Small Latex Research Articles

The Effect of Shear Rate on Heteroaggregation Behavior of Latex Polymers and Suspension Polymers in Aqueous Media

The effect of shear rate on heteroaggregation behavior of latex polymers and suspension polymers in aqueous media was investigated. Heteroaggregation was carried out in a stirred vessel under various stirring rates and temperatures. Large suspension polymer particles were selectively coated by small latex polymer particles at specific stirring rates corresponding to each temperature. The heteroaggregation dynamics were analyzed from the cluster strength of the coating latex polymer layer and external shear force. The cluster strength of the latex polymer was determined by using Usui’s rheology model, where the inter-particle bonding energy was derived from both the rheological data and the rate of energy dissipation per unit mass in the stirred vessel. In contrast, a relation between the diameter of the cluster of the latex polymer particles and apparent shear rate was derived from Kobayashi’s theory, which is based on the theoretical treatment on the break-up of a droplet. By combining both theories, the heteroaggregation process was characterized by the cluster strength of the latex polymer layer against the external shear force. The homogeneous coating was only formed in a specific condition where the favorable balance between the external shear force and the cluster strength of the latex polymer layer was achieved.

Spherical vesicles distorted by a grafted latex bead: An exact solution

We present an exact solution to the problem of the global shape description of a spherical vesicle distorted by a grafted latex bead. This solution is derived by treating the nonlinearity in bending elasticity through the (topological) Bogomol'nyi decomposition technique and elastic compatibility. We recover the "hat-model" approximation in the limit of a small latex bead and find that the region antipodal to the grafted latex bead flattens. We also derive the appropriate shape equation using the variational principle and relevant constraints.

Catalytic Emulsion Polymerization of Olefins: Ab Initio Polymerization of Norbornene

It has recently been shown that it is possible to polymerize homo- and copolymers of olefins in aqueous media by using late transition metal catalysts. This has opened a new set of opportunities to produce simple and composite latex particles based on ethylene and its olefinic derivatives. Here we report some of our experience in creating water-based latices from the strained cyclic olefin, norbornene. This has been done as ab initio batch emulsion polymerizations using two different allylpalladium catalysts and a lithium-based activator as substitutes for the free radical initiator in standard emulsion polymerization. Such experiments produce small latex particles (ca. 50 nm) and can be burdened with large amounts of coagulum. In studying the effects of catalyst levels, ionic strength, and temperature on the reaction rates, conversion levels, and particle size, we have determined that the coagulum is produced by the migration of the catalyst and activator to the emulsified monomer droplets, producing lar...

Bimodal particle distribution for emulsions: The effect of interstitial functional particles

The location of hydroxyl functionality was investigated for thermosetting acrylic latexes. Large and small latex particles with and without hydroxyl functionality were synthesized and characterized. Such large and small latex particles with and without hydroxyl functionality were blended together and a melamine-formaldehyde (M-F) resin was added to crosslink the hydroxyl groups. Mechanical and thermo-mechanical properties were evaluated as function of blend ratio and functionality location. The packing of the latexes was dependent on small to large particle ratio. It was shown that the mechanical properties were also dependent on the location of the functionality. The higher concentration of hydroxyl groups in the small latex particles contributed more to the tensile properties of the latexes than the functionality of the large particles. The location of the M-F resin in the small latex particles resulted in a lowering of the volume fraction needed for a continuous network.

