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Freychet, Guillaume

Publications and source records attributed to Freychet, Guillaume.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Chemo-mechanical-microstructural coupling in the tarsus exoskeleton of the scorpion Scorpio palmatus

The multiscale structure of biomaterials enables their exceptional mechanical robustness, yet the impact of each constituent at their relevant length scale remains elusive. Here, we used SAXD analysis to expose the intact chitin-fiber architecture within the exoskeleton on a scorpion's claw, revealing varying orientations, including Bouligand and unidirectional regions different from other arthropod species. We uncovered the contribution of individual components’ constituent behavior to its mechanical properties from the micro- to the nanoscale. At the microscale, in-situ micromechanical experiments were used to determine site-specific stiffness, strength, and failure of the biocomposite due to fiber orientation, while metal-crosslinking of proteins is characterized via fluorescence maps. At the constituent level, combined with FEA simulations, we uncovered the behavior of fiber-matrix deformation with fiber diameter <53.7 nm and protein modulus in the range 1.4–11 MPa. The unveiled microstructure-mechanics relationship sheds light on the evolved structural functionalities and constituents' interactions within the scorpion cuticle.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Physical Models from Physical Templates Using Biocompatible Liquid Crystal Elastomers as Morphologically Programmable Inks For 3D Printing

Advanced manufacturing has received considerable attention as a tool for the fabrication of cell scaffolds however, finding ideal biocompatible and biodegradable materials that fit the correct parameters for 3D printing and guide cells to align remain a challenge. Herein, a photocrosslinkable smectic-A (Sm-A) liquid crystal elastomer (LCE) designed for 3D printing is presented, that promotes cell proliferation but most importantly induces cell anisotropy. The LCE-based bio-ink allows the 3D duplication of a highly complex brain structure generated from an animal model. Vascular tissue models are generated from fluorescently stained mouse tissue spatially imaged using confocal microscopy and subsequently processed to create a digital 3D model suitable for printing. The 3D structure is reproduced using a Digital Light Processing (DLP) stereolithography (SLA) desktop 3D printer. Synchrotron Small-Angle X-ray Diffraction (SAXD) data reveal a strong alignment of the LCE layering within the struts of the printed 3D scaffold. The resultant anisotropy of the LCE struts is then shown to direct cell growth. This study offers a simple approach to produce model tissues built within hours that promote cellular alignment.

3D cell culture↗
DOE OSTI2022

Observation of a uniaxial ferroelectric smectic A phase

We report the observation of the smectic A F , a liquid crystal phase of the ferroelectric nematic realm. The smectic A F is a phase of small polar, rod-shaped molecules that form two-dimensional fluid layers spaced by approximately the mean molecular length. The phase is uniaxial, with the molecular director, the local average long-axis orientation, normal to the layer planes, and ferroelectric, with a spontaneous electric polarization parallel to the director. Polarization measurements indicate almost complete polar ordering of the ∼10 Debye longitudinal molecular dipoles, and hysteretic polarization reversal with a coercive field ∼2 × 10 5 V/m is observed. The SmAF phase appears upon cooling in two binary mixtures of partially fluorinated mesogens: 2N/DIO, exhibiting a nematic (N)–smectic Z A (SmZ A )–ferroelectric nematic (N F )–SmA F phase sequence, and 7N/DIO, exhibiting an N–SmZ A –SmA F phase sequence. The latter presents an opportunity to study a transition between two smectic phases having orthogonal systems of layers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Application of the core shell model for strengthening polymer filament interfaces

While surface segregation has been intensively studied in thin films, relatively little has been investigated in filament geometries. In contrast to thin films, the filament surface forms a continuum, with interactions both at the free air and internal filament interface, which makes it difficult to achieve an equilibrium configuration. This asymmetry has become particularly apparent with the increasing use of additive manufacturing where entire structures are constructed via layered deposition of filamentous layers from a moving thermal nozzle. In addition, this process is highly non-equilibrated with poor thermal retention and is responsible for insufficient filament–filament interfacial fusion and internal pore formation along the printing direction. These features all contribute to poor mechanical and structural properties, which are exacerbated in semi-crystalline polymers, such as Polylactic Acid (PLA), where the melting point, T m , is much higher than the glass transition, T g . Even though system is liquid the molecules become ordered within the crystal structure and this ordering interferes with interdiffusion, which in turn prevents proper interfacial fusion. Capitalizing on the differential in surface tension, we show that addition of less than 1%, or trace amounts, of longer chain polymers, an oriented core shell structure, will be formed with a self-limiting thickness of three time the radius of gyration, R g , of the tracer chains. The lower T g of the tracers and their orientation makes them poised for interdiffusion when subsequent layers are deposited producing structures with significant improvement of the mechanical properties and internal structural integrity.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Metal-like Charge Transport in PEDOT(OH) Films by Post-processing Side Chain Removal from a Soluble Precursor Polymer

