Viscosity Of Dilute Solutions Research Articles

Determination of viscosity and critical concentrations of commercial low methoxyl pectin

Abstract Determining viscosity and critical concentrations is essential for industrial application of pectin solution. Critical concentration can be determined rheologically based on zero shear viscosity, apparent viscosity, specific viscosity, and consistency index of dilute polymer solution. Direct experimental comparison of the aforementioned methods for critical concentration determination is still lacking. Therefore, this study aims to experimentally compare different viscosity methods to determine critical concentration of three different pectin solutions (sun flower, citrus, and apple). The three pectin sources at concentrations of 0.1–3.0 % (w/v) showed Newtonian to shear thinning behavior. The critical concentration ranges of pectin, from the lowest to highest, was sunflower (0.6792−0.9589 % (w/v)), citrus (0.7172−1.0347 % (w/v)), and apple (0.7645−1.1233 % (w/v)). Critical concentration determined based on consistency index was relatively close to the result obtained from zero shear viscosity. Whereas critical concentrations of the pectin solutions determined from specific viscosity and apparent viscosity were significantly different from critical concentration determined from zero shear viscosity.

Salt-Added Solutions of Markov Polyampholytes: Diagram of States, Antipolyelectrolyte Effect, and Self-Coacervate Dynamics

Field-theoretic and scaling approaches are combined to predict conformational behaviors of single-chain globally neutral polyampholytes (PAs) in the presence of salt, the viscosity of their dilute solutions, and the rheology of condensed self-coacervate phases. To reveal the role of the monomer sequence, we consider PAs with Markov statistics of positive and negative charges. The diagram of globular regimes of single-chain PAs in Θ solvent is constructed with the coordinates of the charge blockiness and salt concentrations. For highly flexible chains, it contains six scaling regimes corresponding to low/high salt concentrations and (i) almost alternating, (ii) random correlated, and (iii) highly blocky sequences of ionic monomers. At increasing salt concentration, PAs of any sequence swell until reaching an ideal-coil size. The amplitude of the salt-induced globule-to-coil transition increases with increasing charge blockiness. So does the change in the viscosity of dilute PA solutions, indicating the sequence specificity in the antipolyelectrolyte effect. The similarity between the internal structure of the globules and macroscopic self-coacervate phases enables prediction of the viscosity of the latter. The respective scaling dependencies for self-coacervates of short unentangled and long entangled PAs are provided. Self-coacervate viscosity is the highest for the most blocky PAs and, for any sequence, decreases with the addition of salt. Our findings serve as important guidelines for understanding the dynamics of intracellular condensates, which form from polyampholytic disordered proteins/regions and exhibit the salt-induced viscosity drop described herein.

Hydration Numbers of Polyethylene Glycols Based on a New Viscosity Model

AbstractDue to the high solubility in water and the structural compatibility of polyethylene glycol with water molecules, it is a good model system for studying the mechanisms of interaction between water and biopolymers. The behavior of biopolymers in living organisms strongly depends on the hydration of macromolecules in the aquatic environment. In this work the effective hydration numbers of polyethylene glycols are determined using a new viscosity model developed for electrolytes and experimental data on the viscosity of dilute aqueous solutions of polyethylene glycols (300–35000). The calculated hydration numbers are in good agreement with the literature data and increase with increasing molecular mass of polyethylene glycol: as the molecular mass increases, starting from a molecular mass of 1000, the chain begins to fold in on itself, forming segment‐segment interactions, trapping additional, more loosely bound water between the segments. Based on the dependence of the intrinsic viscosity on the molecular mass according to the Mark‐Houwink equation, it is shown that PEGs are the flexible polymers and highly soluble in water.

Viscosity of Polymer Solutions and Molecular Weight Characterization.

