Aqueous suspensions of highly stable Mg/Al layered double hydroxide (LDH) nanoparticles were obtained via a direct and fully colloidal route using asymmetric poly(acrylic acid)-b-poly(acrylamide) ...(PAA-b-PAM) double hydrophilic block copolymers (DHBCs) as growth and stabilizing agents. We showed that hybrid polyion complex (HPIC) micelles constituted of almost only Al(3+) were first formed when mixing solutions of Mg(2+) and Al(3+) cations and PAA3000-b-PAM10000 due to the preferential complexation of the trivalent cations. Then mineralization performed by progressive hydroxylation with NaOH transformed the simple DHBC/Al(3+) HPIC micelles into DHBC/aluminum hydroxide colloids, in which Mg(2+) ions were progressively introduced upon further hydroxylation leading to the Mg-Al LDH phase. The whole process of LDH formation occurred then within the confined environment of the aqueous complex colloids. The hydrodynamic diameter of the DHBC/LDH colloids could be controlled: it decreased from 530 nm down to 60 nm when the metal complexing ratio R (R = AA/(Mg + Al)) increased from 0.27 to 1. This was accompanied by a decrease of the average size of individual LDH particles as R increased (for example from 35 nm at R = 0.27 down to 17 nm at R = 0.33), together with a progressive favored intercalation of polyacrylate rather than chloride ions in the interlayer space of the LDH phase. The DHBC/LDH colloids have interesting properties for biomedical applications, that is, high colloidal stability as a function of time, stability in phosphate buffered saline solution, as well as the required size distribution for sterilization by filtration. Therefore, they could be used as colloidal drug delivery systems, especially for hydrosoluble negatively charged drugs.
Ordered mesoporous silica materials were prepared under different pH conditions by using a silicon alkoxide as a silica source and polyion complex (PIC) micelles as the structure-directing agents. ...PIC micelles were formed by complexation between a weak polyacid-containing double-hydrophilic block copolymer, poly(ethylene oxide)-
-poly(acrylic acid) (PEO-
-PAA), and a weak polybase, oligochitosan-type polyamine. As both the micellization process and the rate of silica condensation are highly dependent on pH, the properties of silica mesostructures can be modulated by changing the pH of the reaction medium. Varying the materials synthesis pH from 4.5 to 7.9 led to 2D-hexagonal, wormlike or lamellar mesostructures, with a varying degree of order. The chemical composition of the as-synthesized hybrid organic/inorganic materials was also found to vary with pH. The structure variations were discussed based on the extent of electrostatic complexing bonds between acrylate and amino functions and on the silica condensation rate as a function of pH.
Using aminoglycoside antibiotics as drug models, it was shown that electrostatic complexes between hydrophilic drugs and oppositely charged double-hydrophilic block copolymers can form ordered ...mesophases. This phase behavior was evidenced by using poly(acrylic acid)-block-poly(ethylene oxide) block copolymers in the presence of silica precursors, and this allowed preparing drug-loaded mesoporous silica directly from the drug-polymer complexes. The novel synthetic strategy of the hybrid materials is highly efficient, avoiding waste and multistep processes; it also ensures optimal drug loading and provides pH-dependence of the drug release from the materials.
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•Continuous flow processes allow scaling-up of LDH production with constant quality.•Morphology and size of particles are controlled.•Evolution of the reactor design from tank to ...microfluidic technology is evidenced.•Heat and mass transfers are improved, and residence times are reduced.•Nanosheets, LDH-based hybrids and nanocomposites are obtained.
