Structure and dynamics of colloids and polymers

Micellar Dynamics of Block Copolymers for Controlled Drug Delivery

The slow kinetics of block copolymer micelles make their dynamic pathways as crucial as their architecture, particularly for self-assembly and drug delivery. These dynamics are governed by chain insertion/expulsion and micelle fusion/fission, whose equilibrium quantification remains limited. This study employs a fluorescence technique based on the randomization of a hydrophobic pyrene derivative between micelles to quantify fusion and fission at equilibrium. The analysis, carried out on aqueous solutions of PEO-PPO-PEO triblock micelles, shows that fusion and fission rates decrease with increasing hydrophobic block length (NPPO). The study of fission rates using thin-corona and star micelle models suggests that the interfacial tension of the micellar core is the main factor, in line with the predictions of Halperin et al. Furthermore, fusion and fission exhibit the same dependencies on temperature and core length, confirming the dominant role of interfacial tension in their kinetics. These findings are key to optimizing the stability and controlled release of active compounds in drug delivery systems.

Figueroa-Ochoa, E. B., Bravo-Anaya, L. M., Vaca-López, R., Landázuri-Gómez, G., Rosales-Rivera, L. C., Diaz-Vidal, T., ... & Soltero-Martínez, J. F. A. (2023). Structural Behavior of Amphiphilic Triblock Copolymer P104/Water System. Polymers, 15(11), 2551.

Landazuri, G., Fernandez, V. V. A., Soltero, J. F. A., & Rharbi, Y. (2021). Length of the core forming block effect on fusion and fission dynamics at equilibrium in PEO–PPO–PEO triblock copolymer micelles in the spherical regime. Macromolecules, 54(5), 2494-2505.

Rheoalloy, polymers for shock absorption

This work aims to develop new thermoplastic materials capable of absorbing shocks to protect both objects and people. Two main approaches are commonly used to design such materials:
i) the spatial dispersion of forces, which reduces local stress by distributing the impact over a larger surface area, as achieved with rigid protective materials;
ii) shock damping through the temporal dissipation of energy, which reduces the stress peak, as is the case with absorbing foams.
The objective of this study is to exploit the shear-thickening properties of thermoplastics such as PBMDS to design a material that combines both protection mechanisms while maintaining flexibility and, more importantly, long-term durability. To achieve this, composites based on PBMDS, ethylene-vinyl acetate (EVA), and a silica network were developed into micrometer-scale fibrillar structures. Within this architecture, PBMDS and silica form a sub-network embedded in a larger PBMDS/silica/EVA structure, thus optimizing both spatial and temporal dispersion of energy during impact.
Performance tests carried out under conditions close to real use demonstrated efficient shock absorption and enhanced durability. Unlike conventional foams, which quickly lose effectiveness, these materials retained their properties even after more than 700 impacts. Another major advantage lies in their self-healing capability, ensuring reliable and long-lasting protection.

Rharbi Y. et al., Matériau composite apte à absorber les impacts et procédé de fabrication d’un tel matériau. FR3134579A1 (2022)

Patarin, J., Darsy, G., & Rharbi, Y. (2021). U.S. Patent No. 11,091,638. Washington, DC: U.S. Patent and Trademark Office.

Shear/ultrasound-induced structuring

In systems of cellulose nanocrystals (CNC) forming liquid-crystalline phases, carbon black suspensions in mineral oil, oleogels, clay suspensions, or milk proteins, the goal was to elucidate the mechanisms of nanoparticle organization under various external fields (shear, ultrasound, thermal) and to link them with the associated changes in viscosity or viscoelastic moduli. to achieve this, original setups were developed to enable in situ studies of nanoparticle organization under these external fields using x-ray scattering (SAXS) or light scattering (SALS).
 

For CNC suspensions, several advances were obtained regarding flow properties and the mechanisms of shear-induced destructuring and restructuring upon flow cessation. notably, SALS measurements revealed for the first time that in the shear-thinning regime I, large cholesteric domains of the liquid-crystalline phase are progressively fragmented into micrometric tactoids, with their cholesteric axis aligned perpendicularly to the flow direction. Even more originally, SALS showed that upon flow cessation, the relaxation process proceeds via a three-step restructuring mechanism: (i) rapid reassembly of individual CNC into a nematic organization established up to micrometric scales, (ii) slower formation of large, oriented cholesteric domains through a nucleation-and-growth process, and (iii) their isotropic redistribution.

