Research ArticleMATERIALS SCIENCE

Nanofibrillar networks enable universal assembly of superstructured particle constructs

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Science Advances  08 May 2020:
Vol. 6, no. 19, eaaz7328
DOI: 10.1126/sciadv.aaz7328
  • Fig. 1 CNFs are robust, flexible, and nanoscaled plant-based building blocks.

    (A) The fibrils form a highly entangled and networked 3D structure with multiple, entangled contact points. (B) The special topology of the CNF nanonetwork is loose in suspension, thus allowing the co-dispersion of a broad variety of particles within the interconnected nanofibrillar structure. (C) During self-assembly from aqueous media, a dried interlocked network of particles and fibrils is formed. Extremely high cohesion is introduced from minimal fibril-particle interactions, which is essential to maintain the surface access to the primary particles and their functionalities.

  • Fig. 2 Formation of robust, dried particle assemblies induced by CNF for a wide range of particle sizes.

    (A) CNFs with colloidal particles (20 nm), (B) 230 nm, (C) 500 nm, (D), 1.15 µm and (E) 40 µm in diameter. The micrographs show a change from fully formed 3D network of disconnected CNFs (A) to 2D entangled networks (E) as the particle size is increased. (F) Isolation of the CNF networks for the evaluation of their characteristics. (G to I) SEM images of the isolated CNF network formed from (G) 20-nm, (H) 230-nm, and (I) 40-μm SiO2 particles, showing networks ranging from continuous nanoscaled to microscaled cellular architectures.

  • Fig. 3 Development of cohesion by using CNFs in SP assemblies and scaling as a function of the particle size and the surface chemistry.

    (A) Typical uniaxial compression force-strain profile of 230-nm SiO2-based SPs prepared in the presence of CNF (5% loading) and for SiO2 SPs sintered at 600°C for 2 hours in the absence of CNF. The panel includes the critical points that are used for comparison and the different regimes (I to III) that define the reinforcement effect of CNF in the system. The inset SEM image shows the morphology of the cracking area of a CNF-bound SiO2 (230 nm) SP. (B) Schematic representation of the cracking hindrance effect and cohesion brought by the CNF and comparison with their sintered counterparts. (C) Scaling of the yield point of the SP as a function of the particle size and CNF fraction, here approached as relative surface area (SSA ratio). (D) Proportionality constant (a) and decay rate (k) obtained from the power law fittings. (E) Scaling of the yield point of the SP as a function of the surface chemistry and CNF fraction, here approached as relative surface area (SSA ratio). (F) Proportionality constant (a) and decay rate (k) obtained from the power law fittings.

  • Fig. 4 Assessment of the cohesion capacity of CNFs with particles varying in both chemical complexity and morphology.

    Particles of different shapes, origins, packing ability, and aspect ratio are used in the synthesis of robust SPs. (A) Scaling of the SPs’ robustness as a function of their respective SSA ratio. (B) Photograph of the obtained materials and a 3D printed object (direct ink writing) to illustrate the prospects for scalability of the CNF-particle materials (230-nm SiO2 and CNF). (C to E) SEM images of few examples of biological materials and high aspect ratio particles that are superstructured with CNFs. In (D) and (E), the particles were artificially colorized. (F) Demonstration of the preserved functionalities (fermentation process) of the living yeast particles after superstructuring with CNFs from aqueous suspensions. Photo credits: Bruno D. Mattos (Aalto University).

  • Fig. 5 Physical interpretation of CNF morphological attributes inducing cohesion in particulated networks.

    (A) Conformability of the CNFs modeled as a linear chain of rigid segments of length L and maximum deformation angle θ between subsequent segments as demonstrated in (B). (C1 to C5) Conformability threshold of CNF around SiO2 particles of given sizes. Within the area shown in red, only two segments touch the particle, whereas in the blue (bottom) area, the CNF fully conforms around a SiO2 particle of given diameter. (D) Mechanical performance of the SPs as a function of the ratio between the CNFs and the SiO2 particles (nCNF/nSiO2) and CNF fraction (%). (E) CNF-to-SiO2 number density fraction (nCNF/nSiO2) as a function of CNF fraction (%) in the SPs. The red arrows in (D) and (E) show nCNF/nSiO2 of DSiO2 = 230 nm approaching 1 at CNF = 15%. (F) Probe of the parameter space for optimized compressive strength based on the experimental results shown in (D), in which the highest mechanical strength is found when nCNF/nSiO2 ≈ 3.7 at 15% CNF. The likely values for the length (L) and diameter (D) of CNF are shown to attain nCNF/nSiO2 ≈ 3.7 at 15% CNF at given SiO2 diameter. Other grades of nanocelluloses are marked in (F), suggesting the particle size range where they could induce cohesion. CNF, cellulose nanofibrils (39); CNC, cellulose nanocrystal (57); TCNF, TEMPO-oxidized CNFs; TCNC, TEMPO-oxidized cellulose nanocrystals; BCNC, bacterial nanocellulose from coconut pulp (58); TuCNC, cellulose nanocrystals from tunicate (59); MFC, microfibrillated cellulose; WF, wood fibers (22).

Supplementary Materials

  • Supplementary Materials

    Nanofibrillar networks enable universal assembly of superstructured particle constructs

    B. D. Mattos, B. L. Tardy, L. G. Greca, T. Kämäräinen, W. Xiang, O. Cusola, W. L. E. Magalhães, O. J. Rojas

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