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pH-responsive water-in-water Pickering emulsions.
Bach T Nguyen1, Wenkai Wang2, Brian R Saunders2
1†LUNAM, Université du Maine, IMMM UMR CNRS 6283, PCI, Le Mans, 72085 Cedex 9, France.
Langmuir : the ACS Journal of Surfaces and Colloids
|March 7, 2015
Summary
pH-sensitive microgels stabilize water-in-water emulsions. These emulsions, formed from dextran and PEO, show stability only within a narrow pH range, influenced by microgel size and salt concentration.
Area of Science:
- Colloid and Surface Science
- Materials Science
- Polymer Chemistry
Background:
- Water-in-water emulsions offer tunable properties by utilizing phase separation of polymers.
- Microgels, as responsive materials, can influence interfacial properties and emulsion stability.
- Controlling emulsion stability is crucial for applications in food, cosmetics, and pharmaceuticals.
Purpose of the Study:
- To investigate the role of pH-sensitive microgels in stabilizing water-in-water emulsions.
- To determine the optimal pH range and conditions for emulsion stability.
- To understand how microgel properties and environmental factors affect emulsion structure and longevity.
Main Methods:
- Formation of water-in-water emulsions using dextran and polyethylene oxide (PEO) solutions.
- Incorporation of spherical, pH-sensitive poly(N-isopropylacrylamide-co-acrylic acid) microgels.
- Confocal laser scanning microscopy for visualizing droplet size and distribution.
- Systematic variation of pH, salt concentration, microgel concentration, and polymer composition.
Main Results:
- Microgels exhibited a significant radius increase from 60 to 220 nm around pH 7.0.
- Stable emulsions were observed exclusively between pH 7.0 and 7.5, correlating with specific microgel swelling states.
- Emulsion stability was sensitive to small pH fluctuations and salt addition, which shifted the stable pH range.
- Smallest droplet sizes were achieved within the stable pH window.
Conclusions:
- pH-sensitive microgels can effectively stabilize water-in-water emulsions within a narrow, tunable pH range.
- Microgel size modulation and interfacial activity are key factors governing emulsion stability.
- The findings provide insights into designing responsive Pickering stabilizers for complex fluid systems.
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