Number Of Surface Groups Research Articles

Egg White-Mediated Fabrication of Mg/Al-LDH-Hard Biochar Composite for Phosphate Adsorption.

Phosphorus is one of the main causes of water eutrophication. Hard biochar is considered a promising phosphate adsorbent, but its application is limited by its textural properties and low adsorption capacity. Here, an adhesion approach in a mixed suspension containing egg white is proposed for preparing the hybrid material of Mg/Al-layered double hydroxide (LDH) and almond shell biochar (ASB), named L-AE or L-A (with or without egg white). Several techniques, including XRD, SEM/EDS, FTIR and N2 adsorption/desorption, were used to characterize the structure and adsorption behavior of the modified adsorbents. The filament-like material contained nitrogen elements at a noticed level, indicating that egg white was the crosslinker that mediated the formation of the L-AE hybrid material. The L-AE had a higher phosphate adsorption rate with a higher equilibrium adsorption capacity than the L-A. The saturation phosphate adsorption capacity of L-AE was nearly three times higher than that of L-A. Furthermore, the number of surface groups and the density of the positively charged surface sites follow the ASB < L-A < L-AE order, which is consistent with their phosphate adsorption performance. The study may offer an efficient approach to improving hard biochar's adsorption performance in wastewater treatment.

Contradictory tendency of As(V) releasing from Fe–As complexes: Influence of organic and inorganic anions

The strong ability of ferrihydrite and its aged minerals for fixing arsenate is a key factor in remediating arsenate-polluted environments. It is therefore crucial to clarify the stability of Fe–As complexes and the release conditions for As(V). The As(V) release amount was evaluated and compared in the presence of six representative anions, namely, phosphate, silicate, sulfate, inositol hexaphosphate, citrate, and oxalate. It was found that the As(V) release amount changed with the aging time of ferrihydrite and that this tendency generally followed two rules. These are, longer aging time leads to lower As(V) release (Rule 1), and longer aging time leads to higher As(V) release (Rule 2). Whether Rule 1 or Rule 2 dominated As release depended on the number of surface groups, size of competing anions, and contribution of As(V) re-adsorption. Characterization results using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) provided evidence for the predicted mechanisms of As(V) release under various circumstances. In this work, it was demonstrated that when inorganic anions such as sulfate and silicate are present, ferrihydrite with longer aging time led to decreased As(V) release. When organic anions are present, ferrihydrite with less aging time results in reduced As(V) leaching. For anions such as phosphate, the As(V) release amount in relation to the ferrihydrite aging time depends on the concentration of phosphate ions. Nevertheless, the ligand concentration and As(V) loading rate on ferrihydrite should be simultaneously considered for the rule governing As(V) releasing.

Highly sensitive and reproducible quantification of oxygenated surface groups on carbon nanomaterials

The quantification of surface groups is a key characterization for different carbon materials as their behavior in colloidal dispersion, their interaction with proteins, drugs or polymers as well as their aggregation behavior strongly depend on the type and number of surface groups. Some of the most challenging groups are those containing oxygen as the typical characterization methods do not allow for a highly sensitive and reproducible quantification of carboxylic, lactonic and alcoholic groups. The only known wet-chemical method that is able to yield quantitative results is the Boehm titration. However, this method is also known to be extremely demanding regarding procedure compliance, requires large amounts of sample, and leads to rather large standard deviations. Here we report on a significantly improved titration method for the quantification of oxygen containing surface groups. All methodical aspects like sample preparation, reaction time, filtration medium, volumetric and gravimetric methods have been optimized, leading to the detection of carboxylic, lactonic and alcoholic groups with a standard deviation of ±1 μmol/g while using only small amounts of sample material. The method has been successfully applied on a broad variety of hydrophilic and hydrophobic carbon materials including nanodiamond, partially graphitized nanodiamond, multiwall carbon nanotubes and acetylene black.

