Aqueous Hydroxyethyl Cellulose Solutions Research Articles

Evaluating bubble chain phenomena as a mechanism for open system degassing in basaltic systems

Passive degassing – i.e., the open-system degassing of a magmatic gas phase that is decoupled from the melt phase – is common at many basaltic volcanic systems and consistently makes a greater contribution to total volcanic gas emissions than eruptive degassing. However, the mechanism for passive degassing is not fully understood. We investigate the feasibility of permeable gas flow through connected bubbles or pathways using experiments with aqueous solutions of hydroxyethyl cellulose (HEC), a non-Newtonian analogue material for magma. Stable chains of connected bubbles have previously been reported in similar non-Newtonian polymer solutions. We observe a range of bubble chain phenomena and identified five regimes, numbering in order of increasing gas flow rate: 1) small individual bubbles; 2) chains of rounded bubbles; 3) chains of elongate bubbles; 4) pipe-like ‘winding flue’; 5) large individual bubbles. The bubble chain phenomena (regimes 2–4) are observed over a restricted interval of gas flow rates. We determine the rheology of the solutions and conclude that the HEC solutions that produced bubble chain phenomena in our experiments are well scaled to shear-thinning and viscoelastic magmas, hence bubble chain phenomena could form in magmas. Our analysis also suggests that the viscoelastic rheology of HEC plays a fundamental role in the observed bubble chain phenomena.

Path-dependent rheology of carbon particle-hydroxyethylcellulose fluids

Polymeric fluids with tunable viscosity find application in different sectors, ranging from enhanced oil recovery to environmental remediation. This study investigates polymeric fluids obtained with hydroxyethylcellulose (HEC) and biocarbon particles prepared at low (650⁰C, LM) and high (900⁰C, HM) temperature of pyrolization. High pyrolization temperatures increased the hydrophobicity of biocarbon particles. In the absence of HEC, HM particles partitioned preferentially in non-polar solvents (e.g. toluene, rather than in water). Without particles, the shear loss (G”) and storage (G’) moduli of aqueous hydroxyethylcellulose solutions slowly increased over time, due to HEC hydration. The progressive increase in molecular crowding and microviscosity due to the hydration of HEC was demonstrated using steady-state fluorescence spectroscopy with the molecular rotor 9-(dicyanovinyl)julolidine (DCVJ) as a probe. Particles added to HEC increased the viscoelastic moduli of HEC solutions only slightly (i.e. less than doubled them) when HEC was pre-hydrated, and significantly when HEC was not pre-hydrated. Specifically, addition of LM and HM particles (1−30 g/L) to non-hydrated HEC (16 g/L) increased the viscoelastic moduli of HEC solutions in water from below detection to G”>9 Pa and G’>6 Pa (in the whole range of biocarbon particle concentrations analyzed). Our study investigates for the first time the effect of path-dependence of the preparation method on the rheology of HEC-carbon particle fluids. The viscoelastic moduli increase of HEC is ascribed to hydrophobic interactions between biocarbon particles and non-hydrated HEC. The preferential particle partitioning in aqueous HEC solutions (rather than in toluene) is also attributed to these interactions. Such interactions were attributed to the partially hydrophobic nature of HEC, which partitioned at the air-water interface (rather than exclusively in bulk water), lowering the interfacial tension and producing interfacial films with compressional rigidity. HEC interfacial film rigidity changed upon particle addition, supporting the hypothesis of HEC-particle interactions. Compression isotherms modelled using the theory by Marczak et al. were used here for the first time as an indirect tool to gain insights regarding HEC-carbon particle interactions. Partial HEC hydrophobicity was also indicated by the higher viscosity measured in ethanol-water solutions than in water, which showed that ethanol-water was a better solvent than pure water. Steady state fluorescence measurements confirmed that the amount of HEC-bound solvent was greater in ethanol-water mixtures than in pure water. Biocarbon particles mixed with non-hydrated HEC were well-dispersed. Instead, biocarbon particles aggregated when they were mixed with hydrated HEC, indicating that the magnitude of attractive forces between particles and HEC decreased when HEC was hydrated. Compression isotherms measured at the air-water interface with non-hydrated HEC alone and with non-hydrated HEC-biocarbon particle mixtures differed, indicating HEC-particle co-adsorption at the air-water interface and the formation of HEC-particle aggregates.

