Jacopo Vialetto

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Vialetto

First Name

Jacopo

ORCID

0000-0002-4617-4386

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Publications 1 - 10 of 15

Modulating the conformation of microgels by complexation with inorganic nanoparticles
Vialetto, Jacopo; Ramakrishna, Shivaprakash N.; Stock, Sebastian; et al. (2024)
Journal of Colloid and Interface Science
Hypothesis: The complexation of microgels with rigid nanoparticles is an effective way to impart novel properties and functions to the resulting hybrid particles for applications such as in optics, catalysis, or for the stabilization of foams/emulsions. The nanoparticles affect the conformation of the polymer network, both in bulk aqueous environments and when the microgels are adsorbed at a fluid interface, in a non-trivial manner by modulating the microgel size, stiffness and apparent contact angle. Experiments: Here, we provide a detailed investigation, using light scattering, in-situ atomic force microscopy and nano-indentation experiments, of the interaction between poly(N-isopropylacrylamide) microgels and hydrophobized silica nanoparticles after mixing in aqueous suspension to shed light on the network reorganization upon nanoparticle incorporation. Findings: The addition of nanoparticles decreases the microgels' bulk swelling and thermal response. When adsorbed at an oil-water interface, a higher ratio of nanoparticles influences the microgel's stiffness as well as their hydrophobic/hydrophilic character by increasing their effective contact angle, consequently modulating the monolayer response upon interfacial compression. Overall, these results provide fundamental understanding on the complex conformation of hybrid microgels in different environments and give inspiration to design new materials where the combination of a soft polymer network and nanoparticles might result in additional functionalities.
Influence of the interfacial tension on the microstructural and mechanical properties of microgels at fluid interfaces
Vialetto, Jacopo; Nussbaum, Natalie; Bergfreund, Jotam; et al. (2022)
Journal of Colloid and Interface Science
Microgels are soft colloidal particles constituted by cross-linked polymer networks with a high potential for applications. In particular, after adsorption at a fluid interface, interfacial tension provides two-dimensional (2D) confinement for microgel monolayers and drives the reconfiguration of the particles, enabling their deployment in foam and emulsion stabilization and in surface patterning for lithography, sensing and optical materials. However, most studies focus on systems of fluids with a high interfacial tension, e.g. alkanes/ or air/water interfaces, which imparts similar properties to the assembled monolayers. Here, instead, we compare two organic fluid phases, hexane and methyl tert-butyl ether, which have markedly different interfacial tension () values with water and thus tune the deformation of adsorbed microgels. We rationalize how controls the single-particle morphology, which consequently modulates the structural and mechanical response of the monolayers at varying interfacial compression. Specifically, when is low, the microgels are less deformed within the interface plane and their polymer networks can rearrange more easily upon lateral compression, leading to softer monolayers. Selecting interfaces with different surface energy offers an additional control to customize the 2D assembly of soft particles, from the fine-tuning of particle size and interparticle spacing to the tailoring of mechanical properties.
Novel Insights on the Three-dimensional Shape of Microgels at Fluid Interfaces
Vialetto, Jacopo (2022)
Chimia
Mechanically soft colloids (microgels) adsorbed at the interface between two fluids offer superior advantages over hard counterparts for a variety of applications ranging from foams/emulsion stabilization to the assembly of two-dimensional (2D) materials. Particle deformability and compressibility impart additional responses to microgel-laden interfaces that can be controlled on-demand by varying single-particle properties (e.g. crosslinking content and polymer density profile) and/or external parameters (e.g. interfacial compression and tension, temperature, oil polarity). In order to understand how single-particle softness influences the resulting material properties, a detailed quantification of the microgel's 3D conformation when confined at the fluid interface is of utmost importance. This article describes how different methodologies can be used to visualize, and in some case quantify, the conformation of adsorbed microgels, putting particular emphasis on the multiple advantages offered by in situ atomic force microscopy imaging at the fluid interface. The influence of the internal particle architecture, as well as that of temperature, interfacial tension and solubility in the organic phase, will be discussed. Finally, some perspectives on how softness can be exploited to tune the structural and mechanical properties of microgel monolayers will be provided.
Microgels as globular protein model systems
Nussbaum, Natalie; Bergfreund, Jotam; Vialetto, Jacopo; et al. (2022)
Colloids and Surfaces B: Biointerfaces
