Search

Rheological properties of cellulose and chitin solutions with additions of montmorillonite nanoparticles in NaOH/urea/thiourea aqueous-alkaline solutions were studied. X-ray diffraction analysis shows that montmorillonite nanoparticles in hydrated cellulose and chitin films are in the intercalated state. Analysis of the Fourier IR spectra of the composite films reveals the shift of the Si–O absorption band in both polymer systems. Introduction of montmorillonite into hydrated cellulose and chitin matrices leads to an increase in the residual weight (at 800°C) and to a slight decrease in the degradation onset temperature and in the temperature of the maximal degradation rate.

The kinetics of the development of the structural phase transition of the first order in monodisperse samples of tetracosane C24H50 has been studied using Fourier-transform IR spectroscopy. Temperature dependences of frequencies and intensities of rocking (in the region of ν ~ 720 cm–1) and bending (in the region of ν ~ 1470 cm–1) vibration modes of CH2 groups in trans methylene sequences in crystalline cores of elementary lamellae has been analyzed. It has been shown that the solid-phase transition of the first order develops by the heterogeneous mechanism in a narrow temperature interval ΔT ~ 2 K according to the theory of diffuse phase transitions of the first order and is caused by changes in the symmetry of crystallographic cells.

We study colloids of nanobiocomposites (NBC) containing Au nanoparticles (NP) obtained by reduction of gold precursor with functional groups of κCAR. The AuNPs content was changed from 2.0 to 5.6 w/w %. Hydrolysis of κCAR during reduction of gold ions produced carboxylate groups supporting nanobioconjugation (FT-IR data) and electrostatic stabilization through increased negative ζ-potential. The self-assembly of AuNPs took place after storing NBC, as shown by UV/vis. extinction and transmission electron microscopy. Analysis of the structure-sensitive R g / R h ratios obtained by dynamic and static light scattering showed that the colloids have core-shell structure. The macromolecules in the shell exhibited polyelectrolyte expansion at [NaCl] and [KCl] R h was similar to that of the pristine κCAR observed previously by optical rotation. Monitoring the equilibration of light scattering intensity at each mini-quenching step of the cooling run allowed further insight into the hysteresis origin. These colloids are interesting for sensing applications because of enhanced scattering of plasmonically coupled AuNPE. Their thermo- and ion-sensitivity can be useful in drug delivery.

The structural changes in crystalline lamella cores of tridecanoic acid CH3(CH2)11COOH during heating in the range from the temperature T1 = 13.5°C to T2 > Tm = 41.6°C have been investigated using Fourier transform infrared spectroscopy. The behavior of the bands of rocking (in the region of 720 cm–1) and bending (in the region of 1470 cm–1) vibrations of CH2 groups in tridecanoic acid methylene segments has been analyzed. It has been shown that, in the first-order phase transition region (Ts–s ~ 36°C) within a narrow temperature range (ΔT1 ≤ 1 K), there is a gradual transformation of the initial triclinic subcell into the hexagonal subcell. The mechanism of this transition has been considered in terms of the theory of diffuse first-order phase transitions.

Studies of the solubility of chitin from North Sea shrimp shells in aqueous NaOH solutions with urea and thiourea additives showed that chitin was totally dissolved in aqueous NaOH (10%) + urea (5%) + thiourea (5%). A thermally reversible gel formed if the solutions were stored at room temperature. The structures of chitin films obtained from the solutions were studied using IR spectroscopy and x-ray diffraction.

Polymeric and organo-inorganic sorbents molecularly imprinted with cholesterol were synthesized to create selective hemosorbents for efferent therapy of hypercholesterlemia. These sorbents are block copolymers of 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate and granulated organo-inorganic sorbents in which the imprinting was performed in the layer of the above copolymer on the surface of selenium (Se) nanoparticles stabilized with polyvinyl pyrrolidone. The physicochemical and sorption properties of the sorbents were studied.

The solubility of wood cellulose of various molecular weights in aqueous NaOH solutions with added urea and thiourea was studied with variable temperature, solvent composition, and sequence of dissolution stages. It was shown that cellulose of average degree of polymerization up to 500-600 dissolved. Thermally reversible gels formed in solutions held at 20°C for 2 d. The structural organization of cellulose-hydrate films prepared from the solutions was studied using IR spectroscopy and x-ray diffraction.