Since the pioneering research by Staudinger on dilute solution viscosity and its relation to the polymer molecular weight, viscosity analysis has become a valuable technique for polymer characterization. The conventional approach is based on the Huggins approximation of the solution-specific viscosity by a quadratic function of concentration, c. We show how to reformulate this approach in a universal form by representing a solution-specific viscosity, ηsp, as a generalized universal function ηsp(c) = α(c/c*) + (1 - α)(c/c*)2 of chain overlap concentration, c*, determined at ηsp = 1, with numerical coefficients α = 0.745 ± 0.005 for good and 0.625 ± 0.008 for a θ solvent. This viscosity representation can be viewed as a calibration curve for molecular weight determination from a measurement of the solution viscosity at a given solution concentration. Furthermore, the molecular weight dependence of the overlap concentration provides a means for quantifying the polymer/solvent affinity and the solvent effect on chain flexibility. The extension of the approach to semidilute solutions opens a path for obtaining molecular weight in a broad concentration range without requiring a dilution and monitoring its change during the polymerization reaction from solution viscosity.

Assessing rheometry for measuring the viscosity-average degree of polymerisation of cellulose in paper degradation studies

In paper degradation studies, the viscosity-average degree of polymerisation (DPv) is often used as a key indicator of the extent of degradation of cellulosic paper. DPv can be deduced from the viscosity of dilute paper solutions, as typically measured through glass capillary viscometry. The current study proposes an efficient, alternative method to evaluate DPv of cellulosic paper, which is based on rotational rheometry. The proposed methodology relies on the application of a shear flow in a thin film of cellulose solution to measure its dynamic viscosity, from which DPv can be subsequently derived in a straightforward fashion. Rheometry allows to measure the viscosity for a range of shear rates, which results in multiple DPv evaluations per sample, and thus in statistically representative data from an individual test. Further, rheometry typically requires considerably less paper mass per test than glass capillary viscometry, which makes the method attractive for paper degradation studies with limited sample availability. Also, rheometry measurements are less work-intensive than glass capillary viscometry measurements. The rheometry method has been applied to 4 hygrothermally aged cellulose paper samples and the unaged counterpart. The measurement results regarding the age-dependency of DPv and the number of cellulose chain scissions are compared to those obtained by glass capillary viscometry, showing a very good agreement. At a longer ageing time, both experimental methods reveal a non-linear decrease in time of DPv, and a non-linear increase in time of the number of cellulose chain scissions, which indicate that the cellulose ageing process is realistically captured. The agreement in measurement results further demonstrates that rheometry is an easy-to-use, accurate and efficient alternative for DPv measurements by glass capillary viscometry.

Fully Automated Instrument for Solution Viscosity in Polymeric Materials

AbstractThe determination of the solution viscosity of polymeric materials is very important to the industry, both to research and manufacturing, since it can be used to estimate molar mass, thus providing valuable information relating to the physical properties of polymers. The relative viscosity of a dilute polymer solution to that of the pure solvent itself is measured, and from this, the intrinsic viscosity of the polymer can be calculated. Due to the popularity of dilute solution viscosity measurements and the availability of those methods in many manufacturing laboratories, this method has been traditionally used to specify and to control production grades. The operation of a new fully automated instrument for determining solution viscosity is described in detail here. A series of applications are presented demonstrating the operation of this method, including for the first time water‐soluble polymers (maltodextrins) and other ambient temperature soluble polymers (cellulose esters) in addition to other polymers requiring elevated temperature and organic solvents for dissolution and analysis (polyolefins, PET).

Effects of Hydroxypropyl and Lactate Esterified Glutinous Rice Starch on Wheat Starch Gel Construction.