Macropinocytosis: regulated coordination of endocytic and exocytic membrane traffic events

Macropinocytosis, a form of bulk uptake of fluid and solid cargo into cytoplasmic vacuoles, called macropinosomes, has been studied mostly in relation to antigen presentation. Early membrane traffic events occurring in this process are, however, largely unknown. Using human dendritic cells we show that a marked increase in the rate of macropinocytosis occurs a few minutes after application of two markers (small latex beads or dextran), depends on a slow intracellular Ca2+ concentration ([Ca2+](i)) rise that precedes the PI3K-dependent step, and is preceded and accompanied by exocytosis of enlargeosomes compensating in part for the macropinocytic plasma membrane internalization. Unexpectedly, macropinosomes themselves, which share markers with endosomes, undergo Ca2+ -dependent exocytosis so that, after approximately 20 minutes of continuous bead or dextran uptake, an equilibrium is reached preventing cells from overloading themselves with the organelles. Large [Ca2+](i) increases induced by ionomycin trigger rapid (<1 minute) exocytic regurgitation of all macropinosomes, whereas endosomes remain apparently unaffected. We conclude that, in dendritic cells, the rate of macropinocytosis is not constant but increases in a regulated fashion, as previously shown in other cell types. Moreover, macropinosomes are not simple containers that funnel cargo to an endocytic pathway, but unique organelles, distinct from endosomes by their competence for regulated exocytosis and other membrane properties.

Morphological and Physical Properties of Triblock Copolymers of Methyl Methacrylate and 2-Ethylhexyl Methacrylate

Triblock copolymers of methyl methacrylate (MMA) and 2-ethylhexyl methacrylate (EHMA) [that is, poly(MMA-EHMA-MMA)] were prepared by an emulsion atom-transfer radical polymerization. The relationships of their structural, morphological, and physical properties were investigated. The latex particles had core-shell morphologies and the block copolymers experienced phase separation. Small latex particles with a low number of cores could deform and wet silicon-wafer surfaces, but the deformation of large latex particles was restricted by the internal two-phase morphology of the particles. Latex casting produced continuous pinholefree films, in which hard poly(MMA) (PMMA) cores of different latex particles merged and provided interparticle connections. The morphology of solution-cast films depended on block composition, solvent type, and film thickness. For all the prepared polymer samples, thick films cast in toluene had poly(EHMA) (PEHMA) materials at air surface, whereas those cast in tetrahydrofuran had a sponge-like PMMA surface structure. Thin toluene-cast films from P(MMA-EHMA-MMA) with the block degrees of polymerization (DP) 200-930-200 showed spherical PMMA domains and those from 380-930-380 yielded a protruded worm-like PMMA structure. The copolymer materials were coated on a glass surface for peeling tests. The films gave good hot-melt adhesion properties when the DP of the PEHMA block was over 600. The peeling strength depended on the lengths of both PEHMA and PMMA blocks. The P(MMA-EHMA-MMA) sample with DPs of 310-930-310 yielded the highest peeling strength of 7.4 kgf·inch -1 . The developed material is demonstrated to be a good candidate for a solvent-free, hotmelt, pressure-sensitive adhesives for special-purpose applications such as medical tapes and labels.

Plate–sphere hybrid dispersions: Heterocoagulation kinetics and DLVO evaluation

We have studied the formation of colloidal composite particles through the controlled heterocoagulation of anionically charged polystyrene (PS) and poly(isobutyl methacrylate) (PiBMA) latex spheres with positively charged gibbsite platelets. The latex particles, synthesized by emulsion polymerization, varied in size and surface charge density. The heterocoagulation was studied as a function of the number ratio between small latex particles and large gibbsite platelets ( N S/ N P), ionic strength and pH of the aqueous medium. The coagulation kinetics of latex spheres with inorganic platelets in aqueous dispersions were determined by time resolved dynamic light scattering (TR-DLS) experiments. The N S/ N P values should be sufficiently high to prevent the formation of multilayer aggregates. It was shown that the heterocoagulated colloidal particles were stable up to an ionic strength of 2.5 mM for latex particles with a diameter of about 80 nm and ∼30 mM for those of 35 nm, respectively. The effect of pH on the colloidal dispersions was verified by the classical DLVO theory.

Are ball‐rolling (Scarabaeini, Gymnopleurini, Sisyphini) and tunnelling scarabaeine dung beetles equally choosy about the size of ingested dung particles?