A study on Thermodynamic, Acoustic and Elastic properties of aqueous solutions of Hydroxyethyl Cellulose

Hydroxyethyl cellulose is a thickening and gelling derived from cellulose. It is broadly used in household products, cosmetics and cleaning solutions. Hydroxyethyl cellulose is frequently used with hydrophobic drugs in capsule formulations, to improve the drugs dissolution in the gastrointestinal fluids. Ultrasonic technique is one of the basic nondestructive methods for evaluation of materials and structures. A significant part of every ultrasonic inspection is the way in which the ultrasonic energy is transferred between the transducer and the tested object. In the present investigation, we have tried to compute the activation energy, ultrasound investigations, elastic property (bulk modulus) and molecular interaction properties of aqueous solutions of Hydroxyethyl cellulose at different concentrations (0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45% and 5%) for different temperatures (303K, 308K, 313K, 318K) by determining the relative viscosity.

Aqueous solutions of HEC and hmHEC: effects of molecular mass versus hydrophobic associations on hydrodynamic and thermodynamic parameters

Aqueous solutions of amphiphilic polymers usually comprise of inter- and intramolecular associations of hydrophobic groups often leading to a formation of a rheologically significant reversible network at low concentrations that can be identified using techniques such as static light scattering and rheometry. However, in most studies published till date comparing water soluble polymers with their respective amphiphilic derivatives, it has been very difficult to distinguish between the effects of molecular mass versus hydrophobic associations on hydrodynamic (intrinsic viscosity [η]) and thermodynamic parameters (second virial coefficient A 2), owing to the differences between their degrees of polymerization. This study focuses on the dilute and semi-dilute solutions of hydroxyethyl cellulose (HEC) and its amphiphilic derivatives (hmHEC) of the same molecular mass, along with other samples having a different molecular mass using capillary viscometry, rheometry and static light scattering. The weight average molecular masses (M W ) and their distributions for the non-associative HEC were determined using size exclusion chromatography. Various empirical approaches developed by past authors to determine [η] from dilute solution viscometry data have been discussed. hmHEC with a sufficiently high degree of hydrophobic modification was found to be forming a rheologically significant network in dilute solutions at very low concentrations as opposed to the hmHEC with a much lower degree of hydrophobic modification which also enveloped the hydrophobic groups inside the supramolecular cluster as shown by their [η] and A 2. The ratio A 2 M W /[η], which takes into account hydrodynamic as well as thermodynamic parameters, was observed to be less for associative polymers compared to that of the non-associative polymers.

Effect of Hydrophobic Modification on Rheological and Swelling Features during Chemical Gelation of Aqueous Polysaccharides

Rheological characteristics during chemical gelation with the cross-linker ethylene glycol diglycidyl ether (EGDE) of semidilute aqueous solutions of hydroxyethylcellulose (HEC) and of two hydrophobically modified analogues (HM-1-HEC and HM-2-HEC) are reported. In addition, rheological features of gelling samples (dextran and its hydrophobically modified analogue (HM-dextran)) of a different structure have been examined. Some swelling experiments on these gels in the postgel region are also reported. The gelation time of the hydroxyethylcellulose systems decreased with increasing cross-linker concentration, and incorporation of hydrophobic units of HEC resulted in a slower gelation. The time of gelation for the dextran system was only slightly affected by the incorporation of hydrophobic groups (HM-dextran). At the gel point, a power law frequency dependence of the dynamic storage modulus (G' proportional to omegan') and loss modulus (G'' proportional to omegan'') was observed for all gelling systems with n' = n'' = n. The attachment of hydrophobic moieties on the dextran chains had virtually no impact on the value of n (n = 0.77), and the percolation model describes the incipient dextran gels. By increasing the number of hydrophobic groups of the HEC polymer, the value of n for the corresponding incipient gel drops significantly, and the value of the gel strength parameter increases strongly. Incorporation of hydrophobic units in the HEC chains promotes the formation of stronger incipient gels because of the contribution from the hydrophobic association effect. The frequency dependence of the complex viscosity reveals that all the investigated gels become more solidlike in the postgel domain. Far into the postgel region, the hydrophobicity of HEC plays a minor role for the strength of the gel network, whereas the values of the complex viscosity are significantly higher for HM-dextran than for the corresponding dextran gel. The swelling experiments on HEC, HM-1-HEC, and HM-2-HEC systems disclose that the degree of swelling of the postgels in water is quite different, depending on the relative distance from the gel point at which the cross-linker reaction is quenched. At a given distance from the gel point, the swelling of the HEC gel is less pronounced than for the corresponding hydrophobically modified samples. At this stage, the swelling of the HM-dextran gel is stronger than for the dextran gel.

