Semidilute solutions of poly(methacrylic acid) in the absence of salt: Dynamic light-scattering study

Water solutions of poly(methacrylic acid) of molecular weight M_w = 3.0 × 10⁴ and M_w = 4.0 × 10⁵, neutralized with NaOH, were investigated by photon correlation spectroscopy. At a low degree of neutralization α, the short-time decay only is observed. When α > 0, a second, much slower, process becomes noticeable. It gains quickly in influence when α increases. The reciprocal values of characteristic relaxation times for both dynamic processes were found to decrease linearly with the square of the scattering vector, showing that both processes are diffusive. The following interpretation of these processes founded on the concentration and angle dependences of the corresponding diffusion coefficients and scattering amplitudes is given: (1) for the low-molecular-weight sample (M_w = 3.0 × 10⁴), D_∫ (fast process) and be attributed to the Nernst-Hartley diffusion coefficient of polyions, and D_s (slow process) to a diffusion of interchain domains (clusters) with a radius of gyration R_G ≈ 50 nm; (2) for the high-molecular-weight sample (M_w = 4.0 × 10⁵), where an overlap of polymer chains occurs, D_f can be attributed to a cooperative diffusion coefficient reflecting the concentration fluctuations due to the polyions and counterions, and D_s to slow concentration fluctuations having a large correlation length (≈ 100 nm). The existence of two diffusive modes in salt-free solutions of polyelectrolytes cannot be explained within the framework of the scaling approach as proposed by de Gennes and Odijk.     

Copper separation from nitrate/nitric acid media using Acorga M5640 extractant: Part II. Supported liquid membrane study

The facilitated transport of copper(II) from nitrate/nitric acid media through a flat-sheet supported liquid membrane (FSSLM) is investigated, using the commercially available oxime Acorga M5640 as ionophore, as a function of hydrodynamic conditions, concentration of copper (7.9×10⁻⁵ to 1.3×10⁻³ M) and H⁺ (pH 1.0–2.0) and ionic strength in the feed solution, carrier concentration (5–40% v/v) in the membrane and support characteristics. The performance of the system is also compared using various diluents for the organic phase and against other available oxime extractants (MOC-55TD, LIX 860 and LIX 622). A model is presented that describes the transport mechanism, consisting of diffusion through a feed side aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and its metal complex through the organic membrane. The organic membrane diffusional resistance (Δ_o) and aqueous diffusional resistance (Δ_a) were calculated from the proposed model, and their values were 7.6×10⁶ and 273 s/cm, respectively. It was observed that the copper flux across the membrane tends to reach a plateau at high concentration of copper or a low concentration of H⁺ owing to carrier saturation within the membrane, and leads to a diffusion-controlled process. The values of the apparent diffusion coefficient (D_o^a) and limiting metal flux (J_lim) were calculated from the limiting conditions and found to be 2.0×10⁻⁸ cm²/s and 2.3×10⁻¹¹ mol/cm² s, respectively. The values of the bulk diffusion coefficient (D_o,b) and diffusion coefficient (D_o) calculated from the model were 5.9×10⁻⁹ and 1.6×10⁻⁹ cm²/s, respectively. The polymeric microporous solid support, Durapore GVHP 04700, was selected throughout the study as it gave the best performance.     

Diffusivity of bacteria

The effects of motility and aggregation on the diffusion coefficient for bacteria were studied in an aqueous system. The effects of cell concentrations, capillary tube sizes, and dilution rates on the diffusion coefficient were examined. In general, motile cells can diffuse about 1000 times faster than non-motile cells.Pseudomonas aeruginosa, a motile cell, andKlebsiella pneumoniae, a non-motile cell, were used for this research. Diffusion coefficients were measured by the capillary tube assay developed by Adler [1969]. From this procedure the diffusion coefficient ofPseudomonas aeruginosa was 2.1×10⁻⁵ (standard deviation: 1.0× 10⁻⁵) cm²/s and that ofKlebsiella pneumoniae was 0.9×10⁻⁵ (standard deviation : 0.5 × 10⁻⁵) cm²/s. The diffusion coefficient ofPseudomonas aeruginosa was about 2.3 times higher than that ofKlebsiella pneumoniae. The Stokes-Einstein equation could not be used for estimating the diffusion coefficients forKlebsiella pneumoniae andPseudomonas aeruginosa. The experimental value for the diffusion coefficient ofKlebsiella pneumoniae was about 2000 times higher than that (4.5×10⁻⁹ cm₂/s) obtained from the Stokes-Einstein equation. This discrepancy was due to the aggregation ofKlebsiella pneumoniae.     

