Surprising Insensitivity of Homogeneous Acetylation of Cellulose Dissolved in Triethyl(n‐octyl)ammonium Chloride/Molecular Solvent on the Solvent Polarity

The homogeneous acetylation of microcrystalline cellulose (MCC) by acetyl chloride and acetic anhydride in triethyl(n‐octyl)ammonium chloride (N₂₂₂₈Cl)/molecular solvents (MSs) is investigated. The reaction with both acylating agents shows the expected increase of the degree of substitution (DS) on reaction temperature and time. Under comparable reaction conditions, however, DS is surprisingly little dependent on the MS employed, although the MSs differ in empirical polarity by 7 kcal mol^?1 as calculated by use of solvatochromic probes. The empirical polarities of (MCC + N₂₂₂₈Cl + MS) differ only by 0.8 kcal mol^?1. The formation a polar electrolyte sheath around cellulose chains presumably contributes to this “leveling‐off” of the dependence DS on the polarity of the parent MS employed. N₂₂₂₈Cl recovery and recycling is feasible.     

New methods for acylation of pure and sawdust‐extracted cellulose by fatty acid derivatives—Thermal and mechanical analyses of cellulose‐based plastic films

This work deals with the synthesis of cellulosic plastic films obtained in homogeneous conditions by microwave‐induced acylation of commercial or chestnut tree sawdust cellulose by fatty acids. The acylation reaction was studied according to N,N‐dimethyl‐4‐aminopyridine (DMAP) amount, DMAP simultaneously playing the role of catalyst and proton trapping base. This study clearly showed that DMAP does not influence degrees of substitution (DS), massic, and molar yields. Plastic films synthesized in the absence of DMAP showed a decrease in mechanical behavior. Organic (tributylamine) or inorganic bases (CaCO₃, Na₂CO₃) were then added to replace DMAP basic activity, and no changes were observed. Concerning thermal and mechanical properties of plastics obtained with various bases, glass transition temperatures (T_g) and degradation temperature (T_d) were found constant whatever the base, and the best mechanical properties were obtained for films synthesized in the presence of CaCO₃. The same remarks were made concerning the valorization of chestnut tree sawdust cellulose. Microbial biodegradation of plastic films with DS = 2.2 led to a loss of their mechanical behaviors. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1266–1278, 2005     

One pot blending of biopolymer‐TiO2 composite membranes with enhanced mechanical strength

A biopolymer‐TiO₂ composite membrane was prepared by blending of N‐[(2‐hydroxy‐3‐trimethylammonium) propyl] chloride chitosan and cellulose acetate with nano‐TiO₂ particles as the introduced inorganic components. It was verified that the amino groups (? NH₂) of chitosan (CTS) were partly grafted by stronger hydrophilic group ? according to the ¹H‐nuclear magnetic resonance spectra of N‐[(2‐hydroxy‐3‐trimethylammonium) propyl] chloride chitosan and attenuated total reflectance Fourier transform infrared spectroscopy. The structure, microcosmic morphology, water flux, swelling properties, and thermal stability of the composite membranes were characterized. With the mass ratio of cellulose acetate to CTS being 50 wt %, the mole ratio of CTS to glycidyl trimethylammonium chloride being 1 : 1, and drying temperature being 60°C in 70% acetic acid, the formed biopolymer‐TiO₂ composite membranes exhibited enhanced mechanical strength (84.29 MPa), lower swelling degree (101.36%), and improved antibacterial activity against Gram‐negative Escherichia coli (Rosetta and DH5α) and Gram‐positive Bacillus subtilis. The existence of nano‐TiO₂ particles and the introduction of stronger cationic group synergistically improved the antibacterial properties of the biopolymer‐TiO₂ composite membranes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42732.     

Relationships between the molecular structure and moisture-absorption and moisture-retention abilities of succinyl chitosan

Summary N-Succinyl chitosan (NSC) with various degrees of deacetylation (DD 6–94%) and substitution (DS 0.14–0.79) were successfully prepared from N-acetylchitosans in varying reaction time. Infrared spectroscopy (IR), ¹H NMR and gel-permeation chromatographic (GPC) techniques were used to characterize their molecular structures. The moisture-absorption (R_a) and -retention (R_h) abilities of NSC are closely related to the DD and DS values. Under conditions of high relative humidity, the maximum R_a and R_h were obtained at DD values of about 50%, and when the DD value deviated from 50%, R_a and R_h decreased. Under dry conditions, when the DD value was 50%, the R_h was the lowest. The NSC with DS 0.65 to 0.79 exhibited better R_h than that of HA, and has the potential to prepare HA-like substances in pharmaceutical and cosmetics industries.     

