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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.


Deep XZ confocal slice of refractive index matched but density mismatched 1.65 μm diameter particles dispersed in formamide with 30 mM NaCl.
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f7: Deep XZ confocal slice of refractive index matched but density mismatched 1.65 μm diameter particles dispersed in formamide with 30 mM NaCl.

Mentions: While this system of particles composed of 2 monomers, and a fluid mixture of only 2 components, allows almost perfect matching of the densities, certain experiments may require a controlled density mismatch, for example to templating of crystals on patterned substrates111213, or to ascertain the equation of state.33 In the system we present here, minute changes to the copolymer ratio allows doing exactly this. These changes do not influence the particle size or polydispersity shown in Fig. 3. To showcase this we prepare particles which can be perfectly refractive index matched in pure formamide, but which exhibit a mild density mismatch of 0.077 g/cm3. A sample at ϕ ≈ 0.02 is equilibrated for 2 days, during which a crystalline sediment forms, a sharp and distinct crystal-fluid interface becomes apparent. The refractive index match allows us to image very deep into the sample, seen in the confocal microscopy image in Fig. 7 which shows a penetration depth of the excitation laser of well over 220 μm into the sample, without significant optical aberrations even in the direction perpendicular to the confocal scanning plane.


Precise colloids with tunable interactions for confocal microscopy.

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

Deep XZ confocal slice of refractive index matched but density mismatched 1.65 μm diameter particles dispersed in formamide with 30 mM NaCl.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: Deep XZ confocal slice of refractive index matched but density mismatched 1.65 μm diameter particles dispersed in formamide with 30 mM NaCl.
Mentions: While this system of particles composed of 2 monomers, and a fluid mixture of only 2 components, allows almost perfect matching of the densities, certain experiments may require a controlled density mismatch, for example to templating of crystals on patterned substrates111213, or to ascertain the equation of state.33 In the system we present here, minute changes to the copolymer ratio allows doing exactly this. These changes do not influence the particle size or polydispersity shown in Fig. 3. To showcase this we prepare particles which can be perfectly refractive index matched in pure formamide, but which exhibit a mild density mismatch of 0.077 g/cm3. A sample at ϕ ≈ 0.02 is equilibrated for 2 days, during which a crystalline sediment forms, a sharp and distinct crystal-fluid interface becomes apparent. The refractive index match allows us to image very deep into the sample, seen in the confocal microscopy image in Fig. 7 which shows a penetration depth of the excitation laser of well over 220 μm into the sample, without significant optical aberrations even in the direction perpendicular to the confocal scanning plane.

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.