Understanding globular protein adsorption to fluid interfaces, their interfacial assembly, and structural reorganization is not only important in the food industry, but also in medicine and biology. However, due to their intrinsic structural complexity, a unifying description of these phenomena remains elusive. Herein, we propose N-isopropylacrylamide microgels as a promising model system to isolate different aspects of adsorption, dilatational rheology, and interfacial structure at fluid interfaces with a wide range of interfacial tensions, and compare the results with the ones of globular proteins. In particular, the steady-state spontaneously-adsorbed interfacial pressure of microgels correlates closely to that of globular proteins, following the same power-law behavior as a function of the initial surface tension. However, the dilatational rheology of spontaneously-adsorbed microgel layers is dominated by the presence of a loosely packed polymer corona spread at the interface, and it thus exhibits a similar mechanical response as flexible, unstructured proteins, which are significantly weaker than globular ones. Finally, structurally, microgels reveal a similar spreading and flattening upon adsorption as globular proteins do. In conclusion, microgels offer interesting opportunities to act as powerful model systems to unravel the complex behavior of proteins at fluid interfaces.
Exploiting Additives for Directing the Adsorption and Organization of Colloid Particles at Fluid Interfaces
Vialetto, Jacopo; Anyfantakis, Manos (2021)
Langmuir
The self-assembly of colloids at fluid interfaces is a well-studied research field both for gaining fundamental insights and for material fabrication. The fluid interface allows the confinement of particles in two dimensions and may act as a template for guiding their organization into soft and reconfigurable structures. Additives (e.g., surfactants, salts, and polymers) in the colloidal suspension are routinely used as a practical and effective tool to drive particle adsorption and tune their interfacial organization. However, some phenomena lying at the heart of the accumulation and self-assembly of particles at fluid interfaces remain poorly understood. This Feature Article aims to critically analyze the mechanisms involved in the adsorption and self-organization of micro- and nanoparticles at various fluid interfaces. In particular, we address the role of additives in both promoting the adsorption of particles from the bulk suspension to the fluid interface and in mediating the interactions between interfacial particles. We emphasize how different types of additives play a crucial role in controlling the interactions between suspended particles and the fluid interface as well as the interactions between adsorbed particles, thus dictating the final self-assembled structure. We also critically summarize the main experimental protocols developed for the complete adsorption of particles initially suspended in the bulk. Furthermore, we highlight some special properties (e.g., reconfigurability upon external stimulation and dissipative self-assembly) and the application potential of structures formed by colloid self-organization at fluid interfaces mediated/promoted by additives. We believe our contribution serves both as a practical roadmap to scientists coming from other fields and as a valuable information resource for all researchers interested in this exciting research field.
Effect of curvature on the diffusion of colloidal bananas
Ulbrich, Justin-Aurel; Fernández Rico, Carla; Rost, Brian; et al. (2023)
Physical Review E
Anisotropic colloidal particles exhibit complex dynamics which play a crucial role in their functionality, transport, and phase behavior. In this Letter, we investigate the two-dimensional diffusion of smoothly curved colloidal rods - also known as colloidal bananas - as a function of their opening angle α. We measure the translational and rotational diffusion coefficients of the particles with opening angles ranging from 0∘ (straight rods) to nearly 360∘(closed rings). In particular, we find that the anisotropic diffusion of the particles varies nonmonotonically with their opening angle and that the axis of fastest diffusion switches from the long to the short axis of the particles when α>180∘. We also find that the rotational diffusion coefficient of nearly closed rings is approximately an order of magnitude higher than that of straight rods of the same length. Finally, we show that the experimental results are consistent with slender body theory, indicating that the dynamical behavior of the particles arises primarily from their local drag anisotropy. These results highlight the impact of curvature on the Brownian motion of elongated colloidal particles, which must be taken into account when seeking to understand the behavior of curved colloidal particles.
Effect of Internal Architecture on the Assembly of Soft Particles at Fluid Interfaces
Vialetto, Jacopo; Camerin, Fabrizio; Grillo, Fabio; et al. (2021)
ACS Nano
Monolayers of soft colloidal particles confined at fluid interfaces are at the core of a broad range of technological processes, from the stabilization of responsive foams and emulsions to advanced lithographic techniques. However, establishing a fundamental relation between their internal architecture, which is controlled during synthesis, and their structural and mechanical properties upon interfacial confinement remains an elusive task. To address this open issue, which defines the monolayer's properties, we synthesize core-shell microgels, whose soft core can be chemically degraded in a controlled fashion. This strategy allows us to obtain a series of particles ranging from analogues of standard batch-synthesized microgels to completely hollow ones after total core removal. Combined experimental and numerical results show that our hollow particles have a thin and deformable shell, leading to a temperature-responsive collapse of the internal cavity and a complete flattening after adsorption at a fluid interface. Mechanical characterization shows that a critical degree of core removal is required to obtain soft disk-like particles at an oil-water interface, which present a distinct response to compression. At low packing fractions, the mechanical response of the monolayer is dominated by the outer polymer chains forming a corona surrounding the particles within the interfacial plane, regardless of the presence of a core. By contrast, at high compression, the absence of a core enables the particles to deform in the direction orthogonal to the interface and to be continuously compressed without altering the monolayer structure. These findings show how fine, single-particle architectural control during synthesis can be engineered to determine the interfacial behavior of microgels, enabling one to link particle conformation with the resulting material properties.
