Crystalline Network Research Articles

Effect of Tween 20 on structure, phase-transition behavior and mechanical properties of monoglyceride oleogels

The aim of this study was to investigate the impact of the addition of a non-gelling non-ionic surfactant, Tween 20 (Tw20), at varying weight ratios with monoglycerides, MGs (0 – 20 g Tw20 to 10 g of MGs as structurant /100 g olive oil) in the crystalline network of the MGs-based oleogels. Several analytical methods such as differential scanning calorimetry (DSC), confocal and polarized optical microscopy, rheometry, and infrared spectroscopy were employed for the characterization of the oleogel structures. The DSC and FT-IR provided evidence that Tween 20 affects the MGs network structure in the oleogels. With addition of Tween 20 the crystal size and the melting/crystallization temperatures of the MGs crystal polymorphs were altered, along with a strengthening of the oleogel structure. Moreover, the presence of Tween 20 in the MGs oleogels accelerated the transformation of the higher free energy crystal forms (α-crystals) to the more thermodynamically stable β-polymorph of the MGs. Apparently, an oil-in-oil emulsion gel is being formed with the MG crystalline entities acting as Pickering particles around the oil/Tween 20 droplets in the oleogel structure. These findings provide valuable information on the synergistic effect of a non-ionic surfactant on monoglyceride-based oleogels, which could be beneficial in constructing multi-component lipid-phases for potential food or cosmetic applications.

Subcritical Water Hydrolysis of Cotton Fibers to Nanocellulose for Producing Poly(vinyl alcohol)/Cellulose Biocomposite

AbstractCellulose nanofibers (CNs) are isolated from cotton wool using subcritical water in a semiflow hydrothermal reactor to achieve green hydrolysis. The yield and crystallinity index (CI) of nanocellulose is optimized via varying temperatures and hydrolysis time while maintaining the pressure at 10 MPa. Under the subcritical condition, water dissociates into H3O+ and OH−, allowing protonation of the β‐glycosidic bond to hydrolyze cellulose strands into short chain fibers. Hydrolysis rates enhance with increasing temperatures, further disintegrating cellulose into smaller nanofibrils. At 180 °C, amorphous cellulose dissolution occurs, increasing the crystallinity without disintegrating the crystalline fibrous network. The concentration of H3O+ increases at 230 °C, further hydrolyzes cotton wool into uniform nanofibril cellulose with 14.3 ± 1.2 nm diameter. The tensile strength and elongation at break enhance using cellulose nanofibers obtained at 220 and 230 °C due to the small nanocellulose sizes that allow efficient dispersion in the poly(vinyl alcohol) (PVA) matrix.

A Fully Conjugated Covalent Organic Framework with Oxidative and Reductive Sites for Photocatalytic Carbon Dioxide Reduction with Water

AbstractConstructing a powerful photocatalytic system that can achieve the carbon dioxide (CO2) reduction half‐reaction and the water (H2O) oxidation half‐reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with a crystalline topological network, named viCOF‐bpy‐Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust −C=C− bond linkages. The charge‐separation ability of viCOF‐bpy‐Re is promoted by low polarized π‐bridges between rhenium complexes and triazine ring units, and the efficient charge‐separation enables the photogenerated electron–hole pairs, followed by an intramolecular charge‐transfer process, to form photogenerated electrons involved in CO2 reduction and photogenerated holes that participate in H2O oxidation simultaneously. The viCOF‐bpy‐Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate (190.6 μmol g−1 h−1 with about 100 % selectivity) and oxygen (O2) evolution (90.2 μmol g−1 h−1) among all the porous catalysts in CO2 reduction with H2O as sacrificial agents. Therefore, a powerful photocatalytic system was successfully achieved, and this catalytic system exhibited excellent stability in the catalysis process for 50 hours. The structure–function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.

A Fully Conjugated Covalent Organic Framework with Oxidative and Reductive Sites for Photocatalytic Carbon Dioxide Reduction with Water.

