The formation of liquid crystalline (LC) phases in aqueous suspensions of cellulose nanocrystals (CNCs) largely depends on the geometric dimensions of the CNC particles, their concentration, polydispersity, and surface charge. Obtaining reproducible LC structures requires meticulous control over the particle production conditions that determine these properties. The objective of this work is to investigate the possibility of formation of LC phases in dilute aqueous suspensions of CNCs and the preservation of nematic and chiral nematic order in dried films. CNCs were prepared via sulfuric acid hydrolysis of filter paper. Their properties were characterized using transmission electron microscopy, polarized optical microscopy, FTIR spectroscopy, dynamic light scattering, X-ray diffraction and elemental analysis. The rheological properties of dilute CNC suspensions and the morphology of films formed from these suspensions were examined. Additionally, the effect of ultrasonic treatment on the properties of CNC suspensions was evaluated. It was found that LC phase formation begins at a CNC suspension concentration of approximately 1 wt

The absence of a universal method for isolating cellulose nanocrystals (CNCs) has prompted researchers to explore alternative approaches to traditional sulfuric acid hydrolysis. In this study, the authors continue their previous research by investigating CNC synthesis through cellulose solvolysis in an alcoholic environment. The CNCs were successfully obtained utilizing controlled sulfuric acid solvolysis of sulfate cellulose in a butanol-1/benzene mixture. The highest CNC yield (over 60 %) was achieved at strictly controlled acid-to-benzene ratios in a butanol-1/benzene/sulfuric acid reaction mixture, with a significant reduction in the optimal acid concentration. The study also analyzes the physicochemical properties of the isolated CNCs. No surface alkylation of the synthesized CNCs was observed during the cellulose solvolysis in the butanol-1/benzene mixture. Besides, the properties of these CNCs closely resembled those obtained through traditional sulfuric acid hydrolysis. The paper also discusses the potential mechanism of cellulose solvolysis in the process of CNC production.

The lack of a universal method for isolating cellulose nanocrystals (CNCs) has encouraged researchers to look for new methods and approaches as alternatives to traditional sulfuric acid hydrolysis. Acid alcoholysis has long been actively used in cellulose depolymerization processes to obtain a variety of alkyl glycosides and further alcoholysis products. In the present article, the authors continue their earlier research on the synthesis of CNCs in the presence of a sulfuric acid catalyst in an alcoholic environment. In this work, CNCs were obtained from sulfate- bleached pulp in a medium of primary monohydric alcohols (& Scy; n H 2 n +1 OH, n = 5-8). A maximum CNC yield of 60 % was achieved with pentanol-1 at a sulfuric acid concentration of 50 %. The work revealed that the alcohols studied can be ranked in descending order based on both the acid concentration corresponding to the maximum CNC yield and the yield itself, as follows: pentanol-1, hexanol-1, heptanol-1, and octanol-1. For octanol-1 the maximum CNC yield was 20 % at an acid concentration of 40 %. The physicochemical properties of the isolated CNCs were studied. No surface alkylation of the synthesized CNCs was found to occur during cellulose treatment in the media of the alcohols studied, as the properties of the CNCs, in general, were similar to those of CNCs obtained by standard sulfuric acid hydrolysis. This study broadens the scope of alternative methods to traditional sulfuric acid hydrolysis, and is likely to appeal to researchers engaged in developing novel approaches for CNC extraction.

The lack of a universal method for isolating cellulose nanocrystals (CNCs) has encouraged researchers to look for new methods and approaches as alternatives to traditional sulfuric acid hydrolysis. Moreover, acid alcoholysis has long been actively used in cellulose depolymerization processes to obtain a variety of alkyl glycosides and further alcoholysis products. In the present article, the authors continue their earlier research on the synthesis of CNCs by cellulose alcoholysis in an alcoholic environment. In this work, CNCs were obtained by controlled sulfuric acid alcoholysis of sulfate cellulose in a medium of primary monohydric alcohols (СnH2n+1OH, n = 5–8). A maximum CNC yield of 60% was achieved with pentanol-1 at a sulfuric acid concentration of 50%. The paper showed that in descending order of both the acid concentration corresponding to the maximum CNC yield and the yield itself, the alcohols studied can be arranged as follows: pentanol-1, hexanol-1, heptanol-1, and octanol-1. For 1-octanol, the maximum CNC yield was 20% at an acid concentration of 40%. The physicochemical properties of the isolated CNCs were studied. No surface alkylation of the synthesized CNCs was found to occur during cellulose alcoholysis in the media of the alcohols studied, as the properties of the CNCs, in general, were similar to those of CNCs obtained by standard sulfuric acid hydrolysis.

