Characterization of vertically aligned carbon nanotube forests grown on stainless steel surfaces

Vertically aligned carbon nanotube (CNT) forests are a particularly interesting class of nanomaterials, because they combine multifunctional properties, such as high energy absorption, compressive strength, recoverability and super-hydrophobicity with light weight. These characteristics make them suitable for application as coating, protective layers and antifouling substrates for metallic pipelines and blades. Direct growth of CNT forests on metals offers the possibility to transfer the tunable CNT functionalities directly onto the desired substrates. Here, we focus on characterizing the structure and mechanical properties, as well as wettability and adhesion of CNT forests grown on different types of stainless steel. We investigate the correlations between composition and morphology of the steel substrates with the micro-structure of the CNTs, and reveal how the latter ultimately controls the mechanical and wetting properties of the CNT forest. Additionally, we study the influence of substrate morphology on the adhesion of CNTs to their substrate. We highlight that the same structure-property relationships govern the mechanical performance of CNT forests grown on steels and on Si

Characterization of vertically aligned carbon nanotube forests grown on stainless steel surfaces

Vertically aligned carbon nanotube (CNT) forests are a particularly interesting class of nanomaterials, because they combine multifunctional properties, such as high energy absorption, compressive strength, recoverability, and super-hydrophobicity with light weight. These characteristics make them suitable for application as coating, protective layers, and antifouling substrates for metallic pipelines and blades. Direct growth of CNT forests on metals offers the possibility of transferring the tunable CNT functionalities directly onto the desired substrates. Here, we focus on characterizing the structure and mechanical properties, as well as wettability and adhesion, of CNT forests grown on different types of stainless steel. We investigate the correlations between composition and morphology of the steel substrates with the micro-structure of the CNTs and reveal how the latter ultimately controls the mechanical and wetting properties of the CNT forest. Additionally, we study the influence of substrate morphology on the adhesion of CNTs to their substrate. We highlight that the same structure-property relationships govern the mechanical performance of CNT forests grown on steels and on Si

Stress-strain response of polymers made through two-photon lithography: Micro-scale experiments and neural network modeling

Photopolymerization is the governing chemical mechanism in two-photon lithography, a multi-step additive manufacturing process. Negative-tone photoresist materials are widely used in this process, enabling the fabrication of structures with nano- and micro-sized features. The present work establishes the relationship among the process parameters, the degree of polymerization, and the nonlinear stress-strain response of polymer structures obtained through two-photon polymerization. Honeycomb structures are fabricated on a direct laser writing system (Nanoscribe) making use of different laser powers for two widely applicable, commercially available resins (IP-S and IP-Dip). The structures are then tested under uniaxial compression to obtain the corresponding stress-strain curves up to 30% strain. Raman spectroscopy is used to correlate the degree of conversion achieved upon different laser exposures of the base photoresist material with the selected mechanical properties (Young's modulus, tangent modulus, deformation resistance) after polymerization. Significant differences are recorded in the observed constitutive responses. Higher degrees of conversion result in higher elastic moduli and strength at large strains. Moreover, it is found that the IP-Dip resin yields higher degrees of conversion for the same laser power compared to the IP-S resin. A neural network model is developed for each resin that predicts the stress-strain response as a function of the degree of conversion. For each material, an analytical form of the identified constitutive response is provided, furnishing basic formulas for engineering practice.ISSN:2214-860

Carposome productivity of Pleurotus ostreatus and Pleurotus eryngii growing on agro-industrial residues enriched with nitrogen, calcium salts and oils