New composite membrane with a poly(γ-benzyl- l -glutamate) (PBG) separation layer on a micro-porous poly(amide-imide) support was prepared and tested as a pervaporation membrane for selective separation of toluene/ n -heptane mixtures. Composite membrane was formed by coating a solution of PBG in chloroform on the top surface of micro-porous PAI-SO 2 support. PBG layer fulfils indispensable requirement for the preferential adsorption of the most penetrating component (toluene) of a separated mixture. The structure of the membrane was studied in detail. X-ray diffraction, electron microscopy and IR spectroscopy measurements were performed. Crystalline regions formed by backbones of macromolecules are low permeable barriers to penetrants, but also limiters for swelling of high permeable polymer phase. The knowledge of the material structure in dependence of conditions of its preparation enabled to adapt the process of the membrane formation to reach the efficiency of separating aromatic/aliphatic compounds. The separation ability was tested by pervaporation measurements for different toluene concentrations in binary mixtures toluene/ n -heptane. Diffusion coefficients, fluxes and separation factors were evaluated. It was shown that conformation of α-helix PBG molecules in the coating layer of the composite membrane does not change in the pervaporation. The membrane retains its integrity and can be used in subsequent cycles of a process. The obtained results during this study could be used for the design of highly efficient PBG/PAI-SO 2 composite membranes for separation of mixtures aromatic and aliphatic hydrocarbons by pervaporation.

The interaction of chitosan in the basic form with montmorillonite at different concentrations in composite films is studied with the use of dielectric spectroscopy and FTIR measurements. It is shown that the interaction of amino groups and primary hydroxyl groups of chitosan with local charges on the surfaces of montmorillonite nanoparticles is responsible for a change in the system of intramolecular and intermolecular hydrogen bonds that is typical for polysaccharides. The glass-transition temperature of chitosan in the composite systems is measured.

Solubility of cellulose, chitin, and chitosan in seven ionic liquids of varied structure was studied. It was found that pressure, temperature, and amount of an aprotic diluent (dimethyl sulfoxide) affect the dissolution of cellulose and chitin in an ionic liquid. The variation of the degree of polymerization of cellulose and chitin in ionic liquid solutions was studied. IR Fourier spectroscopy and X-ray diffraction analysis were used to examine the structural organization of hydrated cellulose and chitin films obtained.

Fourier transform infrared spectroscopy (FTIR) was used for determination of orientational and conformational characteristics of plane polypeptide brushes with different density of polypeptide chains grafted to modified silicon surface. The determination of grafting density of polypeptide chains in brushes, which depends on chemical structure of spacer groups, was carried out using ultraviolet (UV) spectroscopy. The influence of chemical structure of modifying spacer groups and outer conditions on the characteristics of plane polypeptide brushes was established. The peculiarities of α-helical structure (random coil transfer of polymer chains in brushes under the action of denaturants) were investigated.

The interrelation between the transport properties of pervaporation membranes (used to separate toluene-n-heptane mixtures) and the structure of poly-γ-benzyl-L-glutamate diffusion layers has been studied. The decrease in the membrane selectivity while increasing the flux at the transition from 3 to 50 wt % toluene in the mixture under separation is accompanied by a change in the ordered structure of poly-γ-benzyl-L-glutamate structure without variation in the α-helical conformation of the polypeptide chain.

The product of condensation of tetraethoxysilane with diphenylsilanediol was studied by gel permeation chromatography, 29Si NMR, and IR spectroscopy, and its structure was suggested.

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH2)22OH and HO(CH2)44OH, in the spectral range of 400–5000 cm−1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm−1 (rocking vibrations of CH2 groups) and 1463–1473 cm−1 (bending vibrations of CH2 groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH2 wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.

Synthetic conditions have been determined for obtaining sulfoethyl cellulose (SEC) from flax fiber manufacturing waste, namely, short fibers and lignified parts of pedicels (boon). The outcomes of sulfoethylation depend on the synthetic method, the molar ratio of the reactants, and the reaction time. Depending on the synthetic method, the resulting SEC is either insoluble or partially soluble in water. The products synthesized can be used as heavy-metal ion sorbents and as a substitute for carboxymethyl cellulose.

The conditions of preparation of mixed cellulose ethers containing carboxy and amino groups by the reaction of samples of short flax fiber and cotton linter with monochloroacetamide were examined. The influence of the amino groups of the mixed cellulose ethers on the rheological properties of their aqueous solutions was elucidated.

The optical constants have been measured by the techniques of IR transmission and ATR spectroscopy in the range 4000–400 cm−1 for four industrial polymers: polymethyl methacrylate, polystyrene, polyethylene, and polytetrafluorethylene.

The conditions under which carboxymethyl ethers of cellulose with various degrees of substitution can be prepared from wastes formed in production of flax fibers were studied. The structure of the cellulose ethers synthesized was studied by IR Fourier spectroscopy and physicochemical methods.

The method for the synthesis of fullerols C60(OH) x was developed, allowing to obtain products with low number of hydroxy groups attached to fullerene molecule. At the first stage, product C60(tert‐BuO) x was obtained by the radical reaction of C60 with tert‐butyl‐peroxide under heating or UV‐irradiation. At the second stage, fullerol C60(OH) x was synthesized after the elimination of tert‐butyl groups by acid treatment. Several samples C60(OH) x containing different numbers (x = 2–5) of hydroxy groups were obtained, the main product had x = 2. The structure of the fullerols was confirmed by UV‐ and Fourier‐transform infrared (FTIR)‐spectroscopy and MALDI‐TOF mass‐spectrometry.

A comparative analysis of phase transitions in diols with various chain lengths [(CH2)(44)(OH)(2) and (CH2)(22)(OH)(2)] and changes in their absorption spectra with temperature have been investigated by DSC and FTIR. Analysis of the DSC data has led to the conclusion that the low-temperature phase transition of (CH2)22(OH)2 in a solid state (Ts-s = 367.1 K) is a phase transition of the first order, while the high-temperature phase transition (T-m = 376.3 K) is of the second order, i.e., a transition of the order-disorder type. Splitting of the IR absorption bands into doublets at 720-730 cm(-1) and 1463-1473 cm(-1) indicates that crystalline subcells in the lamellae of both diols are orthorhombic lattices with the parameters typical of hydrocarbons. IR spectra showed that at the phase transition temperature Ts-s transformation of an orthorhombic subcell into a hexagonal one occurs. This type of molecular chain packing remains the same up to the melting temperature T-m. In a (CH2)44(OH)2 diol, the ortho-hexagonal subcell transition occurs only at the melting temperature (390.0 K). The wide IR band in the region from 3000 cm(-1) to 3600 cm(-1) shows that end hydroxyl groups of diol molecules form, on the surfaces of lamellar crystals, long (polymer) regular sequences consisting of intermolecular hydrogen bonds.

Single-stage synthesis of carboxymethyl cellulose amides was studied. The influence exerted by introduction of amide groups with bulky alkyl radicals on the thermodynamic affinity of mixed cellulose ethers for a solvent and their solubility in water was evaluated.

Morphology and molecular structure of three nascent ultra high molecular weight polyethylene (UHMWPE) powders synthesized on unsupported and supported Ziegler-Natta heterogeneous catalysts were stu...

Formation of liquid crystalline (LC) order in thermotropic main-chain random copolymers (containing mesogens of one type and spacers of different lengths) were investigated by IR spectroscopy, DSC, X-ray and polarized microscopy methods. It was demonstrated that in such copolymers (CPLs) smectic liquid crystalline (LC) order can exist. Peculiarities in spacers behavior during transition to LC state are found. Conclusion about the dependence of the mechanism of smectic LC order formation on chemical structure of rigid components of CPLs is made.

Conformational transitions in thermotropic main-chain polymers of complex chemical structure including homopolymers with possibility of conformational transformations in mesogens and random copolymers (CPLs) containing mesogens of the same type and spacers of different lengths were investigated. It was demonstrated that liquid crystalline (LC) state influences conformational transformations in fragments of chain restraining them in comparison with an isotropic melt. It was found that CPLs studied form LC order of smectic type. Peculiarities in spacers behaviour during transition to LC state ensure formation of such type of LC order. Conclusion about dependence of mechanism of smectic LC order formation on chemical structure of rigid components of CPLs is made.