Abstract. 1. The maximum size of ingested particles was determined in 11 species of ball‐rolling, adult dung beetle (Scarabaeidae: Scarabaeinae) by mixing small latex or glass balls of known diameter into their food. The tribes Scarabaeini, Gymnopleurini, and Sisyphini (four, four, and three species respectively) were represented, with mean body sizes ranging from 0.33 to 4.0 g fresh weight.2. Only particles with maximum diameters of 4–85 µm were ingested. Hence rollers, like other known beetles feeding on fresh dung, filter out larger, indigestible plant fragments and confine ingestion to small particles of higher nutritional value.3. The maximum diameter of ingested particles increased significantly with body weight, whereas taxon (tribe) had no additional effect. Because big rollers accept larger particles than do tunnellers (which make dung stores for feeding and breeding in the soil immediately below the pat) of similar weight, the slope of the diameter‐against‐weight regression for rollers was significantly higher than that found earlier for tunnellers.4. An explanation could be that a typical food ball made by a roller is considerably smaller than the amount of dung available to a feeding tunneller of the same size. If the roller were as choosy about particle size as the tunneller, it might not get enough food. This applies to large rollers in particular because their food balls contain a higher proportion of coarse fibres than those made by small species.

DNA and cationic surfactants at solid surfaces

The behavior of DNA at different types of interfaces and how the formed structures DNA at an interface could be affected by cationic surfactant has been studied. Particular attention was paid to how the type of cationic surfactant and DNA (single or double stranded and length) affects the compaction/decompaction of DNA. Adsorption of DNA–cationic surfactant complexes is determined by a delicate balance of DNA–surface, cationic surfactant–surface, and cationic surfactant–DNA interactions. DNA do not adsorb on hydrophilic negatively charged surfaces due to effective electrostatic repulsion between DNA and the surfacs. However, the interaction between DNA cationic surfactant ions leads to a substantial adsorption of the formed DNA–cationic surfactant complex once the charge density of both the DNA macromolecule and the surface is sufficiently decreased. On hydrophobic surfaces, where both DNA and cationic surfactant interact with the surface, the presence of the cationic surfactant leads to a considerable increase in adsorbed amount and a significant layer compaction of DNA. The stability of the mixed adsorbed layer largely depends on the strength of the interactions between DNA and the cationic surfactant, as well as between the surface and the cationic surfactant. DNA interacts with small latex particles in a similar way as to the macroscopic hydrophobic flat surfaces.

Do Cells "See" Each Other?

Investigation of a 3T3 cell variant (3T3 x ) that forms clusters on solid substrates led Albrecht-Buehler to make the intriguing proposal that mammalian cells are able to detect each other through light scattering. Noting that cells in the center of 3T3 x aggregates had large numbers of lysosomes--which, along with other perinuclear organelles, are the main light-scattering regions of mammalian cells--Albrecht-Buehler allowed cells to ingest small latex and diamond particles, which markedly enhanced their light-scattering ability. In aggregates formed by these hyperscattering cells, the center cells were those that scattered the most light. When hyperscattering cells were mixed with particle-free 3T3 x cells, dispersed into dishes, and observed with time-lapse photography, the hyperscattering cells--which initially settled randomly--moved toward each other and aggregated. When cells were cultured on adhesive strips surrounded by nonadhesive substrate (to constrain movement to a single dimension) so that the distance over which cells could be influenced to move together could be estimated, cells appeared to detect each other at distances substantially greater than one cell diameter. Moreover, the distance over which cells could influence each other's movement ( R a ) increased in parallel with their ability to scatter near-infrared light. Irradiation at 600 nm (visible light) decreased R a , whereas irradiation at 800 nm (near-infrared) increased it. The ability of cells to aggregate inside unlighted incubators suggested that aggregation signals involved light in the near-infrared range. Thus, the author proposed that cells are able to detect each other through scattered near-infrared light and to use this information to direct their movements. G. Albrecht-Buehler, A long-range attraction between aggregating 3T3 cells mediated by near-infrared light scattering. Proc. Natl. Acad. Sci. U.S.A. 102 , 5050-5055 (2005). [Abstract] [Full Text]