The suitability of the abundant agro-industrial residues wheat straw (WS; control), barley and oats straw (BOS) and rice husk (RH), supplemented with various sources of oils (sunflower, corn oil), nitrogen (peptone, yeast extract) and calcium salts (CaSO4·2H2O, CaCl2), as novel substrates in solid-state fermentation of selected Pleurotus ostreatus and P. eryngii mushrooms was investigated. The possible effect of different additives on mycelial growth rate, biomass production and endoglucanase, laccase and lipase biosynthesis were evaluated. Moreover, their impact on essential cultivation aspects (earliness, total mushroom yield, biological efficiency) and carposome quality parameters (weight, morphological characteristics) was assessed. Both fungi showed their highest growth rates on BOS substrates and the most positive implementation was CaSO4·2H2O 6 % w/w (Kr = 9.58 mm/ day; P. ostreatus, Kr = 9.42 mm/ day; P. eryngii), while different additives led to enhancement of biomass production. Pleurotus species demonstrated minimal levels of endoglucanase activity, with values ranging from 0.01 to 0.42 U/g of dry weight, regardless of the substrate and the stage of colonization. On the contrary, the maximum values of laccase activity were observed at 50 % of colonization on BOS and RH, while supplementation with nitrogen and calcium sources positively affected its biosynthesis. P. ostreatus and P. eryngii cultivated on BOS supplemented with peptone at 2 and 5 % w/w, synthesized significant laccase amounts, i.e., 12,165.78 and 8,624.55 U/g d.w., respectively. Satisfactory amounts of lipase were produced, especially in substrates supplemented with sunflower 2 % w/w, in quantities up to 1.42 U/g d.w., whereas the highest lipase activity was achieved by P. eryngii on WS supplemented with corn oil at 2 % w/w, with a value of 4.25 U/g d.w. being recorded. Regarding fermentation of Pleurotus species in polypropylene bags, WS and BOS supported faster colonization and shorter earliness period than RH substrates, whereas supplementation did not seem to affect these culture parameters. Furthermore, oils supplementation had a positive effect on BE of both species, with values up to 100 % for P. ostreatus and 80 % for P. eryngii on WS and BOS, whereas on RH the lowest BE values were detected. Morphological characteristics were not significantly affected by the additives. Results indicate the positive impact that certain additives have on mushroom productivity and production of enzymes with great financial and environmental importance

Mechanics of beams made from chiral metamaterials: Tuning deflections through normal-shear strain couplings

In the current work, we demonstrate the potential of structures made of chiral artificial materials to balance bending loads through tensile loads, exploiting their inner normal to shear strain coupling. To that scope, we employ beam structures which we architecture with tetrachiral unit-cells. For the latter, we quantify their inherently coupled normal to shear strain behavior, making use of homogenization analysis techniques. We subsequently derive the equations that characterize the bending mechanics of beams with an inner bending to normal loading coupling, starting from first principles. Thereupon, we compute the normal forces required to equilibrate the effect of bending loads on beam structures, providing relevant closed-form parametric expressions. Using the derived analytical formulas, we carry out both numerical simulations and experiments for the case of cantilever beams. Results suggest that the coupling of normal and shear deformations can be used as a primal load-balancing mechanism, providing new possibilities in the control of the artificial structure's kinematics and overall mechanics.ISSN:0264-1275ISSN:1873-419

Double-wall ceramic nanolattices: Increased stiffness and recoverability by design

Lightweight ceramic nanolattices exhibiting high stiffness and good recoverability are obtained by leveraging base material size effects in combination with smart structural design. Here, the double-wall tube (DWT) lattice architecture is introduced to increase the stiffness of brittle nanolattices, while maintaining their recoverability. The DWT architecture consists of two nested simple-cubic hollow-truss nanolattices. The superposition of two nanolattices leads to a reduced wall thickness for a given relative density thereby preventing the built-up of large stresses at the cell wall level when crushing the lattices. In this work, DWT alumina nanolattices are fabricated and compressed in situ to demonstrate the improvement in recoverability with decreasing alumina wall thickness. The results from finite element simulations reveal that double-wall architectures are up to two times stiffer than their single wall counterparts of equal mass, suggesting that superior recoverability (thinner ceramic coatings) coupled with enhanced stiffness can be achieved. The DWT lattice is proposed as a new architecture to expand the design space of highly recoverable brittle nanolattices. The new double-wall design concept is expected to provide an efficient tool for improving the mechanical performance of shell-nanolattices in general including triply-periodic minimal surfaces.ISSN:0264-1275ISSN:1873-419