The next DEADLINE for the submission of beam time requests for the Swiss spallation neutron source SINQ will be:

*********  01 July 2024, midnight, C.E.S.T.   *********

The call is open for the following instruments:*

* PLEASE NOTE:

• The reflectometer AMOR has recently undergone a major upgrade. Therefore new proposals must be discussed in advance (before the submission) with the instrument scientists: jochen.stahn@psi.ch, thomas.geue@psi.ch
• The new small angle scattering facility SANS-LLB that is presently being installed in collaboration with our French partners from LLB might take some friendly users later this year. Please contact the instrument team for further information: urs.gasser@psi.ch
• The Neutron Microscope can be chosen as experimental setup option on POLDI, ICON and BOA.

_____________________________________________________________

PERIOD:
Herewith we call for proposals for the beam time period II-24 between 16 October - 23 December 2024. Another proposal deadline is envisaged for 15 November 2024 to cover the beam time period  May - August 2025.

_____________________________________________________________
PROPOSAL-SUBMISSION:
New users are kindly asked to contact the instrument scientists before submitting a proposal to discuss instrumental options and reasonable beam time requests. Please make use of the option to link related previous proposals with their experimental reports to the new one. A proper mention of previous results will provide a certain 'bonus' during the evaluation process.
 

Guidelines for the proposal submission and further useful information can be found on the SINQ webpages:
http://www.psi.ch/sinq/access-to-sinq
http://www.psi.ch/sinq/call-for-proposals
http://www.psi.ch/sinq/guidelines
Further detailed information about the SINQ instruments can be obtained here:
http://www.psi.ch/sinq/instrumentation

The feasibility of complex experiments should always be discussed in advance with the instrument and sample environment scientists.

_____________________________________________________________
DIGITAL USER OFFICE, DUO:
Proposals can only be submitted electronically via the PSI Digital User Office 'DUO': https://duo.psi.ch

_____________________________________________________________
CONTACT ADDRESS:
Paul Scherrer Institute
User Office
CH-5232 Villigen - PSI              
Switzerland    

Phone :        +41-56-310-4666
e-mail :        useroffice@psi.ch

Un appel à projet collaboratif (APiCone) est ouvert afin d’impliquer dans le projet ICONE des équipes françaises ayant des expertises reconnues en instrumentation et/ou analyse de données.

Il est proposé des financements de doctorat ou de post-doctorat – avec une priorité donnée pour les projets co-financés - dans les grands domaines scientifiques utilisant les techniques neutroniques (physique de la matière condensée, science des matériaux, chimie, biologie et santé, matière molle, patrimoine, physique nucléaire et des particules, applications industrielles, etc.).

Clôture de l’appel jeudi 12 septembre 2024.

• Date limite d’envoi des lettres d’intention : mercredi 17 juillet 2024
• Date limite du dépôt des projets : jeudi 12 septembre 2024
• Lettres d’intention et dossiers des projets à envoyer à apicone@icone-neutron.fr
• Démarrage des projets : automne 2024.

Tout sur :

https://iramis.cea.fr/llb/Phocea/Vie_des_labos/Ast/ast_sstechnique.php?id_ast=2755&voir=3656

Next deadline for standard proposal submission : 16 September 2024

Proposal submission guidelines - Proposal writing hints - Detailed information

If you are submitting a proposal for the first time please consult our New User page and contact an ILL scientist or the User Office.

Proposals must be submitted via the Electronic Proposal Submission (EPS) system on our User Club. Log with your personal username and password.
In case of problems, support from the User Club team (club@ill.eu).
Please allow sufficient time for any unforeseen computing hitches.

Easy Access requests for short measurements and DDT requests for full experiments to be performed as soon as possible can be submitted at any time.

Beamtime allocation policy: "two-thirds rule"
Proposals from non-member country proposers will only be guaranteed a chance of acceptance if they are part of a collaboration with at least two-thirds of the proposers coming from one of the Associate or Scientific Member Countries of the ILL. ILL scientists listed as co-proposers are not taken into account in the calculation. Not satisfying this rule will not be a blocking condition for proposal submissions: proposals not fulfilling the 2/3 can still be allocated time, but then from Directors discretion time. These proposals should still be reviewed by the subcommittees and they have to be truly world class and addressing hot-topics (judged by the subcommittees and the science director).