Bi-seeded emulsion polymerization in the presence of poly(methyl methacrylate) and polystyrene

Bi-Seeded emulsion polymerization was investigated in the presence of polymethyl methacrylate (PMMA) and polystyrene (PSt). The experimental results indicate, when using styrene (St) as the second-stage monomer, the latexes had bimodal size distribution and the two kinds of seeds had competition for St. It is found that when the second-stage polymerization was carried out with large PSt latex particles and small PMMA latex particles as seeds, the PMMA seeds increased more evidently and more St polymerized on them. The possible reason is that the specific surface area of seeds decides the polymerization locus and St is apt to polymerize on smaller seeds. Nevertheless, when using large PMMA and small PSt as bi-seeds, the PMMA seed particles grew more obviously and showed a higher chance of obtaining more St than that of the PSt seed particles. The explanation is the formation of PMMA/PSt composite particles has lower interfacial free energy change, which has more significant effect on the polymerization locus of second-stage monomer than the specific surface area. Adding methods have little effect on the distribution of second-stage monomer in bi-seeded polymerization system, but through dropping method, it is easier to form composite particles with core-shell structure. In addition, anomalous particles were produced when adding crosslinker into St.

A novel method of collecting fecal samples from spiny lobsters

A novel method is described for collecting feces from the spiny lobster Panulirus ornatus. Established methods for the collection of feces from crustacean species are not effective with P. ornatus. The feces produced by adults and juveniles of this species are not in a form that can be easily recovered by traditional methods. To overcome this problem, a plastic flange was glued onto the integument, around the anal pore. A small latex balloon was placed over the flange and provided a watertight collection vessel for voided feces. The flange was made from the modified cap from a 2 ml Eppendorf vial. Fixing the flange and changing the balloon after feeding was achieved without the use of anaesthetics and appears not to impose undue stress on the lobsters and they continued to feed. The method was successfully used to collect uncontaminated fecal samples from lobsters ranging from 150 to 800 g. This method may have wider application for other crustacean species.

Cellular pharmacokinetics and pharmacodynamics of the glycopeptide antibiotic oritavancin (LY333328) in a model of J774 mouse macrophages.

The intracellular pharmacokinetics and pharmacodynamics of oritavancin (LY333328) were studied in cultured cells. Oritavancin was avidly accumulated by J774 and THP-1 macrophages and rat fibroblasts and to a lesser extent by LLC-PK1 and Caco-2 cells. In J774 macrophages, the level of accumulation reached a plateau (at 370-fold the extracellular concentration) within 24 h and was partly defeated by a rise in serum protein levels. Efflux was incomplete (with a plateau at two-thirds of the original level at 6 h). In short-term kinetic studies, oritavancin uptake was linear for up to 4 h (as was the case for horseradish peroxidase and small latex beads, used as markers of the fluid phase and adsorptive endocytosis, respectively), which was in contrast to azithromycin and chloroquine uptake (which accumulate in cells by diffusion and segregation). The rates of clearance of oritavancin and latex beads were comparable (150 and 120 microl x mg of protein(-1) x h(-1), respectively) and were approximately 200 times higher than that of horseradish peroxidase. Oritavancin accumulation was partially reduced by monensin but was unaffected by acidic pH (these conditions abolished chloroquine accumulation). Cell-associated oritavancin was found in lysosomal fractions after homogenization of J774 macrophages and fractionation by isopycnic centrifugation. Oritavancin was bactericidal against intracellular Staphylococcus aureus (phagolysosomal infection) but was unable to control the intracellular growth of Listeria monocytogenes (cytosolic infection), even though its cellular concentration largely exceeded the MIC (0.02 mg/liter) and minimal bactericidal concentration (2 mg/liter). We conclude that oritavancin enters cells by adsorptive endocytosis (favored by its lipophilic side chain and/or the presence of three protonatable amines), which drives it to lysosomes, where it exerts antibiotic activity.