Constructing powerful photocatalytic system that can achieve the carbon dioxide (CO2) reduction half-reaction and the water (H2O) oxidation half-reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with crystalline topological network, named viCOF-bpy-Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust -C=C- bond linkages. The charge separation ability is promoted by low polarized π-bridges between rhenium complexes and triazine ring units, and the efficient charge separation enables the photogenerated electron-hole pairs separated by intramolecular charge transfer process to form photogenerated electrons involved in CO2 reduction and photogenerated holes participated in H2O oxidation simultaneously. The powerful viCOF-bpy-Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate of 190.6 μmol g-1 h-1 with about 100% selectivity and oxygen (O2) evolution of 90.2 μmol g-1 h-1 among all the porous materials in CO2 reduction with H2O as sacrificial agents. Therefore, a powerful photocatalytic system is successfully achieved, and this catalytic system exhibits excellent stability in the catalysis process for 50 hours. Meanwhile, the structure-function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.

Large-Scale Synthesis of Covalent Organic Frameworks: Challenges and Opportunities.

Connecting organic building blocks by covalent bonds to design porous crystalline networks has led to covalent organic frameworks (COFs), consequently transferring the flexibility of dynamic linkages from discrete architectures to extended structures. By virtue of the library of organic building blocks and the diversity of dynamic linkages and topologies, COFs have emerged as a novel field of organic materials that propose a platform for tailor-made complex structural design. Progress over the past two decades in the design, synthesis, and functional exploration of COFs in diverse applications successively established these frameworks in materials chemistry. The large-scale synthesis of COFs with uniform structures and properties is of profound importance for commercialization and industrial applications; however, this is in its infancy at present. An innovative designing and synthetic approaches have paved novel ways to address future hurdles. This review article highlights the fundamental of COFs, including designing principles, coupling reactions, topologies, structural diversity, synthetic strategies, characterization, growth mechanism, and activation aspects of COFs. Finally, the major challenges and future trends for large-scale COF fabrication are outlined.

A monolayer crystalline covalent network of polyoxometalate clusters

Monolayer two-dimensional (2D) materials are of great interest because of their unique electronic structures, noticeable in-plane confinement effect, and exceptional catalytic properties. Here, we prepared 2D covalent networks of polyoxometalate clusters (CN-POM) featuring monolayer crystalline molecular sheets, formed by the covalent connection between tetragonally arranged POM clusters. The CN-POM shows a superior catalytic efficiency in the oxidation of benzyl alcohol, and the conversion rate is five times higher than that of the POM cluster units. Theoretical calculations show that in-plane electron delocalization of CN-POM contributes to easier electron transfer and increases catalytic efficiency. Moreover, the conductivity of the covalently interconnected molecular sheets was 46 times greater than that of individual POM clusters. The preparation of monolayer covalent network of POM clusters provides a strategy to synthesize advanced cluster-based 2D materials and a precise molecular model to investigate the electronic structure of crystalline covalent networks.

The impact of glycerol monostearate's similarity to fats and fatty acid composition of fats on fat crystallization, destabilization, and texture properties of ice cream.

Fat significantly affects the properties of ice cream. Prior studies have investigated the correlation between fat crystallization, fat destabilization, and ice cream quality. However, the role of fatty acid composition, the similarity between fat and emulsifier in these characteristics, and their impact on final product quality remains unclear. To investigate the influence of the fatty acid composition of fats, as well as their similarity to glycerol monostearate (GMS), on fat crystallization and destabilization during the aging and freezing stages, ice creams were formulated using a combination of two types of fats (coconut oil and palm olein) in five different ratios. In oil phases, decreased saturation of fatty acids (from 93.38% to 46.69%) and increased similarity to GMS (from 11.96% to 46.01%) caused a reduction in the maximum solid fat content. Moreover, the rise in unsaturated long-chain fatty acids (from 34.61% to 99.57%) and similarity to GMS enhanced the formation of rare and coarse fat crystals, leading to a sparse crystalline network. This, in turn, reduced the crystallization rate and the stiffness of the fat in emulsions. Assuming consistent overrun across all ice creams, the enhanced interactions between fat globules in ice cream improved its hardness, melting properties, and shrinkage. The crystalline properties of fat in emulsions were influenced by oil phases, impacting fat destabilization and ultimately enhancing the quality of ice cream. The present study offers valuable insights for the optimization of fat and monoglyceride fatty acid ester selection, with the potential to improve ice cream quality. © 2023 Society of Chemical Industry.

