| Organic/Inorganic Hybrids and Nanocomposites |
The underlying theme behind this research is to use the polymerisation reaction as a means of assembling organic and inorganic phases into composite colloids. In order to circonvent the incompatibility between the two components, it is necessary to modify the surface of the mineral with certain chemical functions (usually, but not always reactive) in order to promote the growth of the polymer on the surface of the mineral particles. This includes the grafting of substances such as organosilanes that can form covalent bonds, or the modification of the mineral surface in such a way that one can form ionic-covalent complexes (e.g. acid-base bonds). This approach can be used with a multitude of inorganic systems (e.g. metals, metal oxides, clays, etc.) which means that we can envisage the synthesis of a wide variety of organic-inorganic particles with different morphologies (e.g. core-shell, hairy particles, raspberry-type, hollow particles, etc.) and with different properties. Evidently the polymerisation process will also play a role in the definition of the properties and morphologies, along with the type of functionalisation. This activity began with conventional emulsion polymerisation, but now includes approaches based on CFRP, anionic polymerisation, and the sol-gel process just to name a few.
The activity in Polymer Colloids and Composites is split into 3 major themes :
THEME 1. Colloidal Nanocomposites
THEME 2. Controlled Polymerization from Particle Surfaces
THEME 3. Polymer/Inorganic Hybrid Colloids
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Colloidal nanocomposites
Activities directed by Elodie Bourgeat-Lami. Collaborations with the ICMCB and the CRPP at the University of Bordeaux. | |
The incorporation of inorganic particles into polymers allows a substantial improvement of the physical properties of the resulting composite materials, that is to say their optical electrical, mechanical or magnetic properties, for instance.
Work is carried out at LCPP to synthesize colloidal particles that are both organic and inorganic. A typical example of this approach is the coating of inorganic particles by a polymer layer forming a core-shell morphology. The coating allows to improve the compatibity of the inorganic filler with a variety of fluids, resins and polymers.
These composite colloids are produced by in situ emulsion, miniemulsion, dispersion or suspension polymerizations performed in the presence of colloidal suspensions of mineral particles which had been previously functionalized by appropriate chemical reactive groups.
Applications concern various fields of material science, including the coating industry and the biotechnologies.
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Examples of current topics of interest include:
Control of the morphology of composite silica/polystyrene particles made by emulsion polymerisation in cooperation with E. Duguet (ICMCB) and S. Ravaine (CRPP)
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TEM and SEM analysis indicate that organic/inorganic particles may present a huge variety of morphologies depending on :
| | • | the nature, size and concentration of the inorganic particles |
| | • | the nature and concentration of the surface functional groups and |
| | • | the polymerization conditions. |
By controlling the number ratio of inorganic and polymer particles and by doing the appropriate surface chemistry, one can obtain dumbell-like particles. These nanoparticles can be selectively functionalized on the inorganic side in order to generate Janus nanospheres after removal of the protecting latex mask.
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Elaboration of polymer/clay (Laponite) composite particles through emulsion polymerization
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Polymer/clay composite colloids elaborated through emulsion polymerization can exhibit advantageous properties in comparison to pure polymer colloids. Water-borne hybrid coatings with improved tensile strength and modulus can be obtained from the composite latexes without loss of optical clarity.
| | • | Development of advanced synthetic strategies allowing to produce aqueous suspensions of polymer/laponite composite particles with long term colloidal stability and high clay content. |
| | • | Characterization of the morphology of the composite particles shows that the clay platelets are localized at the surface of the polymer latextes forming a rigid shell. |
| | • | Studies on film formation and film properties indicate a substantial improvement of their thermal and mechanical behaviour. |
The approach is being currently extended to miniemulsion (NAPOLEON project in interaction with Dr. Tim McKenna.) |
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Controlled Polymerizations from particle surfaces
Activities of Elodie Bourgeat-Lami developed in collaboration with the LMPB and the ICSI.
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The grafting of polymers to inorganic surfaces is a topic of current interest. Immobilized polymers chains enable to significantly alter and control the surface properties of minerals. The grafting can be done in various ways using anionic, cationic or free radical processes. In order to achieve a high density of grafts with well-defined architectures and controlled molecular weights, living polymerization techniques are preferred. These techniques usually involve growth of the polymer chains from the solid surface by means of immobilized initiators using the so-called « graft-from » method.
Two polymerization processes have been envisaged :-nitroxide-mediated polymerization and anionic-coordinated ring-opening polymerization of lactones, lactides and oxiranes.
Grafting of polymers with controlled molecular weight, molecular weight distributions and well-defined architectures from the surface of mineral particles (silica and clay colloids) via nitroxide-mediated polymerization.
Collaboration with E. Beyou and P. Chaumont 6 (LMPB, UMR 5627 CNRS)
| | • | Synthesis and grafting of novel functional macroinitiators |
| | • | Study of polymerization kinetics and mechanism. |
| | • | Structure/properties relationship. |
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Anionic-coordinated ring-opening polymerization.
Collaboration with C. Delaite (ICSI, UPR 9069).
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| | • | Grafting of poly(e-caprolactone) and polyethylene oxide « from » and « to » the surface of silica and iron oxide particles. |
| | • | Development of new grafting procedures |
| | • | Process optimization in order to yield high grafting densities. |
| | • | Study of the polymerization mechanism |
| | • | Extension to polymerizations in dispersed media. |
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Polymer/Inorganic Hybrid Colloids
Activities directed by Elodie Bourgeat-Lami. Collaborations with the LAGEP
The objective of this research activity is to introduce inorganic moieties into polymer colloids by combining the free radical polymerization and the sol-gel process. These inorganic entities are mainly metal oxo networks that are incorporated into polymer latexes by copolymerizing vinyl alkoxysilanes and acrylic monomers or styrene. This allows the elaboration of latex particles containing silanol groups both in their internal volume and on their surface. These latexes are self-crosslinkable and can also be used as templates to coat a mineral oxide layer on their surface. Hollow inorganic spheres are obtained after removal of the template by calcination.
Synthesis of SiOH-functionalized polymer latexes in interaction with N. Sheibat-Othman and G. Fevotte (LAGEP, UMR 5007 CNRS) and with the support of Saint Gobain Recherches. | |
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| | • | Analysis of the process parameters allowing a better control of the poly mer microstructure, particles morphology and stability. |
| | • | Advanced modelling of the polymerization kinetics and mechanism. |
| | • | Hybrid nanocapsules synthesis through miniemulsion polymerization by internal phase separation. |
| | • | Additives for sol-gel matrices. |
| | • | Analysis of structure-properties relationships. |
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