Multimodal Cleavable Reporters for Quantifying Carboxy and Amino Groups on Organic and Inorganic Nanoparticles

Organic and inorganic nanoparticles (NPs) are increasingly used as drug carriers, fluorescent sensors, and multimodal labels in the life and material sciences. These applications require knowledge of the chemical nature, total number of surface groups, and the number of groups accessible for subsequent coupling of e.g., antifouling ligands, targeting bioligands, or sensor molecules. To establish the concept of catch-and-release assays, cleavable probes were rationally designed from a quantitatively cleavable disulfide moiety and the optically detectable reporter 2-thiopyridone (2-TP). For quantifying surface groups on nanomaterials, first, a set of monodisperse carboxy-and amino-functionalized, 100 nm-sized polymer and silica NPs with different surface group densities was synthesized. Subsequently, the accessible functional groups (FGs) were quantified via optical spectroscopy of the cleaved off reporter after its release in solution. Method validation was done with inductively coupled plasma optical emission spectroscopy (ICP-OES) utilizing the sulfur atom of the cleavable probe. This comparison underlined the reliability and versatility of our probes, which can be used for surface group quantification on all types of transparent, scattering, absorbing and/or fluorescent particles. The correlation between the total and accessible number of FGs quantified by conductometric titration, qNMR, and with our cleavable probes, together with the comparison to results of conjugation studies with differently sized biomolecules reveal the potential of catch-and-release reporters for surface analysis. Our findings also underline the importance of quantifying particularly the accessible amount of FGs for many applications of NPs in the life sciences.

СОРБЦИЯ СУЛЬФАНИЛОВОЙ КИСЛОТЫ И ИОНОВ МЕДИ АКТИВИРОВАННЫМ УГЛЕМ, МОДИФИЦИРОВАННЫМ ОКСИДАМИ МЕТАЛЛОВ

The possibility of using activated carbon brand Filtrasorb 300 modified with metal oxides (F300 M) in comparison with unmodified (F300 H) for the simultaneous extraction of organic com-pounds and copper ions from water has been established. A solution of metal chloride obtained by acid-thermal activation of waste from alumina production "red mud" is used as a modifier. The process of sulfanilic acid and copper ions sorption by modified and unmodified activated carbon Filtrasorb 300 (AC F300) is investigated. The structural-sorption characteristics of the studied materials, such as: static exchange cationic and anionic capacities and the number of surface groups (carboxyl, lactone, phenolic), are determined. Positive effect of activated carbon modification by metal oxides that has been obtained as a result of acid-thermal treatment of “red mud” is shown. The presence of negatively charged active centers on modified activated carbon surface makes it possible to increase by 59 % the value of sulfanilic acid adsorption due to the interaction of the ma-terial surface with –NH2 group of the acid with the absence of copper ions in the solution, which is 24 % more than AB F300. Simultaneous presence of copper ions and sulfanilic acid reduces their adsorption on the modified sorbent as a result of blocking the active groups and reducing the electrostatic interaction. Taking into account the complex nature of physical-chemical interactions in a system that contains sulfanilic acid with acidic and basic groups, and the competing effect under certain conditions, it can be expected that the modification of activated carbon with a metal chloride solution (obtained by acidic activation of alumina production wastes with their subsequent conversion to oxide form), is a promising direction in water treatment in case of containing both organic compounds and non-ferrous metal ions.

Cytotoxicity of Dendrimers.

Drug delivery systems are molecular platforms in which an active compound is packed into or loaded on a biocompatible nanoparticle. Such a solution improves the activity of the applied drug or decreases its side effects. Dendrimers are promising molecular platforms for drug delivery due to their unique properties. These macromolecules are known for their defined size, shape, and molecular weight, as well as their monodispersity, the presence of the void space, tailorable structure, internalization by cells, selectivity toward cells and intracellular components, protection of guest molecules, and controllable release of the cargo. Dendrimers were tested as carriers of various molecules and, simultaneously, their toxicity was examined using different cell lines. It was discovered that, in general, dendrimer cytotoxicity depended on the generation, the number of surface groups, and the nature of terminal moieties (anionic, neutral, or cationic). Higher cytotoxicity occurred for higher-generation dendrimers and for dendrimers with positive charges on the surface. In order to decrease the cytotoxicity of dendrimers, scientists started to introduce different chemical modifications on the periphery of the nanomolecule. Dendrimers grafted with polyethylene glycol (PEG), acetyl groups, carbohydrates, and other moieties did not affect cell viability, or did so only slightly, while still maintaining other advantageous properties. Dendrimers clearly have great potential for wide utilization as drug and gene carriers. Moreover, some dendrimers have biological properties per se, being anti-fungal, anti-bacterial, or toxic to cancer cells without affecting normal cells. Therefore, intrinsic cytotoxicity is a comprehensive problem and should be considered individually depending on the potential destination of the nanoparticle.