Complexing curcumin and resveratrol in the starch crystalline network alters in vitro starch digestion: Towards developing healthy food materials

Starch is an abundant and common food ingredient capable of complexing with various bioactive compounds (BCs), including polyphenols. However, little information is available about using native starch network arrangement for the starch-BCs inclusion. Herein, two BCs, curcumin, and resveratrol, were undertaken to delineate the role of different starch crystalline types on their encapsulation efficiency. Four starches with different crystalline types, botanical sources, and amylose content were examined. The results suggest that B-type hexagonal packing is necessary to encapsulate curcumin and resveratrol successfully. The increase in XRD crystallinity while maintaining the FTIR band at 1048/1016 cm−1 suggests that BCs are likely entrapped inside the starch granule than attaching to the granule surface. A significant change in starch digestion is seen only for the B-starch complexes. Embedding BCs in the starch network and controlling starch digestion could be a cost-effective and valuable approach to designing and developing novel starch-based functional food ingredients.

Boosting thermoelectric performance of conjugated polymers via interchain molecular docking: Significance of highly crystalline and percolated morphology

The development of organic materials with high thermoelectric performance requires the exploration of organic molecules having various structures and a deep understanding of the relationship between their structure and thermoelectric properties. In this study, a series of donor–acceptor-type conjugated copolymers with an isoindigo (IID) unit as a building block are synthesized and compared to investigate the effect of the molecular structure of the IID-based conjugated polymers on the microstructure and thermoelectric properties of polymer films. The crystallinity and molecular packing of the polymers change significantly depending on the symmetry of the donor unit copolymerized with the IID unit, resulting in considerable differences in the doping and charge transport characteristics of the polymers. Importantly, the polymer with high crystallinity and fibril-like crystalline network shows excellent thermoelectric performance, exhibiting a high power factor of 212 µW m−1 K−2 upon doping; this is attributed to the high electrical conductivity and high Seebeck coefficient, which result from its highly ordered structure. This study not only demonstrates the potential of the IID unit as a promising building block for high-performance conjugated polymers for thermoelectric applications but also provides important guidelines for the design of IID-based polymers having high thermoelectric performance.

Polymeric Dynamic Crosslinker for Upcycling of Fragile Low-Molecular-Weight Polypropylene

While tremendous progress has been made in the dynamic crosslinking of polypropylene (PP) for plastic upcycling, the efficacy in addressing low-molecular-weight (MW) PP waste remains untapped. In this work, we demonstrate a simple and scalable method to convert brittle low-MW PP to vitrimer materials with enhanced thermal and mechanical properties, enabling their use in circular upcycling. Different from most previous work employing small-molecule crosslinkers, we prepare PP vitrimers (PPv) using polymeric crosslinkers, containing polyethylene glycol segments, which leads to altered crystalline structures and network formation. Importantly, by increasing the MW of crosslinkers from 200 to 1000 Da, the PPv exhibit more than 50 times increase in their fracture energy with strong ductility, which can be attributed to combined effects of strengthened amorphous regions of semi-crystalline PP domains and the phase separation between soft polyethylene glycol segments and the PP matrix. Moreover, when blending the PPv with high MW PP (PPh), the PPh/PPv blends show comparable elastic modulus, yield strength, and stretchability to that of the PPh, in sharp contrast to the widely known embrittlement of low-MW PP/PPh blends. These results demonstrate the use of polymeric dynamic crosslinkers as an important strategy for upcycling low-MW PP waste to value-added products.

