Influence Of Molecular Mass Research Articles

Effect of SWCNT volume fraction on the viscosity of water-based nanofluids

Nanofluids have received a great deal of interest in recent years because of their various unique features. According to the findings, the addition of nanotubes to the base materials can drastically alter their properties. In the present work, the viscosity of a typical water-based nanofluid containing single-walled carbon nanotubes is estimated using the molecular dynamics simulation for different volume fractions ranging between 0.557 and 3% at two temperatures (298K and 313K). The temperature of the systems is controlled using a Nose-Hoover thermostat. For calculating viscosity, the Green-Kubo equilibrium method is used. The enthalpy, potential, kinetic, and total energies are calculated to determine the system's stability. In addition, the influence of molecular mass on these energies is studied. The nanotube under investigation is an armchair(6,6)-type single-walled carbon nanotube. The results highlight the promise of the molecular dynamics simulation technique as a powerful tool in the prediction of nanofluid properties besides the experimental results. The value of viscosity will decrease as the temperature rises, much like the base fluid. Furthermore, it is shown that the viscosity is proportional to the volume fraction of water-SWCNT nanofluid. According to the results, a new viscosity relationship for volume fractions in the range of ϕ ≤ 3% is proposed. The viscosity, temperature, and volume fraction are all linked together in this equation.

Linear and Cyclolinear Polysiloxanes in the Bulk and Thin Films on Liquid and Solid Substrate Surfaces

The special features of self-organization and structure formation observed at the interface between different-polarity phases of macromolecules with various hydrophilic-lipophilic balances are reviewed by the example of amphiphilic siloxanes: polymers, oligomers, and low-molecular compounds. The structure of polyorganosiloxanes, the peculiarities of their behavior and conformational changes at the phase interface, and the influence of molecular mass, end groups, hydrophobic bulk substituents, chemical structure of the main (linear or cyclolinear) chain, and the subphase on the surface properties of the compounds mentioned above are analyzed.

Photonics and nanophotonics and information and communication technologies in modern food packaging.

The analysis of the problem of conjunction of information and communication technologies (ICT) with packaging industry and food production was made. The perspective of combining the latest advances of nanotechnology, including nanophotonics, and ICT for creating modern smart packaging was shown. There were investigated luminescent films with zinc oxide nanoparticles, which change luminescence intensity as nano-ZnO interacts with decay compounds of food products, for active and intelligent packaging. High luminescent transparent films were obtained from colloidal suspension of ZnO and polyvinylpyrrolidone (PVP). The influence of molecular mass, concentration of nano-ZnO, and film thickness on luminescent properties of films was studied in order to optimize the content of the compositions. The possibility of covering the obtained films with polyvinyl alcohol was considered for eliminating water soluble properties of PVP. The luminescent properties of films with different covers were studied. The insoluble in water composition based on ZnO stabilized with colloidal silicon dioxide and PVP in polymethylmethacrylate was developed, and the luminescent properties of films were investigated. The compositions are non-toxic, safe, and suitable for applying to the inner surface of active and intelligent packaging by printing techniques, such as screen printing, flexography, inkjet, and pad printing.

Dextran molecular mass effect on particle size distribution of CaCO3 for 1st and 2nd carbonatation

The presence of dextran in the raw juice leads to a disruption of normal processing operations, particularly at the 1st and the 2nd filtration. The blockage of filters is mainly caused by decreasing the average particle size of calcium carbonate precipitated during carbonatation. The effect of dextran on the juice purification process depends not only on its content but probably also on its average molecular mass. The paper presents studies of the influence of molecular mass of dextran on particle size distribution in juice after the 1st and the 2nd carbonatation.

