Dilute Solution Properties Research Articles

Numerical Study of Extension Rheological Properties of Polymer Solutions using FENE Model

Dilute polymer solutions represent a complex rheological response. A finitely extensible nonlinear elastic (FENE) bead-spring chain model for dilute solutions of polymer molecules in a Newtonian solvent is employed to describe the bead-bead interaction within a molecule. Brownian dynamics simulation is used to capture the most important rheological properties of dilute polymer solutions. A program based on this model is developed to simulate the steady elongational flow and inception of elongational flow, and the flow situations and the rheological material functions are investigated. Semi-implicit predictor-corrector methods are introduced and the results qualitatively agree with rheological theory.

DFT Based Monte Carlo Simulations of Poly(9,9-dialkylfluorene-2,7-diyl) Polymers in Solution

The dilute solution properties of poly(9,9-dihexylfluorene-2,7-diyl) (PDHF) were studied by coupled SEC/light scattering and MALDI-TOF over a large molecular weight (MW) span ranging from PDHF oligomers (1-8-mer) to high MW polymer. The results were compared with Monte Carlo simulations based on realistic PDHF models obtained from X-ray data and density functional theory (DFT) calculations and with a DFT based Kratky-Porod-Benoit-Doty (KPBD) worm-like chain. The simulations called "selective random walk" (SRW) and the corresponding "selective self-avoiding random walk" (SSAW) explicitly take into account the rotationally labile bonds between the fluorene units in that four distinct torsion angles (+/-37.5 and +/-143 degrees) between the units are chosen randomly. The simulations better account than the KPBD model for the experimental data obtained by us and others for various poly(9,9-dialkylfluorene-2,7-diyl) polymers but still give somewhat larger values for the radii of gyration and hydrodynamic volumes. The torsion angle selectivity of the SRW and SSAW simulations predict long chain sections punctuated by sudden sharp loops.

Volumetric Properties of Dilute Solutions of Water in Acetone between 288.15 and 318.15 K

Densities of dilute solutions of water in acetone, with solute mole fractions ranging up to 0.03, have been measured with an error of 8 ×10−6 g⋅cm−3, at 288.15, 298.15, 308.15 and 318.15 K, using a precision vibrating-tube densimeter. The partial molar volumes of the solute water (down to infinite dilution) and solvent acetone, as well as the excess molar volumes of the specified mixtures, have been calculated. The effects of the solute concentration and temperature on the volume packing changes, caused by solvation of water in acetone, have been considered.

Microstructure and aggregation behavior of methylcelluloses prepared in NaOH/urea aqueous solutions

Three water-soluble methylcelluloses (MCs) were prepared through homogeneous reaction in NaOH/urea aqueous solution, using dimethyl sulfate as a methylation reagent. The microstructure of the MC samples was characterized by IR, GC/MS, NMR, while dilute solution properties were measured by SEC–LLS, DLS and viscometer. The total degrees of substitution (DS) of the MC samples were 1.09, 1.42 and 1.56, respectively. However, we found that the relative DS value varies with the position of the hydroxyl group, i.e., C-2 > C-3 ≈ C-6, indicating the difference of reaction activity of different hydroxyl groups. In aqueous solution, MC has a trendency to form aggregates and hard to form actual solution, even at low concentration and low temperature, which was confirmed by the SEC–LLS and DLS result that isolated MC chains and large aggregates coexisted in the dilute aqueous solution. MC aqueous solutions showed two-stage temperature dependence of hydrodynamic radius. In the first stage, i.e., the temperature ranges from 20 to 65 °C, the hydrodynamic radius of MC displayed bimodal distribution, corresponding to the single chains and large aggregates. While in the second stage, i.e., the temperature higher than 70 °C, only large aggregates appeared. The results also proved that the microstructure of MC had a great influence on its physical properties.