Reversible Electronic Patterning of a Dynamically Responsive Hydrogel Medium

AbstractA dynamically responsive hydrogel medium is prepared from two self‐assembling components, a polysaccharide (chitosan) and a surfactant (sodium dodecyl sulfate; SDS). It is shown that this medium can be patterned using an electrode “pen” to reconfigure supramolecular structure: cathodic writing induces neutral chitosan chains to form a crystalline network, while anodic writing generates cationic chitosan chains that electrostatically crosslink with anionic SDS micelles. Both supramolecular structures are re‐configurable and each is stabilized by structure‐induced shifts in chitosan's pKa, thus electronically written patterns can be erased, new patterns can be written, and patterns can be written in three dimensions. Further, it is shown that NaCl‐induced morphological transitions of the SDS micelles allow patterns to be reversibly concealed or revealed. To demonstrate the versatility of this medium for information storage, a quick response (QR) code is electronically written and it is shown that this code can be recognized by a standard cellphone app. This QR code can be concealed by making the medium opaque (i.e., by obscuring the pattern) or by making the pattern evanescent (i.e., by making pattern invisible). Overall, this work demonstrates that a dynamically responsive medium composed of simple, safe and sustainable components can be reversibly patterned with spatial and quantitative control using top‐down electronic inputs.

Long-Range Ordered Organic Bulk-Heterojunction: C60 and O-IDTBR Single Crystals Penetrated by Crystalline P3HT Fibrous Networks.

The long-range ordering of bulk-heterojunctions (BHJs) significantly facilitates exciton diffusion and dissociation as well as charge transport. A feasible bio-inspired strategy to realize such a heterostructure is crystallization in gel media where the growing host crystals incorporate the surrounding guest materials of gel networks. Until now, the host-guest pairs forming ordered BHJs are still very limited and, more importantly, the used gel-network guests are structurally amorphous, spurring investigation toward crystalline gel-networks. Here, single crystals of fullerene and non-fullerene acceptors (NFAs) in poly(3-hexylthiophene) (P3HT) organogel are prepared, forming C60 :P3HT and (5Z,5″Z)-5,5″-((7,7″-(4,4,9,9-tetraoctyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b″]dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-7,4-diyl))bis(methanylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one) (O-IDTBR):P3HT BHJs. The crystalline P3HT network penetrates the crystal matrix without significantly disturbing the single crystallinity, resulting in long-range ordered BHJs. This bi-continuous structure, together with an improved overall ordering, contributes to enhanced charge/energy transfer. As a result, photodetectors based on these ordered BHJs exhibit ameliorated responsivity, detectivity, bandwidth, and stability as compared to the conventional BHJs with short-range ordering. Therefore, this work further extends the scope of long-range ordered BHJs toward crystalline polymer donors and NFAs, providing a generally applicable strategy for the design of organic optoelectronic devices with superior performance.

S-Scheme Porphyrin Covalent Organic Framework Heterojunction for Boosted Photoelectrochemical Immunoassays in Myocardial Infarction Diagnosis

Cardiac troponin I (cTnI) is an extremely sensitive biomarker for early indication of acute myocardial infarction (AMI). However, it still remains a tough challenge for many newly developed cTnI biosensors to achieve superior sensing performance including high sensitivity, rapid detection, and resistance to interference in clinical serum samples. Herein, a novel photocathodic immunosensor toward cTnI sensing has been successfully developed by designing a unique S-scheme heterojunction based on the porphyrin-based covalent organic frameworks (p-COFs) and p-type silicon nanowire arrays (p-SiNWs). In the novel heterojunction, the p-SiNWs are employed as the photocathode platform to acquire a strong photocurrent response. The in situ-grown p-COFs can accelerate the spatial migration rate of charge carriers by forming proper band alignment with the p-SiNWs. The crystalline π-conjugated network of p-COFs with abundant amino groups also promotes the electron transfer and anti-cTnI immobilizing process. The developed photocathodic immunosensor demonstrates a broad detection range of 5 pg/mL-10 ng/mL and a low limit of detection (LOD) of 1.36 pg/mL in clinical serum samples. Besides, the PEC sensor owns several advantages including good stability and superior anti-interference ability. By comparing our results with that of the commercial ELISA method, the relative deviations range from 0.06 to 0.18% (n = 3), and the recovery rates range from 95.4 to 109.5%. This work displays a novel strategy to design efficient and stable PEC sensing platforms for cTnI detection in real-life serums and provides guidance in future clinical diagnosis.