Melt miscibility and solid-state properties of metallocene LLDPE blends with HDPE: Influence of MM of LLDPE

The influence of relative molecular mass (MM) of LLDPE on the rheological, thermal and mechanical properties of two sets of m-LLDPE/HDPE blends of low and high branch content (BC) was studied. Blends of m-LLDPE with linear HDPE reveal no influence of MM (60–100 kg/mol) on melt miscibility at low BC (about 20 branches/1 000 C). However, at high BC levels (about 40 branches/1 000 C), MM affects the melt miscibility of m-LLDPE/HDPE blends. The DSC results suggest that compatibility in the solid state is independent of MM and BC. For all blends studied, the HDPE-rich blends are found to contain single crystal populations, suggesting high degree of cocrystallization, whereas, m-LLDPE rich phase shows separate crystallization. Mechanical properties of these blends are found to be a strong function of blend compatibility and the specific properties of the blend components. In general, the high BC pairs show poor mechanical properties.

Influence of molecular mass on the liquid crystal alignment of photosensitive fluorinated polyester films

Photosensitive fluorinated polyesters (polymer‐n) of varying molecular mass M n (number‐average molecular mass) were synthesized. The thin films formed from polymer‐n samples could induce liquid crystal (LC) alignment after irradiation by linearly polarized ultraviolet light. The LC alignment direction on the irradiated films was investigated in detail by linearly polarized infrared spectroscopy and polarizing optical microscopy. It was found that LC alignment behaviour changed with change in the molecular mass of polymer‐n: irradiated films with lower or higher M n induced homeotropic or homogenous alignment, respectively. There was no clear morphological anisotropy in these aligned films, as observed by atomic force microscopy. The surface energies of the irradiated films were also measured using the indirect contact angle method, where both surface energy and its polar component increased with increasing M n. The variation in M n could be considered as a main reason for varying alignment behaviour.

Kinetics of Helix Untwisting in Photosensitive Cholesteric Polymer Mixtures: Influence of Molecular Mass and Ordered Phase Formation

Photooptical behavior of cholesteric mixtures based on two fractions of nematic polymer with different molar masses containing chiral-photosensitive dopant with C=C double was studied. UV irradiation of planarly oriented films of the mixtures leads to E-Z photoisomerization of dopant, helix untwisting and shift of selective light reflection peak to the longer wavelength spectral region. Kinetics of this process was studied at different temperatures. It was shown that a relative rate of helix untwisting for the mixture with the high molar mass fraction (DP ∼ 87) is 2 orders of magnitude less than for the mixture containing a low-molar-mass fraction (DP ∼ 22), whereas the activation energies of the helix untwisting for both mixtures have almost the same values. The formation of the ordered TDK* phase during annealing of the blend at 50 °C for 1 week completely prevents the helix untwisting. This fact is worthy of attention because it provides a possibility of fixing a helical structure even at temperatures above the glass transition; this advantage makes this system promising for optical data recording and storage.

Comparison of enthalpy relaxation between two different molecular masses of a bisphenol-A polycarbonate

The present work is an extension of an earlier study that compared the stress relaxation between two molecular masses of a bisphenol-A polycarbonate due to thermal aging. The enthalpy relaxation of the same materials has been characterized. First, by measuring the change in enthalpy loss (ΔHa) and fictive temperature (Tf) as a function of aging temperature (Ta) ranging from -25 to 120°C, using differential scanning calorimetry. For the limited aging time of 120 h, ΔHa and Tf changes were only appreciable for (Tg -70 K)<Ta<Tg . While the influence of molecular mass was somewhat discernible, enthalpy measurements were not as sensitive as stress relaxation tests in differentiating molecular mass effects. In a second investigation, the kinetics of enthalpy relaxation upon isothermal aging at 130°C was evaluated using the peak shift method and found to be comparable to literature values. The plot of ΔHa as a function of log (aging time) showed two distinct regions: a brief non-linear portion (less than 1 h aging) which is followed by a linear relationship as typically reported in the literature. In contrast to the linear region, the non-linear relaxation behaviour of the poorly aged state does not appear to be dependent on molecular mass.

