A finger-jointing model for describing ultrastructures of cellulose microfibrils

In this paper, we propose a finger-jointing model to describe the possible ultrastructures of cellulose microfibrils based on new observations obtained through heating of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofibrils (CNFs) in saturated water vapor. We heated the micrometers-long TEMPO-CNFs in saturated water vapor (≥ 120 °C, ≥ 0.2 MPa) and observed a surprising fact that the long TEMPO-CNFs unzipped into short (100 s of nanometers long) fibers. We characterized the heated TEMPO-CNFs using X-ray diffraction (XRD) and observed the XRD patterns were in consistent with Iβ. We observed also jointed ultrastructures on the heated TEMPO-CNFs via high-resolution transmission electron microscopy (HR-TEM). Thus we concluded that cellulose microfibrils are not seamlessly long structures, but serial jointed structures of shorter blocks. Polysaccharide chains of the short blocks organized in Iβ. The jointed region can be either Iα or amorphous, depending on positions and distances among the chains jointed in proximity. Under heating, Iα was not converted into Iβ but was simply destroyed. The jointed structure implies a “working and resting rhythm” in the biosynthesis of cellulose.

Effect of Gas Type and Its Pressure on Nanobubble Generation

The dependence of the volume number density of ion-stabilized gas nanobubbles (bubstons) on the type of gas and the pressure created by this gas in deionized water and saline solution has been investigated. The range of external pressures from the saturated water vapor (17 Torr) to 5 atm was studied. It turned out that the growth rate of the volume number density of bubstons is controlled by the magnitude of the molecular polarizability of dissolved gases. The highest densities of bubstons were obtained for gases whose molecules have a dipole moment. At fixed external pressure and the polarizability of gas molecules, the addition of external ions leads to a sharp increase in the content of bubstons.

OPTIMIZATION OF THE HEAT AND HUMIDITY MODE OF MULTI-LAYER BUILDING ENCLOSING STRUCTURES

The article presents a methodology for determining the required resistance to vapor permeation of the outer layer of a multilayer building envelope, based on the condition that there is no condensation of water vapor in it. When deriving the formula, an analytical dependence was used to determine the elasticity of saturated water vapor, obtained by the authors of this article. With the help of the proposed technique, the assessment of the thermal and humidity regime of the outer wall, insulated facade system using thin-walled plaster, as well as layered masonry using expanded polystyrene and basalt plates as insulation was made. The results of the calculation of the indicated external walls are presented, which show that condensation of water vapor is possible in layered masonry. The proposed analytical dependence for determining the maximum allowable resistance to vapor permeation of the outer layer of a multilayer enclosing structure is recommended to be used in engineering calculations of the humidity mode of external enclosures of buildings and structures.

A finger-jointing model for describing nanostructures of cellulose microfibrils

We propose a finger-jointing model to describe the possible nanostructures of native cellulose microfibrils based on new observations obtained through thermal decomposition of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofibers (CNFs) in saturated water vapor. We heated the micrometers-long TEMPO-CNFs in saturated water vapor (≥ 120 °C, ≥ 0.2 MPa) for ≤ 8 h. The long TEMPO-CNFs unzipped into short (100 s of nanometers long) cellulose nanowhiskers (CNWs). We characterized the CNWs using Raman spectroscopy and Fourier transform infrared spectroscopy, observing similar spectra as TEMPO-CNFs. Thus, the native cellulose microfibrils are not seamlessly long structures, but serial “jointed structures” of CNWs. The finger-jointing model implies a “working and resting rhythm” in the biosynthesis of cellulose. CNWs are highly dispersible in water and polar organic solvents, and are much easier to combine with other classes of polymers at nano-levels. The findings can enhance the feasibility and applicability of native cellulose to achieve sustainable development goals.

Neutral water clusters in the Earth’s atmosphere: The effect of orientational isomerism on their concentrations and thermodynamic parameters.

In order to estimate the effect of orientational isomerism on the thermodynamic parameters and concentrations of water clusters in the gas phase, all possible structures of book, cageand prismconformations of water hexamer (H2O)6have been studied using the DFT (B3LYP/6-311++G(2d,2p)), G4, DFTB, W1BD and MB-pol calculations. It was found that taking into account of the orientational isomerism leads to the values of water cluster gas-phase concentrations different by 1–2 orders of magnitude from the results obtained when only single or several most energetically favorable structures are considered. The concentrations of all the considered hexamer structuresin the saturated water vapor at T= 298.15 K are estimated as 1.61 103(G4) and 8.17 105 (DFT) molecules/cm3.