Structural properties and optical modeling of thermally annealed silicon carbide thin films

Non–hydrogenated amorphous silicon carbide films were processed by electron beam-physical vapour deposition on c-Si (100) and glass substrates. The films were isochronally annealed at varying temperatures. FTIR and Raman spectroscopies as well as XRD studies were used for structural investigation. For the pristine sample, it is found that the film is Si rich in an amorphous SiC matrix and that the observed graphitization is exclusively described by a single broad D-band in Raman. During the annealing process, a start of rearrangement of the network is observed at low temperatures of annealing but the amorphous phase still dominates in the microstructure. Still at low temperatures, the graphitization band broadens and expands to the G-bands region while at higher temperatures, an improved stochiometric crystalline SiC phase is achieved and distinct graphitic D and G bands are resolved. The induced crystalline network through annealing is prone to oxidation both in Si-O, bridged oxygen Si-O-Si and/or to silicon oxycarbide SiCx -O groups. An optical model based on effective medium approximation (EMA) theory is proposed in order to extract the optical properties of the material. It is established, from the evolution of the bandgap, that the films become transparent over a wider region of the visible spectrum as the temperature of annealing is increased to high values.

Microstructural Considerations of a Multi-Pass Rolled Ti-Nb-Ta-Zr Alloy.

The microstructural characteristic evolution was investigated during thermomechanical processing of Ti-29Nb-9Ta-10Zr (wt %) alloy, which consisted of, in a first stage, in a Multi-Pass Rolling with increasing thickness reduction of 20%, 40%, 60%, 80%, and 90%; in step two, the multi-pass rolled sample with the highest thickness reduction (90%) was subjected to a series of three variants of static short recrystallization and then to a final similar aging. The objective was to evaluate the microstructural features evolution during thermomechanical processing (phase's nature, morphology, dimensions, and crystallographic characteristics) and to find the optimal heat treatment variant for refinement of the alloy granulation until ultrafine/nanometric level for a promising combination of mechanical properties. The microstructural features were investigated by X-ray diffraction and SEM techniques through which the presence of two phases was recorded: the β-Ti phase and the α″-Ti martensitic phase. The corresponding cell parameters, dimensions of the coherent crystallite and the micro-deformations at the crystalline network level for both recorded phases were determined. The majority β-Ti phase underwent a strong refinement during the Multi-Pass Rolling process until ultrafine/nano grain dimension (about 9.8 nm), with subsequent slow growing during recrystallization and aging treatments, hindered by the presence of sub-micron α″-Ti phase dispersed inside β-Ti grains. An analysis concerning the possible deformation mechanisms was performed.

Understanding Photomechanical Behavior of Liquid Crystalline‐Based Actuators

AbstractLiquid crystalline‐based actuators containing azobenzene photoswitches have been used to demonstrate light‐responsive motion in soft actuator systems. Understanding the mechanical performance of these light‐responsive actuators as a function of the polymer chemistry as well as the nature and concentration of the photoswitches is crucial for developing advanced applications. A systematic study is presented here that clarifies the role of azobenzene photoswitches and the liquid crystalline networks in generating the desired photomechanical performance. Through measurement of photo stimulated mechanical behavior, in particular generated force and strain, a generalized set of guidelines concerning the appropriate subset of polymer chemistry and photoswitches required to achieve the desired performance for actuator design is derived.

Building a phenomenological chain-level understanding of mechanics of semicrystalline polymers: 2. Conceptual

To rationalize the comprehensive phenomenology in Paper 1 (this volume, p. 125878), we present a qualitative description for the mechanical behavior of semicrystalline polymers (SCPs) through a synthesis of prior understandings about the mechanical characteristics of glassy and semicrystalline polymers. Based on the central idea to regard an SCP as a crystalline chain network (CCN), in which a test chain can have crystalline and amorphous strands, we emphasize several key concepts: (a) crystallization determines the structure of the CCN, which is generally weaker than the pre-crystallization chain network in the molten state formed by interchain uncrossability, (b) ductility in SCPs is afforded by a sufficiently robust CCN, and (c) yielding and plastic deformation of SCPs require a successful structural transformation involving shape-change of crystalline phases through appreciable chain pull-out from the crystalline phases without breakdown of the CCN. In other words, it is the CCN that drives ductile SCPs to undergo yielding and subsequent large deformation through massive pull-out of load bearing strands (LBSs), which are the tie and entangling strands. Brittle fracture and lack of drawability occur in those SCPs where the CCN is too weak (due to a sparse population of LBSs) to cause sufficient meltdown of crystalline phases: There are not enough LBSs to undergo pull-out that is necessary for yielding and crystal transformation. Based on these concepts we can explore the processing-structure-property (P–S–P) relationship by demonstrating how pre-deformation in either crystalline or molten state produces more favorable structures for stronger mechanical characteristics.

