Wavy Graphene-Like Network Forming during Pyrolysis of Polyacrylonitrile into Carbon Fiber.

Carbon fiber (CF) obtained by pyrolysis of polyacrylonitrile (PAN-CF) surpasses metals in properties suitable for diverse applications such as aircraft manufacture and power turbine blades. PAN-CF obtained by pyrolysis at 1200-1400 °C shows a remarkably high tensile strength of 7 GPa, much higher than pitch-based CF (pb-CF) consisting of piles of pure graphene networks. However, little information has been available on the atomistic structure of PAN-CF and on how it forms during pyrolysis. We pyrolyzed an acrylonitrile 9-mer in a carbon nanotube, monitored the course of the reaction using atomic-resolution electron microscopy and Raman spectroscopy, and found that this oligomer forms a thermally reactive wavy graphene-like network (WGN) at 1200-1400 °C during slow graphitization taking place between 900 and 1800 °C. Ptychographic microscopic analysis indicated that such material consists of 5-, 6-, and larger-membered rings; hence, it is not flat but wavy. The experimental data suggest that, during PAN-CF manufacturing, many layers of WGN hierarchically pile up to form a chemically and physically interdigitated noncrystalline phase that resists fracture and increases the tensile strength─the properties expected for high-entropy materials. pb-CF using nearly pure carbon starting material, on the other hand, forms a crystalline graphene network and is brittle.

Thermoreversible Gelation of Associating Polymers in Hydrogen-Bonding Mixed Solvents.

The thermoreversible gelation of associating polymers in hydogen-bonding mixed solvents is studied theoretically on the basis of the model ternary solution in which polymers carrying functional group A are dissolved in a primary solvent SB (mainly water) and cosolvent SC. Functional group A forms intermolecular cross-links (A-A) leading to gelation. It can also form hydrogen bonds with either solvent molecule SB or SC (A-SB, A-SC). If bound to a solvent molecule, A becomes inert. Solvent molecules form complexes with variable association numbers (SB-SC). Ternary phase diagrams for sol-gel transition lines and their cross sections on the temperature-solvent composition plane are constructed. It is shown that a minimum in the polymer concentration along the sol-gel transition line appears at a special solvent composition which depends upon the structure of the complexes. At such an optimal gel point, the sol-gel transition temperature becomes the highest, thus leading to stable, strong gels. The degree of adsorption, preferential adsorption coefficient, average molecular weight of the complexes, and cross-link probability are calculated as functions of the solvent composition. At the optimal gel point, the preferential adsorption coefficient changes its sign and the average molecular weight of the complexes reaches a maximum. Results are compared with the experimental data on poly(vinyl alcohol) in a mixed solvent of water/dimethyl sulfoxide, dimethyl sulfoxide/urea, or water/methanol.

Comparative Study on the Models of Thermoreversible Gelation.

A critical survey on the various theoretical models of thermoreversible gelation, such as the droplet model of condensation, associated-particle model, site-bond percolation model, and adhesive hard sphere model, is presented, with a focus on the nature of the phase transition predicted by them. On the basis of the classical tree statistics of gelation, combined with a thermodynamic theory of associating polymer solutions, it is shown that, within the mean-field description, the thermoreversible gelation of polyfunctional molecules is a third-order phase transition analogous to the Bose-Einstein condensation of an ideal Bose gas. It is condensation without surface tension. The osmotic compressibility is continuous, but its derivative with respect to the concentration of the functional molecule reveals a discontinuity at the sol-gel transition point. The width of the discontinuity is directly related to the amplitude of the divergent term in the weight-average molecular weight of the cross-linked three-dimensional polymers. The solution remains homogeneous in the position space, but separates into two phases in the momentum space; particles with finite translational momentum (sol) and a network with zero translational momentum (gel) coexist in a spatially homogeneous state. Experimental methods used to detect the singularity at the sol-gel transition point are suggested.

Thermoreversible gelation with ion-binding cross-links of variable multiplicity.