Photothermally Reconfigurable Colloidal Crystals at a Fluid Interface, a Generic Approach for Optically Tunable Lattice Properties
Vialetto, Jacopo; Rudiuk, Sergii; Morel, Mathieu; et al. (2021)
Journal of the American Chemical Society
Optically addressable colloidal assembly at fluid interfaces is a highly desired component to generate reconfigurable 2D materials but has rarely been achieved and only with specific interface engineering. Here we describe a generic method to get optically reconfigurable colloidal crystals at the air/water interface and emphasize a new mechanism to convert light into tunable lattice properties. We use light-absorbing anionic particles adsorbed at the air/water interface in the presence of minute amounts of cationic surfactant, which self-assembled into closely packed polycrystalline structures by collectively deforming the surrounding interface. Low-intensity irradiation of these colloidal crystals results in unprecedented control of the interparticle spacing in a preserved crystalline state while, at a higher intensity, cycles of melting/recrystallization with a controllable transition kinetics can be achieved upon successive on/off stimulations. We show that this photoreversible melting originates from an initial thermocapillary stress, expanding the colloidal assembly against the local confinement, and an increase in particles diffusivity imposing the transition kinetics. With this mechanism, local irradiation leads to highly dynamic patterns, including self-healing or self-fed "living" crystals, while multiresponsive assembly is also achieved by controlling particle organization with both light and magnetic stimuli.
Tuning Electrostatic Interactions of Colloidal Particles at Oil-Water Interfaces with Organic Salts
van Baalen, Carolina; Vialetto, Jacopo; Isa, Lucio (2023)
Physical Review Letters
Monolayers of colloidal particles at oil-water interfaces readily crystallize owing to electrostatic repulsion, which is often mediated through the oil. However, little attempts exist to control it using oil-soluble electrolytes. We probe the interactions among charged hydrophobic microspheres confined at a water-hexadecane interface and show that repulsion can be continuously tuned over orders of magnitude upon introducing nanomolar amounts of an organic salt into the oil. Our results are compatible with an associative discharging mechanism of surface groups at the particle-oil interface, similar to the charge regulation observed for charged colloids in nonpolar solvents.
Filter-less separation technique for micronized anthropogenic polymers from artificial seawater
Grob, Lucas; Zeneli, Liridon; Ott, Eileen; et al. (2021)
Environmental Science: Water Research & Technology
Anthropogenic polymer particulates (APPs) are a highly researched topic, from the identification of their different sources to their impact on living organisms, and micronized anthropogenic polymers pose a threat to many ecosystems. Prevalently found are microplastics (MPs) including PMMA. Additionally, micronized rubber powder (MRP), which originates from tire abrasion but is also used as a filler material for various other products, can be found. Due to their small size of less than 100 μm in diameter and relatively low concentrations found in wastewater or seawater, the cleaning from such water sources of MPs or MRP will only be of technological and economic relevance if an efficient, low cost pre-concentration step can be applied before other filtration/separation technologies are applied. Flotation is expected to be such a relevant pre-concentration technique if a high enough affinity of MP/MRP particles to gas bubbles would exist. Accordingly the interaction behavior of MRP and MPs with such gas bubble interfaces was investigated. Based on this, a simple, fast and filter-less technique was developed to remove APPs from seawater by a newly designed process combining flotation and separation in a hydrocyclone type setup. In a first step, we characterized the MRP and found two particle fractions with different gas bubble interaction behaviors. One fraction formed spontaneous air bubble–particle clusters and was prone to attach to the air–water interface. The second fraction sedimented and accumulated at the bottom. Once adsorbed at the interface, the particles remained irreversibly attached. Both MPs and MRP stabilized the foams from air bubbles in artificial seawater as well as in MilliQ water, indicating a preferred localization at the air–water interface. Thus, when treated in the modified hydrocyclone (mHC) based flotation process with controlled swirl flow applied, an extraction ratio of 26% was reached, whereas without bubbles, only 3.7% was reached. The investigated model mHC enabled us to concentrate and separate APPs, in the diameter range d90,3 ≤ 105 μm with particle density very close to water, with the use of their promotion of the air–water interface. These promising results in a first test step for our system encourage further investigation of the applied technology for microplastic-contaminated water.

Publications 1 - 10 of 15

Jacopo Vialetto

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