Panel meetings: 13-14 November 2024 (Wednesday, Thursday)
Scheduling period: From April 2025
Next deadline: 15 February 2025

News on instruments:

• Commissioning of the LLB CRG instrument SAM started this spring. It will be available as the 4th ILL's SANS instrument.
• D007, D11, PANTHER and SHARPER (the new upgraded SHARP instrument)  will be again available from this round.
• D4 and IN1-Lagrange share the same beamtube, therefore they are operated for 50% of the total available beamtime.
• D19 instrument is not available to the user programme anymore.
• D3, D9 and IN8 will operate for 50% of the time.

Be aware of these new requirements when writing your proposal:

1. Supervisors of PhD students who submit proposals must demonstrate their involvement in the project by being listed as proposers and actively participating in the experiment.
2. In your scientific explanation, it would be helpful to add a brief section outlining the roles and responsibilities of each person participating in the proposal or experiment.
3. We remind you that - for multi-instruments proposals - you should  make sure that the scientific case, experimental plan and time requested is sufficiently detailed for each instrument. If the available space is not enough, consider submitting different proposals for different instruments.

To ensure the best possible outcomes, you are strongly encouraged to reach out to our facility scientist before finalising and submitting your proposal. Engaging with our facility scientist can significantly enhance the clarity and feasibility of your project, especially in cases where technically challenging or complex set-ups are involved. This collaboration will not only refine your proposal but also increase its chances of success.

Giovanna CICOGNANI
Scientific coordinator
Institut Max von Laue - Paul Langevin (ILL)
71, avenue des Martyrs - CS 20156, 38042 Grenoble cedex 9 - France
+33 (0)4 76 20 71 79
cicognani@ill.eu
For urgent matters: communication@ill.eu

Porquerolles

Organisées par la SFN, les JDN2024 se dérouleront du lundi 30 septembre après-midi au jeudi 3 octobre midi (déjeuner inclus) . L’accueil des participants débutera le lundi vers 14h30.

Merci de noter que dans le cadre des JDN2024 le Village Club Igesa nous accueille du 30 septembre au 3 octobre. Si vous souhaitez arriver la veille ou poursuivre votre séjour sur l’île de Porquerolles, il vous revient de trouver individuellement un hébergement.

La remise du prix de thèse SFN aura lieu pendant les JDN.

Glaive, AS ; Coeur, C ; Guigner, JM ; Amiel, C ; Volet, G The amphiphilic heterograft copolymers bearing biocompatible/biodegradable grafts [poly-(2-methyl-2-oxazoline-co-2-pentyl-2-oxazoline)-g-poly-(D-L-lactic acid)/poly-(2-ethyl-2-oxazoline)] were synthesized successfully by the combination of cationic ring-opening polymerization and click chemistry via the <"grafting to"> approach. The challenge of this synthesis was to graft together hydrophobic and hydrophilic chains on a hydrophilic platform based on PMeOx. The efficiency of grafting depends on the chemical nature of the grafts and of the length of the macromolecular chains. The self-assembly of these polymers in aqueous media was investigated by DLS, cryo-TEM, and SANS. The results demonstrated that different morphologies were obtained from nanospheres and vesicles to filaments depending on the hydrophilic weight ratio in the heterograft copolymer varying from 0.38 until 0.84. As poly-(2-ethyl-2-oxazoline) is known to be thermoresponsive, the influence of temperature rise on the nanoassembly stability was studied in water and in a physiological medium. SANS and DLS measurements during a temperature ramp allowed to show that nanoassemblies start to self-assemble in "raspberry like" primary structures at 50 degrees C, and these structures grow and get denser as the temperature is increased further. These amphiphilic heterograft copolymers may include hydrophobic drugs and should find important applications for biomedical applications which require stealth properties. https://doi.org/10.1021/acs.langmuir.3c02772