Comparison of succinylation methods for bacterial cellulose and adsorption capacities of bacterial cellulose derivatives for Cu<Superscript>2+</Superscript> ion

Bacterial cellulose (BC) was homogenously modified with succinic anhydride in N,N-dimethylacetamide/LiCl in the presence of triethylamine and heterogeneously in pyridine in the presence of 4-dimethylaminopyridine. FTIR, XRD, 13C CP MAS NMR, SEM were used to characterize BC and succinylated bacterial cellulose (SBC). For homogeneous modification, the degree of substitution (DS) of SBC differs from 0.21 to 1.45 with the variation of the adding amount of succinic anhydrate, temperature, reaction time, and the amount of triethylamine. DS and XRD profiles reveal that heterogenous reaction mainly happens on the surface of BC membrane. The adsorption capacity and mechanism of Cu²⁺ onto BC and SBC were investigated. The result shows the adsorption is affected by the morphology and the DS of adsorbents.     

Cellulose furoate. III. Properties and applications

Cellulose furoates synthesized by a homogeneous reaction was used to make film and fiber. Either colorless or light yellow, transparent cellulose furoate film can be made by solvent cast. Cellulose furoate film with a DS of 2.56 and 20% PEG-400 as the plasticizer displayed 5441 psi maximum tenacity and 21.5% maximum strain. The film without plasticizer has a water vapor permeability of 0.124 ng · m/m² · s · Pa. DMTA study identified the T_g of cellulose furoate with a DS of 2.77 was 225°C. As the DS decreased, the T_g shifted toward higher temperature. The success of wet-spun fibers from LiCl/DMAc solution of cellulose and cellulose furoate substantiated cellulose furoate is compatible with cellulose. Unfortunately, the wet-spun fibers lost their mechanical and surface properties, and bioresistant property against Myrothecium verrucaria, Cheatomium globosum, and Aspergillus terreus. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 253–257, 2001     

Cellulose derivatives with adamantoyl groups

A new synthesis pattern of adamantoyl esters of cellulose (AdTMSC) is described. The process was approached by two steps. The first one consists in the obtaining of trimethylsilylcellulose (TMSC), by reacting cellulose in N,N‐dimethylacetamide/lithium chloride (DMA/LiCl) solution with chlorotrimethylsilane and hexamethyldisilazane. The AdTMSC was synthesized by reacting trimethylsilylcellulose with 1‐adamantanecarbonyl chloride, at 130°C. The obtained compounds were characterized by elemental analysis, ¹H and ¹³C NMR, FTIR spectroscopy, thermogravimetry method, and X‐ray diffraction. From ¹H NMR spectroscopy and elemental analyses, the degree of substitution (DS) of the cellulose derivatives was established. The AdTMSC is soluble in common organic solvent like chloroform, THF, and DMSO. As revealed by ¹³C NMR spectroscopy, a faster reaction takes place at the O (6)H group from AGU compared with O (2)H or O(3)H groups. Furthermore, other important properties were established by X‐ray diffraction and thermogravimetry method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 105–112, 2006     

Aerobic biodegradation of cellulose acetate

Two separate assay systems were used to evaluate the biodegradation potential of cellulose acetate: an in vitro enrichment cultivation technique (closed batch system), and a system in which cellulose diacetate (CDA) films were suspended in a wastewater treatment system (open continuous feed system). The in vitro assay employed a stable enrichment culture, which was initiated by inoculating a basal salts medium containing cellulose acetate with 5% (v/v) activated sludge. Microscopic examination revealed extensive degradation of CDA (DS = 2.5) fibers after 2–3 weeks of incubation. Characterization of the CA fibers recovered from inoculated flasks demonstrated a lower average degree of substitution and a change in the mol wt profiles. In vitro enrichments with CDA (DS = 1.7) films were able to degrade > 80% of the films in 4–5 days. Cellulose acetate (DS = 2.5) films required 10–12 days for extensive degradation. Films prepared from cellulose triacetate remained essentially unchanged after 28 days in the in vitro assay. The wastewater treatment assay was less active than the in vitro enrichment system. For example, approximately 27 days were required for 70% degradation of CDA (DS = 1.7) films to occur while CDA (DS = 2.5) films required approximately 10 weeks before significant degradation was obtained. Supporting evidence for the biodegradation potential of cellulose acetate was obtained through the conversion of cellulose [1-¹⁴C]-acetate to ¹⁴CO₂ in the in vitro assay. The results of this work demonstrate that cellulose acetate fibers and films are potentially biodegradable and that the rate of biodegradation is highly dependent on the degree of substitution. © 1993 John Wiley & Sons, Inc.     

