Latex Samples Research Articles

Particle sizing of flocculated latex particles by physisorption of nitrogen

AbstractPhysisorption of nitrogen at one specific pressure is used to determine the specific surface area of a flocculated polystyrene latex by applying BET theory. Assuming that a flocculated sample of Polymer latex is composed of distinct spherical latex particles (i.e., there is no coagulation of particles), the volume–surface‐average diameter can be calculated. The resulting diameters are compared to sizes obtained using a disc centrifuge sedimentometer, which fractionizes the particles by sedimentation. The diameters from both techniques were in good agreement, showing that physisorption of nitrogen, which is a simple technique, can be used to determine sizes of flocculated latex particles. This agreement also shows that the flocculation of the polystyrene latex produced separate nonporous spherical particles. When flocculation of a latex is done above its glass transition temperature, coagulation will occur. While other particle sizing techniques can produce particle size distributions, the physisorption of nitrogen only gives the volume–surface‐average diameter. However, one advantage of the physisorption of nitrogen is that it covers a broad range of particle sizes compared to most other techniques. © 1994 John Wiley & Sons, Inc.

The effect of methyl methacrylate monomer on latex gloves

Medical personnel require protection from chemical and biological hazards during clinical procedures. Methyl methacrylate monomer (MMA), used in orthopaedic and dental surgery, is capable of permeating latex gloves and can cause painful skin irritation. In this study, scanning electron microscopy has been used to demonstrate degradation of surgical latex gloves by immersion in methyl methacrylate monomer, with and without extension of the gloves. A considerable quantity of monomer was absorbed into the latex samples (7–12% of the original weight), which slowly evaporated over 10 days. A 2–3% weight loss was determined for the two types of gloves tested. Fissuring of one type of latex glove was observed after 30 min immersion in MMA.

Morphological study of structured latex particles by Transmission Electron Microscopy

Transmission electron microscopy plays an important role in the study of the influence polymerization conditions have on the morphology of structured latex particles and thus in the understanding of the morphological effect of such particles on the structure-property relationships of polymeric end products.Structured latex particles are prepared by seeded emulsion polymerization, where the first stage is a polymerization of ”the core” poly(n-butyl acrylate) (PBA), followed by a second stage polymerization of ”the shell” poly(benzyl methacrylate/styrene) (P(BM/St)) at various ratios. The changes in polymerization conditions include such variables as the polymerization mode (batch vs. semicontinuous), core/shell ratio, shell thickness, and shell composition. Morphology studies of the structured latex particles are performed by transmission electron microscopy on preferentially stained samples. In a small vial, a few drops of latex sample are combined with a few drops of uranyl acetate (UAc) 2% solution. The uranyl acetate serves as a negative staining to better delineate the particles edges.

ON SOME ASPECTS OF THE ADSORPTION OF IMMUNOGLOBULIN-G MOLECULES ON POLYSTYRENE MICROSPHERES

ABSTRACT An experimental investigation on the adsorption of immuno-globulin-G on polystyrene microspheres is described. Two negatively charged polystyrene latexes of different surface charge density (σ0) were prepared by an emulsifier-free method. Rabbit IgG molecules were adsorbed on both latex samples. Adsorption isotherms at different ionic strengths and pH were performed. In all cases the adsorption isotherms showed well-defined plateau. The more negatively charged polystyrene latex showed a higher adsorption of IgG molecules at pH values lower than 8. Both samples of latex reached a maximum adsorption at pH = 6.0. The isoelectric point of the IgG-latex complex was around 5.5, it was lower than the isoelectric point range of the IgG molecules, which was from 6.1 to 8.7. This difference indicates that the negative charge of the latex surface at least partially compensates the positive charged groups of the protein The differences in the colloidal stability of the sensitized particles is not explained b...

Low temperature transmission electron microscopy and differential scanning calorimetry characterization of latexes stabilized with surface active block oligomers

The spatial distribution of a short-chain amphiphilic diblock copolymer (i.e. block oligomer), used as an emulsifier during the preparation of a latex, is determined by low temperature transmission electron microscopy and differential scanning calorimetry (d.s.c.). The main question is whether intermixing of the amphiphilic block oligomer and latex core materials actually takes place to a significant extent. Electron microscopy gives a clear indication that a surfactant-rich layer exists in all latex samples examined. At very high surfactant concentration (>6%, not typically used in commercial latexes), electron beam radiation damage reveals the presence of a surfactant gradient from the particle surface to its core. These results are in good agreement with our d.s.c. data.