The possibility of using C60F48 fluorofullerene molecules as sources of fluorine in reactions involving Au(111) has been demonstrated. Ultrahigh-vacuum scanning tunneling microscopy and X-ray photoelectron spectroscopy studies have shown that C60F48 molecules lose some fluorine atoms with time, forming molecules with the stoichiometric composition close to C60F36 fluorofullerene, which is confirmed by X-ray photoelectron spectroscopy data. The interaction of fluorine with the Au(111) surface occurs only under islands formed by fluorofullerene molecules losing some fluorine atoms. It has been shown that a С60F18 molecule does not react with the Au(111) surface. At the submonolayer coating of the gold surface with С60F18 fluorofullerene, the “herringbone” ( 22 ×√(3) ) reconstruction characteristic of the clean Au(111) surface remains unchanged both in the region free of formed fluorofullerene islands and under them, and С60F18 molecules keep their initial configuration in time.

We report the first observation of well-ordered fluorine monolayers (MLs) on the Cu(111) surface. Fluorine atoms were adsorbed on the copper surface through the controlled decomposition of fluorinated fullerene (C60F18) molecules, which were previously deposited on the substrate at submonolayer coverage. The desorption of fluorine atoms from the C60F18 fullerene molecules and their adsorption on the Cu surfaces were evidenced by X-ray photoelectron spectroscopy experiments. Analysis of the core-level shifts indicates a strong F-Cu interaction, but the formation of copper fluoride (CuF2) can be ruled out. Two types of ordered fluorine structures were observed in scanning tunneling microscopy measurements. We found a kagome lattice with 5 x 5 cell with a fluorine coverage of 0.48 ML and a distorted, kagome-like structure with a 7 x 7 cell with a fluorine coverage of 0.49 ML, where some of the 6 rings of the ideal kagome lattice become 5 or 7 rings. The two structures coexist at temperatures up to 200 degrees C. Density functional theory calculations show that the observed structures are stable and that the F atoms occupy face-centered cubic (fcc)-hollow (the fcc-hollow site is situated in the gap between three atoms in the upper layer with no atom in the layer below), hexagonal close-packed (hcp)-hollow site (which is also located in the gap between three atoms, but with the atom in the layer below), and bridge sites. The energy difference between the two structures is very small (11 meV/F atom), which may explain their coexistence at room temperature. Simpler structures of comparable coverage, in particular a honeycomb lattice with a 2 x 2 cell and a coverage of 0.5 ML, are found to be less stable. The present results provide new insight into the fluorine-copper interfacial interaction, which is of great importance for technological applications such as fluorine ion shuttle batteries.

Composite materials filled with cellulose particles (microcrystalline cellulose and nanocellulose) have good prospects for use in various fields. Microcrystalline cellulose (MCC) and nanocellulose (NC) were isolated by chemical and physical methods and investigated. Composite materials based on polyethylene (PE) were obtained using MCC and NC as fillers (5–20 wt.%) and maleic anhydride grafted low molecular weight polyethylene (MA-g-LMPE) as a compatibilizer. The structure and morphology of the composites and fillers were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, thermal analysis (TA), transmission electron microscopy (TEM), atomic force microscopy (AFM), and the strength properties were determined by tensile testing. An increase in the crystallinity index and mechanical strength of composites at low filler contents (up to 5 wt.%) was revealed. The size of the cellulose particles significantly affects the structure and properties of composites. Although the general picture of the effect of fillers on the crystalline structure and mechanical properties is similar, the addition of NC had a greater effect than МСС. The results of this study showed the possibility of using MCC and NC as reinforcement materials in composites, and they have biodegradable properties.

The lack of an alternative universal method for obtaining cellulose nanocrystals (CNCs), that would replace traditional sulfuric acid hydrolysis, encourages researchers to look for new methods and approaches. At the same time, alcoholysis of cellulose has long been known as a method of obtaining various alkyl glycosides and products of their further alcoholysis. In this paper, the authors propose to use controlled alcoholysis of cellulose in a medium of simple alcohols for CNC synthesis. Specifically, in this study, CNCs are prepared by controlled sulfuric acid alcoholysis of sulfate cellulose in a medium of four aliphatic alcohols (methanol, ethanol, propanol, and butanol-1). The paper also discusses the possible mechanism of cellulose alcoholysis during CNC preparation and shows that, in contrast to hydrolysis, cellulose alcoholysis can produce CNCs with a higher yield and under milder conditions (at a lower acid concentration). The physicochemical properties of the CNCs synthesized are studied. On the whole, the properties of the CNCs obtained by alcoholysis and hydrolysis are found out to be similar. However, alcoholysis is shown to produce CNC particles with a higher surface charge, which increases the colloidal stability of aqueous CNC suspensions and can be used to study their liquid crystal properties. Under the given conditions of CNC synthesis in alcoholic media (concentration of sulfate cellulose suspension of 0.025 g/mL, temperature of 50 °C, duration of 2 h), butanol-1 makes it possible to achieve the maximum possible CNC yield of 60%.