Characterization of mixed-ligand shells on gold nanoparticles by transition metal and supramolecular surface probes.

We report herein two methods to characterize the surface of mixed-ligand shell gold nanoparticles, which was explored with gold nanoparticles containing varying molar ratios of 3-mercaptopropionic acid (MPA) and 3-mercapto-1-propanesulfonate (MPS) or 11-mercaptoundecanoic acid (MUA) and triethylene glycol mono-11-mercaptoundecyl ether (TEG) in their ligand shell. Incubation of gold nanoparticles with a solution containing the transition metal cation Ni2+ allows the extraction of Ni2+ depending on the number of negatively charged surface groups and the reaction of surface carboxylic acid groups with an aminomethyladamantane derivative allows the extraction of the supramolecular host molecule cucurbit[7]uril (CB7) depending on the number of reactive surface groups. In both the methods, the remaining surface probes in the supernatant could be conveniently quantified in a homogeneous solution after a simple centrifugation step. An excellent linear correlation between the amount of Ni2+ extracted and the ligand density of MPA and MPS in MPA/MPS gold nanoparticles or MUA in MUA/TEG gold nanoparticles afforded a simple and reliable assay method to determine the number of negatively charged surface groups. The supramolecular CB7 assay enabled the determination of the accessible ligand density of reactive surface carboxylic acid groups and revealed a striking difference in the number of surface groups that can be reacted with MPA/MPS gold nanoparticles or MUA/TEG gold nanoparticles, which suggests a simple method to probe the surface structure of mixed monolayer gold nanoparticles.

Three-Dimensional Directionality Is a Pivotal Structural Feature for the Bioactivity of Azabisphosphonate-Capped Poly(PhosphorHydrazone) Nanodrug Dendrimers

Dendrimers are nanosized, nonlinear, hyperbranched polymers whose overall 3D shape is key for their biological activity. Poly(PhosphorHydrazone) (PPH) dendrimers capped with aza-bisphosphonate (ABP) end groups are known to have anti-inflammatory properties enabling the control of inflammatory diseases in different mouse models. Here we screen the anti-inflammatory activity of a series of PPH dendrimers bearing between 2 and 16 ABP end groups in a mouse model of arthritis and confront the biological results with atomistic simulations of the dendrimers. We show that only the PPH dendrimers capped with 10 and 12 ABP end groups can control the flare of the inflammatory disease. All-atom accelerated molecular dynamics simulations show that dendrimers with a low number of ABP end groups are directional but highly flexible/dynamic and have thereby limited efficiency in establishing multivalent interactions. The largest dendrimer appears as nondirectional, having 16 ABP end groups forming patches all over the dendrimer surface. Conversely, intermediate dendrimers having 10 or 12 ABP end groups reach the best compromise between the number of surface groups and their stable directional gathering, a real maximization of multivalency.

The acid–base, morphological and structural properties of new biosorbent obtained by oxidative hydrothermal treatment of peat

Samples of natural peat (NP) were hydrothermally treated at different temperatures in oxidative and acidic aqueous medium to tailor their acid–base, adsorption, morphological and other properties. The obtained materials were thoroughly characterized by SEM, XRD and FTIR techniques, followed by determination of pHpzc, examination of adsorption characteristics and the extent of organic matter leaching in water. Acid–base characteristics of these materials were examined by potentiometric and conductometric titration of corresponding aqueous suspensions. Experimental potentiometric data were interpreted using ProtoFit software (NEM, non-electrostatic model) which provided pKa values and concentrations of surface sites which are compared with corresponding values obtained by conductometric titration method. There are two main types of surface groups (carboxylic and phenolic) that are dominant in the materials and determine their acid–base behavior in the aqueous medium. Temperature during oxidative hydrothermal treatment has no significant effect on the total number of surface groups, but influences the ratio of carboxylic and phenol-type groups. Hence, acid–base properties of peat can be tailored, which is useful in designing and improving adsorptive characteristics of peat for the preferential removal of certain pollutants from water.