Cellulose-based fibers from liquid crystalline solutions. III. Processing and morphology of cellulose and cellulose hexanoate esters

Cellulose and a cellulose hexanoate ester (DS 0.69) exhibited liquid crystalline behavior in dimethylacetamide/lithium chloride and dimethylacetamide, respectively. The experimentally observed critical volume fraction (V^c_p) of cellulose was lower than that predicted by Flory's theory, whereas the experimental and theoretical values of V^c_p were within 70% of prediction for cellulose hexanoate. The V^c_p value obtained for cellulose hexanoate was lower than that previously reported for cellulose acetate butyrate with a maximum degree of butyration (CAB-3). This indicates that bulky substituents may lower V^c_p values. Fibers were spun from isotropic and anisotropic solutions of cellulose and cellulose hexanoate by a dry jet/wet spinning method. There was an increase in mechanical properties through the isotropic to anisotropic transition with moduli reaching 152 g/d (20.8 GPa) for cellulose fibers. The formation of cellulose fibers with high modulus at large extrusion rates and large takeup speeds (draw ratio) is explained with molecular organization prior to coagulation. This unexpected enhancement is attributed to the air gap that exists in the dry jet/wet spinning process. Similar improvements were not observed for cellulose hexanoate fibers. This is explained with incomplete development of liquid crystalline structure at the solution concentrations from which the fibers were spun. © 1993 John Wiley & Sons, Inc.     

Investigations on esterification reactions of starches in 1‐N‐butyl‐3‐methylimidazolium chloride and resulting substituent distribution

The ionic liquid (IL) 1‐N‐butyl‐3‐methylimidazolium chloride ([C₄mim]⁺Cl^?) was used as solvent for different esterification reactions of the biopolymer starch. Therefore, maize starches with varying content of amylose were used. Different carboxylic acid anhydrides were applied to esterify starch with a degree of substitution (DS) in the range of 0.7–3.0. For example, starch acetates with the mentioned DS are accessible within 30 min at a 105°C‐reaction temperature. The DS distribution of starch acetates synthesized in IL was compared with the common starch acetate synthesis of Mark and Mehltretter. Also, a consideration of starch acetates and cellulose acetates synthesized in [C₄mim]⁺Cl^? is given. The starch esters were characterized by means of Raman spectroscopy for qualitative‐ and nuclear magnetic resonance spectroscopy for quantitative determination of the functionalization pattern. Moreover, the molecular mass distribution was determined after saponification by means of GPC‐MALLS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and Photocrosslinking Reaction of N-Allylcarbamoylmethyl Cellulose Leading to Hydrogel

Summary The reaction of the carboxymethyl cellulose sodium salt (Na-CMC) (degrees of substitution (DS) = 1.2) with N-hydroxysuccinimide (Su-OH) in the presence of 1-hydroxybenzotriazole and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) was carried out in water to obtain the Su-OH ester of carboxymethyl cellulose, Su-CMC, with the DS values of 0.19 – 1.04. N-Allylcarbamoylmethyl cellulose (Allyl-CMC), which was prepared from the reaction of Su-CMC with an excess amount of allylamine, was crosslinked by UV-irradiation. In addition, the photocrosslinked Allyl-CMC film was swollen with water to form a hydrogel having a relatively high water-swelling property, e.g., the degree of swelling (ds) was ca. 360% for Allyl-CMC with the DS of 0.93.     

