Mechanical Stretching.

Elastomers based on block copolymers can self-organize into ordered nanoscale structures, making them attractive for use as flexible conductive nanocomposites. Understanding how ordered structures impact electrical properties is essential for practical applications. This study investigated the morphological evolution of flexible conductive elastomers based on polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) block copolymers with aligned single- or multi-wall carbon nanotubes (SWCNTs or MWCNTs) and their electrical conductivity under large deformations. Oriented nanocomposites were obtained through injection molding and characterized using two different setups: tensile testing monitored by in situ small-angle X-ray scattering (SAXS) and tensile testing with simultaneous electrical conductivity measurements. Our findings demonstrate that structural orientation significantly influences electrical conductivity, with higher conductivity in the longitudinal direction due to the preferred orientation of carbon nanotubes. Tensile testing demonstrated that carbon nanotubes accelerate the process of realignment of the ordered structure. As a consequence, higher deformations reduced the conductivity of samples with longitudinal alignment due to the disruption of percolation contacts between nanotubes, while in samples with a transverse alignment the process promoted the formation of a new conductive network, increasing electrical conductivity.

Updates on inulinases: Structural aspects and biotechnological applications.

Inulinases are inulin catalyzing enzymes which belongs to glycoside hydrolases (GH) family 32. Bacteria, fungi and yeasts are the potential sources of inulinases. In the present biotechnological era, inulinases are gaining considerable attention, due to their wide range of applications which includes the production of high fructose syrup, fructooligosaccharides and many other important metabolites like bioethanol, organic acids, single cell oil, 2,3-butanediol, single cell proteins, etc. These applications of inulinases have attracted the researchers world-wide to understand the inulin-inulinase interactions for polyfructan hydrolysis. To understand these interactions, the information on structural organization of inulinases is very important which is scarce in literature. The current review highlights the structural and functional properties of inulinases, and difference in their structural organization. The biotechnological potential of inulinases for the production of different bio-products from inulin/inulin-rich raw materials using different bioprocessing strategies has also been elaborated.

Modulating the Mechanical Performance of Macroscale Fibers through Shear-Induced Alignment and Assembly of Protein Nanofibrils.

Protein-based fibers are used by nature as high-performance materials in a wide range of applications, including providing structural support, creating thermal insulation, and generating underwater adhesives. Such fibers are commonly generated through a hierarchical self-assembly process, where the molecular building blocks are geometrically confined and aligned along the fiber axis to provide a high level of structural robustness. Here, this approach is mimicked by using a microfluidic spinning method to enable precise control over multiscale order during the assembly process of nanoscale protein nanofibrils into micro- and macroscale fibers. By varying the flow rates on chip, the degree of nanofibril alignment can be tuned, leading to an orientation index comparable to that of native silk. It is found that the Young's modulus of the resulting fibers increases with an increasing level of nanoscale alignment of the building blocks, suggesting that the mechanical properties of macroscopic fibers can be controlled through varying the level of ordering of the nanoscale building blocks. Capitalizing on strategies evolved by nature, the fabrication method allows for the controlled formation of macroscopic fibers and offers the potential to be applied for the generation of further novel bioinspired materials.

On the fracture mechanisms of nacre: Effects of structural orientation.

The nacre of mollusk shells is distinguished by an exceptional mechanical efficiency which is derived essentially from its lamellar structure and frequently acts as a source of inspiration for the development of biomimetic materials. The structure and mechanical properties of nacre have been intensively investigated with a special focus on its toughening strategies; nevertheless, the fracture mechanisms, more specifically the critical stress/strain conditions for the failure of nacre, and the effects of structural orientation and hydration state remain largely unexplored. Here uniaxial compression tests were performed on nacre of both dry and hydrated states with different off-axis angles, i.e., the inclination of loading axis with respect to the lamellar structure, ranging from 0° to 90°. The mechanical properties and fracture characteristics of nacre and their dependences on the structural orientation and hydration state were elucidated in terms of mechanics behind failure. Quantitative relationships were established between the mechanical properties and off-axis angle based on different failure criteria. The competition between the fracture modes of fragmentation and shearing was quantified by comparing their respective driving force and resistance on the interfacial plane. This study may aid the understanding on the mechanical behavior of nacre and nacre-inspired synthetic materials and promote a better replication of the underlying design principles of nacre in man-made systems.

Enhanced protective role in materials with gradient structural orientations: Lessons from Nature.

UNLABELLED: Living organisms are adept at resisting contact deformation and damage by assembling protective surfaces with spatially varied mechanical properties, i.e., by creating functionally graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the two prime characteristics of many biological materials to be translated into engineering design. Here, we examine one design motif from a variety of biological tissues and materials where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation over multiple length-scales, without manipulation of composition or microstructural dimension. Quantitative correlations are established between the structural orientations and local mechanical properties, such as stiffness, strength and fracture resistance; based on such gradients, the underlying mechanisms for the enhanced protective role of these materials are clarified. Theoretical analysis is presented and corroborated through numerical simulations of the indentation behavior of composites with distinct orientations. The design strategy of such bioinspired gradients is outlined in terms of the geometry of constituents. This study may offer a feasible approach towards generating functionally graded mechanical properties in synthetic materials for improved contact damage resistance. STATEMENT OF SIGNIFICANCE: Living organisms are adept at resisting contact damage by assembling protective surfaces with spatially varied mechanical properties, i.e., by creating functionally-graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the prime characteristics of many biological materials. Here, we examine one design motif from a variety of biological tissues where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation at multiple length-scales, without changes in composition or microstructural dimension. The design strategy of such bioinspired gradients is outlined in terms of the geometry of constituents. This study may offer a feasible approach towards generating functionally-graded mechanical properties in synthetic materials for improved damage resistance.