Adsorption of butanol from aqueous solution onto a new type of macroporous adsorption resin: Studies of adsorption isotherms and kinetics simulation

BACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of bio‐butanol has attracted much attention. However, low butanol productivity severely limits its potential industrial application. It is important to establish an approach for recovering low‐concentration butanol from fermentation broth. Experiments were conducted using batch adsorption mode under different conditions of initial butanol concentration and temperature. Batch adsorption data were fitted to Langmuir and Freundlich isotherms and the macropore diffusion, pseudo‐first‐ and second‐order models for kinetic study. RESULTS: The maximum adsorption capacity of butanol onto KA‐I resin increase with increasing temperature, ranged from 139.836 to 304.397 mg g^?1. The equilibrium adsorption data were well fitted by the Langmuir isotherm. The adsorption kinetics was more accurately represented by the macropore diffusion model, which also clearly predicted the intraparticle distribution of the concentration. The effective pore diffusivity (D_p) was dependent upon temperature, but independent of initial butanol concentration, and was 0.251 × 10^?10, 0.73 × 10^?10, 1.32 × 10^?10 and 4.31 × 10^?10 m² s^?1 at 283.13, 293.13, 303.13 and 310.13 K, respectively. CONCLUSION: This work demonstrates that KA‐I resin is an efficient adsorbent for the removal of butanol from aqueous solutions and available for practical applications for future in situ product recovery of butanol from ABE fermentation broth. Copyright © 2012 Society of Chemical Industry     

Charge carrier lifetime in DLC films

Diamond-like carbon (DLC) layers deposited at room temperature in 13.56 MHz radio-frequency methane (CH₄) plasma have been studied. The results of transient currents for DLC thin films are reported. The carrier's lifetime was determined based on the transient current analysis for the surface and bulk recombinations: t_rs=0.3 ms, t_rv=0.11 ms. These values seem to be relatively high for structures of this type. The diffusion length for DLC films L*=0.67×10⁻⁴ cm. Other parameters such as the diffusion coefficient D*=4×10⁻⁵ cm²/s and surface recombination rate S=0.37 cm/s are exceptionally small here.     

A corrosion study and minority carrier diffusion length determination of n-type SnS2 and SnSSe

Corrosion behaviour of n-type SnS₂ and SnSSe single crystals in aqueous solutions has been studied. It has been shown that SnS₂ and SnSSe undergo a corrosion reaction in the dark when electrolytes contain oxidizing agents such as Fe(CN)³⁻₆ (KOH) and Ce⁴⁺ (H₂SO₄). Corrosion has a chemical nature. Values of absorption coefficient and hole diffusion length has been determined for both materials using the Gärtner model. A hole diffusion length of (2±0.5)×10⁻⁵ cm and (5±2)×10⁻⁷ cm was obtained, respectively, for samples prepared by Bridgman and Transport methods. The difference in hole diffusion length is explained by the existence of recombination centers produced by the transporting agent in the crystal bulk. A quantum yield of greater than one is found for SnSSe at high photon energies (greater than 2eV). This phenomenon has been explained by activation of a second electron from surface states above the valence band to the surface states below the conduction band.     