Thermoreversible gelation and liquid-liquid phase separation are theoretically studied for the gels of polyfunctional molecules (polymers) whose network junctions are formed by complexation of functional groups on the polymer chains with added metal ions. Phase diagrams on the polymer/ion/solvent concentration plane, including both sol-gel transition lines and liquid-liquid phase separation lines (spinodals), are derived as functions of the polymer functionality, molecular weight, maximum coordination number of ions, and temperature. Binding isotherms of ions are also calculated as functions of the ion concentration. Results of the calculated sol-gel transition lines are compared with our recent experimental data on gelation of star block and telechelic, acrylic copolymers cross-linked by iron ions. It is shown that, owing to reaction stoichiometry, there is an optimal ion concentration at which the solution gels for the lowest polymer concentration and also that a re-entrant sol phase appears in the ion concentrations higher than the optimal one. The effect of stepwise complex formation constants on the re-entrant phase is studied in detail.

Phase Behavior of Co-Nonsolvent Systems: Poly( N-isopropylacrylamide) in Mixed Solvents of Water and Methanol.

Cloud points of poly( N-isopropylacrylamide) in aqueous mixed solvents, with methanol as the cosolvent, are experimentally measured for polymer concentrations varied up to as high as the weight fraction 0.25. They are shown to form closed loops on the ternary phase plane in the temperature region between 5 and 30 °C, and hence co-nonsolvency is complete. Miscibility loops shrink by cooling, or equivalently, they exhibit lower critical solution temperature behavior. For a fixed polymer concentration, there is a composition of the mixed solvent at which the cloud-point temperature takes the lowest value. This minimum cloud-point temperature composition of the mixed solvent turned out to be almost independent of the polymer concentration, at least within the measured dilute region below the weight fraction 0.25. On the basis of the assumption that the phase separation is closely related to the preferential adsorption of the solvents by hydrogen bonding, we employ a model solution of Flory-Huggins type, augmented with direct and cooperative polymer-solvent hydrogen bonds, to construct the ternary phase diagrams. Theoretical calculation of the spinodal curves is performed, and the results are compared with the obtained experimental cloud-point data. The effect of molecular volume of the cosolvent is also studied within the same theoretical framework. Possibility for a upper critical solution temperature co-nonsolvency to appear for cosolvents with larger molecular volume is discussed.

Rate effect in the fracture of rubbers and chemically cross-linked gels.

Stationary crack propagation in rubbers and chemically cross-linked gels is studied by a new molecular theory of fracture in polymer networks. The fracture energy G (energy required to create a unit free surface by fracture) as a function of the crack velocity V is shown to obey, when measured in the unit of νlkBT, a master curve as a function of the dimensionless velocity 2tan θV/lß0(T), where ν is the number density of the network chains, T is absolute temperature, θ is the angle of the crack tip, l is the mean distance between the adjacent cross-links, and ß0(T) is the scission rate of the chains. The slope of the master curve in logarithmic scale depends on the nature of chain rupture; it takes a small value 0.16-0.2 in the low velocity region, and exhibits a crossover to the three times larger value 0.5-0.6 in the high velocity region. The ultimate strength G0 as defined by the fracture energy in the limit of zero crack velocity is obtained as a function of the molecular weight of the network chain, the bond energy, and temperature. The theoretical model is applied specifically to peeling and tearing experiments of rubbers and gels to study how the velocity affects the fracture energy in different geometry of network breakage. All results are qualitatively compared with the data reported in the literature.

Improvement of cross-linked films based on chitosan/diepoxy-poly (ethylene glycol) incorporating trans-cinnamaldehyde essential oil: Preparation, properties, and application in banana storage.

In this study, development of bioactive coatings containing 1 % (w/v) chitosan (CS), 0.6 % (w/v) diepoxy-polyethylene glycol (PEG), and trans-cinnamaldehyde (CIN) was achieved. The physicochemical and biological properties of the coatings were investigated. The tensile strength, light transmission, water vapor permeability (WVP), and antibacterial properties were enhanced by the incorporation of CIN. The CIN-containing films appeared compact and rough, as observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the quality attributes of the bananas were evaluated at room temperature for 24 days, and the results showed that the CS/PEG/CIN coating delayed the respiration peak, weight loss, sugar content loss, and maintained firmness, color, total soluble solids (TSS), titratable acid (TA), and the appearance of the bananas. Principal component analysis (PCA) revealed that the bioactive coating significantly affected the respiration rate and weight loss of bananas.