Prediction of processability at extrusion coating for low‐density polyethylene

AbstractThe neck‐in level and the maximum drawdown speed at extrusion coating for low‐density polyethylene are studied with the evaluation of the rheological properties in the molten state and the dilute solution properties. It is found that the viscous properties in the molten state and the dilute solution properties are not sensitive to the processability, whereas the elastic nature has a great impact. In particular, the elastic response in the nonlinear region, such as drawdown force and strain‐hardening behavior in elongational viscosity, can be employed for the prediction of the processability at extrusion coating. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Well-defined [3,3′]bicarbazolyl-based electroactive compounds for optoelectronics

Well-defined electroactive compounds were synthesized from 9 H,9′ H-[3,3′]bicarbazolyl and different halo-substituted arylamines by the modified Ullmann coupling reaction. Photophysical properties of dilute solutions of the derivatives were investigated in detail. The new materials were found to constitute glasses with glass transition temperatures ranging from 34 to 130 °C as characterized by differential scanning calorimetry. The compounds possess good solubility in common organic solvents and high thermal stability with 5% weight loss temperatures of 359–440 °C. The electron photoemission spectra for amorphous layers of the compounds have been recorded and the ionization potentials of 5.23–5.47 eV have been established. Room temperature hole drift mobility in the layers of some compounds molecularly dispersed in polymeric host exceed 10 −5 cm 2/V s at an electric field of 10 6 V/cm.

Overlap concentration of an aqueous poly(N‐vinylcaprolactam) solution in the dynamic and static states

AbstractThe overlap concentration of poly(N‐vinylcaprolactam)s (PVCLs) of low molecular weights was studied with dynamic and static methods (with viscosity and refractive‐index measurements) at three temperatures (25, 30, and 35°C). This concentration, determined by viscometry, was lower than the overlap concentration determined by refractometry. Also, the influence of the temperature and molecular weight on the viscosity and refractive index was investigated, and the opposite effect of the temperature on the viscosity and refractive index of PVCL solutions was observed. The experimental overlap concentration values were compared with those calculated with the Rao, Huggins, and Fuoss equations. The results showed that the Huggins equation is the best equation to describe the dilute solution properties of this polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Rheological properties of dilute aqueous solutions of cassava starch

The effects of starch concentration on the rheological properties of dilute aqueous solutions of cassava starch were investigated. Cassava starch suspensions at different starch concentrations (0.2, 0.4, 0.6, 0.8, and 1.0 wt. %) were heated at 90 °C for 1 h and then rapidly cooled to 25 °C. The apparent viscosities of starch solutions were measured as a function of starch concentration. The cassava starch solution with a concentration of 0.2% showed Newtonian behavior, and as the concentration was increased beyond 0.4%, the solutions showed shear-thinning behavior. The flow behavior (apparent viscosity against shear rate) of the solutions was well described using a power law model. The consistency indices increased and the flow behavior indices decreased with the increasing of starch concentration. After storing the solutions at 25 °C for 24 h, precipitation of starch took place instead of gelation. The volume of precipitation bed increased linearly with starch concentration.

10.1007/s11498-008-2016-9

The properties of dilute solutions of regular polyampholytes in the presence of a low-molecularmass salt were studied by means of stochastic dynamics simulation. The number-average concentration of polymer units in solution did not exceed 0.038, a value that is below the coil overlap concentration at N= 1024. The effect of charge (valence) of ions of an added salt on the macromolecule size and distribution of the salt inside the polymer coil at different temperatures was considered. It was found that the condensation of salt ions over the temperature range examined (1 ≤T≤2e/kB) takes place in the case of multiply charged systems of the (+4−4) or (+4−2) type. The maximal penetration of salt ions into the volume of the macromolecule was observed in the case of a (+2−2) salt.

Solution Properties of Conventional Gum Arabic and a Matured Gum Arabic (Acacia (sen) SUPER GUM)

Dilute solution properties of two specially matured gum arabic samples (EM1 and EM2) were compared to the conventional gum (EM0) using static light scattering. The apparent molar mass (M(w,app) and radius of gyration (R(g,app)) for the three samples showed unusual concentration dependence. These data were satisfactorily interpreted by a simple association model that takes into account the repulsive interaction among clusters, which allowed us to obtain the true molar mass (Mw(0)) and radius of gyration (Rg(0)). A common power law relation was observed between Mw(0) and Rg(0) , giving a somewhat higher exponent than expected for linear and branched polymers in a good solvent. Mw(0) and Rg(0) obtained for the three gums do not differ significantly from each other. However, the data showed clearly a constant increase of the association from EM0 to EM2 with increasing concentration. This is in accordance with the previously observed improved functional properties for the matured products.