Continuous production processes allow scaling up of layered double hydroxides (LDHs) and avoid the drawbacks induced by conventional coprecipitation. These drawbacks result from variable supersaturation rate due to non constant pH and concentration of the solutions and from long residence times hindering a fine control of the size and morphology of the particles. Continuous flow processes allow reducing the residence time and maintaining almost constant supersaturation producing LDHs in large amounts with constant quality. We report here the different continuous flow methods for the production of LDHs particles with controlled size and morphology or individual nanosheets, and of LDH-based hybrids and nanocomposites. The paper will focus on the design of the reactors showing a decrease of their volume and an improvement of the mixing and heat and mass transfers. Cylindrical tank under steady-state conditions lead to particles with a narrower size distribution than in batch reactor. Then processes with vigorously stirred microreactors in the so-called in-line dispersion-precipitation method were developed. Counter-current flow reactors with particles formed at the interface of solutions flowing up and down were further used to obtain ultra-fine LDH nanoplates and efficient surface modification with surfactants. Hydrothermal continuous or co-flow reactors exhibit great versatility allowing the preparation of exfoliated or functional LDHs, LDH nanoplates on alumina-coated substrates, and reduced graphene oxide/LDH nanocomposite films. The microfluidic technology is very promising for preparing LDHs of different compositions and functionalities. The reaction conditions as well as the structural and morphological properties of the materials are discussed and applications are reported.
With the necessity for the refining industry to treat heavier feedstocks, there is a clear demand for improved zeolite materials displaying better accessible surface areas and higher pore volumes in ...order to capitalize on their effectiveness. To this end, over the last decade, there has been an intensification of research on the exploration of new routes to synthesize zeolite materials combining micropores with mesopores. Different synthesis strategies are used for their preparation (i.e., by structure breaking or so‐called ‘destructive’ pathways, or structure building or so‐called ‘constructive’ synthesis pathways). This Review discusses the variety of current synthesis strategies, while emphasizing the strengths and weaknesses of the different routes regarding material characteristics; health, safety, and environment aspects; and synthesis costs.
Industrial zeolite and magic: The accessibility of zeolites (see figure) is of paramount importance to capitalize on their effectiveness in industrial catalysis. The variety of synthesis strategies proposed today for the preparation of ‘hierarchical’ zeolite materials combining micro‐ and mesoporosity is discussed.
Abstract Double-hydrophilic block copolymer micelles were designed as vectors for ex vivo dendritic cell engineering to improve the delivery of therapeutic molecules in such immune cells. ...Polymethacrylic acid-b-polyethylene oxide (PMAA2100 -b-POE5000 )/poly- l -lysine micelles were optimised and showed a hydrodynamic diameter of 30 nm with a peculiar core organised with hydrogen bonds as well as hydrophobic domains. The micelles proved high stability in physiological conditions (pH and ionic strength) and were also able to disassemble under acidic conditions mimicking acidic endolysosomes. The efficient endocytosis of the optimised micelles tested on bone marrow-derived dendritic cells was monitored by fluorescence-activated cell sorting and microscopy analysis. Finally, the micelle biocompatibility permitted a complete control of the dendritic cell-maturation process widening the therapeutical potential of such engineered dendritic cells for cancer vaccines as well as for immunomodulation in autoimmune diseases.
This work deals with the determination of polymer effective charge based on the sensitivity of detection in capillary electrophoresis using indirect UV detection. In this detection mode, the ...polyelectrolyte (solute) displaces a certain quantity of probe contained in the background electrolyte and having the same charge as the solute. This quantity of displaced probe is directly correlated to the effective charge of the solute. Contrary to other electrophoretic methods generally used for monitoring changes in effective charge, this methodology is not based on the effective mobility of the polyelectrolyte (i.e., migration times) but on the sensitivity of detection (i.e., peak areas). Experimental values of effective charge obtained for statistical copolymers of poly(acrylamide-co-sodium 2-acrylamido-2-methylpropanesulfonate), for homopolymers of poly(diallyldimethylammonium chloride), poly(acrylic acid), and poly(metacrylic acid), are compared to the Manning theory of charge condensation. Interestingly, this methodology can be used for the characterization of macromolecular architecture since the effective charge of copolymers highly depends on the repartition of the charged monomers along the polymer chain. As an example, this methodology can easily distinguish statistical copolymers from diblock copolymers of similar chemical charge densities. Experiments were carried out on diblock copolymers of poly(acrylic acid)-b-poly(ethylene oxide) (PAA-b-PEO) and poly(methacrylic acid)-b-poly(ethylene oxide) (PMAA-b-PEO). The variation of the sensitivity of detection of statistically charged copolymers in the indirect UV mode with the chemical charge density is also discussed in detail.
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