| 1. |
- Mohanty, P. S., et al.
(författare)
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Dielectric spectroscopy of ionic microgel suspensions
- 2016
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Ingår i: Soft Matter. - 1744-683X. ; 12:48, s. 9705-9727
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Tidskriftsartikel (refereegranskat)abstract
- The determination of the net charge and size of microgel particles as a function of their concentration, as well as the degree of association of ions to the microgel backbone, has been pursued in earlier studies mainly by scattering and rheology. These methods suffer from contributions due to inter-particle interactions that interfere with the characterization of single-particle properties. Here we introduce dielectric spectroscopy as an alternative experimental method to characterize microgel systems. The advantage of dielectric spectroscopy over other experimental methods is that the polarization due to mobile charges within a microgel particle is only weakly affected by inter-particle interactions. Apart from electrode polarization effects, experimental spectra on PNIPAM-co-AA [poly(N-isopropylacrylamide-co-acrylic acid)] ionic microgel particles suspended in de-ionized water exhibit three well-separated relaxation modes, which are due to the polarization of the mobile charges within the microgel particles, the diffuse double layer around the particles, and the polymer backbone. Expressions for the full frequency dependence of the electrode-polarization contribution to the measured dielectric response are derived, and a theory is proposed for the polarization resulting from the mobile charges within the microgel. Relaxation of the diffuse double layer is modeled within the realm of a cell model. The net charge and the size of the microgel particles are found to be strongly varying with concentration. A very small value of the diffusion coefficient of ions within the microgel is found, due to a large degree of chemical association of protons to the polymer backbone.
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| 2. |
- Dabkowska, A. P., et al.
(författare)
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Temperature responsive lipid liquid crystal layers with embedded nanogels
- 2017
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Ingår i: Chemical Communications. - : Royal Society of Chemistry. - 1359-7345 .- 1364-548X. ; 53:8, s. 1417-1420
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Tidskriftsartikel (refereegranskat)abstract
- Polymer nanogels are embedded within layers consisting of a nonlamellar liquid crystalline lipid phase to act as thermoresponsive controllers of layer compactness and hydration. As the nanogels change from the swollen to the collapsed state via a temperature trigger, they enable on-demand release of water from the mixed polymer-lipid layer while the lipid matrix remains intact. Combining stimuli-responsive polymers with responsive lipid-based mesophase systems opens up new routes in biomedical applications such as functional biomaterials, bioanalysis and drug delivery.
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| 3. |
- 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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| 4. |
- Colla, Thiago, et al.
(författare)
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Self-Assembly of Ionic Microgels Driven by an Alternating Electric Field : Theory, Simulations, and Experiments
- 2018
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 12:5, s. 4321-4337
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Tidskriftsartikel (refereegranskat)abstract
- The structural properties of a system of ionic microgels under the influence of an alternating electric field are investigated both theoretically and experimentally. This combined investigation aims to shed light on the structural transitions that can be induced by changing either the driving frequency or the strength of the applied field, which range from string-like formation along the field to crystal-like structures across the orthogonal plane. In order to highlight the physical mechanisms responsible for the observed particle self-assembly, we develop a coarse-grained description, in which effective interactions among the charged microgels are induced by both equilibrium ionic distributions and their time-averaged hydrodynamic responses to the applied field. These contributions are modeled by the buildup of an effective dipole moment at the microgels backbones, which is partially screened by their ionic double layer. We show that this description is able to capture the structural properties of this system, allowing for very good agreement with the experimental results. The model coarse-graining parameters are indirectly obtained via the measured pair distribution functions and then further assigned with a clear physical interpretation, allowing us to highlight the main physical mechanisms accounting for the observed self-assembly behavior.
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| 5. |
- 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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| 6. |
- Ma, Lichen, et al.
(författare)
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Attentional bias modification in virtual reality
- 2019
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Ingår i: Book of Abstracts. ; , s. 227-227
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Attentional bias modification (ABM) aims to reduce anxiety by attenuating bias towards threatening information. The current study incorporated virtual reality (VR) technology and 3-dimensional stimuli with a dot-probe task to evaluate the effects of a VR-based ABM training on attentional bias and anxiety symptoms. A total of 100 participants were randomised to four training groups. Attentional bias was assessed at pre- and post-training, and anxiety symptoms were assessed at pre-training, post-training, 1-week follow-up, and 3-months follow-up. Change in anxiety did not correlate with change in bias. No significant difference in bias was observed from pre- to post-ABM or between groups. For anxiety symptoms, participants showed significant reduction in anxiety scores over time. However, no other significant main effect or interactions were found. A clinically significant change analysis revealed that 9% of participants were classified as ‘recovered’ at 3-months follow-up.
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| 7. |
- Mohanty, Priti S., et al.
(författare)
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Interpenetration of polymeric microgels at ultrahigh densities
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Soft particles such as polymeric microgels can form ultra-dense phases, where the average center-to-center distance a s can be smaller than the initial unperturbed particle diameter σ 0, due to their ability to interpenetrate and compress. However, despite of the effort devoted to microgels at ultrahigh densities, we know surprisingly little about their response to their environment at effective volume fractions φ eff above close packing (φ cp ), and the existing information is often contradictory. Here we report direct measurements of the size and shape of poly(N-isopropylacrylamide) microgels at concentrations below and above φcp using the zero average contrast method in small-angle neutron scattering. We complement these experiments with measurements of the average interparticle distances using small-angle X-ray scattering, and a determination of the glass transition using dynamic light scattering. This allows us to unambiguously decouple interaction effects from density-dependent variations of the particle size and shape at all values of φeff . We demonstrate that the microgels used in this study significantly interpenetrate and thus change their size and shape only marginally even for φeff > φ cp, a finding that may require changes in the interpretation of a number of previously published studies on the structural and dynamic properties of dense soft particle systems.
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| 8. |
- Nöjd, Sofi, et al.
(författare)
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Deswelling behaviour of ionic microgel particles from low to ultra-high densities
- 2018
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 14:20, s. 4150-4159
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Tidskriftsartikel (refereegranskat)abstract
- The swelling of ionic microgel particles is investigated at a wide range of concentrations using a combination of light, X-ray and neutron scattering techniques. We employ a zero-average contrast approach for small-angle neutron scattering experiments, which enables a direct determination of the form factor at high concentrations. The observed particle size initially decreases strongly with the particle concentration in the dilute regime but approaches a constant value at intermediate concentrations. This is followed by a further deswelling at high concentrations above particle overlap. Theory and experiments point at a pivotal contribution of dangling polymer ends to the strong variation in size of ionic microgels, which presents itself mainly through the hydrodynamics properties of the system.
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| 9. |
- Nöjd, Sofi, et al.
(författare)
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Soft particles in an electric field-a zero average contrast study
- 2019
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 15:31, s. 6369-6374
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Tidskriftsartikel (refereegranskat)abstract
- We report on the structural properties of ionic microgel particles subjected to alternating electric fields, using small-angle neutron scattering. The experiments were performed under so-called zero average contrast conditions, which cancel the structure factor contribution to the scattered intensity, allowing us to obtain direct information on the single particle size and structure as particles align in field-induced strings. Our results reveal only a marginal compression of the particles as they align in strings, and indicate considerable particle overlap at higher field strengths. These findings provide further insight into the origins of the previously reported unusual path dependent field-induced crystal-crystal transition found for these systems (P. S. Mohanty et al., Phys. Rev. X, 2015, 5, 011030).
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