Herein, a route to produce highly electrically conductive doped hydroxymethyl functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films, termed PEDOT(OH) with metal-like charge transport properties using a fully solution processable precursor polymer is reported. Further, this is achieved via an ester-functionalized PEDOT derivative [PEDOT(EHE)] that is soluble in a range of solvents with excellent film-forming ability. PEDOT(EHE) demonstrates moderate electrical conductivities of 20–60 S cm -1 and hopping-like (i.e., thermally activated) transport when doped with ferric tosylate (FeTos 3 ). Upon basic hydrolysis of PEDOT(EHE) films, the electrically insulative side chains are cleaved and washed from the polymer film, leaving a densified film of PEDOT(OH). These films, when optimally doped, reach electrical conductivities of ≈1200 S cm -1 and demonstrate metal-like (i.e., thermally deactivated and band-like) transport properties and high stability at comparable doping levels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Fibrous anisotropy and mineral gradients within the radula stylus of chiton: Controlled stiffness and damage tolerance in a flexible biological composite

Over hundreds of millions of years, organisms have evolved architected structures via precise control over hierarchically assembled components, including the integration of dissimilar materials. One such example is found in the radula system of chitons, intertidal mollusks that feed on algae growing on the rock. Their radula consists of multiple rows of ultrahard teeth, each integrated with a foldable belt-like substrate via a stiff, yet flexible stylus, which is essential for efficient rasping during the feeding process. Here, we investigate the nano and micro-scale components and architectures as well as regional mechanical properties of the stylus, and their subsequent role during the rasping of Cryptochiton stelleri. Three important factors were determined to contribute to the regio-specific stiffness of the stylus: the presence of mineral components, highly oriented chitinous fibers, and a chemically cross-linked protein matrix. All these factors are varied throughout the stylus. There is a high mineral content on the trailing edge close to the tooth and a cross-linked matrix on the leading edge, both with orientational specific oriented chitin fibers that provide force transduction to the tooth. Conversely, there is a significant lack of mineral or cross-linked matrix in the proximal end as well as a low degree of fiber orientation, resulting in a flexible region that can accommodate torsion and flexure during rasping. Understanding the graded composite structure of the stylus and applying this unique design to various engineering fields such as soft robotics, biotechnology, and the medical industry, can inspire the production of high-performance materials.

Lee, Jung-Eun↗
DOE OSTI2022

Identifying the Signatures of Intermolecular Interactions in Blends of PM6 with Y6 and N4 Using Absorption Spectroscopy

Abstract In organic solar cells, the resulting device efficiency depends strongly on the local morphology and intermolecular interactions of the blend film. Optical spectroscopy was used to identify the spectral signatures of interacting chromophores in blend films of the donor polymer PM6 with two state‐of‐the‐art nonfullerene acceptors, Y6 and N4, which differ merely in the branching point of the side chain. From temperature‐dependent absorption and luminescence spectroscopy in solution, it is inferred that both acceptor materials form two types of aggregates that differ in their interaction energy. Y6 forms an aggregate with a predominant J‐type character in solution, while for N4 molecules the interaction is predominantly in a H‐like manner in solution and freshly spin‐cast film, yet the molecules reorient with respect to each other with time or thermal annealing to adopt a more J‐type interaction. The different aggregation behavior of the acceptor materials is also reflected in the blend films and accounts for the different solar cell efficiencies reported with the two blends.

