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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) 2D x–y confocal microscopy slices of a Wigner crystal; particles at ϕ ∼ 0.40 in deionized, refractive index and density matched solution. Scale bar is 20 μm. Inset: higher magnification, with a scale bar of 2 μm. (B) 3D particle reconstruction from particle locations; distances in microns, starting at 15 μm from the coverslip. (C) 2D confocal microscopy images of refractive index and density matched colloidal gels composed of 1.85 μm diameter particles with an anionic (green) and cationic (red) surface charge in ∼0 mM NaCl.
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f6: (A) 2D x–y confocal microscopy slices of a Wigner crystal; particles at ϕ ∼ 0.40 in deionized, refractive index and density matched solution. Scale bar is 20 μm. Inset: higher magnification, with a scale bar of 2 μm. (B) 3D particle reconstruction from particle locations; distances in microns, starting at 15 μm from the coverslip. (C) 2D confocal microscopy images of refractive index and density matched colloidal gels composed of 1.85 μm diameter particles with an anionic (green) and cationic (red) surface charge in ∼0 mM NaCl.

Mentions: Interestingly, if we take the same colloidal particles at an identical volume fraction, and de-ionize the fluid mixture to remove any ionic species and impurities, the particles begin to interact through long-ranged electrostatic repulsions. The conductivity of formamide as received is 68 μS/cm and that of sulfolane is 6.6 μS/cm. After deionization with a mixed bed ion exchange resins, the conductivity decreases to 1.0 μS/cm and 0.23 μS/cm, respectively. While the screened sample at a volume fraction below the freezing limit for hard-spheres exhibited a fluid structure, the particles in this deionized refractive index- and density matching mixture crystallize due to the electrostatic repulsions, forming a so-called colloidal Wigner crystal (Fig. 6A,B), in which distinct and sharp peaks in the radial distribution function are observed (inset Fig. 5).


Precise colloids with tunable interactions for confocal microscopy.

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

(A) 2D x–y confocal microscopy slices of a Wigner crystal; particles at ϕ ∼ 0.40 in deionized, refractive index and density matched solution. Scale bar is 20 μm. Inset: higher magnification, with a scale bar of 2 μm. (B) 3D particle reconstruction from particle locations; distances in microns, starting at 15 μm from the coverslip. (C) 2D confocal microscopy images of refractive index and density matched colloidal gels composed of 1.85 μm diameter particles with an anionic (green) and cationic (red) surface charge in ∼0 mM NaCl.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: (A) 2D x–y confocal microscopy slices of a Wigner crystal; particles at ϕ ∼ 0.40 in deionized, refractive index and density matched solution. Scale bar is 20 μm. Inset: higher magnification, with a scale bar of 2 μm. (B) 3D particle reconstruction from particle locations; distances in microns, starting at 15 μm from the coverslip. (C) 2D confocal microscopy images of refractive index and density matched colloidal gels composed of 1.85 μm diameter particles with an anionic (green) and cationic (red) surface charge in ∼0 mM NaCl.
Mentions: Interestingly, if we take the same colloidal particles at an identical volume fraction, and de-ionize the fluid mixture to remove any ionic species and impurities, the particles begin to interact through long-ranged electrostatic repulsions. The conductivity of formamide as received is 68 μS/cm and that of sulfolane is 6.6 μS/cm. After deionization with a mixed bed ion exchange resins, the conductivity decreases to 1.0 μS/cm and 0.23 μS/cm, respectively. While the screened sample at a volume fraction below the freezing limit for hard-spheres exhibited a fluid structure, the particles in this deionized refractive index- and density matching mixture crystallize due to the electrostatic repulsions, forming a so-called colloidal Wigner crystal (Fig. 6A,B), in which distinct and sharp peaks in the radial distribution function are observed (inset Fig. 5).

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.