Characterization of Interactions in Aqueous Solutions of Hydroxyethylcellulose and Its Hydrophobically Modified Analogue in the Presence of a Cyclodextrin Derivative

The formation of associative networks in semidilute aqueous solutions of hydrophobically modified hydroxyethylcellulose (HM-HEC) is dependent on intermolecular hydrophobic interactions. Addition of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) monomers to the system provides decoupling of these associations via inclusion complex formation with the polymer hydrophobic tails. Results from viscosity, polymer NMR self-diffusion, and dynamic light scattering (DLS) measurements show that the hydrophobic interactions in HM-HEC solutions are effectively suppressed when the level of HP-beta-CD addition increases. Small-angle neutron scattering (SANS) results reveal that the large-scale association complexes in HM-HEC solutions are strongly diminished when the concentration of HP-beta-CD rises. The time correlation data obtained from the DLS experiments unveiled the existence of two relaxation modes: one single exponential at short times followed by a stretched exponential at longer times. The fast mode is always diffusive, whereas the slow mode exhibits progressively stronger wavevector dependence as the intensity of the hydrophobic interactions increases. This feature, as well as the accompanying drop of the stretched exponential beta as the HP-beta-CD concentration decreases, is attributed to enhanced hydrophobic interactions and can be well rationalized in the framework of the coupling model of Ngai.

Dynamical and structural behavior of hydroxyethylcellulose hydrogels obtained by chemical gelation

AbstractRheological, dynamical, de‐swelling, turbidity, and structural features during gelation with a chemical cross‐linking agent of semi‐dilute aqueous solutions of hydroxyethylcellulose (HEC) were investigated at different cross‐linker concentrations. A higher level of cross‐linker leads to faster gelation and stronger incipient hydrogel. The rheological results favor the percolation model. The cross‐linking reaction proceeds over a long time in the post‐gel region, and this produces gels with a solid‐like response. Dynamic light‐scattering experiments reveal a fast and a slow relaxation mode. The slow relaxation time increases and the sample becomes more heterogeneous in the course of gelation. In the post‐gel region, the gels shrink during a long period of time and this phenomenon is accompanied by strong turbidity enhancement. Small‐angle neutron scattering results from samples quenched at a certain stage in the post‐gel regime disclose growth of heterogeneity in the gel with increasing level of cross‐linker addition. At smaller length scales, no effect of cross‐linker addition could be detected on the structural organization, and scattered intensity in this domain suggests that the HEC chains are locally stretched. Copyright © 2006 Society of Chemical Industry

Shear and extensional rheology of solutions of modified hydroxyethyl celluloses and sodium dodecyl sulfate

This work reports on the rheology of aqueous solutions of hydroxyethyl cellulose (HEC) and three derivatives, in the presence of sodium dodecyl sulfate (SDS). The polymers employed were: a hydrophobically modified hydroxyethyl cellulose (HMHEC) containing hexadecyl grafts, a cationically modified hydroxyethyl cellulose (cat-HEC), containing glycidyl-trimethyl-ammonium grafts, and a polymer with both modifications (cat-HMHEC). Rheological measurements were performed in simple shear flow, oscillatory shear flow, opposed-jets flow and flow through porous media. The addition of surfactant increases intermolecular interactions between HMHEC molecules due to the formation of mixed micelles that bridge hydrophobic side groups from different polymer chains. These interactions lead to phase separation in an intermediate SDS concentration range and, at higher surfactant concentrations when a homogeneous phase was obtained, to higher shear and apparent extensional viscosities. Further surfactant addition eventually inhibits hydrophobe interactions due to electrostatic repulsion between micelles, leading to shear viscosities that are even lower than that of the original polymer solution. Hydrophobe interactions are inhibited by the relatively strong nature of flow in opposed-jets. The addition of cationic side groups confers the polymer a polyelectrolytic nature, which translates into higher shear and apparent extensional viscosities. Interchain interactions are strengthened by the presence of surfactant by the formation of intermolecular cross-links between polymer chains.

Gels from modified hydroxyethyl cellulose and ionic surfactants

Abstract The macroscopic properties of aqueous solutions of hydroxyethyl cellulose (HEC) and of modified HEC samples which carry cationic groups (cat-HEC) or a cationic and hydrophobic group (cat-HMHEC) and their interactions with ionic surfactants (SDS and STS) are investigated by rheological, electric birefringence and surface tension measurements. The gel formation of the surfactant free polymer solutions strongly depends on the polymer concentration and the constitution of the polymer. HEC forms thermoreversible gels for T c 3 wt%. HEC does not interact with ionic surfactants. The 1 wt% viscoelastic solutions of cat-HEC and cat-HMHEC can be transformed into physically crosslinked gels by the addition of oppositely charged surfactants. The polymer solutions are first transparent and show an increase in viscosity and elasticity with increasing surfactant concentration (pre-precipitation area). For higher surfactant concentrations associative phase separation occurs because of charge neutralization and then a second single phase area is observed. In this post-precipitation area the viscosity continuously decreases by further addition of surfactants. The concentration dependence of the gel state formed by cat-HMHEC and STS is strongly affected by the history of the complexes: A 1 wt% polymer-STS-gel retains a yield stress value when diluted down to 0.7 wt% polymer concentration while the addition of STS to the 0.7 wt% polymer solution does not result in a gel state. Network formation is also observed for the hydrophobic polyelectrolytes by the addition of anionic surfactants below the critical overlap concentration of the surfactant free cat-HMHEC solutions.