An investigation was conducted into the impacts of hydroxypropyl glutinous rice starch (HPGRS) and lactate-esterified glutinous rice starch (LAEGRS) on a dilute solution and gel properties of wheat starch (WS) at different proportions (0%, 1%, 3%, 5%, and 10%). The results of dilute solution viscosity showed that hydroxypropyl treatment of glutinous rice starch (GRS) could promote the extension of GRS chains, while lactate esterification led to the hydrophobic association of GRS chains, and the starch chains curled inward. Different HPGRS: WS and LAEGRS: WS ratios, β > 0 and ∆b > 0, showed HPGRS and LAEGRS produced attractive forces with WS and formed a uniform gel structure. Compared with WS gel, HPGRS, and LAEGRS could effectively delay the short-term aging of WS gels, and LAEGRS had a more significant effect. HPGRS increased the pasting viscosity, viscoelasticity, and springiness of WS gels, reduced the free water content, and established a tighter gel network structure, while LAEGRS had an opposite trend on WS. In conclusion, HPGRS was suitable for WS-based foods with stable gel network structure and high water retention requirements, and LAEGRS was suitable for WS-based foods with low viscosity and loose gel structure.

Relative viscosity evaluation of low-volume samples using capillary flow under differential pressure

In this study, we newly considered the analysis of capillary flow under differential pressure, which extends the previous study and allows the independent measurement of relative viscosity and the product of relative surface tension and contact angle for low-volume samples. The theory of this method is explained, and it is demonstrated that relative viscosity and surface tension with contact angle can be obtained independently by measuring the capillary flow under differential pressure. We conducted capillary flow experiments with a small sample volume (less than 100 μl) using a measurement system comprising a flow measurement unit, capillary chip, and differential pressure mechanism. The relative viscosities of pure water and dilute ethanol solutions obtained in the experiment were in one-to-one correspondence with the values in the Chemical Handbook. This also shows that relative surface tension can be determined using these measurement results and the separately measured contact angle values.

Prediction of thickening efficiency of olefin copolymers and kinematic viscosities of the blended base oils by determining intrinsic viscosities of the copolymers in cyclohexane

The engine oil contains various performance additives along with polymer-based viscosity index improver, which are made from special types of flexible long chain polymers whose functionality is derived from their thickening efficiency, viscosity-temperature relationship, and shear stability. Olefin copolymers of the type ethylene/propylene copolymer are extensively used as viscosity index improver for engine oil formulations whose performance is a function of their composition, co-monomer sequence distribution and molar mass. Polymer coils interact with base oil and make it increasingly resistant to flow which accounts for substantial changes in viscosity parameters i.e. kinematic viscosities and viscosity index of blended base oils. Intrinsic viscosity of a polymeric solution is an important “dilute solution viscosity” parameter, which is easily measurable using Ubbelohde viscometer.In the present work, intrinsic viscosity of twenty samples of laboratory synthesized olefin copolymer in cyclohexane at 30 °C were correlated with their thickening efficiencies, kinematic viscosities of the olefin copolymer blended base oils at 40 °C and 100 °C. These correlation studies enable prediction of performance of olefin copolymer in blended base oil based on an easily and quickly measurable intrinsic viscosity parameter, leading to faster screening of large number of olefin copolymers for their utility as viscosity index improver in lubricants, in a short span of time with limited resources.

Towards an improved prediction of concentrated antibody solution viscosity using the Huggins coefficient

The viscosity of a monoclonal antibody solution must be monitored and controlled as it can adversely affect product processing, packaging and administration. Engineering low viscosity mAb formulations is challenging as prohibitive amounts of material are required for concentrated solution analysis, and it is difficult to predict viscosity from parameters obtained through low-volume, high-throughput measurements such as the interaction parameter, kD, and the second osmotic virial coefficient, B22. As a measure encompassing the effect of intermolecular interactions on dilute solution viscosity, the Huggins coefficient, kh, is a promising candidate as a parameter measureable at low concentrations, but indicative of concentrated solution viscosity. In this study, a differential viscometry technique is developed to measure the intrinsic viscosity, [η], and the Huggins coefficient, kh, of protein solutions. To understand the effect of colloidal protein–protein interactions on the viscosity of concentrated protein formulations, the viscometric parameters are compared to kD and B22 of two mAbs, tuning the contributions of repulsive and attractive forces to the net protein–protein interaction by adjusting solution pH and ionic strength. We find a strong correlation between the concentrated protein solution viscosity and the kh but this was not observed for the kD or the b22, which have been previously used as indicators of high concentration viscosity. Trends observed in [η] and kh values as a function of pH and ionic strength are rationalised in terms of protein–protein interactions.