Kroh, Daniel↗
DOE OSTI2022

Compact Peptoid Molecular Brushes for Nanoparticle Stabilization

Controlling the interfaces and interactions of colloidal nanoparticles (NPs) via tethered molecular moieties is crucial for NP applications in engineered nanomaterials, optics, catalysis, and nanomedicine. Despite a broad range of molecular types explored, there is a need for a flexible approach to rationally vary the chemistry and structure of these interfacial molecules for controlling NP stability in diverse environments, while maintaining a small size of the NP molecular shell. Here, we demonstrate that low-molecular-weight, bifunctional comb-shaped, and sequence-defined peptoids can effectively stabilize gold NPs (AuNPs). The generality of this robust functionalization strategy was also demonstrated by coating of silver, platinum, and iron oxide NPs with designed peptoids. Each peptoid (PE) is designed with varied arrangements of a multivalent AuNP-binding domain and a solvation domain consisting of oligo-ethylene glycol (EG) branches. Among designs, a peptoid (PE5) with a diblock structure is demonstrated to provide a superior nanocolloidal stability in diverse aqueous solutions while forming a compact shell (similar to 1.5 nm) on the AuNP surface. We demonstrate by experiments and molecular dynamics simulations that PE5-coated AuNPs (PE5/AuNPs) are stable in select organic solvents owing to the strong PE5 (amine)-Au binding and solubility of the oligo-EG motifs. At the vapor-aqueous interface, we show that PE5/AuNPs remain stable and can self-assemble into ordered 2D lattices. The NP films exhibit strong near-field plasmonic coupling when transferred to solid substrates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Binary Superlattices of Gold Nanoparticles in Two Dimensions

Here, we have created two-dimensional (2D) binary superlattices by cocrystallizing gold nanoparticles (AuNPs) of two distinct sizes into √3 x √3 and 2 x 2 complex binary superlattices, derived from the hexagonal structures of the single components. The building blocks of these binary systems are AuNPs that are functionalized with different chain lengths of poly(ethylene glycol) (PEG). The assembly of these functionalized NPs at the air–water interface is driven by the presence of salt, causing PEG-AuNPs to migrate to the aqueous surface and assemble into a crystalline lattice. We have used liquid surface X-ray reflectivity (XR) and grazing incidence small-angle X-ray scattering (GISAXS) to examine the assembly and crystallization at the liquid interface.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Understanding the Role of Order in Y‐Series Non‐Fullerene Solar Cells to Realize High Open‐Circuit Voltages

Abstract Non‐fullerene acceptors (NFAs) as used in state‐of‐the‐art organic solar cells feature highly crystalline layers that go along with low energetic disorder. Here, the crucial role of energetic disorder in blends of the donor polymer PM6 with two Y‐series NFAs, Y6, and N4 is studied. By performing temperature‐dependent charge transport and recombination studies, a consistent picture of the shape of the density of state distributions for free charges in the two blends is developed, allowing an analytical description of the dependence of the open‐circuit voltage V OC on temperature and illumination intensity. Disorder is found to influence the value of the V OC at room temperature, but also its progression with temperature. Here, the PM6:Y6 blend benefits substantially from its narrower state distributions. The analysis also shows that the energy of the equilibrated free charge population is well below the energy of the NFA singlet excitons for both blends and possibly below the energy of the populated charge transfer manifold, indicating a down‐hill driving force for free charge formation. It is concluded that energetic disorder of charge‐separated states has to be considered in the analysis of the photovoltaic properties, even for the more ordered PM6:Y6 blend.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mesocrystalline Ordering and Phase Transformation of Iron Oxide Biominerals in the Ultrahard Teeth of Cryptochiton stelleri

Biological organisms naturally synthesize complex, hierarchical, multifunctional materials through mineralization processes at ambient conditions and under physiological pH. One such example is the ultrahard and wear-resistant radular teeth found in mollusks, which are used to scape against the rock to feed on algae. Herein, the biologically controlled structural development of the hard, outer magnetite-containing shell of the chitin teeth is revealed. Specifically, the formation of a series of mesocrystalline iron oxide phases, templated by chitin-binding proteins, is identified. The initial domains, consisting of ferrihydrite mesocrystals with a spherulite-like morphology, undergo a solid-state phase transformation to form magnetite while maintaining mesocrystallinity, likely via a shear-induced solid-state reaction, without any noticeable architectural changes. Subsequent growth via Ostwald ripening leads to nearly single-crystalline rod-like elements. In addition, an interpenetrating organic matrix is identified that, at early stages of tooth development, potentially contains iron-binding proteins that guide the self-assembly of the mesocrystalline mineral and influence the preferred orientation of the later-formed magnetite nanorods, which ultimately determines the mechanical behavior of the mature chiton teeth.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Decoupling Complex Multi–Length–Scale Morphology in Non–Fullerene Photovoltaics with Nitrogen K–Edge Resonant Soft X–ray Scattering

