| 1. |
- Azari, Arash, et al.
(author)
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Directed Self-Assembly of Polarizable Ellipsoids in an External Electric Field
- 2017
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 33:48, s. 13834-13840
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Journal article (peer-reviewed)abstract
- The interplay between shape anisotropy and directed long-range interactions enables the self-assembly of complex colloidal structures. As a recent highlight, ellipsoidal particles polarized in an external electric field were observed to associate into well-defined tubular structures. In this study, we systematically investigate such directed self-assembly using Monte Carlo simulations of a two-point-charge model of polarizable prolate ellipsoids. In spite of its simplicity and computational efficiency, we demonstrate that the model is capable of capturing the complex structures observed in experiments on ellipsoidal colloids at low volume fractions. We show that, at sufficiently high electric field strength, the anisotropy in shape and electrostatic interactions causes a transition from three-dimensional crystal structures observed at low aspect ratios to two-dimensional sheets and tubes at higher aspect ratios. Our work thus illustrates the rich self-assembly behavior accessible when exploiting the interplay between competing long- and short-range anisotropic interactions in colloidal systems.
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| 2. |
- Cautela, Jacopo, et al.
(author)
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Supracolloidal Atomium
- 2020
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 14:11, s. 15748-15756
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Journal article (peer-reviewed)abstract
- Nature suggests that complex materials result from a hierarchical organization of matter at different length scales. At the nano- and micrometer scale, macromolecules and supramolecular aggregates spontaneously assemble into supracolloidal structures whose complexity is given by the coexistence of various colloidal entities and the specific interactions between them. Here, we demonstrate how such control can be implemented by engineering specially customized bile salt derivative-based supramolecular tubules that exhibit a highly specific interaction with polymeric microgel spheres at their extremities thanks to their scroll-like structure. This design allows for hierarchical supracolloidal self-assembly of microgels and supramolecular scrolls into a regular framework of “nodes” and “linkers”. The supramolecular assembly into scrolls can be triggered by pH and temperature, thereby providing the whole supracolloidal system with interesting stimuli-responsive properties. A colloidal smart assembly is embodied with features of center-linker frameworks as those found in molecular metal–organic frameworks and in structures engineered at human scale, masterfully represented by the Atomium in Bruxelles.
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| 3. |
- Crassous, Jerome J., et al.
(author)
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Asymmetric self-assembly of oppositely charged composite microgels and gold nanoparticles
- 2012
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 8:5, s. 1648-1656
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Journal article (peer-reviewed)abstract
- The electrostatically driven self-assembly of oppositely charged gold nanoparticles (Au NPs) and polystyrene/poly(N-isopropylacrylamide) (PS/PNIPAm) core-shell microgels (CSMs) has been investigated. The co-assembly was accomplished by addition of smaller Au NPs to CSMs in dilute conditions up to a number ratio of about 1 : 1, when the suspension is destabilized. A combination of different techniques (i.e. turbidimetric titration, electrophoretic mobility, UV-visible spectroscopy, dynamic light scattering and microscopy techniques) were used to investigate the association between the two particles and the stability of the different mixtures. Hereby we demonstrate that the size ratio between the two particles (about 4 to 1) and the asymmetric character of the association result in the formation of electrostatic hybrid complexes, analogous to dipolar colloidal molecules, which further rearrange into finite sized clusters for number ratios N(AuNPs)/N(CSMs) < 1.
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| 4. |
- Hazra, Nabanita, et al.
(author)
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Structure of Responsive Microgels down to Ultralow Cross-Linkings
- 2024
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In: Macromolecules. - 0024-9297. ; 57:1, s. 339-355
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Journal article (peer-reviewed)abstract
- Although microgels have been widely used as model systems for soft colloids, their properties are still far from being completely understood. This stems from their heterogeneous structure strongly differing from that of an idealized polymeric network. Indeed, microgels synthesized by conventional precipitation polymerization exhibit not only a fuzzy structure with respect to the difference of reactivity between monomers and cross-linker molecules but also static heterogeneities related to the distribution in the length of the chains constituting their network. These features can be reproduced in computer simulations using the so-called in silico synthesis. Hereby, a designing force acting on the cross-linkers during the in silico synthesis allows us to finely adjust the radial density distribution and, thus, to reproduce both the fuzziness and local heterogeneities present in real microgel systems. In this study, poly(N-isopropylacrylamide) (PNIPAM) microgels were synthesized with different degrees of cross-linking ccross down to cross-linker free conditions corresponding to so-called ultralow cross-linked microgels (ULC microgels). The experimental characterization was accompanied by numerical simulations at different ccross with the same designing force, which is found to be independent of the cross-linker concentration, as well as the size of the microgels. For the ULC microgels, it was found that no designing force is needed, but the number density of the network is much smaller. The number of effective cross-linkers in this case is found to be ∼0.1%. The form factors of all microgels were measured at different temperatures across their volume phase transition with both static light scattering and small-angle X-ray scattering, favorably comparing them to the simulated ones. Furthermore, the swelling behavior was experimentally determined by dynamic light scattering and viscosimetry and also compared to the simulated results. Finally, experimental and simulated results indicate that the cross-linking dependence of the swelling is well-described by theoretical predictions for the isotropic swelling of an ideal network despite the highly heterogeneous character of real microgels.