Simultaneous imaging of lysosomal and mitochondrial viscosity under different conditions using a NIR probe

This article reported a hemicyanine dye fluorescent probe (1), based on benzo[e]indole and aromatic azonia skeleton, for simultaneous detection of viscosity fluctuation in mitochondria and lysosomes. Probe 1 exhibited near infrared emission and high sensitivity towards viscosity of the medium. As the viscosity increases, the rotation of CC single bond between the benzo[e]indole and the nitrogen heterocycle could be suppressed, and the entire molecular scaffold was coplanar and emitted strong fluorescence due to more delocalized electron distribution. The fluorescence intensity of probe 1 was enhanced 16.2 times at 650 nm as the viscosity increased from 0.89 cP to 865 cP. Correspondingly, the fluorescence quantum yield of probe 1 increased from 4.2% to 49.6%. The change of lg (I650nm) had a good linear relationship with lgη (viscosity values: 0.89 cP to 8.6 cP), which meant the viscosity of dilute solution could be detected quantitatively. In cell experiments, probe 1 with low concentration (500 nM) had stronger fluorescence intensity in cancer cells than in normal cells. Besides, probe 1 could monitor the viscosity changes of mitochondria and lysosomes caused by the addition of ionophores (monensin, nystatin and dexamethasone) or in the process of autophagy. The results provide a simple and effective method for the early diagnosis of related diseases.

Rheological modeling of both shear-thickening and thinning behaviors through constitutive equations

Shear-thickening and thinning behaviors are often observed in the rheological measurements of dilute surfactant solutions with drag-reducing ability in wall-bounded turbulent flows. This study proposes a simple rheological modeling method based on combining constitutive equations, such as Giesekus and FENE-P models, with a fluidity equation to determine both thickening and thinning behaviors in simple shear flows simultaneously. The Giesekus and FENE-P models, which are typically used in numerical studies on turbulent drag reduction, cannot capture such complex behaviors. However, the proposed models, called f-Giesekus and f-FENE-P models, can predict the shear-thickening properties. The developed models are inspired by the Bautista–Manero–Puig model, where the Oldroyd-B model (upper-convected Maxwell model) is coupled with the fluidity equation. Parametric studies prove that the proposed models can accurately predict both the shear-thickening and shear-thinning properties. Notably, the f-FENE-P model shows prominent flexibility to determine the plateau region of the shear viscosity as a function of the shear rate. We verify that the analytical solutions of the f-FENE-P model agree with the experimental data of the shear viscosity in dilute drag-reducing surfactant solutions, except for the remarkable steep increase in the shear viscosity. The start-up shear flow is also studied to confirm various transitions accompanied by the overshoot and undershoot of the f-FENE-P model.

Shear viscosity of two-state enzyme solutions.

We discuss the shear viscosity of a Newtonian solution of catalytic enzymes and substrate molecules. The enzyme is modeled as a two-state dimer consisting of two spherical domains connected with an elastic spring. The enzymatic conformational dynamics is induced by the substrate binding and such a process is represented by an additional elastic spring. Employing the Boltzmann distribution weighted by the waiting times of enzymatic species in each catalytic cycle, we obtain the shear viscosity of dilute enzyme solutions as a function of substrate concentration and its physical properties. The substrate affinity distinguishes between fast and slow enzymes, and the corresponding viscosity expressions are obtained. Furthermore, we connect the obtained viscosity with the diffusion coefficient of a tracer particle in enzyme solutions.

A deep insight into the polystyrene chain in cyclohexane at theta temperature: molecular dynamics simulation and quantum chemical calculations.