Rheological and structural properties of dilute active filament solutions

The rheology and the structure of a dilute semiflexible biofilament solution, like F-actin, interacting via molecular motors is probed by molecular dynamics simulations. Oscillatory external shear is used to measure the storage and loss moduli as a function of motor activity in a range of frequencies and for low shear rates. The overall effect of the motor activity on the rheological properties is interpreted as an increase of the temperature, with the effective temperature proportional to the density of motors. However, the effect of motors on the structural properties of the solution, such as the orientation correlation function, is opposite: the motors drastically increase the orientation correlation length whereas thermal fluctuations decrease it.

Structural Characterization and Solution Properties of a Galacturonate Polysaccharide Derived from Aloe vera Capable of in Situ Gelation

A series of highly purified galacturonate polysaccharides have been extracted from the Aloe vera plant and analyzed in terms of chemical composition and molecular weight. This Aloe vera polysaccharide (AvP) has been found to exist as a high molecular weight species and possess a unique chemical composition, including a high galacturonic acid (GalA) content and low degree of methyl ester substitution. These factors facilitate gel formation upon exposure to low concentrations of calcium ions, leading to potential application in formulations designed for in situ nasal or subcutaneous protein delivery. Thorough examination of classic dilute solution properties, the [eta]-M(w), and R(g)-M(w) relationships, persistence length (L(p)), and inherent chain stiffness (B parameter), indicate an expanded random coil in aqueous salt solutions. The critical concentration for transition from dilute to concentrated solution, C(e), was determined by measuring both the zero shear viscosity (eta(o)) and fluorescence emission of the probe molecule 1,8-anilino-1-naphthalene sulfonic acid (1,8-ANS) as a function of polymer concentration. Examination of zeta potential and C(e) as a function of ionic strength indicates that the shift in C(e) from 0.60 to 0.30 wt % is related to an increased occurrence of intermolecular interactions at high salt concentrations. Additionally, dynamic rheology data are presented highlighting the ability of AvP to form gels at low polymer and calcium ion concentrations, exemplifying the technological potential of this polysaccharide for in situ drug delivery.

Dilute-Solution Properties of Polystyrene Polymacromonomer Having Side Chains of over 100 Monomeric Units

Dilute-Solution Properties of Polystyrene Polymacromonomer Having Side Chains of over 100 Monomeric Units

Synthesis and characterisation of soluble block copolymers from NR and TDI based polyurethanes

Soluble block copolymers from toluene diisocyanate (TDI), with chain extender diols, viz., propylene glycol (PG), 1,4-butane diol (1,4-BDO) and 1,3-butane diol (1,3-BDO), were synthesised for the first time by solution polymerisation. Maintaining low hard segment content and keeping optimum NCO/OH ratio, formation of linear, flexible elastomers is achieved. They were characterised by spectral, thermal, microscopic and stress–strain analysis. The dilute solution properties of these block copolymers dissolved in tetrahydrofuran (THF) are studied by viscometry and gel permeation chromatography (GPC). IR and NMR spectral data support the notion that a chemical reaction leads to block copolymerisation. Differential scanning calorimetric (DSC) analysis showed a soft segment glass transition temperature around −58°C and a hard segment glass transition temperature between 75 and 70°C for these samples. This observation and two-stage thermal decomposition of the samples in thermogravimetric analysis (TGA) clearly indicate that the block copolymers are completely phase-segregated systems. SEM indicates the amorphous heterophase morphology of the samples.

Charge Transport along Coiled Conjugated Polymer Chains

The motion of charges on coiled polymer chains was studied using a combination of experimental and theoretical methods. The conductive properties of dilute solutions of polyfluorene and fluorene−binaphthyl copolymers were studied by the pulse-radiolysis time-resolved microwave conductivity technique. This technique enables measurement of the (high frequency, 34 GHz) mobility of charges on isolated polymer chains. The motion of positive charges on the coiled polymer chains was studied theoretically by charge transport simulations with parameters from density functional theory calculations. This combined experimental and theoretical study shows that the mobility of charges decreases with increasing degree of chain coiling. The mobility along (infinitely long) stretched polyfluorene is calculated to be as high as tens of centimeters2/volt·second. Our results imply that the performance of conjugated polymers in optoelectronic devices can be significantly improved by optimization of the organization on a molecular scale.