Investigation of Air Diffusion in a Wet Foam

Coefficients of air diffusion and permeability for surfactant tetradecyltrimethylammonium bromide aqueous solution and synthetic detergent Fairy are estimated by the diminishing bubble method. It is found that the diffusion coefficient is 5.9 × 10^–4 cm²/s for tetradecyltrimethylammonium bromide and is (6.1–6.3) × 10^–4 cm²/s for Fairy, and the volume permeаbility coefficient is 0.05 cm/s for tetradecyltrimethylammonium bromide and 0.06 cm/s for Fairy. The accuracy of experimental measurements is 10–15%. The time dependence of the squared diameter of the air bubble is close to linear.     

A measure of effective crosslinks in formaldehyde-modified cotton celluloses

Sol-gel fractions have been measured for cotton celluloses crosslinked with formaldehyde under widely different conditions of reaction and have been employed for estimation of the efficiency of crosslinking in the various processes. Most efficient utilization of formaldehyde for insolubilization of molecular chains is indicated for an aqueous process (form W′) and least efficient utilization is indicated for a nonaqueous process (form D′), the difference in efficiency being approximately a factor of 40. Interpretation of sol-gel data has been made relative to a model assuming random reaction of crosslinking agent throughout the cotton cellulose and by relationships developed by Charlesby and Pinner and by Shultz. This leads to estimates of relative numbers (moles) of effective chain elements per gram, v_e (i.e., twice the number of effective crosslinks), which decrease in the following sequence for cottons at the 0.20% level of formaldehyde (i.e., 6.7 × 10^?5 mole/g.): aqueous process, higher formaldehyde concentration (W′, v_e = 4.8 × 10^?5), vapor process (V, v_e = 1.75 × 10^?5), bake-cure process (C, v_e = 1.37 × 10^?5), aqueous process, lower formaldehyde concentration (W, v_e = 0.95 × 10^?5), nonaqueous process (D, v_e = 0.03 × 10^?5).     

Order-Disorder Conformation Change of Succinoglycan in Aqueous Sodium Chloride as Studied by Static and Dynamic Light Scattering

Summary Static and dynamic light scattering measurements have been made on a sodium salt sample of succinoglycan in 0.01 M aqueous NaCl at different temperatures between 25 and 75°C where the polysaccharide undergoes a thermally induced change from an ordered (helical) to disordered conformation with raising temperature T. The weight-average molecular weight M _w, the z-average radius of gyration, and the hydrodynamic radius sharply decrease in a relatively narrow T range (around 55°C) in which the specific rotation was previously found to change sigmoidally with T. In particular, the value of M _w (4.55 × 10⁵) in the ordered state at 25°C is twice as large as that (2.27 × 10⁵) in the disordered state at 75°C, giving decisive evidence that the helical structure of the polysaccharide in aqueous NaCl is composed of paired chains. It is concluded that this structure is a double-stranded helix and breaks directly into two disordered chains with increasing T. Received: 6 July 2001 / Accepted: 24 July 2001     

Synthesis and characterization of fluorescent PEG-polyurethane with free carboxyl groups

An innovative spherical poly(vinyl alcohol)(PVA)/peat/clay porous composite bead was prepared and shown to be suitable for use as an adsorbent. The mass transport process for the adsorption of metal ions onto this composite bead in an aqueous system was investigated. In the external mass transport process, the diffusion coefficient (D₁) of Cu⁺² and Zn⁺² ions increased with increasing initial metal ion concentration and the increasing effect was more pronounced in the initial metal ion concentrations range of 18?×?10^-3 to 22?×?10^-3?M. The diffusion rate of Zn⁺² ions was faster than that of Cu⁺² ions. In the intraparticle diffusion process, the diffusion coefficient (D₂) decreased with increasing initial metal ion concentration in the initial concentration range of 1?×?10^-3 to 4?×?10^-3?M, and the value of D₂ maintained an almost constant value in the initial concentration range of 8?×?10^-3 to 22?×?10^-3?M. The rate of ion diffusion within the adsorbent for Cu⁺² ions was faster than that for Zn⁺² ions. The adsorption mechanism was controlled by the intraparticle diffusion process. The adsorption followed the Langmuir adsorption isotherm model. The maximum amount of adsorbed metal ions for Cu⁺² and Zn⁺² ions were 22.57 and 13.62?mg/g composite bead, respectively.     

