| 1. |
- Pal, Antara, et al.
(författare)
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Extending depolarized DLS measurements to turbid samples
- 2022
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 627, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- The application of dynamic light scattering to soft matter systems has strongly profited from advanced approaches such as the so-called modulated 3D cross correlation technique (Mod3D-DLS) that suppress contributions from multiple scattering, and can therefore be used for the characterization of turbid samples. Here we now extend the possibilities of this technique to allow for depolarized light scattering (Mod3D-DDLS) and thus obtain information on both translational and rotational diffusion, which is important for the characterization of anisotropic particles. We describe the required optical design and test the performance of the approach for increasingly turbid samples using well defined anisotropic colloidal models systems. Our measurements demonstrate that 3D-DDLS experiments can be performed successfully for samples with a reduced transmission due to multiple scattering as low as 1%. We compare the results from this approach with those obtained by standard DDLS experiments, and point out the importance of using an appropriate optical design when performing depolarized dynamic light scattering experiments with turbid systems.
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| 2. |
- Pal, Antara, et al.
(författare)
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Structure and dynamics of dense colloidal ellipsoids at the nearest-neighbor length scale
- 2021
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Ingår i: Physical Review Research. - 2643-1564. ; 3:2
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic particles are known to exhibit a richer and more complex phase behavior in comparison to their spherical counterpart. While the majority of the existing studies address structural properties, the dynamic behavior of anisotropic particles is a relatively lesser explored avenue. Using multispeckle ultra-small-angle x-ray photon correlation spectroscopy (USA-XPCS), we have carried out a systematic investigation of the structural and dynamic properties of colloidal ellipsoids at the nearest-neighbor length scale. The USA-XPCS measurements have allowed us to probe, as a function of the volume fraction, the q-dependent effective structure factor, Seff(q), along with the effective long time diffusion coefficient, Deff(q), for this anisotropic system. Our results indicate a scaling behavior of Deff(q) with 1/Seff(q) from which we have estimated the effective amplitude function Aeff(q), which can be directly related to the effective hydrodynamic function Heff(q). Aeff(q) shows a similar q dependence to that of S(q). Our investigation also allows for the precise determination of the volume fraction corresponding to the arrest transition.
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| 3. |
- Bergman, Maxime J., et al.
(författare)
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Controlling the morphology of microgels by ionic stimuli
- 2020
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 16:11, s. 2786-2794
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Tidskriftsartikel (refereegranskat)abstract
- Stimuli-responsive microgels have attracted much interest for their use as vehicles for drug delivery or as the building blocks of adaptive materials. Ionic microgel particles, including popular poly(NIPAM-co-acrylic acid), show strong mechanical responsiveness to many external stimuli, including changes in ionic strength or acidity. In this work, we demonstrate that combining multiple ionic stimuli can enable detailed control over the morphology of microgels. To this extent, we analyze the particle morphology in various surroundings with light-scattering techniques. First, we find strong indications of an inverted density profile in the core of the particles. Secondly, we show that the swelling of this hydrogel core and the corona of dangling polymer ends can be targeted separately by a combination of deionization and deprotonation steps. Hence, this work represents an advance in tailoring particle morphologies after synthesis in a predictable fashion.
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| 4. |
- Bergman, Maxime J., et al.
(författare)
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On the role of softness in ionic microgel interactions
- 2021
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 17:44, s. 10063-10072
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Tidskriftsartikel (refereegranskat)abstract
- Thermoresponsive microgels are a popular model system to study phase transitions in soft matter, because temperature directly controls their volume fraction. Ionic microgels are additionally pH-responsive and possess a rich phase diagram. Although effective interaction potentials between microgel particles have been proposed, these have never been fully tested, leading to a gap in our understanding of the link between single-particle and collective properties. To help resolve this gap, four sets of ionic microgels with varying crosslinker density were synthesised and characterised using light scattering techniques and confocal microscopy. The resultant structural and dynamical information was used to investigate how particle softness affects the phase behaviour of ionic microgels and to validate the proposed interaction potential. We find that the architecture of the microgel plays a marked role in its phase behaviour. Rather than the ionic charges, it is the dangling ends which drive phase transitions and interactions at low concentration. Comparison to theory underlines the need for a refined theoretical model which takes into consideration these close-contact interactions. This journal is
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| 5. |
- Chushkin, Yuriy, et al.
(författare)
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Probing Cage Relaxation in Concentrated Protein Solutions by X-Ray Photon Correlation Spectroscopy
- 2022
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 129:23
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion of proteins on length scales of their size is crucial for understanding the machinery of living cells. X-ray photon correlation spectroscopy (XPCS) is currently the only way to access long-time collective diffusion on these length scales, but radiation damage so far limits the use in biological systems. We apply a new approach to use XPCS to measure cage relaxation in crowded α-crystallin solutions. This allows us to correct for radiation effects, obtain missing information on long time diffusion, and support the fundamental analogy between protein and colloid dynamical arrest.
