Controlling Porosity within Colloidal Heteroaggregates

Preparation of raspberry-like polymer composite particles through adherence of smaller cationic particles of P(St-co-DMHB) (poly(styrene-co-methacryloxyethylhexadecyldimethylammonium bromide)) onto larger PMMA (poly(methyl methacrylate)) anionic particles surface was achieved by heterocoagulation based on electrostatic interaction. A series of P(St-co-DMHB) cationic particles with particle size varied from 43 nm to 105 nm were obtained through emulsion polymerization using different levels of the cationic monomer DMHB. The particles were assembled on the anionic particles surfaces respectively to result in polymer composite particles having different granulations. Light transmittance and particle size and its distribution in the heterocoagulation processes were followed in order to clarify in detail the assembling process of the small cationic polymer particles onto the larger anionic polymer particles. Transmission electron microscope was used to examine the morphologies of the cationic latex particles,the anionic latex particles and that of the composite particles after their heterocoaguculation. It was observed that the degree of coverage of the small cationic particles on the surface of the anionic large particles was adjustable in a range by varying the ratio of the anionic and the cationic latex particles.

By using anionic and cationic iron colloid particles, which are Prussian blue reaction positive and 5-250nm in diameter, the surface charge-related endocytosis of rat macrophages was observed. The anionic particles were solely adhered to the surface of peritoneal and liver macrophages by exposing the cells for a short time period to the particles in vitro as well as in vivo by perfusion. The particles then were taken up selectively by macrophages, but not by neutrophils, eosinophils, lymphocytes, mast cells, fibroblasts and vascular endothelial cells, as observed by light and electron microscopy after intraperitoneal, subcutaneous and intravenous injections of the particles. The anionic iron colloid particles were taken up by macrophages, delivered to lysosomes and disintegrated quickly. Ferritin was first synthesized there and then dispersed into the cytoplasmic matrix. In contrast, cationic iron colloid particles were adhered to the surfaces of all kind of somatic cells and internalized by the process similar to adsorptive endocytosis. The ingested particles were found in thin canalicular structure or tiny vesicles being adhered to their luminal surfaces. The morphology of these compartment was much different from the phagosomes of macrophages formed by ingesting anionic iron colloid particles, and showed no deliverly of the particles to lysosomes as long as 4hr after the incubation. Some particles were found in lysosomes by another 5hr of chase incubation. The results indicate that the “non-specific receptor mediated phagocytosis” by macrophages is induced by the binding of anionic macromolecules to the cationic receptor on the cell surface. And the adsorptive endocytosis will induce two kinds of different mechanism, one is currently accepted concept, the receptor mediated endocytosis and another one is the surface charge-mediated endocytosis.

The formation of colloids based on polyelectrolyte complexes (PECs) of biopolymers was investigated through the complexation between two charged polysaccharides, chitosan as polycation, and dextran sulfate as polyanion. The slow dropwise addition of components, generally used for the formation of PECs, allowed to elaborate both cationic or anionic particles with an excess of chitosan or dextran sulfate, respectively. The PEC particles featured a core/shell structure, the hydrophobic core resulting from the segregation of complexed segments whereas excess component in the outer shell ensured the colloidal stabilization against further coagulation. Considering the host/guest concept for the formation of PECs, the influence of the molecular weight of components on particles sizes could be well explained by the chain length ratios of the two polymers. As an irreversible flocculation occurred with a dropwise approach for both cationic and anionic PEC particles when the mixing ratio was close to unity, a more versatile, and simpler to setup, method was designed: the one-shot addition of one solution to the other. Because process of addition is faster than the flocculation, cationic or anionic particles could be elaborated irrespective of the order of addition of the reactant. Characterization of these particles by quasielastic light scattering, electrophoresis, and scanning electron microscopy revealed very similar properties to those obtained by a slow dropwise approach. Critical coagulation concentrations of 0.12 and 0.09 M (with sodium chloride) for cationic and anionic particles evidenced a mostly electrostatic stabilization.

The influence of a nonionic surfactant (Triton X-405) on the adsorption behavior of single-stranded oligodeoxyribonucleotide (poly(thymidylic acid) (dT35)) onto cationic aminated polystyrene latex particles has been investigated. A preliminary study was performed on the adsorption of Triton X-405 onto these cationic particles, showing a maximum amount of ∼0.5 mg m-2 at the plateau. Desorption of the nonionic surfactant even after an extensive cleaning procedure was not completed, indicating that probably low HLB (hydrophilic and lipophilic balance) species were still strongly adsorbed. The modification of the electrophoretic mobility of the latex particles together with the slight decrease in the colloidal stability suggested that the residual Triton X-405 molecules would adopt a flat conformation at the particles surface. Then, the adsorption behavior of dT35 onto precoated cationic latex was thoroughly examined under various conditions and compared with the case of bare latex particles. It was clearly evidenced that the residual adsorbed amount of nonionic surfactant significantly affected the surface nature, especially at basic pH. It was interesting to notice that dT35 adsorption was strongly reduced at basic pH and that its desorption was favored using basic pH buffer containing Triton X-405 and high ionic strength. Kinetic exchange experiments were also performed using labeled 32P-dT35 and unlabeled dT35, indicating that the exchange took place with no marked differences between coated and bare latex particles.