To enhance the redispersibility of dried nanocellulose, cellulose nanocrystal (CNC) cryogels were produced by freeze-drying CNC-stabilized cyclohexane-in-water Pickering emulsions. The CNC cryogels were easily redispersed in water and organic solvents; thus, the approach proposed made it possible to significantly improve CNC redispersibility in aqueous and nonaqueous media.

The interaction of fluorine atoms with Cu(111) surface has been analyzed by means of scanning tunneling microscopy and x-ray photoelectron spectroscopy (XPS). A submonolayer coverage of fluorinated fullerene C 60 F 18 has been chosen to provide a well controllable arrival of fluorine atoms on copper surface. The appearance of F-induced surface structures on the Cu(111) surface caused by defluorination of C 60 F 18 molecules adsorbed on the surface was shown. XPS measurements unambiguously indicate the existence of chemical state of fluorine not typical for CuF 2 formation. Superstructure of well ordered metastable clusters consisting of fluorofullerene molecules are formed on the Cu(111) surface as a result of the balance of two interactions: the dipole-dipole interaction between fluorofullerene molecules and the interaction of C 60 F 18 molecules with the two-dimensional gas phase, emerging above the copper surface. Regular surface structure formed by fullerene molecules interacting through collective vibrational mode can be used for entanglement formation between two qubits each associated with ground and excited electronic states of the molecule by applying two coherent laser pulses.

The main drawback of cellulose nanocrystals (CNCs) obtained by conventional sulphuric acid hydrolysis is their low thermal stability in consequence of pyrolysis catalyzed by sulfo-groups on the CNC surface. Replacement of surface sulfo-groups by carboxyl groups as a result of oxi-dation allows the thermal stability of CNCs to be enhanced significantly. Although a great num-ber of studies have reported properties of polymer nanocomposites reinforced by CNCs, thermal properties of the composites compared to the neat polymers are discrepant and still poorly under-stood. In this work, CNCs were produced from microcrystalline cellulose by sulfuric acid hydroly-sis and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) oxidation. The CNC composites with water-soluble polymers ??? polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone and poly-acrylamide ??? were obtained. The composites were characterized by various methods, i.e. transmis-sion electron and scanning electron microscopies, energy-dispersive X-ray analysis, Fourier -transform infrared spectroscopy, X-ray diffraction and thermogravimetric analyses, differential scanning calorimetry, and tensile testing. A side-by-side comparison between the thermal and mechanical properties of the polymer composites reinforced by sulfuric acid-hydrolyzed and TEMPO-oxidized nanocellulose was conducted. Analysis of the thermal properties of CNC shows that the surface sulfonate groups replacement with carboxyl groups leads to significant increase of initial temperature of thermal degradation and temperature of the maximum decomposition rate of the CNC. However, the thermal behavior of the composites is much more complicated, and such thermal properties are discussed in detailed. The tensile properties analysis of the compo-sites demonstrates that an addition of TEMPO-oxidized nanocellulose does not improve signifi-cantly the tensile strength and Young???s modulus as compared with sulfuric acid-hydrolyzed one.

Sol–gel method has been employed for preparing porous carbon materials (xerogels and aerogels) using nanocrystalline cellulose (NCC) as a template. The method includes sol–gel synthesis of inorganic silica matrix (using tetraethoxysilane as SiO2 precursor) and carbonization of NCC under inert atmosphere followed by removal of SiO2 by refluxing in alkali solution. Factors affecting formation of porous carbon structure and resultant porous carbon materials have been studied.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/polycaprolactone (PHBV/PCL) polymer mixtures reinforced by cellulose nanocrystals (CNCs) have been obtained. To improve the CNC compatibility with the hydrophobic PHBV/PCL matrix, the CNC surface was modified by amphiphilic polymers, i.e., polyvinylpyrrolidone (PVP) and polyacrylamide (PAM). The polymer composites were characterized by FTIR, DSC, TG, XRD, microscopy, BET surface area, and tensile testing. The morphological, sorption, thermal, and mechanical properties of the obtained composites have been studied. It was found out that with an increase in the CNC content in the composites, the porosity of the films increased, which was reflected in an increase in their specific surface areas and water sorption. An analysis of the IR spectra confirms that hydrogen bonds can be formed between the CNC hydroxyl- and the –CO– groups of PCL and PHBV. The thermal decomposition of CNC in the PHBV/PCL/CNC composites starts at a much higher temperature than the decomposition of pure CNC. It was revealed that CNCs can either induce crystallization and the polymer crystallite growth or act as a compatibilizer of a mixture of the polymers causing their amorphization. The CNC addition significantly reduces the elongation and strength of the composites, but changes Young’s modulus insignificantly, i.e., the mechanical properties of the composites are retained under conditions of small linear deformations. A molecular-dynamics simulation of several systems, starting from simplest binary (solvent-polymer) and finishing with multi-component (CNC—polymer mixture—solvent) systems, has been made. It is concluded that the surface modification of CNCs with amphiphilic polymers makes it possible to obtain the CNC composites with hydrophobic polymer matrices.