Response properties of antral mechanosensitive afferent fibers and effects of ionotropic glutamate receptor antagonists

The ionotropic glutamate receptors N-methyl- d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are present peripherally in the primary sensory afferent neurons innervating the viscera. Multiple studies have reported roles of glutamate receptors in gastric functions. However, no study has previously shown the direct influence of ionotropic glutamate receptor antagonist on vagal sensory neurons. The objective of this study was to investigate the effects of NMDA and AMPA receptor antagonists on mechanotransduction properties of vagal afferent fibers innervating the rat stomach. Action potentials were recorded from the hyponodal vagus nerve innervating the antrum of the Long-Evans rats. For antral distension (AD), a small latex balloon was inserted into the stomach and positioned in the antrum. The antral contractions were recorded with solid-state probe inserted into the water-filled balloon. Antral units were identified to isovolumic (0.2–1 ml) or isobaric AD (5–60 mm Hg). NMDA and AMPA receptor antagonists were injected in a cumulative fashion (1–100 μmol/kg, i.v.). After the conclusion of experiment, the abdomen was opened and receptive field was mapped by probing the serosa of the stomach. Thirty-two fibers were identified to AD. The receptive fields of 26 fibers were located in the posterior part of the antrum. All fibers exhibited spontaneous firing (mean: 7.00±0.97 impulses/s). Twenty fibers exhibited a rhythmic firing that was in phase with antral contractions, whereas 12 fibers exhibited non-rhythmic spontaneous firing unrelated to spontaneous antral contraction. Both groups of fibers exhibited a linear increase in responses to graded isovolumic or isobaric distensions. NMDA (memantine HCl and dizocilpine (MK-801)) and AMPA/kainate (6-cyano-7-nitroquinoxaline 2,3-dione; CNQX) receptor antagonists dose-dependently attenuated the mechanotransduction properties of these fibers to AD. However, competitive NMDA antagonist dl-2-amino-5 phosphopentanoic acid (AP-5) had no effect. The study documents that glutamate receptor antagonists can attenuate responses of gastric vagal sensory afferent fibers innervating the distal stomach, offering insight to potential pharmacological agents in the treatment of gastric disorders.

Controlled Translational Manipulation of Small Latex Spheres by Dynamic Force Microscopy

We report on the application of a home-built scanning force microscope for translation and in-plane rotation of nanometer-sized latex spheres by dynamic surface modification (DSM). This technique is based on the incrementof the amplitude of the oscillating voltage applied at the dither piezo that drives the cantilever vibrations in the dynamic mode of scanning force microscopy. Thus, it is easily possible to switch between the imaging mode and DSM mode, enabling the direct manipulation of nanostructures under ambient conditions with high precision. The main advantage of our technique compared to earlier methods is that it operates with an active feedback loop, allowing a steady manipulation of nanostructures independent of the surface corrugation or sample tilt. Such controlled translations of latex spheres enable us in addition to study their properties regarding friction, adhesion, and cohesion. By translating latex spheres of different sizes (radii between 50 and 110 nm), it was found that the force needed to move a particle depends on its dimensions. Finally, the lateral translation of an intentionally marked sphere gives evidence that sliding is preferred over rolling.

