Martin In

Molecular design of alkoxide precursors for the synthesis of hybrid organic-inorganic gels

Abstract Design, synthesis and characterization of hybrid transition metal oxide gels in which organic polymers are part of the gel network are reported and illustrated with zirconium oxide based materials. Zirconium-oxo-poly(AAEM) copolymers have been synthesized by chemical modification at the molecular level of zirconium propoxide with an organically functionalized chelating ligand (acetoacetoxyethylmethacrylate). Both polymerization reactions have been managed simultaneously, leading to hybrid organic-inorganic bushy polymers intimately interpenetrated at the nanosize scale. Zirconium oxo core is made with oxo-alkoxo AAEM modified species where zirconium is likely in sevenfold coordination. The zirconium oxo species are chemically bonded to polymeric methacrylate chains via the β-diketo complexing function. The complexation ratio (AAEM/Zr) has been varied from 0.25 to 0.75. It appears to be the key parameter which controls the structure and the texture of these hybrid materials.

The Role of Complexing Ligands in the Formation of Non-Aggregated Nanoparticles of Zirconia

The hydrolysis and condensation of zirconium n-propoxide in n-propanol have been chemically controlled via the complexation of the zirconium precursor with acetylacetone. The size of the zirconium oxide-based particles is mainly controlled by the complexation ratio x=[acac]/[Zr]. the mean size increases from nanometric to submicronic range when x decreases from 1 to 0.1. Amorphous colloidal particles are obtained at room temperature. They result from a competitive growth/termination mechanism of zirconium-oxo species in the presence of acac surface capping agents. However non-aggregated nanocrystalline particles of tetragonal zirconia, about 2 nm in diameter are formed upon aging at 60°C when hydrolysis is performed in the presence of paratoluene sulfonic acid (PTSA).

Brownian diffusion of a partially wetted colloid

The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk. We suggest that such a result arises from thermally activated fluctuations of the interface at the solid/air/liquid triple line and their coupling to the particle drag through the fluctuation-dissipation theorem. Our findings should inform approaches for improved control of the kinetically driven assembly of anisotropic particles with a large triple-line-length/particle-size ratio, and help to understand the formation and structure of such arrested materials.

Phase Behavior of Gemini Surfactants

Gemini surfactants are made up of two surfactant‐like moieties connected by a spacer group. This article reviews their phase behavior, considering successively the thermotropism of pure gemini surfactants, the lyotropism in gemini surfactant/water mixtures, and the ability of gemini surfactants to give rise to microemulsions in the presence of oil and water (and eventually of cosurfactant). From the qualitative viewpoint gemini surfactants have been found to behave similarly to the corresponding monomeric surfactants as far as phase behavior is concerned. However, the reported results indicate that the length of the spacer and its chemical nature represent very effective parameters for tuning the thermotropic and lyotropic behaviors. They are the key structural parameters that bring originality and usefulness to the gemini surfactant concept.

Behavior of colloidal particles at a nematic liquid crystal interface

We examine the behavior of spherical silica particles trapped at an air–nematic liquid crystal interface. When a strong normal anchoring is imposed, the beads spontaneously form various structures depending on their area density and the nematic thickness. Using optical tweezers, we determine the pair potential and explain the formation of these patterns. The energy profile is discussed in terms of capillary and elastic interactions. Finally, we detail the mechanisms that control the formation of a hexagonal lattice and analyze the role of gravity for curved interfaces.

Ecodesign of Ordered Mesoporous Materials Obtained with Switchable Micellar Assemblies

Reduce, reuse, recycle: A new methodology allows the synthesis of ordered mesoporous materials in water at room temperature, eliminating the need for organic solvents and reducing the amount of energy consumed. It relies on the reversible formation of micelles of water-soluble block copolymers as structure-directing agents (see picture). After recovery of the mesoporous material, the reaction solution can be used again.

Hybrid Polyion Complex Micelles Formed from Double Hydrophilic Block Copolymers and Multivalent Metal Ions: Size Control and Nanostructure