Persimmon preservation using edible coating of chitosan enriched with ginger oil and visualization of internal structure changes using X-ray computed tomography.

The incorporation of ginger oil (GO) influenced the physical, optical, and structural properties of the chitosan (CH) film including the decreases of moisture content (60.15 %), water solubility (35.37 %) and water vapor permeability (WVP) (32.79 %) and the increases of tensile strength (TS) (125 %), elongation at break (EAB) (2.74 %) and opacity (131.08 %). Antifungal capacity of the CH film was enhanced when GO was added to the film. The CH + GO film showed a less homogeneous surface that the presence of the oil droplets on the film surface. Moreover, the CH and CH + GO coatings reduced weight loss of persimmon by 14.87 %, and 21.13 %, respectively, compared to the control. Moisture content loss of the coated CH- and the coated CH + GO- persimmons was decreased by 1.94 % and 4.92 %, respectively, compared to that of the control persimmon. Furthermore, the CH and CH + GO coatings decreased in color changes, respiration rate, ethylene production, changes in pH and TSS, and remained firmness of persimmon during storage at 25 °C. In addition, X-ray CT images can be used to monitor internal changes and observe the tissue breakdown during storage period. The ΔGS value can be used as a predictor of persimmon internal qualities. Thus, the CH film containing GO can be applied as an active packaging material.

Effect of coatings containing 1-methylcyclopropane or mandarin peel extract on the freshness and metabolic profiles of cold stored strawberry.

The application of coatings is a strategy for maintaining the freshness of highly perishable fruits. This research aimed to evaluate the quality indices of strawberries (Amaou) coated with new coatings based on the sodium carboxymethyl cellulose (CMC) and cellulose nanofibres (CNF) with incorporated mandarin peel extract (ME) or 1-methylcyclopropene (1-MCP) during storage at 20days at 5 °C and 85% relative humidity (RH). Dissolving the coating solution containing ME in 1-MCP maintained its colour for up to 50 days. Coatings enhanced with ME and/or 1-MCP maintained fresh strawberries more effectively than the control, reducing weight loss and maintaining firmness, total soluble solids (TSS), citric acid, colour, and total phenolic content. The CCM2-2 coating solution showed superior effects on the weight loss and relative percentages of strawberry metabolites compared to the other coatings, as confirmed by the different components.

The incorporation of chitosan nanoparticles enhances the barrier properties and antifungal activity of chitosan-based nanocomposite coating films.

The potential alternative of exploring the development of nanocomposites through a single-molecule approach, such as combining chitosan nanoparticles (ChiNP) with chitosan (Chi), remains to be investigated. To maintain the insolubility of the ChiNP filler in the system, the protonation of weakly basic amino groups necessitates the pH of the coating solution above the pKa (6-6.5). This study aimed to evaluate the biofunctional properties improvements of Chi coatings incorporated with ChiNP as filler agents. The coating film forming solution comprised of 0.8 % Chi combined with varying concentrations (0 %, 0.1 %, 0.5 %, and 1 %) of ChiNP. The morphology of ChiNP was characterized via atomic force spectroscopy (AFM). Incorporating the ChiNP (1 %) significantly enhanced antifungal efficacy, i.e., an 88.28 % reduction in fungal activity compared with the control group, and a 65 % reduction compared with pure Chi against Botrytis cinerea. The incorporation of ChiNP improved the ultraviolet and visible light wavelengths, water vapor permeability, hydrophobicity, and thermal properties. Scanning electron microscopy and AFM were performed to assess the surface and internal microstructures of the coating. The findings of this study suggested that the nanocomposite coatings herein presented is potential for use in active packaging, especially in the context of preserving fresh fruit products.

Thermoreversible Gelation with Supramolecularly Polymerized Cross-Link Junctions.