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| 5. |
- Liu, Xiaoyan, et al.
(author)
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Wrapping anisotropic microgel particles in lipid membranes : Effects of particle shape and membrane rigidity
- 2023
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In: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424. ; 120:30
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Journal article (peer-reviewed)abstract
- Cellular engulfment and uptake of macromolecular assemblies or nanoparticles via endocytosis can be associated to both healthy and disease-related biological processes as well as delivery of drug nanoparticles and potential nanotoxicity of pollutants. Depending on the physical and chemical properties of the system, the adsorbed particles may remain at the membrane surface, become wrapped by the membrane, or translocate across the membrane through an endocytosis-like process. In this paper, we address the question of how the wrapping of colloidal particles by lipid membranes can be controlled by the shape of the particles, the particle–membrane adhesion energy, the membrane phase behavior, and the membrane-bending rigidity. We use a model system composed of soft core–shell microgel particles with spherical and ellipsoidal shapes, together with phospholipid membranes with varying composition. Confocal microscopy data clearly demonstrate how tuning of these basic properties of particles and membranes can be used to direct wrapping and membrane deformation and the organization of the particles at the membrane. The deep-wrapped states are more favorable for ellipsoidal than for spherical microgel particles of similar volume. Theoretical calculations for fixed adhesion strength predict the opposite behavior-wrapping becomes more difficult with increasing aspect ratio. The comparison with the experiments implies that the microgel adhesion strength must increase with increasing particle stretching. Considering the versatility offered by microgels systems to be synthesized with different shapes, functionalizations, and mechanical properties, the present findings further inspire future studies involving nanoparticle–membrane interactions relevant for the design of novel biomaterials and therapeutic applications.
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| 6. |
- Meijer, Janne Mieke, et al.
(author)
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Phase Behavior of Bowl-Shaped Colloids : Order and Dynamics in Plastic Crystals and Glasses
- 2018
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In: Small. - : Wiley. - 1613-6810. ; 14:46
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Journal article (peer-reviewed)abstract
- Charged fluorescent bowl-shaped colloids consisting of a polystyrene core surrounded by a poly(N-isopropylmethacrylamide) shell are obtained by nanoengineering spherical composite microgels. The phase diagram of these soft bowl-shaped colloids interacting through long-range Yukawa-type interactions is investigated using confocal laser scanning microscopy. The bowl-shaped structure leads to marked differences in phase-behavior compared to their spherical counterpart. With increasing number density, a transition from a fluid to a plastic crystal phase, with freely rotating particles, followed by a glass-like state is observed. It is found that the anisotropic bowl shape frustrates crystallization and slows down crystallization kinetics and causes the glass-like transition to shift to a significantly lower volume fraction than for the spheres. Quantitative analysis of the positional and orientational order demonstrates that the plastic crystal phase exhibits quasi-long range translational order and orientational disorder, while in the disordered glass-like phase the long-range translational order vanishes and short-range rotational order appears, dictated by the specific bowl shape. It is further shown that the different structural transitions are characterized by decoupling of the translational and orientational dynamics.
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| 7. |
- Månsson, Linda K., et al.