Laser Modification of Silicon and Borosilicate Glass Wettability for Micro-Fluidic Systems

A laser modification method to control the surface wettability of a silicon and borosilicate glass substrate is proposed and demonstrated. The wettability of the silicon surface decreases after 2.5 W laser irradiation without a change in surface morphology. When the laser power is greater than 4 W, it results in the formation of a 10-nm-deep groove and the wettability increases. These phenomena are caused by changes in the number of surface groups and morphology, respectively. On the other hand, the glass surface is modified by infrared laser irradiation and the treated surface is highly hydrophilic. Surface analysis by FT-IR indicates that the modification is the result of an increase in the number of silanol groups. The proposed modification method is applied to micro-fluidic systems. A modified line can function as a surface micro-channel. Furthermore, with a gradient in wettability, the micro-channel has the ability to self-transport water droplets.

Support Functionalization To Retard Ostwald Ripening in Copper Methanol Synthesis Catalysts

A main reason for catalyst deactivation in supported catalysts for methanol synthesis is copper particle growth. We have functionalized the support surface in order to suppress the formation and/or transport of mobile copper species and thereby catalyst deactivation. A Stober silica support was functionalized by treatment with aminopropyltriethoxysilane, which introduces aminopropyl groups on the surface. Copper was deposited on both unfunctionalized and functionalized Stober silica via incipient wetness impregnation with aqueous copper nitrate solutions followed by drying and calcination. Similar particle size distributions (1–5 nm) were obtained for both supports by changing the flow of N2 to a flow of 2% NO/N2 during calcination of the unfunctionalized and amine-functionalized silica, respectively. The effect of support functionalization with aminopropyl groups was an increased stability in the methanol synthesis reaction (40 bar, 260 °C, 23% CO/7% CO2/60% H2/10% Ar, 3% COx conversion) due to more limited copper particle growth as determined by transmission electron microscopy (TEM). Changing the interparticle distance did not have an influence on the deactivation rate, while the addition of few very large copper particles did, indicating that Ostwald ripening was most probably the dominant particle growth mechanism for these samples. In situ TEM images showed the contact angle between the reduced copper particles and the support. As shape and size was similar on silica as on amine-functionalized silica, the thermodynamic stability of the copper particles was unaltered. The driving force for copper particle growth was thus unchanged upon functionalization. We therefore suggest that Ostwald ripening in methanol synthesis catalysts was retarded by inhibiting the transport of copper species over the support surface. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed a decrease in the number of surface groups (hydroxyl, methoxy, and aminopropyl) upon functionalization because aminopropyltriethoxysilane reacted with multiple hydroxyl groups. Because of that, the distance between neighboring functional groups was increased, suppressing the mobility of Ostwald ripening species from one copper particle to another.

Mechanical transformation of fullerene (C60) to aqueous nano-C60 (aqu-nC60) in the presence and absence of light

The present study was carried out to evaluate transformation kinetics of derivatized fullerene species by simulating natural aquatic processes, which will help elucidate biological effects of water-stirred nano-C60 (aqu-nC60). Physicochemical analyses of aqu-nC60 included molecular and agglomerate-scale characterization, surface charge analysis through examination of electrophoretic mobility, and chemical composition analysis using spectroscopy. Detailed analysis of aqu-nC60 transformation over a 28-day stirring period in both light and dark conditions indicated aqu-nC60 agglomerate concentrations can be estimated as a time-function using a predictor model (R 2 > 0.99). Number-weighted agglomerate size did not differ significantly over the 28-day stirring period regardless of photocondition, although size distributions were more uniform as stirring time increased. The total number of surface groups identified through XPS indicated increased derivatization as a function of time with additions assigned to mono-oxygenated carbon moieties while the number of di-oxygenated moieties declined. Earlier-phase stirring (t ≤ 14 days) products were shown to contain epoxide surface groups, which were absent in later-phase (t > 14 days) suspensions, suggesting specific pathways to derivatization with preferential mono-oxygenated states. Filter residue, a by-product of the aqu-nC60 synthesis process, demonstrated high hydrophobicity and FTIR spectra similar to underivatized material, suggesting synthesis process inefficiencies.