Structure and reversibility of cross-link junctions play pivotal roles in determining the nature of thermoreversible gelation and dynamic mechanical properties of the produced polymer networks. We attempt to theoretically explore new types of sol-gel transitions with mechanical sharpness by allowing cross-links to grow without upper bound. We consider thermoreversible gelation of the primary molecules R{Af} carrying the number f of low molecular weight functional groups (gelators) A. Gelators A are assumed to form supramolecular assemblies. Some examples are: telechelic polymers (f=2) carrying π-π stacking benzene derivatives at their both ends, and trifunctional star molecules (f=3) bearing multiple hydrogen-bonding gelators. The sol-gel transition of the primary molecules becomes sharper with the cooperativity parameter of the stepwise linear growth of the cross-links. There is a polymerization transition (crossover without singularity) of the junctions in the postgel region after the gel point is passed. If the gelator A tends to form supramolecular rings competitively with linear chains, there is another phase transition in the deep postgel region where the average molecular weight of the rings becomes infinite (Bose-Einstein condensation of rings). As a typical example of binary cross-links where gelators A and B form mixed junctions, we specifically consider metal-coordinated binding of ligands A by metal ions B. Two types of multi-nuclear supramolecular complexes are studied: (i) linear stacking (ladder) of the sandwich A2B units, and (ii) linear train of egg-box A4B units. To find the strategy towards experimental realization of supramolecular cross-links, the average molecular weight, the gel fraction, the average length of the cross-link junctions are numerically calculated for all of these models as functions of the functionality f, the concentration of the solute molecules, and the temperature. Potential candidates for the realization of these new types of thermoreversible gelation are discussed.

Gelation Time of Network-Forming Polymer Solutions with Reversible Cross-Link Junctions of Variable Multiplicity.

The gelation time tg necessary for a solution of functional (associating) molecules to reach its gel point after a temperature jump, or a sudden concentration change, is theoretically calculated on the basis of the kinetic equation for the stepwise cross-linking reaction as a function of the concentration, temperature, functionality f of the molecules, and multiplicity k of the cross-link junctions. It is shown that quite generally tg can be decomposed into the product of the relaxation time tR and a thermodynamic factor Q. They are functions of a single scaled concentration x≡λ(T)ϕ, where λ(T) is the association constant and ϕ is the concentration. Therefore, the superposition principle holds with λ(T) as a shift factor of the concentration. Additionally, they all depend on the rate constants of the cross-link reaction, and hence it is possible to estimate these microscopic parameters from macroscopic measurements of tg. The thermodynamic factor Q is shown to depend on the quench depth. It generates a singularity of logarithmic divergence as the temperature (concentration) approaches the equilibrium gel point, while the relaxation time tR changes continuously across it. Gelation time tg obeys a power law tg-1∼xn in the high concentration region, whose power index n is related to the multiplicity of the cross-links. The retardation effect on the gelation time due to the reversibility of the cross-linking is explicitly calculated for some specific models of cross-linking to find the rate-controlling steps in order for the minimization of the gelation time to be easier in the gel processing. For a micellar cross-linking covering a wide range of the multiplicity, as seen in hydrophobically-modified water-soluble polymers, tR is shown to obey a formula similar to the Aniansson-Wall law.

UV-Crosslinked Poly(N-isopropylacrylamide) Interpenetrated into Chitosan Structure with Enhancement of Mechanical Properties Implemented as Anti-Fouling Materials.

High-performance properties of interpenetration polymer network (IPN) hydrogels, based on physically crosslinked chitosan (CS) and chemically crosslinked poly(N-isopropylacrylamide) (PNiPAM), were successfully developed. The IPN of CS/PNiPAM is proposed to overcome the limited mechanical properties of the single CS network. In this study, the viscoelastic behaviors of prepared materials in both solution and gel states were extensively examined, considering the UV exposure time and crosslinker concentration as key factors. The effect of these factors on gel formation, hydrogel structures, thermal stabilities of networks, and HeLa cell adhesion were studied sequentially. The sol-gel transition was effectively demonstrated through the scaling law, which agrees well with Winter and Chambon's theory. By subjecting the CS hydrogel to the process operation in an ethanol solution, its properties can be significantly enhanced with increased crosslinker concentration, including the shear modulus, crosslinking degree, gel strength, and thermal stability in its swollen state. The IPN samples exhibit a smooth and dense surface with irregular pores, allowing for much water absorption. The HeLa cells were adhered to and killed using the CS surface cationic charges and then released through hydrolysis by utilizing the hydrophilic/hydrophobic switchable property or thermo-reversible gelation of the PNiPAM network. The results demonstrated that IPN is a highly attractive candidate for anti-fouling materials.