TRANSFER RATE AND SEPARATION OF Sr2+ and Cs+ BY SUPPORTED LIQUID MEMBRANES UTILIZING SYNERGIZED CROWN ETHER CARRIERS

ABSTRACT

The rate of the isotopic exchange of Na? and Cs? between hydrous silicon-titanium(IV) oxide in the relevant ionic form and aqueous solution was determined radiochemically. The rate was controlled by the diffusion of the ions in the exchanger particles. The diffusion coefficients at 5 °C are (3.9±0. 1)×10^?11m² s^?1 and (2.4± 0. 1)×10^?11 m² s^?1respectively, for Na? and Cs? in the exchanger equilibrated with solutions at pH 6. The activation energies are 31±5 kJ mol^?1 and 20±5 kJ mol^?1 for Na? and Cs? diffusion, respectively. The diffusion coefficients of the ions decreases with increasing pH of the solutions equilibrated with the exchanger, whereas their activation energy is independent of pH. The results were interpreted in terms of the strength of the electrostatic interaction between the counter ions and the ion-exchange sites.     

Branched-pore model applied to the adsorption of basic dyes on carbon

The branched-pore adsorption model, expressed by an external mass transfer coefficient k_f, a solid diffusivity D_s, a lumped micropore diffusion rate parameter k_b, and the fraction of macropores f, describes kinetic data from initial contact of adsorbent-adsorbate to the long-term ( > 24 hours) adsorption stages with reasonable accuracy.In this work the model is applied for three basic dye systems, namely Basic Red 22, Basic Yellow 21 and Basic Blue 69, all on carbon. A single value of each parameter describes each dye system. The k_f values are 0.18 × 10⁻²±28%, 0.3 × 10⁻²±17% and 0.2 × 10⁻² ± 20% cm s⁻¹, the D_s values are 0.33 × 10⁻⁹ 21%, 0.72 × 10⁻⁹ ± 9% and 0.72 × 10⁻⁹ ± 9% cm² s⁻¹, the k_b values are 0.65 × 10⁻⁶ ± 7.7%, 1.8 × 10⁻⁶ 0.2 × 10⁻⁶ 1% s⁻¹, while the f values are 0.55 ± 9%, 0.60 ± 10 % and 0.18 ± 11%, each for Basic Red 22, Basic Yellow 21 and Basic Blue 69 respectively.The model is based on the internal structure of the carbon particle being divided into a macropore and a micropore region. The latter has an upper-bound capacity of 241, 245 and 656 mg g⁻¹ for Basic Red 22, Basic Yellow 21 and Basic Blue 69 respectively. A sensitivity analysis for each parameter has been carried out.     

The diffusion of 14C in nuclear graphites

The high temperature exchange of ¹⁴C between ¹⁴CO and ¹²C-graphite has been used to label a large number of samples of various nuclear graphites. The technique has made it possible to obtain data on the self-diffusion of carbon in graphite. Three nuclear graphites are used, Pile Grade A and two isotropic varieties. Diffusion constants at 2473 K lie in the range 0·64 × 10^?19to 2·97 × 10^?19m²/sec. D₀ values vary from 1 ·20 × 10^?12to 1·06 × 10^?6m²/sec and activation energies, E_a, from 337 to 621 kj/mol. The D values found in this work are lower than those found by other workers. Possible reason for this are examined. Activation energies are also compared with values found by other workers and discussed in relation to theoretical calculations on the activation energy for direct interchange, vacancy and interstitial mechanisms for diffusion. It is concluded that direct interchange is the predominant mechanism for the diffusion of ¹⁴C in the highly graphitised samples used in this work.     