Electrokinetic characterization of highly sulfonated polystyrene model colloids

Highly sulfonated polystyrene latex particles were prepared by a two-stage “shot-growth” emulsion polymerization process in the absence of emulsifier. Sodium styrene sulfonate (NaSS) was used as an ionic co-monomer to produce a series of latex particles with nearly the same particle size but with different surface charge densities. The cleaning process used, including centrifugation and redispersion with the aid of strong sonication, proved to exert a strong influence on the final surface charge density of the particles. The electrokinetic behavior of three latex samples with surface charge densities between 13.9 and 19.4 μC cm −2 was very similar, with constant values of the electrophoretic mobilities for pH between 4 and 11 and a maximum in the electrophoretic mobility values when the ionic strength was 5 · 10 −2 M NaCl. This last result was found even after a systematic and long latex cleaning process, and after treatment at high electrolyte concentrations. The experimental results for the electrokinetic characterization of these highly sulfonated polystyrene latexes suggest that the surface of the particles are covered by a layer of oligomers or polymer chains which are chemically bound to the surface, and which control the colloidal properties of this type of latex.

Quaternary nitrogen compounds from south american moraceae

Latex samples from South American Moraceae have been examined for the presence of betaines. Tryptophan and tyrosine betaines were present in Maquira coriacea, Naucleopsis macrophylla, N. stipularis and N. ternstroemiiflora; this last species also had choline. Tryptophan betaine and choline were found in N. caloneura. Only trigonelline occurred in Pseudolmedia laevigata and P. laevis. On the other hand, no quaternary nitrogen compounds were detected in latex samples from M. guianensis, N. mello-barretoi, Castilla ulei, Helicostylis elegans and Perebea mollis subsp. mollis.

Simultaneous determination of particle size and density in polydisperse colloidal samples by sedimentation field‐flow fractionation

AbstractSedimentation Field‐Flow Fractionation (SFFF), which is a one‐phase chromatographic system, is shown to be a rapid and convenient method for the simultaneous determination of particle size and density in polydisperse colloidal samples. This can be done by a methodology based on the variation of the carrier solution density using various aqueous glycerol solutions having different concentrations. A polydisperse polyvinyl chloride (PVC) latex sample was used as a model colloid. The average diameters and densities found by the proposed methodology are in good agreement with those obtained from the normal. SFFF procedure using a carrier of constant density or given by the manufacturer. Number average, dN, and weight average, dw, particle diameters were determined for the PVC sample at various carrier solutions containing glycerol up to 40 % (w/w) in order to show whether sample aggregation has occurred or not in the presence of glycerol. In all cases, the ratio dw/dN was found to be constant, showing that PVC aggregation has not occurred. Therefore our results, obtained by the proposed methodology in SFFF, are accurate, showing that this approach has considerable promise for characterizing complex colloidal materials.

Rapid particle size analysis of ground minerals by flow/hyperlayer field-flow fractionation

Flow/hyperlayer field-flow fractionation (flow/hyperlayer FFF), a recently developed method capable of the rapid separation of particles over 1 μm in diameter according to their size, was applied to the characterization of ground coal and limestone samples. The results of the analysis were found to be consistent and reproducible, in agreement with those obtained from microscopic examination and from the elution profiles of latex particle standards. The results were also in agreement with particle size distributions obtained by laser light scattering. The validity of the size-dependent but density-independent separation by flow/hyperlayer FFF was demonstrated by the comparison of elution profiles for ground coal, ground limestone, glass beads, and polystyrene latex samples, which differ substantially in density. These results show that flow/hyperlayer FFF is a promising tool for the size analysis of ground minerals and similar particulate materials, perhaps even in a process control environment.

Multiple scattering spectra in strongly scattering media: Diffusion and non-diffusion contributions to spectrum halfwidth

Photon correlation technique has been used to study polystyrene latex samples in four concentrations. The optical thickness γ of the samples amounted to 30. It was found that the halfwidth of the multiple scattering can be represented as a sum of two terms: the leading term is proportional to γ 2 and corresponds to the diffusion approximation of the radiation transport theory, while the other is a function of polarization of radiation and is not described by the diffusion equation.