Characterization and bio-functional performance of chitosan/poly (vinyl alcohol)/trans-cinnamaldehyde ternary biopolymeric films.

Bioactive films of chitosan (CS)/polyvinyl alcohol (PVA)/trans-cinnamaldehyde (CIN) were prepared by co-blending, and the impact of varying concentrations (0.5, 1.0 and 1.5 %) of CIN on the physicochemical properties of the ternary films was investigated. The ATR/FT-IR analysis revealed that the bioactive film is modulated by Schiff base (C=N) and hydrogen-bond interactions of CS, PVA, and CIN. Inclusion of CIN into the film improved mechanical properties with tensile strength increased from 0.5 % (68.52 MPa) to 1.5 % (76.95 MPa). The presence of CIN within the CS/PVA film also remarkably affected oxygen permeability and improved light transmittance. Additionally, the water barrier and contact angle properties were improved with increasing CIN content. The morphology of the CIN-containing films appeared non-stratified and dense when observed by SEM and AFM. Moreover, spore germination and in vitro assays confirmed strong antifungal activity of the CIN-containing film against P. italicum (~90 %) and B. cinerea (~85 %). The ternary films also exhibited excellent antioxidant activity, as evidenced by DPPH radical scavenging activity (31.43 %) and ferric reducing power (OD700 nm = 0.172) at the highest CIN concentration tested. Thus, this bioactive CIN films are proposed as a versatile packaging material for the food industry.

Topological classification of Brownian orbits.

This paper presents the exact formula for the bivariate probability distribution function of a Brownian particle as a function of its position and velocity, whose orbit makes a specified number of turns around an infinite straight line. In the limit of large friction constant, the solution reduces to the well-known results for random Wiener paths. Topological entanglements of stiff polymers are discussed on the basis of this solution. The method to find the solution is applied to the velocity space of a Brownian motion, and the probability to find a closed path with a specified winding number is obtained. Hence, closed two-dimensional Brownian orbits are classified into regular homotopy classes, whose statistical weight is derived as a function of the total length and the friction constant.

Examination of the body composition of patients with Werner syndrome using bioelectrical impedance analysis.

AIM: This study performed anthropometric measurements for Werner syndrome (WS) using bioelectrical impedance analysis and compared them with the Japanese reference data. METHODS: The analytical sample included nine participants with WS (four men, five women, 49.6 ± 9.3 years, SD). The height-corrected appendicular skeletal muscle mass index (SMI), upper- and lower-limb muscle mass index (USMI/LSMI) of the patients with WS were compared with the Japanese reference data (40-79 years). The body mass index, SMI, height-corrected fat mass index (FMI) and fat-free mass index (FFMI) were compared with the reference data of Japanese older adults (65-94 years). The SMIs of WS were also compared with the diagnostic criteria for sarcopenia. RESULTS: The SMI and USMI/LSMI of all participants with WS were lower than the Japanese reference data corresponding to gender and age, and the rate of decrease was more pronounced for USMI than for LSMI. The body mass index, SMI and FFMI for all the WS cases were lower than those for the older Japanese, while the FMI was higher in men with WS but lower in women than the reference data of the older Japanese. The SMI was below the cut-off value for the diagnosis of sarcopenia in all patients with WS. CONCLUSION: The SMI for WS is comparable with that for sarcopenia and significantly lower than that for healthy individuals of the same age and older adults. The USMI was significantly lower than LSMI in patients with WS, and FMI was higher in male patients with WS and lower in women than in healthy older people. Geriatr Gerontol Int 2022; 22: 75-80.

Edible film of native jicama starch, agarwood Aetoxylon Bouya essential oil and calcium propionate: Processing, mechanical, thermal properties and structure.

The objective of this study was to determine the properties of natural jicama starch and edible film made from the starch. The film was prepared by adding agarwood aetoxylon bouya essential oil and calcium propionate to investigate its properties as an edible coating for fruit or vegetables. The microstructure of the edible film was observed using scanning electron microscopy. The three main materials mostly had significant effects (P < 0.05) on the properties of the sample films, and starch film incorporating essential oil­calcium propionate showed optimum properties as an edible coating material because it had the highest elongation of 10.81%, the lowest stiffness with a Young's modulus of about 2.53 MPa, the lowest of water vapor transmission rate and permeability of 0.117 g h-1 m-2 and 3.092 g mm h-1 m-2 kPa-1, respectively, and the lowest weight loss of 75.30%. It was also found that the microstructure of starch-essential oil­calcium propionate film had a homogeneous surface and the presence of essential oil droplets was not visible.