Molecular characteristics of an atactic polystyrene (aPS) chain with different lengths in a theta solvent, cyclohexane at 307.65K, were studied via molecular dynamics (MD) simulation. The interaction energy of the aPS dilute solution models and Flory-Huggins (FH) interaction parameter were calculated to investigate the effect of the chain molecular weight on its compatibility with the solvent molecules. The simulation results illustrated that increasing the chain length increased the interactions between the chain and the solvent molecules. The chain dimensions via calculating the radius of gyration (Rg) and end-to-end distance, <r0>, were measured. Mean square displacement (MSD) and diffusivity coefficient of the chains were calculated to determine their dynamic behavior. The results exhibited that two factors of the chain movability and size were important for the diffusion in oligomeric state. Additionally, viscosity of the resultant dilute solutions was calculated via nonequilibrium molecular dynamics simulation (NEMD). Moreover, the steric hindrance of the chains was determined by radial distribution function (RDF) analysis. The calculated characteristics of the chain and solution viscosity results showed a good agreement with experimental published works. Measurement of the potential field of cyclohexane-cyclohexane and aPS-cyclohexane pairs was also based on their potential field via quantum chemical calculations to determine the special orientation of the solvent molecules to each other and to the polymer segments, respectively. Graphical abstract (a) The equilibrated dilute solution model of polystyrene in cyclohexane at theta temperature (the red and yellow balls represent carbon and hydrogen atoms, respectively. The cyclohexane molecules are illustrated in line style in the box), (b) the electrostatic potential field around an optimized structure containing two cyclohexane molecules, and (c) around the sole cyclohexane molecule and polystyrene with two repeating units (carbon and hydrogen atoms are represented in green and yellow, respectively).

Properties of Mixed Aqueous Solutions of Polyethylene Oxide and Carboxymethyl Cellulose with Different Degrees of Ionization and of Composite Films Prepared from Them

Rheological properties of mixtures of dilute and moderately concentrated aqueous solutions of carboxymethyl cellulose with various degrees of ionization and polyethylene oxide were studied. The range of compositions in which the viscosity of dilute solutions of the polymer blends shows negative deviation from the calculated additive values becomes broader in going from carboxymethyl cellulose sodium salt to partially ionized carboxymethyl cellulose. In concentrated mixed polymer solutions, the deviation of the viscosity from the additive values is always positive. Film composite materials were prepared, and their structural organization and compatibility of the polymers in the solid state were studied by dynamic mechanical analysis and X-ray diffraction analysis. Carboxymethyl cellulose with various degrees of ionization is incompatible with polyethylene oxide in the composite films obtained, and no new mixed structures are formed. Polyethylene oxide behaves as an interstructural plasticizer of the cellulose ether.

Self‐Assembly of Polyethylene Glycol Ether Surfactants in Aqueous Solutions: The Effect of Linker between Alkyl and Ethoxylate

AbstractThe aqueous self‐assembly behavior of two homologous series of poly(ethylene oxide) (PEO)‐containing nonionic surfactants based on a C10‐Guerbet hydrophobe is reported. The two families of surfactants, alkyl ethoxylates and alkyl alkoxylates, are commercially available from BASF under the trade name Lutensol® XP‐series and XL‐series, respectively. The latter incorporate propylene oxide (PO) units in the surfactant chain. Dye solubilization was used to determine the critical micellization concentration (CMC) of each surfactant at 22 and 50 °C. The PO‐containing alkyl alkoxylates displayed lower CMC values, which were also more sensitive to temperature. The Gibbs free energy, enthalpy, and entropy of micellization were computed from the CMC data and used to identify the contribution of each surfactant moiety (alkyl chain, PO unit, and PEO block) in controlling the CMC. The micellization properties are compared with compositionally similar surfactants with linear alkyl chains, yielding information about the effects of the Guerbet alkyl chain on micellization. Isothermal titration calorimetry was also used to characterize the CMC and enthalpy of micellization which generally compare well with the dye solubilization results. Cloud point data reveal nonmonotonic relationships for the Lutensol® surfactants with respect to composition, unlike linear alkyl chain surfactants. Finally, dilute solution viscosity measurements performed on some Lutensol® surfactants show a change in the slope, suggesting a structural change that tends to be more pronounced for surfactants with longer PEO blocks. The data presented herein enhance the understanding of surfactant structure–property relationships required for industrial formulation.