Schemes of the various nanostructures that can be formed

Influence of Dy3+ environment on magnetic anisotropy and magnetocaloric effect in Dy3⁢B2⁢C3⁢O12 (B=In, Sc, Te ; C=Ga, Al, Li) garnets F. Damay, S. Petit, D. Sheptyakov, C. V. Colin, E. Suard, S. Rols, J. Embs, U. Stuhr, D. Bounoua, O. Demortier, and C. Decorse, Phys. Rev. B 109 (2024) 014419   In the framework of the general phase diagram published recently for a pseudospin S = 1/2 on a hyperkagome network [Kibalin et al., Phys. Rev. Res. 2, 033509 (2020)], four Dy3B2C3O12 garnets with different species on the B and C sites, namely, Dy3Sc2Al3O12 (DyScAl), Dy3Te2Li3O12 (DyTeLi), Dy3Sc2Ga3O12 (DyScGa), and Dy3In2Ga3O12 (DyInGa), have been studied by neutron powder diffraction and inelastic neutron scattering, to investigate the impact of B and C substitutions on the Dy3+ dodecahedral oxygen environment and crystal field, and thus on the Dy3+ spin magnetic anisotropy. In the four compounds, the magnetic ground state is a multiaxis antiferromagnetic order similar to that of Dy3Al5O12, characterized by an ordered moment close to the theoretical maximum, similar to 6 mu B. The gap between the ground state and the first excited crystal electric field level varies from similar to 3.2 meV (DyInGa) up to 11.2 meV (DyScAl), confirming the rather strong Ising character of the Dy3+ moment in those garnets. For a better understanding of the impact of the distortion of the oxygen environment on the Dy3+ magnetic anisotropy, point-charge calculations were then performed, mapping a magnetic anisotropy diagram versus a wide range of distortions. Results show that Ising-like behaviors mostly predominate, associated with large gx, gy, or gz Lande values, whose stable area is determined by the shape of the DyO8 cage. Magnetic entropy calculations confirm that the magnetocaloric effect increases sharply near those boundaries and validate the use of dysprosium garnets for low temperature, low magnetic field adiabatic demagnetization refrigeration cryostats.

Variations with the surrounding oxygen (xO, yO) coordinates of the energy (in meV) of the first CEF excitation for a Dy3+ in its dodecahedron

Salah Bouazizi, Salah Nasr & Marie-Claire Bellissent-Funel MD simulation and analysis of the pair correlation functions, self-diffusion coefficients and orientational correlation times in aqueous KCl solutions at different temperatures and concentrations, S. Bouazizi, S. Nasr and M.-C. Bellissent-Funel, J Solution Chem (2024) https://doi.org/10.1007/s10953-024-01366-8 Abstract : In this study, we investigate some structural and dynamical properties of aqueous KCl solutions at different temperatures and concentrations. We study a 1.6 mol·kg–1 aqueous KCl solution at five temperatures and five concentrations at ambient conditions only. Molecular dynamics simulations with the flexible SPC water model were conducted to characterize all partial pair correlation functions, the velocities auto-correlation ones, and the dielectric constants. The analysis of the water pair correlation functions shows a disruption of the H-bond network and a decrease of the oxygen-hydrogen coordination number as temperature or salt concentration increases. The increase of each parameter favors the exchange of molecules between the first and the second hydration shells. Ions pair correlation functions show principally that the fraction of K+-Cl− contact ion pairs increases and that of separated ion pairs decreases with increasing temperature or concentration. For all particles, the values of the calculated self-diffusion coefficients rise with temperature and fall with salt concentration. The self-diffusion coefficients of K+ and Cl− tend to towards each other at high concentration. Temperature or salt concentration causes a drop in the dielectric constant. For all studied temperatures or salt concentrations, the calculated ratio of the orientational correlation times τ1/τ2 for the OH vector indicates that the motion of water molecules can be accounted for by an angular jumps model.