Characterization of surface oxygen groups on different carbon materials by the Boehm method and temperature programmed desorption

The surface characteristics of different carbon materials: activated carbon, carbon felt, glassy carbon and a porous carbon monolith were investigated. The specific surface area was examined by the BET method with N2 adsorption, the amount and the type of surface oxygen groups by Boehm titration as well as by temperature-programmed desorption (TPD). By comparing the results obtained using BET analysis with those of TPD and the Boehm method, it was found that the number of surface groups was not proportional to the specific surface area. The total amount of oxygen groups, obtained by TPD, is higher than the amount obtained by Boehm?s method for porous samples. The inconsistencies between these results originate from the fact that the Boehm method is limited to the determination of acidic and basic groups, whereas TPD provides information on the total number of all surface oxygen groups. In addition, the presence of porosity could reduce the solvent-accessible surface in the Boehm method. The TPD profiles of CO evolution showed the presence of a low temperature maximum, below 650 K, which originates from CO2 reduction on the carbon material surface.

On the preparation methods for carbon nanofiber-supported Pt catalysts

A study of the suitability of different methods for preparing highly loaded, well dispersed carbon nanofiber (CNF) supported Pt catalysts intended for application in fuel cells is reported. Preparation routes that are successfully applied on conventional carbon supports are hampered by the lower surface area and number of surface groups on CNFs. Ion exchange, homogeneous deposition precipitation and impregnation are all techniques that are limited to low metal loading on this CNF support. The most promising methods are the colloidal methods. By the modified polyol method, a Pt-content of 24 wt% with a particle size of 2–4 nm was achieved. CNFs could also be completely covered by 2–3 nm Pt oxide particles by using the metal–oxide colloid route, reaching a Pt-content of 17 wt%. The merits that make these methods more suitable than the other methods and the mechanism for deposition of Pt particles on CNFs are discussed.

Influence of M II/M III ratio in surface-charging behavior of Zn–Al layered double hydroxides

Zn–Al layered double hydroxides with different M II/M III ratios were synthesized by the coprecipitation method and the obtained solids were characterized by powder X-ray diffraction, infrared spectroscopy, acid–base potentiometric titrations, electrophoretic mobility and modeling of the electrical double layer. As general behavior, increasing hydroxyl adsorption with increasing pH and decreasing supporting electrolyte concentration takes place between pH 7 and 12. The electrophoretic mobility of the samples are in all cases positive and it decreases when the pH becomes higher than 9. A net positive charge of the particles, with a point of zero charge (PZC) around 11.8, is deduced from electrophoretic data. A modified MUSIC model, where OH −/Cl − exchange at structural sites and proton desorption from surface hydroxyl groups are taken into account, is used to estimate the deprotonation constants, the number of surface groups, the number of sites with structural charges an the affinity constants for Cl − and OH − of the samples with different M II/M III ratios. The modeling of potentiometric titrations and electrophoresis data indicates that anions between the layers and negatively charged groups in the particle surface balance most of the structural charge at the particles surface. It shows an important variation of the number of structural sites with the M II/M III ratio and an important role of surface protonation–deprotonation sites to the electrical behavior and exchange properties of LDHs.

The effect of surface modification with silane coupling agent on suppressing the photo-catalytic activity of fine TiO 2 particles as inorganic UV filter

The effect of surface modification with 3-aminopropyltriethoxysilane (APTES) and n-propyltriethoxysilane (PTES) on photo-catalytic activity and UV-shielding ability of fine TiO 2 particles were investigated. The number of surface groups ( N R) [nm −2] which shows the density of modifier on TiO 2 surface was calculated from the results of elemental analysis and BET measurement. The modified samples of which N R are different were obtained by changing the concentration of modifier. When the photo-catalytic activity and UV-shielding ability of modified samples were evaluated, it was found that APTES was more effective modifier than PTES to obtained samples with low photo-catalytic activity and high UV-shielding ability. This is probably because the adsorption mechanisms on TiO 2 surface between modifiers were different and N R is a key factor to control the performances of fine TiO 2 particles. The result of zeta potential showed that surface character of modified samples was varied by changing N R. It suggested from these results that N R affected the photo-catalytic activity and UV-shielding ability because N R changed surface character of modified samples.

