10 research outputs found
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Synthesis of Polyampholyte Janus-like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization
Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli-responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus-like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self-assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus-like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Recommended from our members
Synthesis of Polyampholyte Janus-like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization
Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli-responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus-like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self-assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus-like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Antarctic geothermal heat flow: future research directions
Antarctic geothermal heat flow (GHF) affects the ice sheet temperature, determining how it slides and internally deforms, as well as the rheological behaviour of the lithosphere. However, GHF remains poorly constrained, with few borehole-derived estimates, and there are large discrepancies in currently available glaciological and geophysical estimates. This SCAR White Paper details current methods, discusses their challenges and limitations, and recommends key future directions in GHF research. We highlight the timely need for a more multidisciplinary and internationally-coordinated approach to tackle this complex problem
Synthesis and solution behaviour of stimuli-sensitive zwitterionic microgels
In this study, we have synthesised small aqueous zwitterionic microgels as model systems for amphoteric microgels. Zwitterions exhibit special behaviour due to defined distance between the opposite charges and provide a possibility to incorporate an identical number of positive and negative charges in microgels. Microgels decorated with zwitterionic groups exhibit unique properties compared with their analogues functionalized with separately incorporated oppositely charged co-monomers. In this work, two series of zwitterionic microgels with N-isopropylacrylamide (NIPAm) and N-vinylcaprolactam (VCL) as main monomers and various amounts of [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl) ammonium hydroxide (referred to as sulfobetaine) as zwitterionic co-monomer have been prepared. We investigated the effect of zwitterionic co-monomer content on the swelling behaviour, particle size, size distribution and volume phase transition temperature of the NIPAm-co-sulfobetaine microgels using various scattering methods, as dynamic and static light scattering and small-angle X-ray/neutron scattering. We found a decrease of particle size with the amount of sulfobetaine in the presence of sodium dodecylsulfate, which is contrary to results published earlier by Das et al. (Chem Mater 20: 7157–7163, 2008) for a similar system of zwitterionic microgels. The decrease of particle size is related to co-surfactant behaviour of sulfobetaine in mixtures with sodium dodecylsulfate. The incorporation of sulfobetaine also increases the polydispersity of the microgels and broadens the volume phase transition
Recommended from our members
Synthesis of Polyampholyte Janus-like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization
Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli-responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus-like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self-assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus-like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Electrostatic Interactions and Osmotic Pressure of Counterions Control the pH-Dependent Swelling and Collapse of Polyampholyte Microgels with Random Distribution of Ionizable Groups
In
this work, different systems of colloidally stable, ampholytic
microgels (μGs) based on poly(<i>N</i>-vinylcaprolactam)
and poly(<i>N</i>-isopropylacrylamide), wherein
the anionic and cationic groups are randomly distributed, were investigated.
Fourier transmission infrared spectroscopy and transmission electron
microscopy confirmed the quantitative incorporation and random distribution
of ionizable groups in μGs, respectively. The control of hydrodynamic
radii and mechanical properties of polyampholyte μGs at different
pH values was studied with dynamic light scattering and in situ atomic
force microscopy. We have proposed a model of pH-dependent polyampholyte
μG, which correctly describes the experimental data and explains
physical reasons for the swelling and collapse of the μG at
different pHs. In the case of a balanced μG (equal numbers of
cationic and anionic groups), the size as a function of pH has a symmetric,
V-like shape. Swelling of purely cationic μG at low pH or purely
anionic μG at high pH is due to electrostatic repulsion of similarly
charged groups, which appears as a result of partial escape of counterions.
Also, osmotically active counterions (the counterions that are trapped
within the μG) contribute to the swelling of the μG. In
contrast, electrostatic interactions are responsible for the collapse
of the μG at intermediate pH when the numbers of anionic and
cationic groups are equal (stoichiometric ratio). The multipole attraction
of the charged groups is caused by thermodynamic fluctuations, similar
to the those observed in Debye–Hückel plasma. We have
demonstrated that the higher the fraction of cationic and anionic
groups, the more pronounced the swelling and collapse of the μG
at different pHs
Early alpha/beta oscillations reflect the formation of face-related expectations in the brain
Although statistical regularities in the environment often go explicitly unnoticed, traces of implicit learning are evident in our neural activity. Recent perspectives have offered evidence that both pre-stimulus oscillations and peri-stimulus event-related potentials are reliable biomarkers of implicit expectations arising from statistical learning. What remains ambiguous, however, is the origination and development of these implicit expectations. To address this lack of knowledge and determine the temporal constraints of expectation formation, pre-stimulus increases in alpha/beta power were investigated alongside a reduction in the N170 and a suppression in peri-/post-stimulus gamma power. Electroencephalography was acquired from naive participants who engaged in a gender classification task. Participants were uninformed, that eight face images were sorted into four reoccurring pairs which were pseudorandomly hidden amongst randomly occurring face images. We found a reduced N170 for statistically expected images at left parietal and temporo-parietal electrodes. Furthermore, enhanced gamma power following the presentation of random images emphasized the bottom-up processing of these arbitrary occurrences. In contrast, enhanced alpha/beta power was evident pre-stimulus for expected relative to random faces. A particularly interesting finding was the early onset of alpha/beta power enhancement which peaked immediately after the depiction of the predictive face. Hence, our findings propose an approximate timeframe throughout which consistent traces of enhanced alpha/beta power illustrate the early prioritisation of top-down processes to facilitate the development of implicitly cued face-related expectations
Synthesis of Polyampholyte Janus-like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization
Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli-responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus-like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self-assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus-like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA