Formation Of Supermolecular Structures Research Articles

Hyaluronan oligosaccharides form double-helical duplexes in water:1,4-dioxane mixed solvent

Hyaluronic acid (HA) is a hydrophilic natural polysaccharide consisting of alternating monosaccharide units of glucuronic acid and N-acetyl glucosamine. In aqueous solutions the electrostatic repulsion of the carboxylate groups hampers the formation of supermolecular structures that can be partially stabilized by the addition of salt. Increased permittivity of the mixed water:organic solvents causes better compensation of the negative charge of HA chains by dissolved cations which changes their interactions with other molecules. In this study we simulate interactions of two HA chains in water:1,4-dioxane and water:tert-butanol mixed solvents with varying NaCl concentrations using molecular dynamics (MD). Anti-parallel double-helix-like duplexes are formed in NaCl-containing water:1,4-dioxane mixture and remain stable even when NaCl is removed. Parallel duplexes separate after a short time. In water:tert-butanol analogous duplexes are unstable. Stability of HA duplexes is thus determined by the solvent composition and the ability of its components to separate in the solvation shell of HA molecules, as well as by the mutual orientation of the chains.

Effect of fire retardant fillers on thermophysical properties of composite materials of ethylene-vinyl acetate copolymer

The influence of composite materials of ethylene-vinyl acetate copolymer that do not maintain combustion and fire-retardant fillers on thermophysical processes was explored. Ethylene-vinyl acetate copolymer was used in the studies. The content of vinyl acetate is 18 % and 28 %; MFI is 2.5 g/10 min. and MFI is 5 g/10 min. Fire retardant fillers included aluminum oxide trihydrates with average diameter of particles of 1.5 µm and 3.0 µm; magnesium oxide dihydrates with average diameter of particles of 3.0 µm and 3.7 µm and hydromagnesite with average diameter of particles of 1.4 µm. Using the method of thermogravimetric analysis and differential scanning calorimetry TGA/DSC, temperatures of vitrification, melting and decomposition, crystallinity degree, specific thermal capacity, and activation energy were determined. It was found that temperatures of physical transformations (temperatures of vitrification, melting, and decomposition) of polymer compositions that do not maintain combustion depend on properties of ethylene-vinyl acetate copolymer. They increase with decreasing of fluidity indicator of copolymer of ethylene vinyl acetate. EVA 1 has lower values of the indicator of melt fluidity and content of vinyl acetate than EVA 2. During an increase in content of fire retardant fillers, temperatures of physical transformations are shifted in the direction of increasing: vitrification temperature increases from – 85 °C to 53 °C, melting temperature – from 68 °C to 90 °C. At the same time, crystallinity degree decreases from 8.8 % to 1.0 % and specific thermal capacity increases from 0.4 to 8.6 J/gK. This is due to formation of supermolecular structure of the derived compositions. The influence of the polymeric matrix, composition and dispersity of fire retardant fillers on thermal-physical characteristics of polymeric compositions was determined. In case of using a polymer matrix with lower MFI and fire retardants fillers with smaller average diameter of particles, temperature characteristics are shifted towards higher temperatures than in the case of selection of polymer matrix with large MFI and fire-retardant fillers with a larger diameter of particles. Obtained results will be useful during development of formulations of polymer compositions that do not maintain combustion for cable products, considering their thermophysical characteristics.

Antifrictional composites based on chemically modified UHMWPE. Part 2. The effect of nanofillers on the mechanical and triboengineering properties of chemically modified UHMWPE

The mechanical and tribological properties of nanocomposites based on chemically modified ultra-high molecular weight polyethylene are determined. The super-molecular and chemical structure of the nanocomposites based on the block copolymers UHMWPE-grafted UHMWPE and UHMWPE-grafted HDPE are studied by the methods of X-ray structural analysis, IR spectroscopy, scanning differential calorimetry, and electron microscopy. The mechanical and tribological properties of the nanocomposites based on the block copolymers are found to differ insignificantly from those of the nanocomposites on the base of non-modified UHMWPE. The crystallization and formation of super-molecular structure in the heterogeneous materials under study are shown to depend on the heterogeneity of the distribution of the nanofillers. The authors believe that chemical modification in terms of grafting polar monomers is unable to improve the adhesion of the nanofillers to the high-molecular matrix (UHMWPE). Thus, the wear resistance of the UHMWPE-based nanocomposites is mostly governed by the crystallization conditions and type of supermolecular structure formed during crystallization (either spherulitic or lamellar).

Pure Cellulose Nanoparticles from Trimethylsilyl Cellulose

AbstractSilyl ethers of cellulose are promising derivatives of the biopolymer because they exhibit thermoplastic behavior at higher functionalization, may be applied as intermediate in subsequent reactions and have a high tendency to form defined supramolecular structures. Trimethylsilylation can be carried out by applying ionic liquids (ILs) such as 1‐ethyl‐3‐methylimidazolium acetate (EMIMAc) as reaction medium. Pure trimethylsilyl cellulose (TMSC) can be efficiently synthesized with 1,1,1,3,3,3‐hexamethyldisilazane (HMDS) yielding products with degrees of substitution (DS) up to 2.89. During the synthesis of highly functionalized derivatives, precipitation of the TMSC occurred, which simplifies the recycling of the IL. The tendency of TMSC toward the formation of supermolecular structures was exploited for the formation of pure cellulose nanospheres by a simple dialysis process. FTIR spectroscopy confirmed the complete removal of the TMS functions during this process. Scanning electron microscopy, dynamic light scattering, atomic force microscopy, and particle size distribution analysis showed that cellulose particles with a size of 100 to 200 nm are accessible in this simple manner.

Polarization of Fluorescence of Asphaltene Containing Systems

Formation of supermolecular structures in petroleum disperse systems is determined by interactions of asphaltenes. Petroleum systems are lyophilic oleocolloids with low polar dispersive media which is in dynamic balance with elements of disperse structure. Supermolecular scale of organization is most important for determining the macroscopic parameters. Levshin-Perrin equation for depolarization of fluorescence was modified for polydispersed systems. Interfacial tension coefficient of model asphaltene solution was calculated in a case of Volmer's function. For technogenic mixtures the temperature dependences of the sizes near the point of phase transition are presented. Enthalpy of asphaltene association per one molecule was calculated. Polarization degree together with macroscopic parameters correlates with appearance of asphaltene dispersed phase in system.

Interactions of ionic liquids with polysaccharides. VI. Pure cellulose nanoparticles from trimethylsilyl cellulose synthesized in ionic liquids

AbstractTrimethylsilyl cellulose (TMSC) can be efficiently synthesized with 1,1,1,3,3,3‐hexamethyldisilazane (HMDS) by applying the ionic liquids (ILs) 1‐ethyl‐3‐methylimidazolium acetate, 1‐ethyl‐3‐methylimidazolium chloride, and 1‐butyl‐3‐methylimidazolium chloride as reaction medium, yielding pure biopolymer derivatives with degrees of substitution (DS) up to 2.89. Cosolvents, for example, chloroform, could be used to adjust the viscosity of the system and to achieve the miscibility of the components. During the synthesis of highly functionalized derivatives precipitation of the TMSC occurred, which simplifies the recycling of the IL. The high tendency of TMSC toward the formation of supermolecular structures was exploited for the formation of nanoparticles studying a simple dialysis process. Amazingly, pure cellulose nanoparticles can be obtained by dissolving TMSC in tetrahydrofurane or N,N‐dimethyl acetamide and dialysis against water. FTIR spectroscopy confirmed the complete removal of the TMS functions during this process. Scanning electron microscopy, dynamic light scattering, atomic force microscopy, and particle size distribution analysis showed that cellulose particles down to a size of 170 nm are accessible in this simple manner. The nanoparticle suspensions exhibit viscosities in the range of water. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4070–4080, 2008

Effect of γ-irradiation on the properties of poly(ester urethane) elastomer

The influence of irradiation with 60Co γ-rays on gelation, change in the mechanical characteristics, and the formation of supermolecular structure in a poly(ester urethane) elastomer synthesized from oligoether adipate and diisocyanate, as well as a diol with or without double carbon-carbon bonds, was studied. It was found that the presence of double carbon-carbon bonds in the structure of the elastomer ensures the predominance of crosslinking over degradation processes. It was shown that γ-irradiation at a dose of 380 kGy is accompanied by the formation of a microglobular structure of ∼1 μm size. The specifics of changes in the mechanical characteristics depending on the absorbed dose are discussed.

Frequency Dependence of Oil Conductivity at High Pressure

Electric conductivity of materials is defined by a competition of several mechanisms of charge carrier movement: phoretic, ionic and electron‐hole jumping. The relative contribution of them is not constant when thermodynamic conditions are changing. Paraffine and naphtene hydrocarbons are typical dielectrics. Formation of supermolecular structures is accompanied by ordering of asphaltene‐resin and polyaromatic molecules. Solvate shells contain the molecules with less molecular masses. The disperse particle from the centre to periphery is characterized by reduction of conductivity from the values peculiar to “good” semiconductors in a nucleus, “average” in intermediate phase to typical for dielectrics in the disperse media. Threshold of the mobility of charge carriers is determined by temperature, pressure, strength of the external field, width of the forbidden zone, and nature of components of the disperse media and phase. Spectra of conductivity of model asphaltene solutions and Kumkolskaya oil in frequency range from 10−3 up to 106 Hz are measured for pressures up to 1 GPa in temperature interval from 250 to 320 K. Particularly at the analysis of spectra of conductivity the technique offered by Sheu and Mullins is used. Dependences were approximated by power‐law functions according to the concept of Jonscher's “the universal response.” Influence of pressure and temperature to the exponents is analyzed. Values of activation energy are determined. Received data can be useful for prognosis of oil phase behavior at high pressures.

De facto molecular weight distributions of glucans by size-exclusion chromatography combined with mass/molar-detection of fluorescence labeled terminal hemiacetals

A major capability of polysaccharides in aqueous media is their tendency for aggregation and dynamic formation of supermolecular structures. Even extended dissolution processes will not eliminate these structures which dominate many analytical approaches, in particular absolute molecular weight determinations referring to light scattering data. An alternative approach for determination of de facto molecular weight for glucans with free terminal hemiacetal functionality (reducing end group) has been adjusted from carbohydrates for midrange and high-dp glucans: quantitative and stabilized labeling as aminopyridyl-derivatives (AP-glucans) and subsequent analysis of SEC-separated elution profiles based on simultaneously monitored mass and molar fractions by refractive index and fluorescence detection. SEC-DRI/FL of AP-glucans proved as an appropriate approach for determination of de facto molecular weight of constituting glucan molecules even in the presence of supermolecular structures for non-branched (pullulan), branched (dextran), narrow distributed and broad distributed and for mixes of compact and loose packed polymer coils (starch glucan hydrolizate).

Dynamic structure of poly(vinyl pyrrolidone)/ethyl alcohol mixtures studied by time domain reflectometry

AbstractDielectric studies of poly(vinyl pyrrolidone)/ethyl alcohol (PVP–E) binary mixtures with concentration variations were carried out in the frequency range of 10 MHz to 10 GHz by time domain reflectometry at 15, 25, 35, and 45 °C. One relaxation process, corresponding to ethyl alcohol molecules in the poly(vinyl pyrrolidone) (PVP) matrix, was observed in this frequency range for all the mixtures. The static dielectric constant of the PVP–E mixtures decreased linearly with an increase in the weight fraction of PVP. The observed anomalous increase in the value of the relaxation time (τ) of these mixtures was interpreted by the consideration of the variation in the local structure of self‐associated ethyl alcohol molecules and also the PVP behavior as a geometric constraint for the rotational motion of ethyl alcohol molecules. Furthermore, the τ values of these mixtures were independent of the viscosity. The energy parameters for the dielectric relaxation process (the free energy, enthalpy, and entropy of activation for the dipolar orientation) were determined to confirm the transient behavior of the heterogeneous species due to the breaking and re‐forming of hydrogen bonds with the internal rotation of OH groups in the ordered structure of the PVP–E mixtures. On the basis of the evaluated dielectric parameters, the formation of supermolecular structure in the PVP–E mixtures in dynamic equilibrium was sketched and examined by the consideration of the hydrogen bonding between the terminal hydroxyl groups of self‐associated ethyl alcohol flexible chains and the carbonyl groups of monomer units of PVP coiled chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1134–1143, 2005

Synthesis and solid state structures of macromolecular cylindrical brushes with varying side chain length

Cylindrical brushes with a macromolecular backbone and well-defined side chains of different length (4≤ P n sc≤38) were synthesized by polymerization of macromonomers. The effect of side chain length on the intermolecular order has been investigated by means of X-ray scattering on the melt-extruded samples. The increase of the side chain molar mass results in an increase of the intermolecular distance d according to d∼( M n sc) 0.476. The contour length of the cylindrical brush polymers per main chain monomer unit, l m, was determined to slightly vary with side chain molar mass M n sc according to l m∼( M n sc) 0.059. The resulting values are much less than the maximum extension, l m =0.25 nm, which is found to be almost independent of side chain molar mass. Also, supermolecular structure formation of a random copolymer brush prepared by radical copolymerization of methacryloyl end functionalized polyvinylpyridine and polymethylmethacrylate macromonomers has been observed and is interpreted as a consequence of intramolecular phase separation.

Effect of Association of Ionogenic Groups on the Phase Separation and Crystallisation and Formation of Supermolecular Structures

Effect of Association of Ionogenic Groups on the Phase Separation and Crystallisation and Formation of Supermolecular Structures

Bread Staling: Molecular Basis and Control.

The molecular basis of staling is examined by reviewing what is known about the components of wheat flour, factors that affect staling rate, and the various mechanisms that have been proposed. The conclusion reached is that bread staling is a complex phenomenon in which multiple mechanisms operate. Polymer crystallizations with the formation of supermolecular structures are certainly involved. The most plausible hypothesis is that retrogradation of amylopectin occurs, and because water molecules are incorporated into the crystallites, the distribution of water is shifted from gluten to starch/amylopectin, thereby changing the nature of the gluten network. The role of additives may be to change the nature of starch protein molecules, to function as plasticizers, and/or to retard the redistribution of water between components. Nothing more definite can be concluded at this time.

β-MODIFICATION OF ISOTACTIC POLYPROPYLENE: PREPARATION, STRUCTURE, PROCESSING, PROPERTIES, AND APPLICATION

The methods of preparation and formation of supermolecular structures in quiescent and sheared melts and the properties of the β-modification of isotactic polypropylene (β-iPP) are reviewed. The introduction of selective β-nucleants is the most reliable method for preparation of samples rich in β-modification or of pure β-iPP. The advantages and drawbacks of the known β-nucleating agents are summarized. It is emphasized that pure β-iPP can be prepared under laboratory and processing conditions in the presence of highly active and selective β-nucleants. Nevertheless, there are no literature data—apart from that of the author's groups—which evidenced unambiguously the formation of pure β-iPP. It hints at the insufficient selectivity of β-nucleants used or at the inappropriate crystallization or melting conditions applied by other scientists. The structure formation during the high-temperature hedritic crystallization is discussed comprehensively and illustrated by polarized light microscopy and scanning electron microscopy micrographs. Some specific features of β-iPP, namely the high- and low-temperature growth transition, the restricted temperature range of the formation of pure β-iPP, and the unique melting and recrystallization characteristics (melting and annealing memory effect) are summarized. It was emphasized that impact strength and toughness of β-iPP markedly exceed those of α-iPP. Processing of β-nucleated iPP and application of β-nucleated iPP is described briefly.

Formation of 2-D Chiral Monolayers from Chiral Mesogens Studied with Molecular Dynamics Simulation

Monolayer structures of a chiral mesogen, (R)- or (S)-[4′-(1-methylheptyloxy)-3′-nitrobipheny1-4yl] 4-(trans-5-decenyloxy) benzoate, adsorbed on graphite were investigated with molecular dynamics simulations to clarify the mechanism of chiral supermolecular structure formation. We proposed a mechanism model that is based on the coupling between up-down symmetry breaking and the molecular tilt direction symmetry breaking of the monolayer.

Some Problems of Structure Formation in Self-organizing Liquid Oligomer Systems. II. Theoretical Models for Formation of Super-molecular Structure of Oligomer Systems

The driving force for self-organization are the fundamental laws of thermodynamics. We consider some theoretical models which qualitatively explain anomalous properties of these systems.

Improved efficiency of molecular organic EL devices based on super molecular structure

A novel aluminum chelate, tris(5-hydroxymethyl-8-quinolinolato)aluminum (AlOq) as the emitter has been developed. The device (ITO/PVK/AlOq/Al) emitting green light has a luminance of more than 1000 cd/m 2. The highest quantum efficiency of light-emitting devices is about 1.44 lm/W, better by three times than that of similar structure device made with Alq as the emitter duo to the formation of super molecular structure in AlOq thin films.

Cylindrical Micelles of Wormlike Polyelectrolytes

We report on a study of the association behavior in solution of semirigid polymers consisting of a poly(p-phenylene) backbone with alternation of negatively charged and hydrophobic moieties. Small-angle X-ray scattering data of aqueous solutions of sulfonated poly(p-phenylene)s show aggregated polymer chains in the form of cylindrical micelles, in which the phenylene backbone is oriented parallel to the long axis of the micelle. The charge density and the length of the alkyl side chains influence the diameter and aggregation number of the micelles. Micelles with strand aggregation numbers between 3 and 11 are formed depending on the hydrophobic−hydrophilic balance. The observed behavior resembles the formation of supermolecular structures by biogenic semirigid polyelectrolytes.

Formation of supermolecular structures of polysaccharide‐surfactant complexes in aqueous solutions. Influence of the polymer backbone

AbstractNovel water‐soluble derivatives of cellulose, amylose and dextran are synthesized and investigated with regard to their special interactions with the anionic surfactant sodium dodecylsulfate (SDS) by means of rheological flow‐ and oscillatory measurements as well as electrolytic conductivity in aqueous solution. The derivatives of amylose and dextran show a continuous adsorption of SDS with increasing surfactant concentration leading to an increase of the viscosity and of the viscous part of the shear modulus of the solution. Only low elastic parts are detectable. In contrast, the behaviour of cellulose derivatives differs extremely with increasing amount of SDS. The viscosity and the elastic part of the shear modulus of aqueous solutions reach a well pronounced maximum and then drop almost to the initial values. A similar behaviour is also observed by adding the cationic surfactant hexadecyltrimethylammonium bromide. It is concluded that the observed differences in properties of the cellulose derivatives on the one side and derivatives of amylose and dextran on the other are cause by the structure of the polymer main chain, because the side groups for all of these polymers are comparable.

Einfluss des polymerrückgrats auf eigenschaften von thermoplastischen elastomeren

Abstract4‐Urazoyl benzoic acid groups were statistically attached to various hydrocarbon elestomers, polar elastomers and partially crystalline polymer via a polymer‐analogous reaction. Thermal analysis (DSC), infrared spectroscopy (FT‐IR), stress‐strain experiments and dynamic‐mechanical analysis were used to analyses whether these systems, analogous to functionalized polybutadienes, would form ordered supramolecular structures of the polar side‐groups that would lead to a thermoreversible crosslinking. While the structure formation is suppressed for elastomers with a large cross‐sectional area of the chain(e.g. butyl rubber) or polar side‐groups (e.g. polychloroprene), the mechanical properties can be controlled by balancing supermolecular structure formation and crystallization in the case of polyoctenamer.