The peak of potassium–oxygen pair correlation functions of aqueous KCl solutions at different temperatures

Nina Královič-Kanjaková, Ali Asi Shirazi, Lukáš Hubčík, Mária Klacsová, Atoosa Keshavarzi, Juan Carlos Martínez, Sophie Combet, José Teixeira, and Daniela Uhríková The use of an exogenous pulmonary surfactant (EPS) to deliver other relevant drugs to the lungs is a promising strategy for combined therapy. We evaluated the interaction of polymyxin B (PxB) with a clinically used EPS, the poractant alfa Curosurf (PSUR). The effect of PxB on the protein-free model system (MS) composed of four phospholipids (diC16:0PC/16:0–18:1PC/16:0–18:2PC/16:0–18:1PG) was examined in parallel to distinguish the specificity of the composition of PSUR. We used several experimental techniques (differential scanning calorimetry, small- and wide-angle X-ray scattering, small-angle neutron scattering, fluorescence spectroscopy, and electrophoretic light scattering) to characterize the binding of PxB to both EPS. Electrostatic interactions PxB–EPS are dominant. The results obtained support the concept of cationic PxB molecules lying on the surface of the PSUR bilayer, strengthening the multilamellar structure of PSUR as derived from SAXS and SANS. A protein-free MS mimics a natural EPS well but was found to be less resistant to penetration of PxB into the lipid bilayer. PxB does not affect the gel-to-fluid phase transition temperature, Tm, of PSUR, while Tm increased by ∼+ 2 °C in MS. The decrease of the thickness of the lipid bilayer (dL) of PSUR upon PxB binding is negligible. The hydrophobic tail of the PxB molecule does not penetrate the bilayer as derived from SANS data analysis and changes in lateral pressure monitored by excimer fluorescence at two depths of the hydrophobic region of the bilayer. Changes in dL of protein-free MS show a biphasic dependence on the adsorbed amount of PxB with a minimum close to the point of electroneutrality of the mixture. Our results do not discourage the concept of a combined treatment with PxB-enriched Curosurf. However, the amount of PxB must be carefully assessed (less than 5 wt % relative to the mass of the surfactant) to avoid inversion of the surface charge of the membrane https://doi.org/10.1021/acs.langmuir.3c03746

Shematic view of interaction of polymyxinB (PxB) with the poractant alfa Curosurf (PSUR)

Universality of q=1/2 orbital magnetism in the pseudogap phase of the high-Tc superconductor YBa2Cu3O6+x Dalila Bounoua, Yvan Sidis, Martin Boehm, Paul Steffens, Toshinao Loew, Lin Shan Guo, Jun Qian, Xin Yao, and Philippe Bourges, Phys. Rev. B 108 (2023) 214408. Several decades of debate have centered around the nature of the enigmatic pseudogap state in high-temperature superconducting copper oxides. Recently, we reported polarized neutron diffraction measurements that suggested the existence of a magnetic texture bound to the pseudogap phase [Bounoua et al. Commun. Phys. 5, 268 (2022)]. Such a magnetic texture is likely to involve the spontaneous appearance of loop currents within the CuO2 unit cells, which give birth to complex correlated patterns. In the underdoped YBa2Cu3O6.6, the magnetic structure factor of such an orbital magnetic texture gives rise to two distinct magnetic responses at q=0 and q=1/2. As this pattern alters the lattice translation invariance, such a state of matter could contribute to an instability of the Fermi surface. Here, we report polarized neutron scattering measurements on a nearly optimally doped high-quality single crystal of YBa2Cu3O6.9 that exhibits the same q=1/2 magnetism and a weakly overdoped YBa2Cu3O7 sample where this signal is no longer sizable. The in-plane and out-of-plane magnetic neutron scattering intensities in YBa2Cu3O6.9 (at q=1/2) and YBa2Cu3O6.85 (at q=0), reported previously, display the same temperature-dependent hallmarks. The magnitudes of both q=0 and q=1/2 magnetic signals further exhibit the same trends upon doping in YBa2Cu3O6+x, confirming that they are likely intertwined. https://doi.org/10.1103/PhysRevB.108.214408