Fluorescence measurements of the diffusion coefficient for butylated hydroxyanisole in low-density polyethylene

Measurement of the diffusion coefficient (D) of butylated hydroxyanisole (BHA) in low density polyethylene at 31°C was made by two techniques. (1) Measurement of diffusion rate in the absence of solvent was made by use of a film stack with BHA-loaded discs on top and bottom. After a given diffusion time, the films were separated and the BHA extracted from the films into 1 -propanol. The fluorescence of the solutions provided values of BHA concentration as a function of film position in the stack, from which the value 3.4 (SD 0.3) × 10^?9 cm² s^?1 for D was calculated. (2) Fluorescence monitoring, under oxygen free conditions, was used to measure rate of BHA extraction from a film into 1 -propanol at 31°C, and gave the value 3.8 × 10^?9 cm² s^?1 for D which agrees well with the value determined by measurement in the absence of solvent.     

Discharge behaviour of plane nickel hydroxide electrodes

Plane nickel oxide electrodes were prepared by electrochemical deposition of nickel hydroxide on flexible nickel strips. Compact and adherent deposits were obtained, with thickness up to 4 × 10^?3 cm. They were cycled in 6 M KOH solution, and owing to the flexibility of the supporting nickel strips, did not show detaching. The results obtained from galvanostatic discharge curves fit the Peukert equation iⁿt = constant, giving an n value of 1.23 for the 1 × 10^?3 cm thick film and a value of 1.10 for the 4 × 10^?3 cm think film. The diffusion coefficients of moving species are in the order of magnitude of 10^?5 ?10^?6 cm²s^?1; the rate of discharge does not seem to be limited by proton diffusion. The proton diffusion in solid phase is not the only factor to be taken into account in the discharge process; diffusion and migration OH^? and H₂O species play an important role in plane thick nickel oxide film discharge.     

Characterization of modified sawdust, kinetic and equilibrium study about methylene blue adsorption in batch mode

Methylene blue (MB) biosorption by citric acid modified pine sawdust (Pinus tabulaeformis) was studied from aqueous solutions. Batch experiments were conducted to determine the biosorption properties of the biomass. The Langmuir isotherm equation could fit the equilibrium data. The maximal equilibrium quantity of MB from Langmuir model was 111.46 mg g^?1 at 293 K. The Elovich model adequately described the kinetic data in comparison to the pseudo-first-order model and pseudo-second-order model; the process involving rate-controlling step is very complex involving both boundary layer and intra-particle diffusion processes. The effective diffusion parameter D _i and D _f values were estimated at different initial concentration, and the average values were determined to be 5.76×10^?8 and 2.12× 10^?7 cm² s^?1. Thermodynamic parameters showed that the adsorption of methylene blue onto pine sawdust biomass was feasible, spontaneous and endothermic under studied conditions. The physical and chemical properties of the biosorbent were determined by SEM, TG-DSC, XRD, and the point of zero charge (pH _pzc ) and the nature of biomass-dye interactions were evaluated by FTIR analysis, which showed the participation of COOH, OH and NH₂ groups in the biosorption process. Biosorbents could be regenerated using 0.01 mol L^?1 HCl solution at least three cycles, with up to 90% recovery. Thus, the biomass used in this work proved to be effective for the treatment of MB bearing aqueous solutions.     

Insight into dynamics of polyelectrolyte chains in salt-free solutions by laser light scattering and analytical ultracentrifugation

We have investigated the dynamics of xanthan aqueous solutions with and without added salt (NaCl) by using laser light scattering (LLS) and analytical ultracentrifugation (AUC) via sedimentation velocity (SV). The fast and slow modes are observed in salt-free and low-salt xanthan solutions by dynamic light scattering (DLS). The scattering ratio (KC/R_s(q)) and apparent diffusion coefficient (D_s,app(q)) of the slow mode is linearly related to scattering vector (q²), indicating that it is related to the diffusion of scattering objects. The intensity contribution (α_s) of the slow mode is independent of scattering angles, indicating that the slow mode is not related to some scattering objects larger than the LLS observation length. However, the slow mode disappears in SV experiments, indicating that it arises from the temporal aggregates due to long range electrostatic interactions between chains, which can be destroyed in centrifugal field. The diffusion coefficient measured by SV is close to that of the fast mode in DLS measurements, indicating that it is the coupling diffusion of macroions and counterions. The present studies also demonstrate that the chain stiffness does not change the characteristics of the dynamics of polyelectrolyte in solutions.     