Application of the theory of dilute polymer solutions to the assessment of the structure and properties of styrene-acrylic acid copolymers

Properties of dilute solutions of polystyrene and styrene-acrylic acid copolymers in DMF and ethyl acetate were studied in the temperature range 20–35°C. It was shown that the dependences of the intrinsic viscosity and Huggins constants on temperature for the copolymers differ from that for polystyrene. Comparison of the “quality” of the solvents was carried out.

Hydrophobic Interactions of Xenon by Monte Carlo Simulations

Hydrophobic interactions of xenon atoms dissolved in liquid water were studied by NpT Monte Carlo simulations in the temperature range 298.15 to 333K and at ambient pressure. Structural properties of dilute xenon solutions were calculated and compared to those of bulk water in order to show the influence of the hydrophobic solute. It was found that the xenon atoms tend to aggregate with increasing temperature. At low temperatures the aggregates are predominantly solvent-separated pairs; at higher temperatures the quota of contact pairs increases. Furthermore, the residual chemical potentials of xenon and water were calculated with different methods; it was found that the Widom insertion methods works best for this system. For the thermodynamic conditions of this work, the residual chemical potential of water in the presence of xenon was found to be a linear function of temperature.

Jacobus Henricus van’ t Hoff

J H van’ t Hoff is considered as one of the greatest chemists of all time. He started his career as an organic chemist. He solved the vexing problem of optical isomerism by proposing an asymmetric tetrahedral carbon bonded to form different groups. He extended this to include geometric isomerism, and to compounds with heteroatoms in place of asymmetric carbon. Thus he established the ‘chemistry in space’ or stereochemistry. He moved on to work on reaction kinetics, equilibria, thermodynamic properties of dilute solutions and related areas. He laid the foundation for physical chemistry through these discoveries and was awarded the first Nobel Prize in Chemistry in 1901. van’ t Hoff died of tuberculosis at a relatively early age of 59.

Architecture of Prototype Copolymer Brushes by Grafting-from ATRP Approach from Functionalized Alternating Comb-Shaped Copolymers

Atom transfer radical polymerization (ATRP) was applied to a novel synthesis of prototype copolymer brushes. The procedure included the following steps: (1) free-radical copolymerization of vinylbenzyl-terminated polystyrene (PS-VB) macromonomer and N-(4-hydroxyphenyl)maleimide gave well-defined alternating comb-shaped copolymers, (2) subsequent esterification reaction [N-(4-hydroxyphenyl)maleimide sites] of such comb-shaped copolymer with 2-bromoisobutyryl bromide yielded a comb-shaped polyinitiator, and (3) the grafting-from ATRP method of methyl methacrylate (MMA) using comb-shaped polyinitiator provided PS/poly(methyl methacrylate) (PMMA) alternating copolymer brushes. Dilute solution properties and morphological results of both comb-shaped polyinitiator and prototype copolymer brushes were investigated by static and dynamic light scattering and transmission electron microscopy. As a result, prototype copolymer brush composed of short aspect ratio changed the shape from ellipsoid to starlike conforma...

Side‐chain effects on the morphology and properties of fluorene‐based alternating copolymers

AbstractSoluble fluorene‐based alternating copolymers containing benzene as the comonomer were synthesized and characterized, in which three different side chains (hydrogen atom, linear octyloxy and bulky benzyloxy groups) were attached to the phenylene ring. The effect of the side chains with different steric hindrances on the photophysical, thermal and electrochemical properties as well as the morphology were investigated. Moreover, the chain conformation and spectroscopic properties in dilute solution were studied to understand the solvent effect. Aliphatic and aromatic solvents were demonstrated to have different influences on the spectra of the polymers owing to various interaction mechanisms in the excited states. Also, a significant decrease of up to 80 °C in the thermal degradation temperature was observed as a result of the introduction of large benzyloxy units. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the polymers were estimated to be − 5.76 to − 5.82 eV and − 2.19 to − 2.27 eV, respectively, from cyclic voltammetry measurements. In addition, the electronic structures of the polymers were described via quantum chemical calculations. Copyright © 2007 Society of Chemical Industry