Coaligned detwinned single crystals of YBCO7 used for the polarized neutron study

Explorer la matière nécessite des faisceaux sondes de lumière (photons lasers, rayons X…), de neutrons, d'électrons, voire d'atomes, de molécules ou d'ions. Chaque type de faisceau interagit de façon très spécifique avec la matière : les rayons X sont fortement diffusés par les éléments lourds, tandis que les neutrons présentent le grand avantage d'être fortement diffusés par les éléments légers et sensibles au magnétisme. Les faisceaux de neutrons sont ainsi devenus un outil analytique important des scientifiques dans les domaines aussi divers que la physique et la chimie de la matière condensée, la science des matériaux et de la matière molle, les sciences de la vie ou encore la géoscience. Ils sont aussi utilisés comme sonde dans de nombreux domaines industriels, l’identification de matériaux, la radiographie, la validation de résistance aux rayonnements, la qualification d’assemblages métallurgiques…  

Les techniques de diffusion neutronique permettent de sonder à des échelles extrêmement larges, de taille, jusqu’à des dimensions sub-atomiques, et d’énergies, jusqu’au nano electron-volt (voir Figure).   Les larges échelles de taille et de temps couvertes par les études par des faisceaux de neutrons.   Cependant, les sources de neutrons sont peu lumineuses. Lorsque des flux importants de neutrons sont nécessaires, il faut actuellement recourir à des infrastructures de grandes tailles tels que des réacteurs de recherche ou des sources à spallation. Ces installations produisent de très grandes quantités de neutrons (jusqu’à 1018 neutrons par seconde) dont seule une fraction infinitésimale est effectivement utilisée pour générer les faisceaux utiles. Cela est lié au fait que les neutrons sont produits au sein du combustible ou de la cible dans des volumes importants et émis dans des directions aléatoires.

Depuis quelques années, plusieurs instituts dont l’IRAMIS, modélisent les performances ultimes d’une source de neutrons dont on pourrait réduire la taille à un volume de l’ordre de 1 litre (partie cible + modérateur). Ce volume est à comparer à un volume typique de l’ordre du mètre cube dans un réacteur de recherche. La réduction du volume source permettrait de largement augmenter la brillance des sources de neutrons. Les modélisations numériques de ces sources compactes pointent vers des performances potentielles équivalentes à celle d’un réacteur de recherche ou d’une source à spallation de puissance moyenne. Ces travaux permettent d’envisager la construction d’une 3ème génération de sources de neutrons (après les réacteurs de recherche dans les années 1950 et les sources à spallation dans les années 1970), que l'on dénomme "HiCANS", pour "High-Current Accelerator – driven Neutrons Sources". Ces sources utiliseraient les développements récents dans le domaine des accélérateurs de protons à basse énergie (quelques dizaines de MeV) qui peuvent maintenant opérer à des courants de protons de l’ordre de 100 m. Par diffusion sur une cible, ces protons sont partiellement convertis en neutrons, qui sont ensuite modérés en énergie (i.e. leur longueur d'onde) selon l'expérience souhaitée. A ces avancées s'ajoutent d'autres développements sur la meilleure compréhension des phénomènes de modération des neutrons et les nouvelles techniques d’instrumentation neutronique qui maximisent l’utilisation des neutrons.

Exemple d’une installation de diffusion neutronique de type HiCANS. La surface de l’installation est inférieure à celle d’un terrain de football avec un accélérateur d’une longueur de 20 à 30 mètres.   Ces sources ne visent pas à obtenir des performances ultimes mais à construire des sources "accessibles" à l’échelle d’un pays, et qui ne recourent ni à la construction de réacteurs nucléaires coûteux, ni à la construction d’accélérateurs à haute énergie. Cette proposition technologique a conduit à des réflexions dans différentes instances [1]. La DRF a engagé un programme de R&D sur le sujet depuis plusieurs années, en particulier autour de la plate-forme PHI-Neutrons [2].  Ces travaux ont conduit à la rédaction d’un livre blanc sur la proposition de construction d’une nouvelle source de diffusion neutronique française, ICONE, qui utiliserait la technologie des HiCANS [3]. Le CEA et le CNRS ont lancé cette année la rédaction d’un Avant-Projet Détaillé autour de ce projet. Cette installation aurait pour vocation de servir la communauté française des utilisateurs des techniques neutroniques, forte d’un millier de chercheurs environ répartis sur plus de 300 laboratoires français.