The Role of Crosslinker Molecular Structure on Mechanical and Light-Actuation Properties in Liquid Crystalline Networks.

Phase behavior modulation of liquid crystalline molecules can be addressed by structural modification at molecular level. Starting from a rigid rod-like core reduction of the symmetry or increase of the steric hindrance by different substituents generally reduces the clearing temperature. Similar approaches can be explored to modulate the properties of liquid crystalline networks (LCNs)-shape-changing materials employed as actuators in many fields. Depending on the application, the polymer properties have to be adjusted in terms of force developed under stimuli, kinetics of actuation, elasticity, and resistance to specific loads. In this work, the crosslinker modification at molecular level is explored towards the optimization of LCN properties as light-responsive artificial muscles. The synthesis and characterization of photopolymerizable crosslinkers, bearing different lateral groups on the aromatic core is reported. Such molecules are able to strongly modulate the material mechanical properties, such as kinetics and maximum tension under light actuation, opening up to interesting materials for biomedical applications.

Erasable Photopatterning of Stilbene-Based Metal-Organic Framework Films.

The development of photosensitive materials for erasable photopatterning is of significant interest in anti-counterfeiting and information storage applications. Herein two kinds of stilbene-based metal-organic framework (MOF) films with layer by layer method for studying photopatterning is reported. The resulting 2D Zn2 (sdc)2 MOF film (sdc = 4,4'-stilbenedicarboxylate) exhibits excellent photosensitive features with a very short photoconversion time (<35s) while the 3D MOF Zn4 O(sdc)6 film does not have the property due to the fact that only parallel and short distance arrangement of olefin groups in the adjacent MOF layers can trigger [2+2] photocycloaddition. Furthermore, the Zn2 (sdc)2 film indicates obvious reversible fluorescent photoswitch behavior between yellow and blue fluorescence emission, which can achieve high-efficient, erasable photopatterning with various sizes (ca. 20 microns to decimeter). This study not only develops a new kind of photosensitive crystalline network film but also provides erasable photopatterning from macroscopic to microscopic in optical applications.

Spin-Resolved Band Structure of Hoffman Clathrate [Fe(pz)2Pt(CN)4] as an Essential Tool to Predict Optical Spectra of Metal–Organic Frameworks

Paramount spin-crossover properties of the 3D-Hoffman metalorganic framework (MOF) [Fe(pz)2Pt(CN)4] are generally described on the basis of the ligand field theory, which provides adequate insight into theoretical and simulation analysis of spintronic complexes. However, the ligand field approximation does not take into account the 3D periodicity of the actual complex lattice and surface effects and therefore cannot predict a full-scale periodic structure without utilizing more advanced methods. Therefore, in this paper, the electronic properties of the exemplar MOF were analyzed from the band structure perspective in low-spin (LS) and high-spin (HS) states. The density-of-states spectra determined for both spin-up and spin-down electrons of Fe d6 orbitals indicate spin-orbital splitting and delocalization for HS due to spin polarization in the iron atom ligand field. Presence of the surface states in the real crystal causes a red shift of the metal-metal charge transfer (MMCT) and metal-ligand charge transfer (MLCT) peaks for both HS and LS states. The addition of residual water molecules and disorder among the pyrazine rings reveal additional influences on the positions of the pyrazine band and, therefore, on the absorption spectra of the crystal. The results show a magnification of the peak correlated with the MLCT in the HS state and a significant red shift of the LS characteristic absorption band. The presented approach involving band structure analysis delivers a more complete image of the electronic properties of the [Fe(pz)2Pt(CN)4] crystalline network and can be a landmark for insightful studies of other MOFs.