With object to evaluate the effect of spacer chemical composition on chain conformation of thermotropic polymers in liquid crystalline (LC) state, linear and combined (main chain/side chain) polymers, containing fragment of malonic acid (FMA) in methylene spacer were studied. It is shown that owing to presence of FMA chain conformations of the studied polymers differ substantially from those of RF-polymers with simple methylene spacer. Tn 1c melt the main chain of polymers investigated has “hairpin”- like conformation with parallel allignment of neighbouring mesogens. In the case of combined polymers the side chain is located inside the hairpin, and mesogens of both main and side chains are round to be mutually parallel Described polymer structure in LC melt provides the explanation for experimentaily observed similarities between properties of LC melts of studied polymers and those of low molecular weight liquid crystalls.

Mesogen conformations in thermotropic polyesters with alternating mesogens and poly(methylene) spacers were investigated by IR spectroscopy with polarized and unpolarized light. The selective deuteration of terephthaloyl-bis(p-oxybenzoate) mesogens gave a possibility of assigning part of the IR bands to terephthalic or to oxybenzoic fragments. It is shown that in the liquid crystalline melt the mesogen conformation is planar, but in the semicrystalline state it is mainly nonplanar. Differences in mesogen conformations of polymers containing an even or an odd number of methylene units in the spacer are detected. Thus, LC ordering seems to affect not only the conformation of the spacer but also the conformation of the mesogen.

The conformations of thermotropic polyesters with alternating mesogens and poly(methylene) spacers in the main chain were investigated by conformational calculations using the data of linear-dichroism IR-spectroscopy, X-ray analysis and differential scanning calorimetry. The conformations of monomeric units and of the macromolecules as a whole in different phase-aggregated states were estimated. It is shown that in the liquid-crystalline (LC) state the polymer chains are strongly extended. The results are compared with the data of various theories of LC ordering.

In terms of the rotational-isomeric state approximation, the conformations of the flexible spacer and the mean order parameters of the spacer and of the mesogenic fragment were calculated for LC-polyesters with mesogenic fragments and spacers in the main chain. A comparison of the results with IR-spectroscopic data and X-ray structural analysis indicates that both the monomeric units, and the macromolecules as a whole, exist in a considerably extended state.

The effect of the formation of LC order on the conformational structure of a number of thermotropic polyesters containing mesogenic and flexible fragments in the backbone with conformationally labile units in the mesogenic fragments has been studied. In the LC state of the polymers studied conformers are realized in the mesogenic fragments ensuring maximum asymmetry of the mesogenic fragment and the chain as a whole.

Features of the orientation of thermotropic polyesters were observed by methods of IR spectroscopy with polarized and non-polarized radiation. Differences in the character of orientation of mesogenic fragments with respect to the shear direction are explained in terms of the polydomain model of the structure of polymer liquid crystals, and by the non-equilibrium character of the liquid-crystalline state in polymers.

Computer modeling of the emissivity of a Globar lamp in the IR region has been carried out on the basis of a three-layer optical model. The metrological possibilities of calculating the high-temperature spectral emissivity of a composite multicomponent substance are estimated by the methods of classical dispersion analysis.

This paper discusses the possibilities of using IR Fourier spectroscopy to investigate the orientational and conformational characteristics of single layers of polymers attached by one end to an impermeable surface (polymeric brushes). The method is used to determine the structural parameters of the polymeric branches of brushes attached to a cylindrical or flat surface. © 2005 Optical Society of America

IR and NMR spectroscopy has been used to show that the liquid-crystalline state of poly-(γ-benzyl-L-glutamate) solutions persists in the presence of the weak chloroacetic acid (CAA) as well as the strong difluorochloro-acetic acid (DFCAA). The unusual progress of the NMR signal splits as a function of the acid concentration, and the differences detected for CAA and DFCAA have been explained by the binding mechanism of these acids with the polymer molecules. The structure of the liquid-crystalline polymeric arcs has been investigated. The dependence of the size of NMR signal splits on the polymer concentration present in the solution, but also the similar upper limits of polymer-acid binding efficiencies in dilute and concentrated solutions, determined by IR spectroscopy, have led to the conclusion that there exists a regular distribution of the polymer and solvent molecules in the liquid-crystalline polymers arcs.