Références : [1] Low-energy accelerator-driven neutrons sources (LENS Report, 2020) ; Compact Accelerator-based Neutron Sources (IAEA TECDOC 1981, 2021) [2] Les développements instrumentaux peuvent être suivis sur "ICONE : an accelerator-driven neutron source" et "The IPHI-Neutron platform". [3] ICONE, une nouvelle source de diffusion neutronique française (2023) Contact CEA-IRAMIS : Frédéric OTT (LLB/INFRA) Ce travail est réalisé en collaboration avec l’IRFU (contact Jérôme Schwindling IRFU/DACM) et le Forschungs Zentrum Jülich (Contact : Paul Zakalek, FZJ, Jülich Center for Neutron Scattering).

On De Gennes narrowing of fluids confined at the molecular scale in nanoporous materials Wanda Kellouai, Jean-Louis Barrat, Patrick Judeinstein, Marie Plazanet, Benoit Coasne, J. Chem. Phys. 160, 024113 (2024). Beyond well-documented confinement and surface effects arising from the large internal surface and severely confining porosity of nanoporous hosts, the transport of nanoconfined fluids remains puzzling in many aspects. With striking examples such as memory, i.e., non-viscous effects, intermittent dynamics, and surface barriers, the dynamics of fluids in nanoconfinement challenge classical formalisms (e.g., random walk, viscous/advective transport)—especially for molecular pore sizes. In this context, while molecular frameworks such as intermittent Brownian motion, free volume theory, and surface diffusion are available to describe the self-diffusion of a molecularly confined fluid, a microscopic theory for collective diffusion (i.e., permeability), which characterizes the flow induced by a thermodynamic gradient, is lacking. Here, to fill this knowledge gap, we invoke the concept of “De Gennes narrowing,” which relates the wavevector-dependent collective diffusivity D0(q) to the fluid structure factor S(q). First, using molecular simulation for a simple yet representative fluid confined in a prototypical solid (zeolite), we unravel an essential coupling between the wavevector-dependent collective diffusivity and the structural ordering imposed on the fluid by the crystalline nanoporous host. Second, despite this complex interplay with marked Bragg peaks in the fluid structure, the fluid collective dynamics is shown to be accurately described through De Gennes narrowing. Moreover, in contrast to the bulk fluid, the departure from De Gennes narrowing for the confined fluid in the macroscopic limit remains small as the fluid/solid interactions in severe confinement screen collective effects and, hence, weaken the wavevector dependence of collective transport.

Fluid adsorption and structure in a nanoporous material.

M. Warburton, J.M. Ablett, J.-P. Rueff, P. Baroni, L. Paolasini, L. Noirez We examine the influence at room temperature of the deposit of a water layer on the phonon dynamics of a solid. It is shown that the water wetting at the surface of an Alumina monocrystal has deep effects on acoustic phonons, propagating over several hundred µm distance and taking place on a relatively long time scale. The effect of the wetting at the boundary is two-fold: a hardening of both transverse and longitudinal acoustic phonons is observed as well as a relaxation of internal stresses. These acoustic phonon energy changes were observed by inelastic X-ray scattering up to 40 meV energy loss, allowing us to probe the solid at different depths from the surface. https://doi.org/10.1016/j.molliq.2023.123342

Dispersion curves of dry (black full lines) and wet samples probed down to 150 µm depth (dotted lines) in α-Al2O3 in the Gamma-Z direction.