Polymerization of propynes bearing diphenylamino or indolyl groups

Summary Nitrogen-containing acetylenic monomers including 3-(N,N-diphenylamino)-1-propyne (DPAP), N-(2-propynyl)indole (PI), 2-methyl-N-(2-propynyl)indole (2-MePI) and 3-methyl-N-(2-propynyl)indole (3-MePI) polymerized in the presence of various transition metal catalysts. Poly(DPAP) was obtained with WCl₆, MoCl₅, Rh and Fe catalysts, and its weight-average molecular weights (M _w) reached 140x10³. Polymerization of PI and 2-MePI by Rh and Fe catalysts gave good yields of high molecular weight polymers with M _w of 340x10³ and 640x10³, respectively. Polymerization of 3-MePI by WCl₆- and MoCl₅-based catalysts resulted in a soluble polymer (M_w= 52x10³), whereas the use of Rh and Fe catalysts led to the formation of an insoluble polymer. All the polymers exhibited cutoff wavelengths around 450–500 nm, meaning the moderate to fair conjugation along the polymer backbones. Received: 24 June 1998/Accepted: 5 August 1998     

Simultaneous sorption and diffusion of a 4-aminoazobenzene derivative and its conjugate acid in cellulose membrane carrying sulfonic acid groups

An azo dye, 2-methyl-N,N-bis(2-hydroxyethyl)-4-aminoazobenzene (nonionic dye) and its conjugate acid (cationic dye) are simultaneously adsorbed by the cellulose membranes carrying sulfonic acid groups from a slightly acidic aqueous solution. Sorption equilibria of the nonionic and the cationic dye are described in terms of the Henry's partition and the ionic exchange mechanism, respectively, in the latter case, the ion exchange constants obtained for the membrane with sulfonic acid group content (SAG) = 261 meq/kg at 30°C are K = 1.43 × 10^?5 and K = 0.542, respectively, where Na, H, and DH refer to sodium, hydrogen, and cationic dye ions. The diffusion coefficients of the nonionic dye (D_N) and the cationic dye (D_C) in the membranes were estimated from the permeation data of the dyes through the membrane. Both D_N and D_C decrease with increasing SAG. The ratio D_N/D_C ranged in 2.2–10, the ratio increases with the SAG.     

Preparation of cellulose derivatives containing carbazole chromophore

Cellulose derivatives containing long hydrocarbon side chains and the carbazole chromophore are prepared. N‐4′‐Bromobutylcarbazole is first synthesized from carbazole and 1,4‐dibromobutane. Alkylated carbazole is then reacted with cellulose acetate in dimethyl sulfoxide solution to produce cellulose ethers containing the desired chromophore. Polymers containing a mixture of alkyl side chains are also prepared by the subsequent addition of 1‐bromododecane to the reaction mixture. Characterization of the resulting cellulose derivatives by FTIR spectroscopy indicates that the deacetylation of cellulose acetate and the subsequent etherification are both complete. In addition, the incorporation of the carbazole chromophore is clearly shown by ¹H‐ and ¹³C‐NMR spectroscopy. Polymers of different carbazole content, ranging from 2.9 to 1.1 chromophores per anhydroglucose repeat unit, are obtained by varying the reaction conditions. Substitution is found to be controlled primarily by the quantity of alkylating agent introduced while variation of the reaction time has little effect. This method is used to prepare (dodecyl)_y(N‐4′‐carbazolylbutyl)_xcellulose, (decyl)_y(N‐4′‐carbazolylbutyl)_xcellulose, and (butyl)_y(N‐4′‐carbazolylbutyl)_xcellulose. Cellulose acetate can be replaced by (methyl)cellulose as the starting material to obtain analogous products. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2764–2772, 1999     

Viscosity‐molecular weight relationship for cellulose solutions in either NMMO monohydrate or cuen

The intrinsic viscosities, [η], of nine cellulose samples, with molar masses from 50 × 10³ to 1 390 × 10³ were determined in the solvents NMMO*H₂O (N‐methyl morpholin N‐oxide hydrate) at 80°C and in cuen (copper II‐ethlenediamine) at 25°C. The evaluation of these results with respect to the Kuhn–Mark–Houwink relations shows that the data for NMMO*H₂O fall on the usual straight line in the double logarithmic plots only for M ≤ 158 10³; the corresponding [η]/M relation reads log ([η]/mL g⁻¹) = –1.465 + 0.735 log M. Beyond that molar mass [η] remains almost constant up to M ≈ 10⁶ and increases again thereafter. In contrast to NMMO*H₂O the cellulose solutions in cuen behave normal and the Kuhn–Mark–Houwink relation reads log ([η]/mL g⁻¹) = −1.185 + 0.735 log M. Possible reasons for the dissimilarities of the behavior of cellulose in these two solvents are being discussed. The comparison of three different methods for the determination of [η] from viscosity measurements at different polymer concentrations, c, demonstrates the advantages of plotting the natural logarithm of the relative viscosities as a function of c. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fungicidal and Insecticidal Activity of O-Acyl Chitosan Derivatives