Hybrid polyion complex (HPIC) micelles are nanoaggregates obtained by complexation of multivalent metal ions by double hydrophilic block copolymers (DHBC). Solutions of DHBC such as the poly(acrylic acid)-block-poly(acrylamide) (PAA-b-PAM) or poly(acrylic acid)-block-poly(2-hydroxyethylacrylate) (PAA-b-PHEA), constituted of an ionizable complexing block and a neutral stabilizing block, were mixed with solutions of metal ions, which are either monoatomic ions or metal polycations, such as Al(3+), La(3+), or Al(13)(7+). The physicochemical properties of the HPIC micelles were investigated by small angle neutron scattering (SANS) and dynamic light scattering (DLS) as a function of the polymer block lengths and the nature of the cation. Mixtures of metal cations and asymmetric block copolymers with a complexing block smaller than the stabilizing block lead to the formation of stable colloidal HPIC micelles. The hydrodynamic radius of the HPIC micelles varies with the polymer molecular weight as M(0.6). In addition, the variation of R(h) of the HPIC micelle is stronger when the complexing block length is increased than when the neutral block length is increased. R(h) is highly sensitive to the polymer asymmetry degree (block weight ratio), and this is even more true when the polymer asymmetry degree goes down to values close to 3. SANS experiments reveal that HPIC micelles exhibit a well-defined core-corona nanostructure; the core is formed by the insoluble dense poly(acrylate)/metal cation complex, and the diffuse corona is constituted of swollen neutral polymer chains. The scattering curves were modeled by an analytical function of the form factor; the fitting parameters of the Pedersens model provide information on the core size, the corona thickness, and the aggregation number of the micelles. For a given metal ion, the micelle core radius increases as the PAA block length. The radius of gyration of the micelle is very close to the value of the core radius, while it varies very weakly with the neutral block length. Nevertheless, the radius of gyration of the micelle is highly dependent on the asymmetry degree of the polymer: if the neutral block length increases in a large extent, the micelle radius of gyration decreases due to a decrease of the micelle aggregation number. The variation of the R(g)/R(h) ratio as a function of the polymer block lengths confirms the nanostructure associating a dense spherical core and a diffuse corona. Finally, the high stability of HPIC micelles with increasing concentration is the result of the nature of the coordination complex bonds in the micelle core.

Surfactant behavior of ionic liquids involving a drug: from molecular interactions to self-assembly.

Aggregates formed in an aqueous medium by three ionic liquids CnMImIbu made up of 1-alkyl-3-methyl-imidazolium cation (n = 4, 6, 8) and ibuprofenate anion are investigated. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), (1)H nuclear magnetic resonance measurements, and atom-scale molecular dynamics simulations are used to shed light on the main interactions governing the formation of the aggregates and their composition. At high concentration, mixed micelles are formed with a composition that depends on the imidazolium alkyl chain length. For the shortest alkyl chain, micelles are mainly composed of ibuprofenate anions with some imidazolium cations intercalated between the anions. Upon increasing the alkyl chain length, the composition of the aggregates gets enriched in imidazolium cations and aggregates of stoichiometric composition are obtained. Attractive interactions between these aggregates led to the formation of larger aggregates. As suggested by molecular simulations, these larger aggregates might constitute the early stage of phase separation. Transitions from micelles to vesicles or ribbons are observed due to dilution effects and changes in the chemical composition of the aggregates. We also show that aggregation can be probed using simple microscopic quantities such as radial distribution functions and average solvation numbers.

Hydrolysis and Condensation Reactions of Transition Metal Alkoxides: Calorimetric Study and Evaluation of the Extent of Reaction

The behavior of titanium and zirconium alkoxides towards complexation and water addition is analyzed through water titration and calorimetric experiments. A simple model is presented, which allows evaluation of the mean hydrolysis and condensation constants, Kh and Kc, of both pure and complexed transition metal alkoxides in the sol state, through the analysis of consumed water versus initial hydrolysis ratio curves. These constants allow comparison of the extents of the hydrolysis and condensation reactions for sols obtained from several alkoxide precursors. The complexation ratio only affects the condensation constant Kc, whereas the hydrolysis constant Kh remains unchanged. Analysis of the Kh/Kc ratios has shown that in the sol state, silanol Si–OH groups are more stable than the Ti–OH or Zr–OH groups. Moreover, this study has shown that the proton concentration not only affects the kinetics, but also the final composition of the system. Calorimetric studies of the complexation and hydrolysis/condensation reactions have highlighted the role of coordination unsaturation of the transition metal alkoxides in the exothermicity of these reactions, clearly demonstrating that coordination unsaturation is the driving force behind the reactivity of these alkoxides towards nucleophilic species (e.g. water, complexing ligands, polar solvents).

Transition metal based hybrid organic-inorganic copolymers

The synthesis of transition metal based hybrid copolymers is achieved by using transition metal alkoxides modified by chelating ligands functionalized with polymerizable organic groups. The heterofunctional precursor is an acetoacetoxyethylmethacrylate modified zirconium propoxyde. The hybrid copolymers obtained by double polymerization of heterofunctional precursors are characterized in the liquid and in the solid state by using light scattering, SAXS measurements, UV-visible, FTIR, 13C MAS NMR spectroscopies and several chemical and gravimetric analyses. Both inorganic polycondensation and organic polymerization occured and the chemical bond between organic and inorganic moities is conserved. These hybrids consist of polyzirconates chemically bonded to polymeric methacrylate chains via the β-diketo complexing function. The determination of the conversion degree of both polymerization reactions reveals the competition between the two types of reactions. This competition controls the scale of homogeneity. The modification ratio (R = AAEM/Zr) of zirconium alkoxide appears to be the key parameter for the tuning of the homogeneity. A careful adjustment of this parameter leads to zirconium oxo species with more or less open structures and to the tailoring of the ratio between organic and inorganic components.