Capillary Electrophoretic Separation of DNA Restriction Fragments in Mixtures of Low- and High-Molecular-Weight Hydroxyethylcellulose

Previous studies (Barron et al., 1993, 1994) have shown that dilute aqueous solutions of hydroxyethylcellulose (HEC) polymers provide an excellent alternative to gel-based DNA separation media for capillary electrophoresis (CE) of DNA restriction fragments (72−23 130 base pairs). DNA separation by CE in HEC solutions is strongly influenced by the average HEC molecular weight as well as by the HEC concentration in the electrophoresis buffer. Here we describe a systematic investigation of the effects of a mixture of low- and high-molecular weight HEC polymers, over a range of concentrations, to form a DNA separation medium with a broad range of polymer chain lengths. Our results show that, relative to separation media containing solely low-molecular-weight or high-molecular-weight HEC polymers, the mixed polymer solutions provide superior separation over the DNA size range of interest, while providing a five-fold viscosity reduction. The addition of a very small amount of high-molecular-weight HEC to a solution of low-molecular-weight HEC leads to a significant improvement in the separation of larger DNA fragments (>603 base pairs), while retaining resolution of smaller DNA fragments. The consequences of these results on the proposed mechanism of DNA separation in un-cross-linked polymer solutions are discussed.

Comparison of the extensional and shear viscosity characteristics of aqueous hydroxyethyl cellulose solutions

The extensional viscosity characteristics of aqueous solutions of varying concentrations of three samples of hydroxyethylcellulose (HEC) of differing molecular masses have been determined using a commercially available opposed jet extensional rheometer. The results have been compared to the shear flow characteristics of the solutions and the Trouton ratio, T R , of the various systems calculated. For all polymer solutions studied, T R was found to approach the predicted Newtonian value of 3 at low extensional strain rates. This observation was taken as a strong indication that the opposed jet rheometer was producing reliable extensional viscosity data. At higher strain rates, T R generally increased with increasing strain rate and, for any given sample, with increasing polymer concentration thereafter. All HEC solutions studied were found to exhibit strain-thinning behavior in extensional flow and shear-thinning behavior in shear flow, with the most pronounced effects being observed with the highest molecular mass sample (M v ∼4.5×10 5 g/mol). The relative degrees of strain and shear thinning exhibited by the various HEC solutions have been quantified using the power law analysis. For the two samples of lowest molecular mass (M v ∼6.5×10 4 and ∼1.9×10 5 g/mol) the value of a power law index, n, in both extensional and shear flow, was close to unity. For all solutions of the sample of highest molecular mass, the value of n in extensional flow was significantly higher than that observed in shear flow. Regions of apparent strain thickening were observed for a few of the lowest viscosity solutions, but these observations were attributed to the onset of significant inertial effects rather than any coil-stretch transition phenomena

Laminar mixed convection heat transfer to viscoelastic fluids in a 5:1 rectangular channel

The fully established friction factors and heat transfer coefficients of the laminar flow of viscoelastic fluids in a 5:1 rectangular duct were measured experimentally. The bottom wall, one of the longer sides of the duct was heated by passing direct electric current through it, yielding constant peripheral wall temperature and constant heat input per unit length along the bottom wall. The other surfaces were adiabatic. The test section is 150 hydraulic diameters long. Aqueous solutions of two different polymers (polyacrylamide and hydroxyethylcellulose) were used as viscoelastic fluids. The measured laminar friction factors agree well with the Newtonian correlation when plotted as a function of Kozicki generalized Reynolds number (i.e., f=16/ Re ∗ ). The established laminar Nusselt values for aqueous solutions of hydroxyethylcellulose, a weakly elastic fluid, are not significantly different from the values for water when compared at about the same values of Prandtl number and Rayleigh number. The Nusselt numbers for polyacrylamide solutions are about 25% higher than those for water at comparable values of Prandtl number and Rayleigh number.

