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Precise colloids with tunable interactions for confocal microscopy.

Kodger TE, Guerra RE, Sprakel J - Sci Rep (2015)

Bottom Line: The interactions between particles are accurately tuned by surface grafting of polymer brushes using Atom Transfer Radical Polymerization (ATRP), from hard-sphere-like to long-ranged electrostatic repulsion or mixed charge attraction.We also modify the buoyant density of the particles by altering the copolymer ratio while maintaining their refractive index match to the suspending solution resulting in well controlled sedimentation.The tunability of the inter-particle interactions, the low volatility of the solvents, and the capacity to simultaneously match both the refractive index and density of the particles to the fluid opens up new possibilities for exploring the physics of colloidal systems.

View Article: PubMed Central - PubMed

Affiliation: School of Engineering and Applies Sciences, Harvard University, Cambridge, 02138, USA.

ABSTRACT
Model colloidal systems studied with confocal microscopy have led to numerous insights into the physics of condensed matter. Though confocal microscopy is an extremely powerful tool, it requires a careful choice and preparation of the colloid. Uncontrolled or unknown variations in the size, density, and composition of the individual particles and interactions between particles, often influenced by the synthetic route taken to form them, lead to difficulties in interpreting the behavior of the dispersion. Here we describe the straightforward synthesis of copolymer particles which can be refractive index- and density-matched simultaneously to a non-plasticizing mixture of high dielectric solvents. The interactions between particles are accurately tuned by surface grafting of polymer brushes using Atom Transfer Radical Polymerization (ATRP), from hard-sphere-like to long-ranged electrostatic repulsion or mixed charge attraction. We also modify the buoyant density of the particles by altering the copolymer ratio while maintaining their refractive index match to the suspending solution resulting in well controlled sedimentation. The tunability of the inter-particle interactions, the low volatility of the solvents, and the capacity to simultaneously match both the refractive index and density of the particles to the fluid opens up new possibilities for exploring the physics of colloidal systems.

No MeSH data available.


(A) SEM image of core particles, a ∼ 710 nm (B) SEM image of final particles, a ∼ 1.8 μm (C) 2D confocal microscopy image of the fluorescent core with shell outlines (dotted lines) determined by simultaneous bright-field microscopy, not shown. The single small particle seen in (B) is a core from (A) that was not encapsulated during shell polymerization. Scale bar in all images is 2 μm.
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f8: (A) SEM image of core particles, a ∼ 710 nm (B) SEM image of final particles, a ∼ 1.8 μm (C) 2D confocal microscopy image of the fluorescent core with shell outlines (dotted lines) determined by simultaneous bright-field microscopy, not shown. The single small particle seen in (B) is a core from (A) that was not encapsulated during shell polymerization. Scale bar in all images is 2 μm.

Mentions: We prepare core-shell particles by seeded-dispersion polymerization in the presence of cross-linked core particles in which a fluorescent dye is covalently attached to the polymer chains. These crosslinked cores are prepared using precipitation polymerization, which yields monodispersed particles with a clean surface free of dispersant or surfactant34 (Fig. 8A). These polymerizations are performed at low volume fractions of monomer; reactions in which the monomer concentration was increased to >5 vol%, and with crosslinker concentrations in excess of 2 vol%, produced an undesirably large number of dimers and trimers. Subsequently, a non-fluorescent shell is formed around the cross-linked core particles by a seeded dispersion polymerization. During polymerization, the cosolvent ratio determines the maximum particle size possible; secondary nucleation can be avoided by using low amounts of cosolvent. This results in high yields of monodisperse core-shell particles (Fig. 8B), whose surface can be functionalized using the same surface-initiated ATRP procedure as discussed above. Confocal imaging of these particles yields distinctly separated fluorescent centers, even when the particles are in direct contact (Fig. 8c).


Precise colloids with tunable interactions for confocal microscopy.

Kodger TE, Guerra RE, Sprakel J - Sci Rep (2015)

(A) SEM image of core particles, a ∼ 710 nm (B) SEM image of final particles, a ∼ 1.8 μm (C) 2D confocal microscopy image of the fluorescent core with shell outlines (dotted lines) determined by simultaneous bright-field microscopy, not shown. The single small particle seen in (B) is a core from (A) that was not encapsulated during shell polymerization. Scale bar in all images is 2 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588590&req=5

f8: (A) SEM image of core particles, a ∼ 710 nm (B) SEM image of final particles, a ∼ 1.8 μm (C) 2D confocal microscopy image of the fluorescent core with shell outlines (dotted lines) determined by simultaneous bright-field microscopy, not shown. The single small particle seen in (B) is a core from (A) that was not encapsulated during shell polymerization. Scale bar in all images is 2 μm.
Mentions: We prepare core-shell particles by seeded-dispersion polymerization in the presence of cross-linked core particles in which a fluorescent dye is covalently attached to the polymer chains. These crosslinked cores are prepared using precipitation polymerization, which yields monodispersed particles with a clean surface free of dispersant or surfactant34 (Fig. 8A). These polymerizations are performed at low volume fractions of monomer; reactions in which the monomer concentration was increased to >5 vol%, and with crosslinker concentrations in excess of 2 vol%, produced an undesirably large number of dimers and trimers. Subsequently, a non-fluorescent shell is formed around the cross-linked core particles by a seeded dispersion polymerization. During polymerization, the cosolvent ratio determines the maximum particle size possible; secondary nucleation can be avoided by using low amounts of cosolvent. This results in high yields of monodisperse core-shell particles (Fig. 8B), whose surface can be functionalized using the same surface-initiated ATRP procedure as discussed above. Confocal imaging of these particles yields distinctly separated fluorescent centers, even when the particles are in direct contact (Fig. 8c).

Bottom Line: The interactions between particles are accurately tuned by surface grafting of polymer brushes using Atom Transfer Radical Polymerization (ATRP), from hard-sphere-like to long-ranged electrostatic repulsion or mixed charge attraction.We also modify the buoyant density of the particles by altering the copolymer ratio while maintaining their refractive index match to the suspending solution resulting in well controlled sedimentation.The tunability of the inter-particle interactions, the low volatility of the solvents, and the capacity to simultaneously match both the refractive index and density of the particles to the fluid opens up new possibilities for exploring the physics of colloidal systems.

View Article: PubMed Central - PubMed

Affiliation: School of Engineering and Applies Sciences, Harvard University, Cambridge, 02138, USA.

ABSTRACT
Model colloidal systems studied with confocal microscopy have led to numerous insights into the physics of condensed matter. Though confocal microscopy is an extremely powerful tool, it requires a careful choice and preparation of the colloid. Uncontrolled or unknown variations in the size, density, and composition of the individual particles and interactions between particles, often influenced by the synthetic route taken to form them, lead to difficulties in interpreting the behavior of the dispersion. Here we describe the straightforward synthesis of copolymer particles which can be refractive index- and density-matched simultaneously to a non-plasticizing mixture of high dielectric solvents. The interactions between particles are accurately tuned by surface grafting of polymer brushes using Atom Transfer Radical Polymerization (ATRP), from hard-sphere-like to long-ranged electrostatic repulsion or mixed charge attraction. We also modify the buoyant density of the particles by altering the copolymer ratio while maintaining their refractive index match to the suspending solution resulting in well controlled sedimentation. The tunability of the inter-particle interactions, the low volatility of the solvents, and the capacity to simultaneously match both the refractive index and density of the particles to the fluid opens up new possibilities for exploring the physics of colloidal systems.

No MeSH data available.