Sujet de stage / Master 2 Internship

The aim of this internship is to study the insertion of metal-organic frameworks (MOFs) into PVDF polymer membranes to form nanocomposite materials. This type of MOF/polymer piezoelectric composite has already been studied in the literature, showing good piezoelectric responses. After synthesizing these materials, their intrinsic parameters will be characterized using a wide range of physico-chemical techniques (FTIR, UV-visible absorption spectroscopy, SEM), and their piezoelectric response will be measured to link the experimental results with the theoretical model already established.

PVDF (Polyvinylidene difluoride) has been a piezoelectric polymer of great interest in the recent years. This flexible material can be used as autonomous generators of micro captors, capable of converting mechanical energy from the vibration of the surrounding environment (industry, wind, waterflow, cars, trains) in electrical energy.
Designing new structures of polymer piezogenerators has been a trend for over a decade [1] and the synthesis of new piezopolymer-based systems is in constant development to improve their piezoresponse.
In our team, we are aiming to a better understanding of the parameters that rules the piezoelectricity in such polymers. This knowledge will allow us to directly predict the parameters settings in order to obtain the best conversion of mechanical energy in electrical energy. To this end, a mechanical and physical model was developed on commercial PVDF films (10 micron-thick), taking into account different intrinsic parameters of this material (dielectric permittivity, Young’s modulus, Poisson’s ratio, thickness, piezoelectric coefficient).

As a way to validate and extend this model, experimental measurements are planned on piezopolymer-based membranes. In order to tune the intrinsic parameters of these membranes, we propose a modification of the polymer through two complementary pathways: the nanostructuration (mechanical parameters) and the formation of composites (physical parameters). Our nanostructuration strategy relies on the creation of porous PVDF membranes and then on filling the pores with inorganic nano-objects to form nanocomposite materials. Previous works in the group, on the formation of Ni nanowires in PVDF matrices, already showed an improvement of the piezoresponse by a factor 2.5 [2] and by 3.5 when irradiated with electrons, in addition, to modify the mechanical parameters of the composite [3].

In this internship, we propose the insertion of metal-organic frameworks (MOF) within PVDF membranes to form nanocomposites. Indeed, such MOF/piezopolymer composites have already been studied in the literature and have shown promising piezoresponses [4] [5]. After synthesis, the nanocomposite membranes intrinsic parameters will be characterized using a wide range of physico-chemical techniques and the piezoresponse will be studied as a way to correlate the experimental results with the theoretical model.

He/she will, then, proceed to the inclusion of MOF within the membrane following various incorporation processes (grafting of MOF crystals, self-assembly of the MOF within the membrane, in situ synthesis). Although MOF synthesis is widely described in the literature, our team has only worked with the well-studied [7] [8] UiO-66(Zr) MOF. During this internship, the intern will research from literature and adapt the synthesis of other MOF species with properties of interest (flexibility, piezoelectric response) in accordance to the needs of the project.

For all experimental processes, the intern will have to perform complete characterization of the materials using a wide range of techniques. These techniques are declined in routine techniques (FTIR, UV-visible spectroscopy, SEM) but also analysis on platform equipment (TEM, fluorescence). He/she will be educated in the theoretical principles of all techniques, and will be formed to using the routine analysis equipment (spectrometers, SEM).
Depending on the timeline of the internship, and the advances in the synthesis development, the intern may also be charged to develop tracking techniques (grafting of tracking species such as fluorophores or contrast agents) in order to follow precisely the various steps of the nanostructuration.

In parallel of the experimental synthetic work, measurement of the composite piezoresponse will be performed on the laboratory home-made set-up. These results will be treated in regard to the intrinsic parameters of the materials, which will also be characterized using adapted techniques. A knowledge of the theoretical model will be provided so to help the understanding of the system.

REFERENCES:
[1] Zhang W et al., “Challenges and progress of chemical modification in piezoelectric composites and their applications.” Soft Sci 2023;3:19. http://dx.doi.org/10.20517/ss.2022.33
[2] Melilli, G. et al., “Enhanced Piezoelectric Response in Nanostructured Ni/PVDF Films” J. Mat. Sci. &
Eng. (2018) 7:2
[3]Potrzebowska, N. et al., “Mixing nanostructured Ni/piezoPVDF composite thin films with e-beam
irradiation: A beneficial synergy to piezoelectric response” Mat. Today Com. 28 (2021) 102528
[4] Neetu Prajesh et al., “Flexible Piezoelectric Nanogenerators Based on One-Dimensional Neutral Coordination Network Composites”, ACS Sustainable Chemistry & Engineering 2022 10 (30), 9911-9920 DOI: 10.1021/acssuschemeng.2c02296
[5] Sasmal, A et al., “Two-Dimensional Metal-Organic Framework Incorporated Highly Polar PVDF for Dielectric Energy Storage and Mechanical Energy Harvesting” Nanomaterials 2023, 13, 1098. https://doi.org/10.3390/nano13061098
[6] Cuscito, O. et al., "Nanoporous PVDF membranes with selectively functionalized pores" NIM B 265
(2007) 309-313
[7] Tran My-An, “Hybrid MOF-solid-state nanopores to develop biosensors”, Thesis manuscript, Institut des Materiaux Poreux de Paris, February 2022
[8] X. Liu, «Metal-organic framework UiO-66 membranes,» Chemical Science Engineering, vol. 14, n° %12, pp. 216-232, 2020. https://doi.org/10.1007/s11705-019-1857-5

SKILLS AT THE END OF THE INTERNSHIP:
- Nanostructuration of thin polymer films through physico-chemical and chemical process, and their characterization (spectroscopies)
- Inorganic synthetic routes and, especially, syntheses of metal-organic frameworks
- Understanding of the irradiation processes in polymer-based materials
- Knowledge of the characterization techniques of nanomaterials and of the challenges in characterizing at the nanoscale
- Better understanding of the piezoelectric property of piezopolymers
- Knowledge of the electron microscopy techniques (SEM, TEM) and related analysis (diffraction, EDX)
- Working in a research team, focused on materials physico-chemistry, under the supervision of a PhD student, in an academic pluridisciplinary laboratory.