(author)
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A microgel-Pickering emulsion route to colloidal molecules with temperature-tunable interaction sites
- 2020
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 16:7, s. 1908-1921
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Journal article (peer-reviewed)abstract
- A simple Pickering emulsion route has been developed for the assembly of temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles into colloidal molecules comprising a small number of discrete microgel interaction sites on a central oil emulsion droplet. Here, the surface activity of the microgels serves to drive their assembly through adsorption to growing polydimethylsiloxane (PDMS) emulsion oil droplets of high monodispersity, prepared in situ via ammonia-catalysed hydrolysis and condensation of dimethyldiethoxysilane (DMDES). A dialysis step is employed in order to limit further growth once the target assembly size has been reached, thus yielding narrowly size-distributed, colloidal molecule-like microgel-Pickering emulsion oil droplets with well-defined microgel interaction sites. The temperature-responsiveness of the PNIPAM interaction sites will allow for the directional interactions to be tuned in a facile manner with temperature, all the way from soft repulsive to short-range attractive as the their volume phase transition temperature (VPTT) is crossed. Finally, the microgel-Pickering emulsion approach is extended to a mixture of PNIPAM and poly(N-isopropylmethacrylamide) (PNIPMAM) microgels that differ with respect to their VPTT, this in order to prepare patchy colloidal molecules where the directional interactions will be more readily resolved.
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| 8. |
- Ninarello, Andrea, et al.
(author)
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Modeling Microgels with a Controlled Structure across the Volume Phase Transition
- 2019
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:20, s. 7584-7592
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Journal article (peer-reviewed)abstract
- Thermoresponsive microgels are soft colloids that find widespread use as model systems for soft matter physics. Their complex internal architecture, made of a disordered and heterogeneous polymer network, has been so far a major challenge for computer simulations. In this work, we put forward a coarse-grained model of microgels whose structural properties are in quantitative agreement with results obtained with small-angle X-ray scattering experiments across a wide range of temperatures, encompassing the volume phase transition. These results bridge the gap between experiments and simulations of individual microgel particles, paving the way to theoretically address open questions about their bulk properties with unprecedented nano- and microscale resolution.
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| 9. |
- Pal, Antara, et al.
(author)
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Anisotropic dynamics and kinetic arrest of dense colloidal ellipsoids in the presence of an external field studied by differential dynamic microscopy
- 2020
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In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 6:3
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Journal article (peer-reviewed)abstract
- Anisotropic dynamics on the colloidal length scale is ubiquitous in nature. Of particular interest is the dynamics of systems approaching a kinetically arrested state. The failure of classical techniques for investigating the dynamics of highly turbid suspensions has contributed toward the limited experimental information available up until now. Exploiting the recent developments in the technique of differential dynamic microscopy (DDM), we report the first experimental study of the anisotropic collective dynamics of colloidal ellipsoids with a magnetic hematite core over a wide concentration range approaching kinetic arrest. In addition, we have investigated the effect of an external magnetic field on the resulting anisotropic collective diffusion. We combine DDM with small-angle x-ray scattering and rheological measurements to locate the glass transition and to relate the collective short- and long-time diffusion coefficients to the structural correlations and the evolution of the zero shear viscosity as the system approaches an arrested state.
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| 10. |
- Peng, Feifei, et al.
(author)
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A droplet-based microfluidics route to temperature-responsive colloidal molecules
- 2019
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 123:43, s. 9260-9271
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Journal article (peer-reviewed)abstract
- Small clusters of spherical colloids that mimic real molecules, so-called colloidal molecules, hold great promise as building blocks in bottom-up routes to new materials. However, their typical hard sphere nature has hampered their assembly into ordered structures, largely due to a lack of control in the interparticle interactions. To provide easy external control of the interactions, the present work focuses on the preparation of colloidal molecules from temperature-responsive microgel particles that undergo a transition from a soft repulsive to a short-range attractive state as their characteristic volume phase transition temperature (VPTT) is crossed. Preparation of the colloidal molecules starts with the use of a droplet-based microfluidics device to form highly uniform water-in-oil (W/O) emulsion droplets containing, on average and with a narrow distribution, four microgels per droplet. Evaporation of the water then leads to the formation of colloidal molecule-like clusters, which can be harvested following cross-linking and phase transfer. We use a mixture of two types of microgels, one based on poly(N-isopropylacrylamide) (PNIPAM) and the other on poly(N-isopropylmethacrylamide) (PNIPMAM), to prepare bicomponent colloidal molecules, and show that the difference in VPTT between the two allows for induction of attractive interparticle interactions between the PNIPAM interaction sites at temperatures in between the two VPTTs, analogous to the interactions among patchy biomacromolecules such as many proteins.
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