Summary A series of O-(acyl) chitosan (OAC) derivatives with a degree of substitution (DS) between 0.02 and 0.28 were synthesized by reaction of alkanoic acid derivatives with chitosan in the presence of H₂SO₄ as a catalyst. The reaction was performed at 80 °C for 4 h with different mol ratios of alkanoic acids to chitosan. The synthesized compounds were analyzed by ¹H- and ¹³C-NMR spectroscopy. A high DS was obtained with O-(butyroyl) chitosan (DS 0.28) at a mol ratio of (1:5) chitosan to butyric acid. Their fungicidal activity against the grey mould Botrytis cinerea (Leotiales: Sclerotiniaceae) and the rice leaf blast pathogen Pyricularia grisea (Teleomorph: Magnaportha grisea) has been evaluated. O-(decanoyl) chitosan at mol ratio of 1:2 (chitosan to decanoic acid) was the most active compound against B. cinerea (EC₅₀=1.02 g.l^-1) and O-(hexanoyl) chitosan displayed the highest activity against P. grisea (EC₅₀=1.11 g.l^-1). It has been mentioned that some derivatives also repressed spore formation at rather high concentrations (1.0, 2.0 and 5.0 g.l^-1). The insecticidal activity has been screened at 5 g.kg^-1 artificial diet against the larvae of the cotton leafworm Spodoptera littoralis (Lepidoptera: Noctuidae). The results revealed that all of the synthesized derivatives showed high inhibition of growth of the larvae of S. littoralis compared to chitosan (7% growth inhibition) and the most active one was O-(decanoyl) chitosan (64% growth inhibition) after 5 days of feeding on treated artificial diet.     

Dielectric investigation of isotropic and anisotropic solutions of cellulose acetate in dioxane

The dielectric and optical characteristics of a sample of cellulose acetate (DS = 2.45) in dioxane solutions were studied at 10–50°C of concentration 10–50 wt% to include both isotropic and anisotropic phases. The study showed that the loss maximum, ε_max″, magnitude of polarization, (ε₀ ? ε_∞), static dielectric constant, ε₀, time of relation, (2πf_m)^?1, and refractive index, n_D, steadily increase with concentration up to the critical concentration (41 wt%) and then decrease. The mean-square dipole moment, 〈gμ²〉, decreases steadily up to the critical concentration then remains nearly constant, indicating that the isotropic solution changes to anisotropic, with smaller mean-square dipole moment. Comparison between the results of cellulose acetate (CA) and those of hydroxypropyl cellulose (HPC) reveals that, at the critical concentration in dioxane, the cholesteric structure of HPC possesses a greater mean-square dipole moment with higher temperature coefficient than does CA. The activation energy of the relaxation process for hydroxypropyl cellulose is higher, indicating a greater intrachain interaction compared with cellulose acetate.     

Rheological characterization of cellulose solutions in N‐methyl morpholine N‐oxide monohydrate

Three different modes of rheological properties were measured on 11 and 13 wt % solutions of cellulose in N‐methyl morpholine N‐oxide (NMMO) monohydrate, in which concentration range lyocell fibers of much reduced fibrillation are preferably produced. The dynamic rheological responses revealed that the Cox–Merz rule did not hold for these cellulose solutions. Both cellulose solutions showed a shear thinning behavior over the shear rate measured at 85, 95, 105, and 115°C. However, 13 wt % solution gave rise to yield behavior at 85ºC. The power law index ranged from 0.36 to 0.58. First normal stress difference (N₁) was increased with lowering temperature and with increasing concentration as expected. Plotting N₁ vs shear stress (τ_ω) gave almost a master curve independent of temperature and concentration, whose slope was about 0.93 for both cellulose solutions over the shear rate range observed (τ_ω > 500 Pa). In addition, the cellulose solutions gave high values of recoverable shear strain (S_R), ranging from 60 to 100. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 216–222, 2002     

