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A new look at effective interactions between microgel particles.

ABSTRACT: Thermoresponsive microgels find widespread use as colloidal model systems, because their temperature-dependent size allows facile tuning of their volume fraction in situ. However, an interaction potential unifying their behavior across the entire phase diagram is sorely lacking. Here we investigate microgel suspensions in the fluid regime at different volume fractions and temperatures, and in the presence of another population of small microgels, combining confocal microscopy experiments and numerical simulations. We find that effective interactions between microgels are clearly temperature dependent. In addition, microgel mixtures possess an enhanced stability compared to hard colloid mixtures - a property not predicted by a simple Hertzian model. Based on numerical calculations we propose a multi-Hertzian model, which reproduces the experimental behavior for all studied conditions. Our findings highlight that effective interactions between microgels are much more complex than usually assumed, displaying a crucial dependence on temperature and on the internal core-corona architecture of the particles.

SUBMITTER: Bergman MJ

PROVIDER: S-EPMC6262015 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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A new look at effective interactions between microgel particles.

Bergman Maxime J MJ Gnan Nicoletta N Obiols-Rabasa Marc M Meijer Janne-Mieke JM Rovigatti Lorenzo L Zaccarelli Emanuela E Schurtenberger Peter P

Nature communications 20181128 1

Thermoresponsive microgels find widespread use as colloidal model systems, because their temperature-dependent size allows facile tuning of their volume fraction in situ. However, an interaction potential unifying their behavior across the entire phase diagram is sorely lacking. Here we investigate microgel suspensions in the fluid regime at different volume fractions and temperatures, and in the presence of another population of small microgels, combining confocal microscopy experiments and num ...[more]

PMID: 30487527

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Project description:Starch-based emulsion microgel particles with different starch (15 and 20 wt %) and oil contents (0-15 wt %) were synthesized, and their lubrication performance under physiological conditions was investigated. Emulsion microgels were subjected to skin mimicking or oral cavity mimicking conditions, i.e., smooth hydrophobic polydimethylsiloxane ball-on-disc tribological tests, in the absence or presence of salivary enzyme (?-amylase). In the absence of enzyme, emulsion microgel particles (30-60 vol % particle content) conserved the lubricating properties of emulsion droplets, providing considerably lower friction coefficients (? ? 0.1) in the mixed lubrication regime compared to plain microgel particles (0 wt % oil). Upon addition of enzyme, the lubrication performance of emulsion microgel particles became strongly dependent on the particles' oil content. Microgel particles encapsulating 5-10 wt % oil showed a double plateau mixed lubrication regime having a lowest friction coefficient ? ? 0.03 and highest ? ? 0.1, the latter higher than with plain microgel particles. An oil content of 15 wt % was necessary for the microgel particles to lubricate similarly to the emulsion droplets, where both systems showed a normal mixed lubrication regime with ? ? 0.03. The observed trends in tribology, theoretical considerations, and the combined results of rheology, light scattering, and confocal fluorescence microscopy suggested that the mechanism behind the low friction coefficients was a synergistic enzyme- and shear-triggered release of the emulsion droplets, improving lubrication. The present work thus demonstrates experimentally and theoretically a novel biolubricant additive with stimuli-responsive properties capable of providing efficient boundary lubrication between soft polymeric surfaces. At the same time, the additive should provide an effective delivery vehicle for oil soluble ingredients in aqueous media. These findings demonstrate that emulsion microgel particles can be developed into multifunctional biolubricant additives for future use in numerous soft matter applications where both lubrication and controlled release of bioactives are essential.

Project description:BACKGROUND:Although this is beginning to change, the content of antenatal care has been relatively neglected in safe-motherhood program efforts. This appears in part to be due to an unwarranted belief that interventions over this period have far less impact than those provided around the time of birth. In this par, we review available evidence for 21 interventions potentially deliverable during pregnancy at high coverage to neglected populations in low income countries, with regard to effectiveness in reducing risk of: maternal mortality, newborn mortality, stillbirth, prematurity and intrauterine growth restriction. Selection was restricted to interventions that can be provided by non-professional health auxiliaries and not requiring laboratory support. METHODS:In this narrative review, we included relevant Cochrane and other systematic reviews and did comprehensive bibliographic searches. Inclusion criteria varied by intervention; where available randomized controlled trial evidence was insufficient, observational study evidence was considered. For each intervention we focused on overall contribution to our outcomes of interest, across varying epidemiologies. RESULTS:In the aggregate, achieving high effective coverage for this set of interventions would very substantially reduce risk for our outcomes of interest and reduce outcome inequities. Certain specific interventions, if pushed to high coverage have significant potential impact across many settings. For example, reliable detection of pre-eclampsia followed by timely delivery could prevent up to ¼ of newborn and stillbirth deaths and over 90% of maternal eclampsia/pre-eclampsia deaths. Other interventions have potent effects in specific settings: in areas of high P falciparum burden, systematic use of insecticide-treated nets and/or intermittent presumptive therapy in pregnancy could reduce maternal mortality by up to 10%, newborn mortality by up to 20%, and stillbirths by up to 25-30%. Behavioral interventions targeting practices at birth and in the hours that follow can have substantial impact in settings where many births happen at home: in such circumstances early initiation of breastfeeding can reduce risk of newborn death by up to 20%; good thermal care practices can reduce mortality risk by a similar order of magnitude. CONCLUSIONS:Simple interventions delivered during pregnancy have considerable potential impact on important mortality outcomes. More programmatic effort is warranted to ensure high effective coverage.

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A new look at effective interactions between microgel particles.

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A new look at effective interactions between microgel particles.

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