Conformation of Polyelectrolyte Chains in Dilute Aqueous Solutions Investigated by Conductometry. 4. Influence of Molecular Mass and Charge Density of the Chains on Conformation of Symmetrical Aliphatic Ionene Bromides

Samples of 3,3-, 4,4-, 6,6-, and 10,10-ionene bromides of different degree of polymerization (DP) were synthesized, fractionated, and characterized. Salt-free dilute aqueous solutions of the sample...

Evidence for Spin Coating Electrostatic Self-Assembly of Polyelectrolytes

The influence of molecular mass on the formation of polyelectrolyte multilayers on an oppositely charged surface of a rotating substrate was explored for a combination of strong cationic and anionic polyelectrolytes, such as poly(1-(N-benzylpyridinio-2-yl)ethylene bromide) (PVP-2B) and ι-carrageenan. UV/visible spectroscopy and ellipsometry measurements confirmed that the amount of material deposited on a substrate is inversely proportional to the logarithm of the molecular weight of PVP-2B at a low concentration of 1 mM in the spin-coated as well as the solution-dipped multilayer assemblies. A quantitative evaluation of the data shows that an increase of the molecular weight Mw of PVP-2B from 3.8K to 6.0M leads to 50 and 23% decreases in the average amount and thickness per bilayer deposited using the spin coating electrostatic self-assembly technique, respectively. Studies were also carried out to determine the effect of polymer concentration and spin speed on the adsorption rate of high molecular weight (HMW) and low molecular weight (LMW) polyelectrolytes. Increase of the spin speed leads to almost the same decrease in the average deposition rate of LMW and HMW polymers on a substrate. In sharp contrast, increasing the concentration of the polymer solution causes a higher increase in the average amount of the layer pair for HMW polyelectrolytes than for LMW. It was also found that there exists a critical concentration in which an equivalent amount of polymer is adsorbed on a solid substrate for two different HMW and LMW polymers; more LMW polyelectrolyte is adsorbed until a critical concentration, above which the trends are reversed. The observation would indicate the fact that the spin coating is less and less determined by the self-assembly process with increasing the concentration, causing enhanced nonspecific interactions among polymer chains. Particularly, some evidence is found for the self-assembly process that plays an essential role in the formation of polyelectrolyte multilayers on a rotating substrate.

Influence of molecular mass, thermal treatment and nucleating agent on structure and fracture toughness of isotactic polypropylene

The influence of processing, crystallization conditions and molecular characteristics on the fracture behaviour of isotactic polypropylene obtained by a new catalyst system was investigated. The sample specimens were prepared by using two extreme crystallization conditions — quenching or slow crystallization — in order to obtain crystals and amorphous phases with different structure. Interesting correlations between fracture parameters and some morphological parameters such as long spacing and lamellar thickness of the samples were found. The SEM fractographic analysis provides useful information on the influence of factors such as molecular weight, spherulite size and undercooling. Nucleating agents were used to tailor the dimensions of spherulites.

Characterization of some thermotropic polyesters by differential scanning calorimetry

The thermal properties of semiflexible thermotropic polyesters and low molecular mass model compounds were investigated by differential scanning calorimetry. An account is given of some peculiar aspects strictly related to the polymeric nature of the specimens. In particular, the influence of molecular mass and thermal treatments on the transition temperatures of the polymers is evidenced. The occurrence of polymesomorphism was revealed by the appearance of multiple DSC peaks.

The influence of molecular mass, acetate group content and synthesis method on the structuring of polyvinyl alcohol (PVA) in aqueous solutions

The influence of certain factors (molecular mass, acetate group content, method of synthesis) on the structuring in aqueous PVA solutions was established using a birefringence method. It was shown that structuring in the PVA-water system weakens with increasing molecular mass of the polymer and as the acetate group content grows. The structuring is much weaker in aqueous PVA solutions obtained from polyvinyl acetate with incomplete polymerization conversion than in similar solutions obtained by complete conversion. The number of particles involved and their size and shape was determined.