Thermoreversible Gelation with Two-Component Mixed Cross-Link Junctions of Variable Multiplicity in Ternary Polymer Solutions.

Theoretical scheme is developed to study thermoreversible gelation interfering with liquid-liquid phase separation in mixtures of reactive f-functional molecules R{Af} and g-functional ones R{Bg} dissolved in a common solvent. Formed polymer networks are assumed to include multiple cross-link junctions containing arbitrary numbers k1 and k2 of functional groups A and B of each species. Sol-gel transition lines and spinodal lines are drawn on the ternary phase plane for some important models of multiple cross-link junctions with specified microscopic structure. It is shown that, if the cross-link structure satisfies a certain simple condition, there appears a special molar ratio of the two functional groups at which gelation takes place with a lowest concentration of the solute molecules, as has been often observed in the experiments. This optimal gelation concentration depends on f and g (functionality) of the solute molecules and the numbers k1 and k2 (multiplicity) of the functional groups in a cross-link junction. For cross-links which allow variable multiplicity, special attention is paid on the perfectly immiscible cross-links leading to interpenetrating polymer networks, and also on perfectly miscible cross-links leading to reentrant sol-gel-sol transition. Results are compared with recent observations on ion-binding polymer solutions, polymer solutions forming recognizable biomolecular complexes, polymer/surfactant mixtures, hydrogen-bonding polymers, and hydrophobically-modified amphiphilic water-soluble polymers.

Antifungal features and properties of chitosan/sandalwood oil Pickering emulsion coating stabilized by appropriate cellulose nanofiber dosage for fresh fruit application.

A novel composite edible coating film was developed from 0.8% chitosan (CS) and 0.5% sandalwood oil (SEO). Cellulose nanofibers (CNFs) were used as a stabilizer agent of oil-in-water Pickering emulsion. We found four typical groups of CNF level-dependent emulsion stabilization, including (1) unstable emulsion in the absence of CNFs; (2) unstable emulsion (0.006-0.21% CNFs); (3) stable emulsion (0.24-0.31% CNFs); and (4) regular emulsion with the addition of surfactant. Confocal laser scanning microscopy was performed to reveal the characteristics of droplet diameter and morphology. Antifungal tests against Botrytis cinerea and Penicillium digitatum, between emulsion coating stabilized with CNFs (CS-SEOpick) and CS or CS-SEO was tested. The effective concentration of CNFs (0.24%) may improve the performance of CS coating and maintain CS-SEO antifungal activity synergistically confirmed with a series of assays (in vitro, in vivo, and membrane integrity changes). The incorporation of CNFs contributed to improve the functional properties of CS and SEO-loaded CS including light transmission at UV and visible light wavelengths and tensile strength. Atomic force microscopy and scanning electron microscopy were employed to characterize the biocompatibility of each coating film formulation. Emulsion-CNF stabilized coating may have potential applications for active coating for fresh fruit commodities.

Transient network theory of wormlike micelles: topological force accelerates relaxation.

A new transient network theory is developed to study the rheological properties of entangled wormlike micelles. The dynamic mechanical moduli are calculated on the basis of the model network in which local structure of the wormlike micelles is represented by the entangled loops. These loops interact with each other by statistical force due to the topological constraints. They are assumed to pass through each other within a finite time to release the internal stress (phantom chain-crossing model). The high frequency plateau modulus G(infinity) and the relaxation time tau as functions of the micellar concentration are calculated and compared with the experimental data on the aqueous solutions of cetyltrimethylammonium bromide (CTAB) mixed with ionic aromatic compound sodium salicylate (NaSal). It turns out that creation and annihilation of the entanglements are strongly coupled to the topological force. The rheological relaxation time decreases with the concentration of the micelles because the average radius (correlation length xi) of the entangled loops, and their contour length L decrease with the CTAB concentration. Hence, the topological force is amplified by the increase in the concentration and, as a result, accelerates the stress relaxation by chain-crossing.