Dung feeding in adult scarabaeines (tunnellers and endocoprids): even large dung beetles eat small particles

Abstract 1. The maximum size of ingested particles was determined in 15 species of adult dung beetle (Scarabaeidae: Scarabaeinae) by mixing small latex or glass balls of known diameter into the dung used as food. Twelve species (tribes Coprini, Onitini, Oniticellini, and Onthophagini) were tunnellers (making dung stores for feeding and breeding in the soil below the pat) and three species (tribe Oniticellini) were endocoprids (feeding and breeding in the dung pat itself).2. The test species, covering a wide range of body size (fresh weights 0.05–7.4 g), ingested minute particles only (maximum diameter 8–50 µm), and there was a statistically significant but numerically small increase in particle size with body weight.3. When the effect of body size was taken into account, taxon (tribe), ecological group (tunneller/endocoprid), and dung preference (coarse/fine) had no significant effect on the size of ingested particles.4. Tests using two tunnelling species did not indicate that beetles use their mandibles to grind dung particles prior to ingestion.5. The results suggest essentially the same feeding mechanism in all adult tunnelling or endocoprid scarabaeines that eat fresh dung. Larger, indigestible plant fragments are avoided by filtration, and ingestion is confined to very small particles of higher nutritional value.

Polymerization of brightly colored emulsions in a glycerol suspension medium

Upon emulsification of a mixture of methyl methacrylate or methacrylic acid monomer, along with divinylbenzene crosslinker and octane porogen into a glycerol suspension medium, brightly colored emulsions form. The bright colors of the emulsion originate from an exact matching of the refractive index of the emulsion droplets with that of the glycerol medium only at certain wavelengths of light – other wavelengths of light scatter. Polymerization of the brightly colored emulsions yields three different latex morphologies depending upon the polymerization temperature and the type of emulsifier, monomer, initiator, or hydrocarbon applied. The latex morphologies obtained range from large porous latex (1–10 µm in size) to medium-sized porous latex (0.1–1 µm in size) to small latex (up to 0.1 µm in size).

Ultrasonically induced microemulsion polymerization of styrene

In this paper, ultrasonically induced microemulsion polymerization of styrene was successfully performed, possessing many merits such as high polymerization rate, the formation of small latex particles with a narrow size distribution, the absence of initiator and relatively low surfactant concentration. The monomer conversion reached 70% in 1 h, and the average diameter of polystyrene (PS) latex was about 30 nm which could be prepared with 3% surfactant (sodium dodecyl sulfate, SDS) concentration. The molecular weight of PS was around 10 6 and the poly-distribution index was 1.06, indicating a very narrow distribution. Several influencing factors were investigated in detail, showing that ultrasonically induced microemulsion polymerization is a new route to prepare PS nanoparticles.

An x-ray extensional flow cell

We have designed an x-ray extensional flow cell based on the crossed-slot geometry that is compatible with x-ray diffraction. Extensional flow within the cell was both confirmed and characterized by examining the trajectories of small latex spheres suspended in water via video microscopy. The cell was then used to examine extensional-flow-induced structural changes in a well-known lamellar surfactant system, and the alignment of the surfactant domains was observed to increase with increasing extension rate.

Synthesis of Polymerizable Anionic Surfactants and Their Emulsion Copolymerization with Styrene

Two polymerizable ionic surfactants sodium 4-(ω-acryloyloxyalkyl)oxy benzene sulfonate (SABS-n, n = 8 or 10) have been synthesized and polymerized. Their critical micelle concentrations (CMC) were determined to be 9.40 × 10-3 M and 2.02 × 10-3 M at 25 °C for SABS-8 and SABS-10, respectively. The rate of micellar polymerization of SABS-8 or SABS-10 was found to be proportional to half an order of the concentration of ammonium persulfate (APS) and first order of the surfactant concentration. Their activation energies of micellar polymerization were relatively low, that is, 58.2 kJ mol-1 for SABS-8 and 45.4 kJ mol-1 for SABS-10. The monomer reactivity ratios for emulsion copolymerization of SABS-8 (M1) and styrene (M2) were determined to be r1 = 0.47 and r2 = 3.91. These emulsion copolymerizations produced small latex particles ranging from 16 to 30 nm in diameter. XPS analysis shows that SABS-8 was significantly enriched on the surface of latex particles, for example, 63.4% surface coverage on latex particl...