The liquid crystal-isotropic solution phase equilibria have been studied by IR spectroscopy and polarized light microscopy on poly- γ -benzyl- L -glutamate concentrates in various solvents. The conditions under which the polymer exists in a non-aggregate in the liquid crystalline solutions have been determined. The “true” concentration dependence of the co-existence of the phases was established, also the degree of orientation of the polymer in the liquid crystalline arcs. The experimental results have been found to agree well with the lattice model for a formation of a liquid crystalline order in the concentrates of rigid chain polymers.

The order parameters of mesogenic ( S m ) and flexible ( S f ) fragments are determined for a range of aromatic thermotropic polyesters containing the same mesogenic and various flexible fragments in the main chain. The S m values are almost independent of the chemical nature and length of the flexible spacer. The relative positions of the axes of the mesogenic and flexible fragments in various states of aggregation are determined.

The conditions for forming lyotropic liquid-crystal order in mixed solutions of polymers having different values of geometrical asymmetry have been studied experimentally. It has been shown that the equilibrium composition of the phases depends essentially on the difference in the asymmetry of the components being mixed.

An analysis of the experimental molar mass dependence of the order parameter and of the threshold concentrations delimiting the region of the lyotropic liquid crystalline state in solutions of semi-flexible polymers led to the conclusion that the mechanism which governs the flexibility of this kind of macromolecules differs from that which applies to the classical worm-like chains.

The effects of polymolecularity and heterogeneity of the chemical structure of the flexible fragments on the conditions of formation and the order parameter of mixed liquid crystal systems are discussed, using aromatic polyesters with mesogenic and flexible fragments in the main chain as examples. It is shown that at close values of the temperature ranges over which liquid crystal order of the mixed components of different molecular weight exists, the order parameter of the mesogenic fragments of the mixture in the liquid crystal state is less than the corresponding values for homopolymers. In the case of a mixture of components with a flexible fragment of different length and the same mesogenic fragments, the components of the system are completely incompatible in the liquid crystal state.

It was shown by IR spectroscopy that the formation of liquid-crystalline order in concentrated solutions of poly-γ-benzyl-L-glutamate in a mixed solvent does not further stabilize the helix structure of a polypeptide chain but increases the helix-coil cooperative inverted conformation transition.

It has been shown that the method of obtaining the samples influences the conformational structure of aromatic polyesters with mesogenic groups in the main chain in the bulk state. In the samples obtained from the liquid crystal state the structure of the liquid crystal melt which does not change on annealing and orientation of the samples persists. The features of of the structure of the samples in bulk obtained from solution are considered.

The influence of the mechanism of flexibility of semirigid polymer molecules on the concentration boundaries of the formation of the liquid crystalline state and the parameters of its order has been studied by polarization microscopy and IR spectroscopy. It is shown that the determinant factor in the formation of liquid crystalline order is the size of the rigid portion of the polymer chain.

IR spectroscopy has been used to investigate liquid crystal solutions of poly-γ-benzyl- l -glutamate oriented through the “wall effect” of the cell walls, in single and two component solvents. The degrees of orientation of the polymer and solvent in the liquid crystal domains have been determined. The kinetics of orientation of the polymer in the liquid crystal solution and the way in which the maximum degree of orientation of the polymer depends on its concentration in the solution have been investigated.

Conformational changes and variations in intermolecular ordering have been investigated for polydecamethyleneterephthaloyl-di-oxybenzoate in various physical states, including the partially crystalline, liquid-crystalline and the isotropic melt. The investigation was based on IR-spectroscopy and polarization microscopy. Transitions from the partially crystalline state to the liquid-crystalline is accompanied by changes occurring in mesogenic as well as in flexible portions of the molecule: in the former portion the mutual placement of benzene rings and ester groups is altered; in the latter it was found that long trans-trans-sequences disappear, and the number of gauche isomers in methylene spacers is increased. Transition from liquid crystalline melt to the isotropic one is not actually accompanied by conformational changes, but is characterized by a redistribution of gauche-trans isomers along the chain, which influences the intermolecular order and the extent of the ordered regions.