Microstructure of ionic liquids mixed with water on the charged graphene surface: A coarse-grained molecular dynamics simulation study

Relatively clean cation-charged polystyrene (PS) latex particles were prepared via a novel and simple route in the absence of steric stabilizers. The reaction system only included medium, styrene, and initiator with quaternary ammonium moiety. The influences of initiator concentration, and medium composition on the diameter and size distribution of PS latex particles were systematically investigated. The particle morphology and size, the surface N content, and the particle size distribution were respectively determined by SEM, XPS, and laser particle size analyzer. The results indicated that monodisperse and cation-charged PS latex particles with diameter of 0.45–0.95 μm could be successfully produced via the simple reaction system, and cationic initiator concentration played a key role in the preparation of uniform PS latex particles. Finally, a plausible mechanism was proposed for explaining nucleation, growth, and stabilization of PS latex particles.

A sulfonated methacrylate monolithic polymer has been synthesized inside fused-silica capillaries of diameters 50-533-microm i.d. and coated with 65-nm-diameter fully functionalized quaternary ammonium latex particles (AS18, Dionex Corp.) to form an anion-exchange stationary phase. This stationary phase was used for ion-exchange capillary electrochromatography of inorganic anions in a 75-microm-i.d. capillary with Tris/perchlorate electrolyte and direct UV detection at 195 nm. Seven inorganic anions (bromide, nitrate, iodide, iodate, bromate, thiocyanate, chromate) could be separated over a period of 90 s, and the elution order indicated that both ion exchange and electrophoresis contributed to the separation mechanism. Separation efficiencies of up to 1.66 x 10(5) plates m(-1) were achieved, and the monoliths were stable under pressures of up to 62 MPa. Another latex-coated monolith in a 250-microm-i.d. capillary was used for in-line preconcentration by coupling it to a separation capillary in which the EOF had been reversed using a coating of either a cationic polymer or cationic latex particles. Several capillary volumes of sample were loaded onto the preconcentration monolith, and the analytes (inorganic anions) were then eluted from the monolith with a transient isotachophoretic gradient before being separated by electrophoresis in the separation capillary. Linear calibration curves were obtained for aqueous mixtures of bromide, nitrite, nitrate, and iodide. Recoveries of all analytes except iodide were reduced significantly when the sample matrix contained high levels of chloride. The preconcentration method was applied to the determination of iodide in open ocean water and provided a limit of detection of 75 pM (9.5 ng/L) calculated at a signal-to-noise ratio of 3. The relative standard deviation for migration time and peak area for iodide were 1.1 and 2.7%, respectively (n = 6). Iodide was eluted as an efficient peak, yielding a separation efficiency of 5.13 x 10(7) plates m(-1). This focusing was reproducible for repeated analyses of seawater.

Cationic latex particles with surface amino groups were prepared by a multistep batch emulsion polymerization. In the first one or two steps, monodisperse cationic latex particles to be used as the seed were synthesized, and in the third step, two different amino‐functionalized monomers [aminoethylmethacrylate hydrochloride (AEMH) and vinylbenzylamine hydrochloride (VBAH)] were used to synthesize the final functionalized latex particles. 2,2′‐Azobisisobutyramidine dihydrochloride was used as the initiator, and different concentrations of two quaternary ammonium emulsifiers with hydrophobic chains of different lengths were examined. To characterize the final latexes yields were obtained gravimetrically, and particle size distributions and average particle diameters were determined by transmission electron microscopy and photon correlation spectroscopy. The amount of amino groups was determined by fluorimetry. The effect of the amino‐functional monomer used on the final latexes and the colloidal behavior of the system were studied. The influence of the different conditions utilized to synthesize the latexes on the colloidal stability of the particles was evaluated in terms of the Fuchs stability ratio and electrophoretic mobility. High yields of the amino‐functional monomers were obtained. Surface amino, amidine, and quaternary ammonium groups provided the cationic character. The colloidal stability behavior of the products obtained was compatible with their cationic character. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2929–2936, 2001