Cationic starch iodophores

Cross‐linked cationic starches N‐(2‐hydroxyl)propyl‐3‐trimethyl ammonium starch chloride (CQS chloride), N‐(2‐hydroxyl)propyl‐3‐trimethyl ammonium starch iodide (CQS iodide), and N‐(2‐hydroxyl)propyl‐3‐trimethyl ammonium starch iodide–iodine (CQS triiodide) with the degree of substitution (DS) according to cationic groups from 0.04 to 0.62, as well as cross‐linked starch–iodine complexes were synthesized and tested as potential antibacterial agents. Cationic starch iodine derivatives were obtained during ion exchange reaction between CQS chloride and iodide or iodide–iodine anions in aqueous solutions. CQS_DS≤0.3 chloride can form several types of iodine complexes, such as the blue amylose–iodine inclusion complex and ionic CQS⁺I^?·(I₂)_m complex (m ≥ 1). The antibacterial activity of modified starches–iodine samples against different pathogenic bacterial cultures and contaminated water microorganisms was evaluated. CQS chloride and CQS iodide were found to be bacteriostatic. A strong antibacterial activity was characteristic of CQS triiodides in which molecular iodine is present in both ionic and inclusion complexes. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Redox chemistry of H2S oxidation by the British Gas Stretford Process Part III: Electrochemical behaviour of anthraquinone 2,7 disulphonate in alkaline electrolytes

Electrochemical reduction of aqueous anthraquinone 2,7 disulphonate (AQ27DS) solutions at pH 9.3 were studied at Hg, Au and Pt electrodes. Cyclic voltammograms showed about 40 mV potential separation of the single pair of current peaks, precluding a simple one or two electron process. Charge measurements in controlled potential exhaustive reductions indicated a 2 mole^– per mol AQ27DS process leading to quinolate anions, whereas the partially reduced solution showed an EPR spectrum, indicating the presence of radical species, which, if produced directly, would involve only a 1 mole^– per mol AQ27DS process. U.v.-visible and EPR spectra of the deep red partially reduced AQ27DS solutions showed that both radical anions (AQ27DS _· ^– ) and fully reduced anthraquinolate were present; AQ27DS _· ^– radicals predominated at low conversions, while complete conversion produced AQ27DSH- ions. The AQ27DS diffusion coefficient was determined as 3.73 × 10^–10m²S^–1 from steady-state voltammetry at a gold rotating disc electrode.The results are congruous with a reduction mechanism involving an initial 2 mole^– per mol AQ27DS process to give anthraquinolate anions, from which electron transfer in solution to AQ27DS species produced AQ27DS - radical anions (a comproportionation). The comproportionation equilibrium constant was estimated as between 0.2 and 4.0 from cyclic voltammograms; together with a value of pK _a2(AQ27DSH₂) = 10.8 from the literature, this enabled the solution composition, and hence the major absorption spectral changes, to be predicted as a function of conversion. From a calculated potential-pH diagram, the AQ27DS reduction mechanism was predicted to involve disproportionation of the radical anions at pH 9.3 and two sequential one electron reductions at pH 9.3Nomenclature A electrode area (m²) - c concentration (mol m^–3) - D diffusion coefficient (m2 s^–1) - E ^° standard reversible electrode potential against SHE (V) - F Faraday constant 96 485C (mole^–)^–1 - HMDE hanging mercury drop electrode (–) - i current density (A m^–2) - i _L mass transport limited current density (A m^–2) - i _sp peak current density at HMDE (A m^–2) - IK, I _K EPR sensitivity factors, constants for a given geometry - mean mass transport rate constant (ms^–1) - l length of EPR cavity (m) - n number of moles of reactant - r radius of the EPR tube (m) - R gas constant (8.31441 J mol^–1 K^–1) - S EPR signal strength (–) - S ₀ EPR signal strength for one mole of spins within cavity (–) - t time (s) - T temperature (K) - V electrolyte volume (m³) - V _f volumetric flow rate (m3 s^–1) - X _e length of electrode (m) - z number of moles e^– per mole of reactant (–) Greek symbols molar absorptivity (m2 mol^–1) - Nernst diffusion layer thickness (m) - kinematic viscosity (m²s^–1) - potential sweep rate (V s^–1) - RDE rotation rate (s^–1)