Resolution of colloidal latex aggregates by sedimentation field-flow fractionation

The observation of a repetitive series of peaks while analyzing two different samples of poly(methyl methacrylate) colloidal latex spheres by sedimentation field-flow fractionation strongly suggests that part of the latex population has aggregated into doublets, triplets, and higher-order particle clusters. The aggregation hypothesis is confirmed for the two samples both by retention calculations and by electron microscopy. It is shown that the resolution of the latex clusters is influenced by flow velocity in a manner predicted by theory but that such resolution is limited by the polydispersities of the two latex samples. Polydispersity values are obtained using plate height versus flow velocity measurements and are shown to be consistent with the different resolution levels observed for the two colloids. A detailed analysis of the results shown that steric effects play an increasing role as cluster size increases. The steric role in this study is examined at some length.

Ordering in monodispersed polymer latices induced by a temperature gradient

The ordering in a monodispersed latex suspension induced by a temperature gradient through the suspension has been investigated systematically using several latex samples with different particle sizes. The behaviour is influenced extensively by the temperature gradient (ΔT), and the critical value of ΔT needed to generate the ordering decreased when either the particle size of the sample or the salt concentration in the medium were decreased. Furthermore, to estimate the interparticle spacing in the ordered layers, the reflection spectra from these layers were measured and the enhanced number ratios with regard to the original value were calculated under different experimental conditions. Experimental results showd that the enhanced ratios ranged from 1.5 to 2.0 and increased when the value of ΔT and the salt concentration in the medium were increased.

A rapid and accurate method for determining the dry rubber content and total solid content of NR latex

The dry rubber content of field latex is determined roughly by means of the hydrometer known as the ‘Metrolac’, which is an instantaneous method. However, accurate determination of the percentage dry rubber content (%DRC) and the percentage total solid content (%TS) of natural rubber latex is important for the export certification of shipments of latex in the producing countries. Accurate determination of %DRC and % TS are also important for many other purposes such as research experiments in the field of chemical modification of rubber. At present, determinations of %DRC and %TS are carried out by the BS methods which involve heating the latex or coagulum samples for over 6 h in a conventional oven. Hence these methods are not suitable for a factory producing large quantities of centrifuged latex for production control purposes or for export. This paper reports convenient methods of determining %DRC and %TS of latex in 10 min and 25 min, respectively, with the same accuracy as the BS or ISO methods.

Micropreparative Sedimentation Field-Flow Fractionation and Quasi-Elastic Light Scattering Spectrometry of Narrow Particle Size Distribution Polystyrene Latexes

Fractions of polystyrene latex sample with very narrow particle size distribution obtained with the aid of micropreparative sedimentation field-flow fractionation (SFFF) were characterized by quasi-elastic light scattering. The measured values of the average particle size of individual fractions confirmed high resolving power of SFFF even for extremely difficult separations of samples with narrow polydispersity.

Microscopic observation of ordered colloids in sedimentation equilibrium and important role of Debye-screening length. II. Monodispersed polystyrene spheres (specific gravity=1.05) in aqueous and methanol aqueous suspension

A metallurgical microscope is used to observe directly the ordered structures of monodispersed polystyrene spheres (specific gravity=1.05) in water and methanol–water mixtures. Sedimentation occurs for all the spheres examined for which the diameters are between 369 and 1020 nm. The interparticle distances (2Dexp) increase with time after the latex sample is set into the cell, and reach equilibrium values after seven to ten days, which shows that complete deionization is essential to get reliable data for 2Dexp. 2Dexp continues to decrease as the initial concentration of the spheres increases and from these data Young’s modulus for the ordered lattices is estimated to be 1 dyn cm−2 for spheres of 0.5 μm. The influences on 2Dexp by the concentration and charge density of the spheres, and ionic strength show that the electrostatic interparticle repulsion and the elongated Debye-screening length around the spheres are essential for the ordering phenomenon.

Separation and Dispersion in Sedimentation Field-Flow Fractionation

Abstract Contributions of separation and dispersion to the total zone width of a polydisperse latex sample under various flow rates and retentions were studied. Both the direct flow and the reverse flow techniques were employed and the experimental results were compared with theoretical relationships. The results showed a good agreement between the theory and the experiment under different conditions. A good agreement between the mean particle diameters calculated from our experimental data and those given by the producer was found. The width of the particle size distribution characterized by the standard deviation was found about two fold higher than that given by the producer.