Deposition of cationic polymeric pigments on pulp fibers

Uptake of anionic gold nanoparticles by cationic microgel particles in dispersion: The effect of pH

pH-Responsive microgels are crosslinked polymer particles that swell when the pH approaches the pKa of the polyacid or polybase chains. In this study we investigate for the first time pH-triggered physical gel (soft particle glass) formation from concentrated mixed dispersions of heteroaggregated pH-responsive microgels. The two microgels studied are poly(ethyl acrylate/methacrylic acid/1, 4-butanediol diacrylate) (referred to as PEAMAA) and poly(2-vinylpyridine/divinylbenzene) (referred to as PVP). The anionic PEAMAA particles are alkali-swellable and the cationic PVP particles are acid-swellable. Concentrated homodispersions formed physical gels at either low pH (PVP) or high pH (PEAMAA). The hard sphere (latex) particle size ratio (R = dPEAMAA/dPVP) was 0.15. Uniquely, the PEAMAA/PVP microgel heterodispersion allowed R to be varied by an order of magnitude (from 0.04 to 0.61) at a fixed particle number ratio simply by adjusting the solution pH. Concentrated PEAMAA/PVP heterodispersions formed physical gels at both low and high pH. Dynamic rheology measurements showed that at low pH the presence of collapsed PEAMAA particles greatly increased the storage modulus (G′) and also the critical yield strain (γc) of the mixed PEAMAA/PVP gels compared to the parent PVP homoparticle gel. A remarkably high G′ value of 0.12 MPa was obtained for a mixed PEAMAA/PVP gel containing 90 vol.% water. Our new, versatile method for preparing pH-responsive dispersions that form physical gels at two different pH values could lead to dual-action injectable gels for soft tissue repair.

Oxidation of lignin model compounds in water with dioxygen and hydrogen peroxide catalysed by metallophthalocyanines

Cellulose nanocrystals are aligned in wrinkled polydimethylsiloxane templates and transferred to polyethyleneimine-coated silica surfaces in a printing process similar to microcontact printing. The highly aligned nanorods were deposited onto the surfaces with a line-to-line distance of 225–600 nm without loss of alignment. It was also possible to repeat the transfer process on the same surface at a 90-degree angle to create a network structure. This demonstrates the versatility of the technique and creates more options for advanced multilayering of materials. To demonstrate that the surface properties of the anionic cellulose nanorods were unaffected by the transfer process and to prove the concept of functionalizing transferred particles, cationic latex particles were electrostatically self-assembled onto the cellulose nanorods. The directed deposition of these particles resulted in excellent site specificity and the highest resolution to date for controlled deposition of colloids on an electrostatically patterned surface.

In the case of cationic polystyrene latex, the adsorption of anionic surfactants involves a strong electrostatic interaction between both the particle and the surfactant, which may affect the conformation of the surfactant molecules adsorbed onto the latex-particle surface. The adsorption isotherms showed that adsorption takes place according to two different mechanisms. First, the initial adsorption of the anionic surfactant molecules on cationic polystyrene surface would be due to the attractive electrostatic interaction between both ionic groups, laying the alkyl-chains of surfactant molecules flat on the surface as a consequence of the hydrophobic interaction between these chains and the polystyrene particle surface, which is predominantly hydrophobic. Second, at higher surface coverage the adsorbed surfactant molecules may move into a partly vertical orientation with some head groups facing the solution. According to this second mechanism the hydrophobic interactions of hydrocarbon chains play an important role in the adsorption of surfactant molecules at high surface coverage. This would account for the very high negative mobilities obtained at surfactant concentration higher than 5×10−7 M. Under high surface-coverage conditions, some electrophoretic mobility measurements were performed at different ionic strength. The appearance of a maximum in the mobility-ionic strength curves seems to depend upon alkyl-chain length. Also the effects of temperature and pH on mobilities of anionic surfactant-cationic latex particles have been studied. The mobility of the particles covered by alkyl-sulphonate surfactants varied with the pH in a similar manner as it does with negatively charged sulphated latex particles, which indicates that the surfactant now controls the surface charge and the hydrophobic-hydrophilic character of the surface.

We report the interactions of cationic latex particles synthesized by RAFT/MADIX-mediated emulsion polymerization with anionic cellulose nanocrystals (CNCs) and cotton fabrics. Latexes in the size range 200-300 nm with poly(butyl acrylate) or poly(2-ethylhexyl acrylate) hydropho-bic cores and hydrophilic shell are synthesized. We show that the latex/CNC interaction is me-diated by electrostatics, the interaction being the strongest with the most charged particles. The adsorption process is efficient and does not require any functionalization step for either cellulose or latex. A major result is the observation by cryogenic transmission electron micros-copy of latexes coated with entangled arrays of CNCs, and for the softer particles a notable deformation of their structure into faceted polyhedra. By labeling the latexes with hydrophobic carbocyanine dyes, their deposition on woven cotton fabrics is studied in situ and quantified by fluorescence microscopy. As with the CNCs, the highest deposition on cotton in the wet and dried states is achieved with the most charged latexes. This demonstrates that CNCs can serve as models to adjust the interactions of latex particles with cotton, and thus optimize manufac-turing processes for the development of advanced textiles.