V. Balédent, A. Vaunat, S. Petit, L. Nataf, S. Chattopadhyay, S. Raymond, and P. Foury-Leylekian In this paper, we investigate the physical properties of the type-II multiferroic GdMn2O5 material by means of neutron scattering, electric polarization, and magnetization measurements. A complex (T,H) phase diagram shows up, with especially a field-induced magnetic transition around 11 T at low temperature. The high-field phase is accompanied by an additional electric polarization along both the a and b directions, as authorized by symmetry, but never observed experimentally up to now. While the magnetic properties recover their initial states after driving the field back to zero, the polarization along a shows a significant increase. This behavior is observed for all directions of the magnetic field. It constitutes a novel and striking manifestation of the magnetoelectric coupling, resulting in the establishment of a new ground state at zero magnetic field. https://dx.doi.org/10.1103/PhysRevB.108.104419

Temperature-magnetic field phase diagram deduced from the neutron diffraction measurements. See full paper for details.

Anne-Charlotte Le Gulluche, Guylaine Ducouret, Ludovic Olanier, Annie Brûlet, Olivier Sanseau, Paul Sotta, and Alba Marcellan Model hybrid hydrogels reinforced by silica nanoparticles were designed by polymerizing and cross-linking the gels in situ. The polymer–particle interactions were tuned by using either poly(dimethylacrylamide) (PDMA), which adsorbs on silica, or poly(acrylamide) (PAAm), which does not. Besides, the dispersion state of silica nanoparticles was tuned from well-dispersed to aggregated by changing the pH from 9, which ensures repulsive interactions between nanoparticles and good dispersion state, to about 6, which affects the surface chemistry of silica and promotes aggregation. The dispersion states were characterized by small-angle X-ray scattering (SAXS). The mechanical behavior of hybrid gels with aggregated nanoparticles is markedly different from those where silica is well-dispersed within the matrix. PDMA-based hybrid gels display pronounced nonlinear behavior, somehow similar to those observed in filled elastomers. The nonlinearities are even more pronounced in gels with aggregated particles, with strong strain stiffening along with large dissipation. For those samples, reinforcement can be attributed to the combination of both reversible interactions between PDMA and silica nanoparticles, which provide strain stiffening and recovery, and the response of the silica network. Recovery processes observed in hybrid gels with dispersed particles are preserved when silica particles are aggregated, but the characteristic time needed to fully recover the mechanical response is extended from a few seconds to several hours. In PAAm-based hybrid gels with aggregated silica nanoparticles, no recovery processes are observed. This implies that the properties, namely, the very high linear tensile modulus and high dissipated energy, are driven by the rigid network formed by nanoparticle aggregation, which provides high dissipative capabilities, especially when compared to PAAm-based hybrid gels with dispersed silica, that remain soft and fragile. These gels exhibit a quite inhomogeneous structure, with permanent damage under elongation. The nonlinear dynamical behavior of hybrid gels was investigated by large amplitude oscillatory shear (LAOS) experiments. While unfilled gels show no nonlinearity up to very large strain amplitude, marked nonlinear effects combining a drop in modulus (similar to the Payne effect) and strain stiffening for increasing strain amplitude are observed in PDMA-based hybrid gels, certainly due to polymer adsorption onto nanoparticles. PAAm-based hybrid gels also show nonlinearity, with a drop in modulus for increasing strain but no strain stiffening, indicating that the presence of fillers alone can induce nonlinearity in the absence of strong, reversible polymer–particle interactions. PAAm-based hybrid gels with aggregated silica show very high stiffness and high dissipative properties at the expense of stretchability, though. Also, the structure seems to be permanently damaged under stress, revealing the importance of silica–polymer interactions for permanent mechanical reinforcement. Altogether, the analysis of the nonlinear behavior indicates the importance of combining dynamic adsorption of polymer chains on silica nanoparticles with mechanical reinforcement provided by the silica network. https://dx.doi.org/10.1021/acs.macromol.3c01440    

Schematics of a PDMA hybrid hydrogel with dispersed silica nanoparticles (denoted NC_D) combining covalent cross-links (orange dots) and physical interactions (layer of adsorbed polymer chains at the surface of nanoparticles, schematized by dashed circles, not to scale)