Dynamic adsorption behaviors between Cu2+ ion and water‐insoluble amphoteric starch in aqueous solutions

Dynamic adsorption behavior between Cu²⁺ ion and water‐insoluble amphoteric starch was investigated. The sorption process occurs in two stages: external mass transport occurs in the early stage and intraparticle diffusion occurs in the long‐term stage. The diffusion rate of Cu²⁺ ion in both stages is concentration dependent. In the external mass‐transport process, the diffusion coefficient (D₁) increases with increasing initial concentration in the low‐ (1 × 10^?3‐4 × 10^?3M) and high‐concentration regions (6 × 10^?3‐10 × 10^?3M). The values of adsorption activation energy (k_d1) in the low‐ and high‐concentration regions are 15.46–24.67 and ?1.80 to ?11.57 kJ/mol, respectively. In the intraparticle diffusion process, the diffusion coefficient (D₂) increases with increasing initial concentration in the low‐concentration region (1 × 10^?3‐2 × 10^?3M) and decreases with increasing initial concentration in the high‐concentration region (4 × 10^?3‐10 × 10^?3M). The k_d2 values in the low‐ and high‐concentration regions are 9.96–15.30 and ?15.53 to ?10.71 kJ/mol, respectively. These results indicate that the diffusion process is endothermic in the low‐concentration region and is exothermic in the high‐concentration region for both stages. The external mass‐transport process is more concentration dependent than the intraparticle diffusion process in the high‐concentration region, and the dependence of concentration for both processes is about equal in the low‐concentration region. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2849–2855, 2001     

Investigation of polyacrylonitrile solution inhomogeneity by dynamic light scattering

Dynamic light scattering (DLS) has been used to quantify nanoscale heterogeneity in the industrially significant polyacrylonitrile (PAN) polymer solution. The heterogeneity in polymer solution, traced by the ratio of amplitudes of the slow to fast mode, is observed to be related to various parameters, such as molecular weight of the polymer, the type of co‐monomer, processing time, concentration of the solution, and the choice of the solvents. It has been identified that low molecular weight PAN homopolymer have the least heterogeneity issues. Amongst the chosen co‐polymers for this study, similar degree of heterogeneity was observed at concentration slightly above the critical concentration at which the polymer chains begin to overlap. Whereas, at higher concentration, PAN‐methacrylic acid (4 wt%) copolymer showed the least heterogeneity issue. The aggregate diffusion coefficient of PAN‐methacrylic acid (4 wt%) copolymer solution in dimethylformamide (DMF) and N,N‐dimethylacetamide (DMAc) are respectively determined to be ～1.6 × 10^?12 cm²/s and ～1.6 × 10^?13 cm²/s, which results in an estimated aggregate size of 9 nm and 90 nm. POLYM. ENG. SCI., 55:1403–1407, 2015. © 2015 Society of Plastics Engineers     

Release of ergotamine from poly (2-hydroxyethyl Methacrylate)

The release of the alkaloid ergotamine from thin discs of poly(2-hydroxyethyl methacrylate) [PHEMA] into an aqueous buffered medium has been effected under sink conditions and monitored by fluorescence spectroscopy. The process was found to be diffusion controlled, the fraction of available drug released being linear in (time)^1/2 during the initial stages. The influences of disc thickness, drug load and temperature were investigated and yielded 2.0 (± 1.0) × 10^?13 m² s^?1 for the diffusion coefficient of ergotamine through the swollen gel at 310K and a value of 69 ± 5 kJ mol^?1 for the activation energy of diffusion. For the uptake of aqueous buffer alone into PHEMA the corresponding values were ca 100 times greater and three times smaller respectively.