Infrared spectra of ice surfaces and assignment of surface-localized modes from simulated spectra of cubic ice

The use of a new method of preparing micron-thick deposits of nanocrystals of ice for Fourier transform infrared sampling, with the nanocrystals supported on a vertical infrared window, has greatly improved the signal-to-noise levels of the spectra available for large ice clusters. High quality spectra of modes of the surface molecules are reported, even for regions that underlie the intense bands of the bulk ice modes. These experimental features are most clearly displayed through the use of difference spectra. For example, the difference between spectra obtained for nanocrystals, before and after an annealing cycle that significantly increases the average cluster size, reflects the decrease in number of surface groups and the corresponding increase in number of interior molecules. Similarly, differences between spectra of bare and adsorbate-covered nanocrystals, obtained at the same temperature for the same ice sample, show the significant shifts of ‘‘surface-localized’’ ice modes caused by the adsorbate molecules. These difference spectra, and similar spectra for amorphous ice, are rich with information about the (three) distinct types of ice surface water molecules and their interactions with small adsorbate molecules. The extraction of that information has been initiated by comparison of the experimental difference spectra from two sizes of D2O cubic ice nanocrystals with simulated difference spectra for a relaxed cubic ice surface compared to bulk cubic ice. From these comparisons specific experimental features have been assigned to modes of the three categories of surface D2O(HDO) molecules: (a) three-coordinated molecules with dangling-D—2725 (2713) cm−1; (b) three-coordinated D2O molecules with dangling-O—2645 (∼2600) cm−1; (c) relaxed four-coordinated molecules—∼2580 (∼2550) cm−1. Also, information has been obtained on the approximate positions (cm−1) of other modes of surface molecules: (a) D-bonded part of dangling-D(H) molecules; ∼2350; (b) dangling-O molecules; ∼2500; (c) four-coordinated molecules; 2300–2500. The computations also indicate that, of the various modes of the surface molecules, only the higher frequency modes of the dangling-D and dangling-O are strongly localized; and only the dangling-D mode is localized on individual surface molecules.

Determination of the Number of Molecules Bonded to a CdSe Nanocrystallite Surface

ABSTRACTElectron excited energy dispersive X-ray spectrometry (EDS) was used to determine the atomic species present in 35 Å diameter CdSe nanocrystallites. Both theoretical modeling and experimental calibration with standard materials were used to relate the relative X-ray intensities to the atomic fractions present in the sample. The EDS results were normalized to those found by elemental analysis, which also detects light elements. With different surface models, and the atomic fractions found by EDS, the number of surface groups per nanocrystallite was determined.

窒化ほう素の表面処理とその表面性状

The surface-treatment of boron nitride with cetanol (Cet), octadecyltri-ethoxysilane (ODTEOS), aminopropyltriethoxysilane (APTEOS) and isopropyl-triisostearoyl-titanate (IPTIST) was investigated by studying its dispersive and pyrolytic properties, and by using Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, the X-ray diffraction method and the number of surface groups. From these results, the followings were recognized: (1) The surfaces of boron nitride could effectively be surface-treated by the reflux method with those reagents; and (2) The surface groups were percieved to be the ones which chemically bonded with the surface of boron nitride.

Inferences on the mechanism of emulsion polymerisation of styrene from characterisation of the polymer end‐groups

AbstractSolute electrolyte and adsorbed emulsifier can be removed by ion exchange from polystyrene latices prepared with persulphate initiator. Rigorous purification of the ion‐exchange resins is necessary to avoid contamination by leached polyelectrolytes. These ion‐exchanged latices are stabilised by strong acid surface groups ‐ sulphate end‐groups of the polymer molecules. The number of surface groups as determined by conductometric titration of the latex, plus the number buried within the particle as determined by conductometric titration of the polymer in solution (or by X‐ray fluorescence), is less than the expected value of two per polymer molecule. The other end‐groups are shown to be hydroxyl groups by oxidation to the carboxyl form followed by ion exchange and titration. The total number of end‐groups thus determined is close to two per molecule. As the pH of the polymerisation medium is decreased, the proportion of hydroxyl end‐groups increases and that of the sulphate end‐groups decreases. No carboxyl groups are detected in ion‐exchanged latices prepared in a nitrogen atmosphere, independent of the nature of the emulsifier. The dye partition method gives end‐group concentrations that are far lower than those determined by titration or X‐ray fluorescence, probably because the formation of the dye end‐group ion‐pair is not complete. Finally, for latices prepared at relatively low emulsifier concentrations, the contribution of the sulphate end‐groups to the surface charge density is significant and cannot be overlooked, as has been done in the past.