In this paper, physical adsorption of polyvinylpyrrolidone (PVP) was used as the method of surface modification of cellulose nanocrystals (CNCs). The work also considers the PVP molecular weight effect on dispersion of the surface-modified CNC in dichloromethane (DCM). The authors analyze the physicochemical properties of the composite with polycaprolactone (PCL) - CNC/PVP/PCL - prepared from a solution of PVP-modified CNCs in DCM, and conduct a molecular dynamics simulation of the interactions between the system (CNC, PVP, PCL) components in vacuum and in a solvent medium (water, DCM). According to the simulation results, the CNC/PVP/PCL composite has the following structure: PCL macromolecules have practically no direct contacts with the CNC surface but are located between the PVP macromolecules that, in their turn, are predominantly located near the CNC particle surface. (C) 2021 Elsevier B.V. All rights reserved.

In this work, we have developed methods of synthesis of cellulose nanocrystal (CNC) conjugates with chlorotriazine reactive dyes (RDs)—reactive violet, reactive-bright red and reactive bright-orange.) The prepared CNC-RD conjugates were characterized by a complex of techniques: UV–Vis, FTIR and solid-state 13C NMR spectroscopy, thermogravimetric and elemental analysis, particle size and zeta potential analysis, scanning electron and polarization optical microscopy. An analysis of the solid state 13C NMR spectra allowed us to conclude that the crystallinity index of the CNC-RD conjugates, compared to CNCs, did not change, i.e. RDs covalently bonded with the surface of the CNC particles and did not affect the CNC crystalline structure. The amount of the dye covalently bonded to the CNC particle surface was determined based on the elemental analysis data and using a square-cross-section model of the cellulose nanocrystal. The results obtained enabled us to make a conclusion that the RD covalent fixation was selective and occurred on one of the CNC ends (the so-called reducing end of the cellulose polymeric chain). Successful modification of the CNC surface was confirmed by UV–Vis spectroscopy. It was found that aqueous suspensions of the CNC-reactive violet dye conjugates possessed indicator properties. The size and charges of the CNC-RD particles in diluted aqueous suspensions were determined; the CNC-RD aqueous suspensions were found to have high colloidal stability. The stabilizing effect of the CNC-reactive violet dye conjugate for the formation of Pickering emulsions of the oil-in-water type was studied. It was shown that the CNC-reactive violet dye conjugate effectively stabilized n-decane emulsions in water.

Composites of polycaprolactone with cellulose nanocrystals were produced, and their morphological, thermal, and strength characteristics were examined. It was found that nanocrystalline cellulose as a filler increased the porosity of the resultant composite materials. A conclusion was made that nanocrystalline cellulose can act as an initiator of polycaprolactone crystallization and affect the growth of the polymer crystallites. Incorporation of cellulose nanocrystals into the polycaprolactone matrix increased the hydrophilicity of the material and promoted an increase in water sorption while making the composite more brittle as indicated by decrease in the elongation at break and icreases in the tensile strength and Young's modulus.

The effect of nanocrystalline cellulose (NCC) in a composite with polycaprolactone (PCL) on calcium carbonate mineralization into various polymorphs (calcite and vaterite) was studied. The composites were manufactured using an acetone organogel of NCC and NCC surface-modified with polyvinylpyrrolidone (PVP). Dimethylformamide (DMF), a mixture of DMF with tetrahydrofuran (THF), and chloroform (CF) were used as solvents in the preparation of the composites. The NCC increases the hydrophilicity and porosity of the composites. In porous films, calcium carbonate crystallization can occur both on the surface and in the bulk of the film. Nanocrystalline cellulose in the composites promotes calcium carbonate mineralization to form vaterite in the bulk of the film. The proposed approach can be used to produce composite materials with desired properties for biomedical purposes.