The Structure of Polymer Clusters in Aqueous Solutions of Hydroxypropyl Cellulose

The viscosity, turbidity, and heat capacity of dilute aqueous solutions of hydroxypropyl cellulose have been studied in a concentration interval of 0.047–1.5 g/l and a temperature interval of 20–80 ∘C. The data obtained testify that, if the temperature does not exceed 40 ∘C, hydroxypropyl cellulose molecules are prolate spheroidal globules with semiaxis lengths of 7 and 490 ˚ A. At temperatures above 70 ∘C, the hydroxypropyl cellulose solution consists of clusters; every cluster is composed of 11 globules and has a prolate spheroidal form with semiaxes of 41 and 490 ˚ A. In the temperature interval from 40 to 70 ∘C, the solution concerned contains both globules and clusters, with the concentration of the latter increasing, as the temperature grows.

Infinite-shear viscosity plateau of salt-free aqueous xanthan solutions

We study aqueous xanthan solutions at shear rates up to about 105 s−1. At these shear rates, the salt-free solutions show an infinite-shear viscosity plateau. Depending on the xanthan concentration, we find two different regimes with scaling laws well known for the zero-shear viscosity of dilute and semidilute solutions: The crossover concentration is considerably higher than in the first Newtonian branch, which can be related to the orientation of the polyelectrolytes. In the second regime, the normal stress differences increase with an exponent of about 1, indicating that the polymer solution behaves like nematic liquid crystals or rigid fiber suspensions. In the first regime, the exponent is smaller suggesting that the polyelectrolytes behave more flexible.

Dissolution behavior and conformation change of chitosan in concentrated chitosan hydrochloric acid solution and comparison with dilute and semidilute solutions

Viscosity, pH and electrolytic conductivity of dilute, semidilute and concentrated chitosan solution with hydrochloric acid adding were compared and the change in conformation of chitosan in concentrated solution was discussed. The dissolution behavior of chitosan in concentrated chitosan hydrochloric acid solution was investigated through determination of solution turbidity, microstate and size of chitosan particle. It was found that the concentration, degree of deacetylation (DD) of chitosan and content of hydrochloric acid in solution showed significant effects on the changes in viscosity, pH, and electrolytic conductivity of chitosan solution as hydrochloric acid added. And the transforms of above properties of chitosan solution during dissolution were corresponding to the proportion of hydrochloric acid to chitosan from which we could deduced that the confirmation of chitosan changed from entangling with each other to becoming compact coils due to electrostatic screen of Cl− and hydrophobic aggregation of chitosan with high concentration. In concentrated suspension solution, chitosan particles agglomerated first and then expended before disintegrating and dissolving with hydrochloric acid adding, resulting in solution turbidity, size and microstate of chitosan particle changed obviously during dissolution.

An Effective Approach for Enhanced Oil Recovery Using Nickel Nanoparticles Assisted Polymer Flooding

The addition of polymer to injection fluid increases the crude oil recovery by improved sweep efficiency. Although it is the most widely used method for chemical enhanced oil recovery (CEOR), limitations such as lower stability of the polymer under reservoir conditions hinder the efficiency of the process. In the current study, a novel nanoparticle assisted polymer flooding approach was carried out to overcome these limitations. To determine whether nanoparticles influence the displacement efficiency of the injected fluid, we used a blend of xanthan gum and nickel nanoparticles. We have evaluated the changes in the dilute solution viscosity of xanthan when the nickel nanoparticles are added and have found out that a xanthan-nickel nanoparticles mixture has a higher intrinsic viscosity of 55.25 dL/g compared to 49.13 dL/g for the gum solution. Efficiency of nanoparticle assisted polymer flooding was evaluated in sand packed bioreactors with ∼0.6 PV of residual oil in place (ROIP). Flooding results demonstr...