In another study, where we aimed to combine shear flow and ultrasonic wave excitations, it was shown that ultrasonic waves in a confined medium generate a slow motion associated with a phenomenon called Rayleigh acoustic streaming, which induces alignment of cellulose nanocrystals (CNC) with their director oriented along the propagation direction of the acoustic waves.

During the combined action of shear and ultrasound, by adjusting the intensity of the shear gradient and the ultrasonic power simultaneously applied to CNC suspensions, it was possible to control both the direction and the degree of CNC orientation over time. This ability to manipulate CNC orientations along different directions using shear or ultrasonic forces has been used to develop cellulose-based nanocomposites with lamellar or orthotropic structuring for applications in optics, photonics, and tissue engineering.

Although ultrasound is widely used at high power to disperse particles in a suspension or to cut soft materials with vibrating blades, no fundamental study has yet precisely detailed its effect on the mechanics of soft solids. This experimental work, employing in situ ultra-small-angle X-ray scattering (TRUSAXS), demonstrates the possibility of probing, over an uncommon wavevector range at the micrometer scale, the effect of ultrasonic waves on colloidal gels composed of carbon black particles dispersed in mineral oil. It was shown that ultrasound above a critical amplitude induces a complex transient viscoelastic response of the gels within seconds: a reduction of the elastic modulus accompanied by a strong increase in the loss modulus. Through in situ TRUSAXS observations, these macroscopic effects were attributed to the formation of intermittent microcracks within the gel bulk, for which fractal-type organizational changes could be revealed.

Dagès, N., Lidon, P., Jung, G., Pignon, F., Manneville, S., & Gibaud, T. (2021). Mechanics and structure of carbon black gels under high-power ultrasound. Journal of Rheology, 65(3), 477-490.

Gibaud, T., Dagès, N., Lidon, P., Jung, G., Ahouré, L. C., Sztucki, M., ... & Manneville, S. (2020). Rheoacoustic gels: Tuning mechanical and flow properties of colloidal gels with ultrasonic vibrations. Physical Review X, 10(1), 011028.

Pignon, F., Semeraro, E. F., Chèvremont, W., Bodiguel, H., Hengl, N., Karrouch, M., & Sztucki, M. (2021). Orientation of cellulose nanocrystals controlled in perpendicular directions by combined shear flow and ultrasound waves st

Pignon, F., Challamel, M., De Geyer, A., Elchamaa, M., Semeraro, E. F., Hengl, N., ... & Djeridi, H. (2021). Breakdown and buildup mechanisms of cellulose nanocrystal suspensions under shear and upon relaxation probed by SAXS and SALS. Carbohydrate Polymers, 260, 117751.

Membrane Interface Properties

An original characterization of the structural organization of the concentration polarization layer (CPL) during the tangential filtration of anisotropic colloidal suspensions was carried out through the development and implementation of dedicated filtration cells for in situ SAXS measurements. The combination of in situ SAXS, in situ PIV, and ex situ TEM enabled the revelation of the CPL’s organization into oriented, homogeneous lamellar layers across length scales ranging from nanometers to micrometers.
The uniqueness of the structural parameters obtained from in situ SAXS measurements during tangential ultrafiltration allows for a detailed discussion of the potential relationships between filtration parameters (thickness, resistance, and permeation flux) and physical characteristics (volume fraction, orientation, shape, and aspect ratio). This new approach opens perspectives for nanometer-scale characterization methods to better understand fouling phenomena in membrane separation processes and the stability of concentration polarization layers.

Mandin, S., Metilli, L., Karrouch, M., Blésès, D., Lancelon-Pin, C., Sailler, P., ... & Pignon, F. (2024). Multiscale study of the chiral self-assembly of cellulose nanocrystals during the frontal ultrafiltration process. Nanoscale, 16(40), 19100-19115.

Rey, C., Hengl, N., Baup, S., Karrouch, M., Gicquel, E., Dufresne, A., ... & Pignon, F. (2019). Structure, rheological behavior, and in situ local flow fields of cellulose nanocrystal dispersions during cross-flow ultrafiltration. ACS Sustainable Chemistry & Engineering, 7(12), 10679-10689.

Semeraro, E. F., Hengl, N., Karrouch, M., Michot, L. J., Paineau, E., Jean, B., ... & Pignon, F. (2020). Layered organization of anisometric cellulose nanocrystals and beidellite clay particles accumulated near the membrane surface during cross-flow ultrafiltration: In situ SAXS and ex situ SEM/WAXD characterization. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 584, 124030.