Complex morphology in organic photovoltaics (OPVs) and other functional soft materials commonly dictates performance. Such complexity in OPVs originates from the mesoscale kinetically trapped non-equilibrium state, which governs device charge generation and transport. Resonant soft X-ray scattering (RSoXS) has been revolutionary in the exploration of OPV morphology in the past decade due to its chemical and orientation sensitivity. However, for non-fullerene OPVs, RSoXS analysis near the carbon K-edge is challenging, due to the chemical similarity of the materials used in active layers. Here, an innovative approach is provided by nitrogen K-edge RSoXS (NK-RSoXS), utilizing the spatial and orientational contrasts from the cyano groups in the acceptor materials, which allows for determination of phase separation. NK-RSoXS clearly visualizes the combined feature sizes in PM6:Y6 blends from crystallization and liquid-liquid demixing, while PM6:Y6:Y6-BO ternary blends with reduced phase-separation size and enhanced material crystallization can lead to current amplification in devices. Nitrogen is common in organic semiconductors and other soft materials, and the strong and directional N 1s → π* resonances make NK-RSoXS a powerful tool to uncover the mesoscale complexity and open opportunities to understand heterogeneous systems.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Self-Assembly of Flexible Linear–Semiflexible Bottlebrush–Flexible Linear Triblock Copolymers

Block copolymer (BCP) self-assembly is a fundamental process in which incompatible blocks spontaneously form organized microstructures with broad practical applications. Classical understanding is that the domain spacing is limited by the contour length of the polymer backbone. Here, using a combination of molecular design, chemical synthesis, small-/wide-angle X-ray scattering, transmission electron microscopy, and electron tomography, we discover that this molecular picture does not hold for architecturally semiflexible BCPs. For strongly segregated linear–semiflexible bottlebrush–linear triblock copolymers, the size of the bottlebrush domain can be twice the bottlebrush backbone contour length. The mechanism of such anomalous self-assembly is likely that the interfacial repulsion between the incompatible blocks is large enough to pull a part of the linear end blocks into the bottlebrush domain. This effectively increases the bottlebrush domain size. Moreover, the semiflexible bottlebrush widens the regime for the cylinder morphology that is associated with the volume fraction of the end blocks fC SFB &isin; (0.10, >0.41). This window is much wider than that for flexible linear BCPs, fC F &isin; (0.14, 0.35), and that predicted by the recent self-consistent field theory for linear-bottlebrush BCPs of the same chemistry and molecular architecture. Finally, our experimental findings reveal previously unrecognized mechanisms for the self-assembly of architecturally complex BCPs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Dynamic processes in transient phases during self-assembly of organic semiconductor thin films

Understanding and manipulating crystallization processes has been an important challenge for solution-processed organic thin films, both for fundamental studies and for fabricating thin films with near-intrinsic charge transport properties. We report an in situ X-ray scattering study of the crystallization of 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C 10 ) during its deposition from solution. At temperatures modestly below the smectic-E/crystalline phase boundary, the crystallization goes through a transient liquid crystal state before reaching the final stable crystalline phase. Significant dynamics occur in the first few seconds of the transition, which are observed through fluctuations in the X-ray scattering intensity, and are correlated with the time interval that the transient thin film coexists with the evaporating solvent. The transition to the stable crystalline phase takes minutes or even hours under these conditions, which may be a result of the asymmetry of the molecule. Transient phases are of potential interest for applications, since they can act as a route to self-assembly of organic thin films. However, our observations show that the long-lived monolayer-stacked intermediate state does not act as a template for the bilayer-stacked crystalline phase. Rather, the grain structure is replaced through nucleation, where the nucleation free-energy barrier is related to a potential barrier that prevents molecules to flip their long axis by 180°.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structure Development of the Interphase between Drying Cellulose Materials Revealed by In Situ Grazing-Incidence Small-Angle X-ray Scattering

The nano- to microscale structures at the interface between materials can define the macroscopic material properties. These structures are extremely difficult to investigate for complex material systems, such as cellulose-rich materials. The development of new model cellulose materials and measuring techniques has opened new possibilities to resolve this problem. We present a straightforward approach combining micro-focusing grazing-incidence small-angle X-ray scattering and atomic force microscopy (AFM) to investigate the structural rearrangements of cellulose/cellulose interfaces in situ during drying. Based on the results, we propose that molecular interdiffusion and structural rearrangement play a major role in the development of the properties of the cellulose/cellulose interphase; this model is representative of the development of the properties of joint/contact points between macroscopic cellulose fibers.

36 MATERIALS SCIENCE↗