Microscopic observation of ordered colloids in sedimentation equilibrium and important role of Debye-screening length. I. Heavy and monodispersed polystyrene type spheres (specific gravity=1.50) in aqueous and aqueous methanol suspensions

A metallurgical microscope is used to directly observe the ordered structures of heavy and monodispersed polystyrene type spheres (specific gravity= 1.50) in sedimentation equilibrium. The interparticle distances (2Dexp) increase with time after the latex sample is set into the cell, and reach an equilibrium value after seven days. 2Dexp continues to decrease as the amount of spheres fed increases and from these data Young’s modulus of the ordered lattices is estimated to be ∼100 dyn cm−2. The hexagonal ordering is observable not only in the deionized state but also in the presence of sodium hydroxide (10−6–10−3 M), and 2Dexp decreases with increasing alkali concentration. The results show that electrostatic interparticle repulsion and the elongated Debye-screening length around the spheres are essential for the ordering.

Natural Higher Fatty Acid Soaps in Natural Rubber Latex Concentrate and Correlations to Other Latex Variables

Abstract The amounts and types of HFA soaps found in latex did not vary greatly from sample to sample. Greater than 95% of the free HFA soaps were associated with the rubber phase of the latex. The distribution of fatty acid soaps were markedly different in the serum and latex samples. About 80–90% of the HFA soaps are in their free form, but only about 50% of the furanoic acid was in its free form. Titration results agree fairly well with the GC results and indicate that titration can be a useful measure of HFA.

Identification and Characterization of Latex-Specific Proteins in Opium Poppy

Latex from the opium poppy, Papaver somniferum L., was analyzed by polyacrylamide gel electrophoresis (PAGE). Two latex-specific bands were identified in protein samples of poppy latex using one-dimensional native PAGE. Second dimension analysis with SDS-PAGE indicates that these proteins have a relative molecular weight of approximately 20 kilodaltons. We have termed these polypeptides the major latex proteins (MLPs). Polyclonal antibodies prepared against the MLPs were used to probe protein gel blots of latex and poppy tissues known to lack laticifers. Laticifer-free tissues showed no reaction with anti-MLP immunoglobulin G indicating that MLPs are found only in poppy latex. MLP distribution was also examined in mature opium poppy tissues by immunocytochemistry. Laticifers were differentially labeled by fluorescein isothiocyanate secondary labeling of anti-MLP immunoglobulin G and could easily be identified in both transverse and longitudinal section. Fractionation studies of isolated latex showed that MLPs are concentrated in the latex cytosol and not in alkaloidal vesicles. Analysis of latex proteins by conventional two-dimensional electrophoresis indicates that the two MLP bands are composed of several distinct polypeptides with similar relative molecular weights. The pIs of these molecules range from 6.0 to 3.5. The role(s) of MLPs in laticifer metabolism has not been determined.

Soil Moisture Effects on Glyphosate Absorption and Translocation in Common Milkweed (Asclepias syriaca)

Absorption and translocation of14C-glyphosate [N-(phosphonomethyl)glycine] by moisture-stressed common milkweed (Asclepias syriacaL. ♯ ASCSY) was studied in greenhouse and growth chamber experiments. Water-stressed [13% (w/w) soil moisture] common milkweed plants treated with glyphosate at 1.1 kg ae/ha produced shoot regrowth equal to untreated plants, whereas shoot regrowth of nonstressed [25% (w/w) soil moisture] glyphosate-treated plants was only 6% of untreated plants. All shoot regrowth originated from buds on the proximal half of roots. Common milkweed plants, maintained at 25% soil moisture, absorbed 44% of the14C-glyphosate applied and translocated 20% from the treated leaf, whereas plants at 13% soil moisture absorbed 29% and translocated 7%. Wiping the leaf with tissue paper wetted with distilled water or chloroform prior to14C-glyphosate application increased absorption from 35 (unwiped leaves) to 62 and 77%, respectively, for plants at 25% soil moisture, and increased absorption from 14 to 42 and 46%, respectively, for plants at 13% soil moisture. Wiping failed to increase translocation out of the treated leaf for plants at either soil moisture regime. Latex samples taken from the abaxial leaf surface opposite14C-glyphosate-treated leaves and from petioles of treated leaves did not contain14C, indicating that glyphosate did not enter laticifers. Proximal root buds accumulated less14C-radioactivity than distal root buds and had lower respiratory rates, suggesting that proximal root buds are more dormant than distal root buds and thus accumulate less glyphosate.