Search results for "Precipitation"

Expanded micro-particles by supercritical antisolvent precipitation: Interpretation of results

2008

Abstract Supercritical antisolvent (SAS) micronization has been used to obtain nanoparticles and micro-particles of several kinds of materials. Sometimes hollow expanded micro-particles have also been obtained. This work is focused on the analysis of this last morphology. We organized literature data and our previous experiments and we added new experiments on previously tested compounds and on compounds never tested before. As a result, expanded micro-particles using several compounds belonging to different categories and precipitated from different solvents in laboratory and pilot scale plants were obtained with diameters between about 10 and 180 μm. They also showed different sub-structu…

On the interlayer spacing collapse of Cloisite (R) 30B organoclay

2011

Abstract When used as a nanofiller for the preparation of polymer/clay nanocomposites (PCNs), Cloisite® 30B (30B) often undergoes a d-spacing collapse, as demonstrated by a shift to wider angles of the XRD basal reflection. Such collapse has been variously attributed to organoclay contamination or, more often, to thermal degradation of the organic modifier with expulsion of the volatile products from the galleries. In this work, several PCNs loaded with 30B have been prepared by melt compounding, using different polymer matrices, and have subsequently been subjected to dissolution in appropriate solvents followed by precipitation in excess non-solvent and room temperature drying. An XRD ana…

Polymer, Metal, and Hybrid Nano- and Mesotubes by Coating Degradable Polymer Template Fibers (TUFT Process)

2000

). Selective reaction with the silver atoms at the interface of the particles occurred and the coated particles were then extracted from reverse micelles. The powder of coated nanocrystals thus obtained was then dispersed in hexane, giving an optically clear solution. The size distribution was still rather large (30 %), and to reduce it a size-selected precipitation process [20] was used. In this process two solvents, such as hexane and pyridine, are mixed. The first is a good solvent and the second a poor solvent for the alkyl chains. With this solvent mixture, the larger coated particles flocculated whereas the smaller ones remain in the solution, thus providing size selection. By repeati…

FORMATION OF A SMALL RIBONUCLEOPROTEIN PARTICLE BETWEEN TAT PROTEIN AND TRANS-ACTING RESPONSE ELEMENT IN HUMAN IMMUNODEFICIENCY VIRUS-INFECTED CELLS

1991

The trans-acting response element (TAR) within the long terminal repeat of human immunodeficiency virus (HIV) is present in all 5' termini of HIV mRNAs and is recognized by the viral Tat protein. Now we describe that the 59-nucleotide-long TAR-RNA exists as a ribonucleoprotein particle in polysomal and heterogeneous nuclear RNP fractions of HIV-1-infected HeLa-T4+ cells. Applying an immunoprecipitation technique this Tat.TAR complex could be isolated from total cell extracts as well as from polysomal or heterogeneous nuclear RNP fractions. The chain length and the identity of the TAR-RNA were established by RNase protection assays while the Tat protein was confirmed by Western blotting tech…

Experimental design approach in the synthesis of molecularly imprinted polymers specific for iprodione fungicide

2015

International audience; An experimental design (ED) approach was applied to study the weight of three factors in the synthesis of a molecularly imprinted polymer (MIP) specific for iprodione fungicide. The objective was to obtain a high specific polymer with the best performance of iprodione binding. Thirteen iprodione-imprinted polymers and 13 non-imprinted polymers (NIP) were synthesized according to ED having 3 influencing factors: the polymerization method, the crosslinker nature and the functional monomer type. For each factor, two levels were studied: bulk and precipitation polymerization for the first factor, trimethylolpropane trimethacrylate (TRIM) and ethylene glycol dimethacrylat…

Surfactant-Induced Helix Formation of Cylindrical Brush Polymers with Poly(L-lysine) Side Chains

2008

The complex formation of oppositely charged surfactants with some polypeptides is known to induce β-sheet or helix formation. Here, we report on the complex formation of cylindrical brush polymers with poly(L-lysine) side chains and sodium dodecylsulfate (SDS). With increasing amount of added surfactant the cylindrical polymers first adopt a helical conformation with a pitch of approximately 14-24 nm followed by a spherically collapsed structure before eventually precipitation occurs. CD measurements suggest that the helix formation of the cylindrical brush polymers is driven by the hydrophobicity of the ,8-sheets formed by the PLL side chain-SDS complexes.

Pleiotropic Role of Recombinant Silaffin-Like Cationic Polypeptide P5S3: Peptide-Induced Silicic Acid Stabilization, Silica Formation and Inhibition …

2016

Silica-mineralizing organisms such as diatoms manage several aspects of silica chemistry when polymerizing monomeric silicic acid into amorphous silica. Silicic acid is undersaturated in the diatoms’ habitats and mechanisms of enrichment and prevention of uncontrolled mineralization are not well understood. Diatom-biosilica is associated with organic compounds, including polycationic, post-translationally modified peptides termed silaffins, which induce the condensation of silicic acid under supersaturated conditions. Here, we report the pleiotropic action of the designed silaffin-like peptide P5S3, which (i) stabilizes 4–8x silicic acid (in supersaturated conditions of 8.3 mm), (ii) decele…

An approximate theoretical impedance analysis of the anodic dissolution of nickel across nickel(II) stabilised by means of competitive anions

2007

Abstract A theoretical impedance function for the anodic dissolution of nickel is developed by considering the hypothesis that there are two competitive anions which participate in the stabilization of the electrogenerated Ni(II) species. The experimental effect of chloride ion concentration on nickel electrodissolution process is analyzed by means of a mechanism that considers this competency. It is observed that an increased Cl − concentration causes an increase in Ni(I) surface concentration and a decrease in the kinetic constant rates of the considered mechanism. Moreover, an increased chloride concentration causes a flattening in the low frequencies inductive loop in the Nyquist plot r…

Factors influencing carbon decomposition of topsoils from the Brazilian Amazon Basin

1999

The influence of texture and local climate, especially precipitation, on C decomposition was evaluated in topsoils under forest and pastures at different sites located in the western, central, and eastern Brazilian Amazon Basin. Independent of the geographical location and vegetation cover, C decomposition was lower in topsoils of fine texture with a sand/clay ratio of less than 1, compared to topsoils of coarse a texture with a sand/clay ratio ranging from 2 to 8. In the former, the low sand/clay ratio appears to reduce C decomposition. In the latter, besides the effect of the high sand/clay ratio, the local climate, especially the annual precipitation, seems to play an important role in c…

1977

The solution polymerization of styrene in methylene dichloride catalysed by trifluoromethanesulfonic acid takes place at a high rate even at low catalyst concentration. The S-shaped course of the conversion curves is explained by a reaction mechanism, in which the catalyst rapidly forms an inactive complex with one monomer molecule, and this monomer-acid complex is in equilibrium with the free catalyst molecule from which the propagating species are formed. Therefore, the formation of active initiating species becomes a slow process which depends also on the change of monomer concentration during polymerization. It is assumed that the active initiating species are formed from two or three m…