HOLOGRAPHIC INTERFEROMETRY MEASUREMENTS OF NATURAL CONVECTION AROUND HORIZONTAL CYLINDERS IN LIQUIDS

Holographic interferometry has been used to measure the temperature profiles around horizontal circular cylinders immersed in a number of fluids. Air, water, silicone oils and aqueous solutions of hydroxyethyl-cellulose were studied, giving a Prandtl number range of 0.87 to 4540. The Rayleigh numbers varied from 102 to 104, whereas the Grashof number range was from 10−2 to 104. A similarity solution for the temperature and velocity distribution for high Rayleigh numbers is developed and shown to be identical to that found for high Grashof numbers. All the data are in agreement with the theory. An expression for the average Nusselt number as a function of the Rayleigh and Prandtl numbers is found from the theory.This expression is of the same form as those developed empirically and is in good agreement with numerical results. The theory indicates that the dependence of the Nusselt number on the Prandtl number decreases with increasing Prandtl number and disappears at high values. The Nusselt numbers predicted by theory and those measured experimentally appear to diverge as the Rayleigh number increases.

The mobility profile around polymer segments as calculated from microviscosity data on polymer solutions and gels

AbstractA mobility profile describes the change of the solvent mobility with the distance from the surface of a suspended particle. By means of numerical integration on a computer, a relationship was found between such profiles and the concentration dependence of microviscosity in suspensions of cylinders (models for polymer segments in polymer solutions and gels) and spheres (e.g., protein molecules).The obtained relationship was used to calculate the mobility profile in aqueous solutions of hydroxyethyl cellulose and ribonuclease A. The influence of the macromolecules on the water mobility was found to change as the inverse distance to the power of 1.6 and 2.2, respectively. At a distance of 40 Å from the cellulose segment, or from the surface of the ribonuclease molecule, the mobility is reduced by 10% from that in bulk solvent.

The Rheology of Hydroxyethyl Cellulose Solutions

A systematic and detailed study of the viscous behavior of aqueous hydroxyethyl cellulose solutions has been made in a cone-and-plate viscometer over very wide ranges of shear rate and temperature. High shear stability and high degrees of pseudoplasticity have been observed. The rheograms have followed the Ostwald-de Waele model. Simple and accurate expressions have been formulated relating temperature, solution-concentration and power law exponent to consistency coefficient; also the solution-concentration to activation energy.

Fluorescence depolarization in sheared solutions of dye-tagged polymers

The micro-Brownian motion of a polymer chain in sheared solutions has been studied by means of fluorescence depolarization. An apparatus for determining the degree of polarization of sheared solutions was designed, and measurements were made on fluorescein in aqueous hydroxyethyl cellulose solutions, both tagged to the polymer chains and freely dispersed. The degree of polarization was independent of rate of shear in the region studied, 0-104 s–1, though the flow viscosity of the solutions showed marked non-Newtonian nature. Similar behaviour was observed for concentrated solutions of dextran and polystyrene.

Laminar‐nonlaminar transition for non‐Newtonian flow in annuli

AbstractExperimental results on the laminar‐nonlaminar transition of aqueous solutions of hydroxyethyl cellulose in axial, isothermal flow in annuli are presented. For each polymer solution the end of the laminar regime is observed to occur at different flow rates at different axial distances from the entrance of the test section. For some polymer solutions in nonlaminar motion, the pressure gradient is not constant over the length of the test section.These data on transition in annuli are compared with predictions made using Hanks' transition criterion where only viscous contributions are considered and where viscous effects are considered and elastic effects accounted for approximately. Predictions where both viscous and elastic properties of the fluids are considered are in fair agreement with experiments. Predictions using purely viscous theory are less accurate than the viscoelastic predictions.

An experimental investigation of the flow of aqueous non‐Newtonian high polymer solutions past a sphere

AbstractThe terminal velocities of spheres falling in aqueous solutions of hydroxyethyl cellulose and polyethylene oxide were determined with ruby and steel spheres. For each sphere the terminal velocity was obtained in seven cylinder sizes covering a range of sphere‐to‐cylinder diameter ratio from 0.0067 to 0.18. The data were used in an extrapolation to correct for the cylindrical wall effect. Several alternative extrapolation procedures for estimating the zero shear viscosity were attempted and the results were compared. An empirical correlation for the drag coefficient was developed in terms of the Ellis parameters of the fluids, and the Faxén wall correction for Newtonian flow. the correlation gives the drag coefficient within 4% for all cases in which the quantity ηvt/Dτ1/2 is less than 0.3.

Steady flow viscosity of aqueous hydroxyethyl cellulose solutions

Steady flow viscosity of aqueous hydroxyethyl cellulose solutions