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| 6. |
- Chushkin, Yuriy, et al.
(författare)
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Probing Cage Relaxation in Concentrated Protein Solutions by X-Ray Photon Correlation Spectroscopy
- 2022
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Ingår i: Physical Review Letters. - 0031-9007. ; 129:23
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion of proteins on length scales of their size is crucial for understanding the machinery of living cells. X-ray photon correlation spectroscopy (XPCS) is currently the only way to access long-time collective diffusion on these length scales, but radiation damage so far limits the use in biological systems. We apply a new approach to use XPCS to measure cage relaxation in crowded α-crystallin solutions. This allows us to correct for radiation effects, obtain missing information on long time diffusion, and support the fundamental analogy between protein and colloid dynamical arrest.
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| 7. |
- Ganguly, Saswati, et al.
(författare)
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Crystal to crystal transformation in soft ionic microgels : Kinetics and the role of local mechanical susceptibilities
- 2023
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Ingår i: Physical Review Materials. - 2475-9953. ; 7:8
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Tidskriftsartikel (refereegranskat)abstract
- We report confocal microscopy experiments of electric-field-driven crystal-crystal transformations in microgel colloids with varying particle softness. The transformation kinetics are well described by phenomenological nucleation and growth theory. Using a spatial projection formalism, we determine local susceptibilities to affine shear deformation and nonaffine defect formation in the parent crystal. Curiously, the softer particles have lower shear strain susceptibility, while nonaffine susceptibility and phenomenological growth coefficients depend nonmonotonically on particle softness.
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| 8. |
- Immink, Jasper N., et al.
(författare)
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ArGSLab : a tool for analyzing experimental or simulated particle networks
- 2021
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 17:36, s. 8354-8362
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Tidskriftsartikel (refereegranskat)abstract
- Microscopy and particle-based simulations are both powerful techniques to study aggregated particulate matter such as colloidal gels. The data provided by these techniques often contains information on a wide array of length scales, but structural analysis methods typically focus on the local particle arrangement, even though the data also contains information about the particle network on the mesoscopic length scale. In this paper, we present a MATLAB software package for quantifying mesoscopic network structures in colloidal samples. ArGSLab (Arrested and Gelated Structures Laboratory) extracts a network backbone from the input data, which is in turn transformed into a set of nodes and links for graph theory-based analysis. The routines can process both image stacks from microscopy as well as explicit coordinate data, and thus allows quantitative comparison between simulations and experiments. ArGSLab furthermore enables the accurate analysis of microscopy data where,e.g., an extended point spread function prohibits the resolution of individual particles. We demonstrate the resulting output for example datasets from both microscopy and simulation of colloidal gels, in order to showcase the capability of ArGSLab to quantitatively analyze data from various sources. The freely available software package can be used either with a provided graphical user interface or directly as a MATLAB script.
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| 9. |
- Immink, Jasper N., et al.
(författare)
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Crystal-to-Crystal Transitions in Binary Mixtures of Soft Colloids
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; , s. 14861-14868
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we demonstrate a method for inducing reversible crystal-to-crystal transitions in binary mixtures of soft colloidal particles. Through a controlled decrease of salinity and increasingly dominating electrostatic interactions, a single sample is shown to reversibly organize into entropic crystals, electrostatic attraction-dominated crystals, or aggregated gels, which we quantify using microscopy and image analysis. We furthermore analyze crystalline structures with bond order analysis to discern between two crystal phases. We observe the different phases using a sample holder geometry that allows both in situ salinity control and imaging through confocal laser scanning microscopy and apply a synthesis method producing particles with high resolvability in microscopy with control over particle size. The particle softness provides for an enhanced crystallization speed, while altering the re-entrant melting behavior as compared to hard sphere systems. This work thus provides several tools for use in the reproducible manufacture and analysis of binary colloidal crystals.
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| 10. |
- Immink, Jasper N., et al.
(författare)
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Using Patchy Particles to Prevent Local Rearrangements in Models of Non-equilibrium Colloidal Gels
- 2020
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 36:1, s. 419-425
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Tidskriftsartikel (refereegranskat)abstract
- Simple models based on isotropic interparticle attractions often fail to capture experimentally observed structures of colloidal gels formed through spinodal decomposition and subsequent arrest: the resulting gels are typically denser and less branched than their experimental counterparts. Here, we simulate gels formed from soft particles with directional attractions ("patchy particles"), designed to inhibit lateral particle rearrangement after aggregation. We directly compare simulated structures with experimental colloidal gels made using soft attractive microgel particles, by employing a "skeletonization" method that reconstructs the three-dimensional backbone from experiment or simulation. We show that including directional attractions with sufficient valency leads to strongly branched structures compared to isotropic models. Furthermore, combining isotropic and directional attractions provides additional control over aggregation kinetics and gel structure. Our results show that the inhibition of lateral particle rearrangements strongly affects the gel topology and is an important effect to consider in computational models of colloidal gels.
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