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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) PVP stabilized particle diameters with changes in co-solvent and inimer type, see Table in SI.  H2O, no inimer;  H2O, acrylate inimer;  H2O, methacrylate inimer;  formamide, acrylate inimer;  formamide, methacrylate inimer. (B) SPMA stabilized particle diameters with cosolvent, H2O, volume varied along with total monomer volume fraction, see Table in SI.  15vol% monomer;  12.5vol% monomer;  10vol% monomer;  5vol% monomer. Reaction compositions within shaded regions yield only polymerized coagulum.
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f3: (A) PVP stabilized particle diameters with changes in co-solvent and inimer type, see Table in SI. H2O, no inimer; H2O, acrylate inimer; H2O, methacrylate inimer; formamide, acrylate inimer; formamide, methacrylate inimer. (B) SPMA stabilized particle diameters with cosolvent, H2O, volume varied along with total monomer volume fraction, see Table in SI. 15vol% monomer; 12.5vol% monomer; 10vol% monomer; 5vol% monomer. Reaction compositions within shaded regions yield only polymerized coagulum.

Mentions: Here we develop a colloidal system which can be suspended in polar solvents, in which the refractive index and density can be controlled precisely, and whose interactions are tunable using controlled living radical polymerisation methods, illustrated in Fig. 1. Fluorinated methacrylate polymers, such as poly(trifluoroethyl methacrylate), have relatively low refractive indices, n ≤ 1.415, yet a very large density, ρ ∼ 1.538 g/ml. Conversely, aliphatic methacrylate polymers have densities that decreases with the length of the alkyl group: ρ∼ methyl methacrylate >ethyl methacrylate >t-butyl methacrylate, but exhibit relatively high refractive indices, nPMMA ≈ 1.495. Combining these two types of monomers at different molar ratios yields a copolymer of which density and refractive index can be tuned; a similar strategy to tune the refractive index of the PMMA system was reported previously29. Here we choose a combination of trifluoroethyl methacrylate (TFEMA) and tert-butyl methacrylate (tBMA). Homopolymers of each exhibit the following properties: PTFEMA [ρ = 1.53 g/ml, n = 1.4185] and PtBMA [ρ = 1.022 g/ml, n = 1.4630]. The dispersion copolymerization of TFEMA and tBMA yields particles with a very low size polydispersity, typically CV ≤ 5% (Fig. 2, see SI). The particle size can be tuned precisely from a ∼ 0.55 μm–8 μm by changing the type and amount of cosolvent and by the monomer volume fraction charged during dispersion polymerization, see Fig. 3. At a ratio of 28:72 of TFEMA:tBMA, by volume, particles have a relatively low density, ρ = 1.16 g/ml, refractive index, n = 1.452, and high glass transition temperature, Tg ∼ 86 °C as measured by differential scanning calorimetry while in the suspending solution. This comonomer ratio is specifically chosen to refractive index and density match the colloids to a mixture of polar solvents, formamide and sulfolane.


Precise colloids with tunable interactions for confocal microscopy.

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

(A) PVP stabilized particle diameters with changes in co-solvent and inimer type, see Table in SI.  H2O, no inimer;  H2O, acrylate inimer;  H2O, methacrylate inimer;  formamide, acrylate inimer;  formamide, methacrylate inimer. (B) SPMA stabilized particle diameters with cosolvent, H2O, volume varied along with total monomer volume fraction, see Table in SI.  15vol% monomer;  12.5vol% monomer;  10vol% monomer;  5vol% monomer. Reaction compositions within shaded regions yield only polymerized coagulum.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: (A) PVP stabilized particle diameters with changes in co-solvent and inimer type, see Table in SI. H2O, no inimer; H2O, acrylate inimer; H2O, methacrylate inimer; formamide, acrylate inimer; formamide, methacrylate inimer. (B) SPMA stabilized particle diameters with cosolvent, H2O, volume varied along with total monomer volume fraction, see Table in SI. 15vol% monomer; 12.5vol% monomer; 10vol% monomer; 5vol% monomer. Reaction compositions within shaded regions yield only polymerized coagulum.
Mentions: Here we develop a colloidal system which can be suspended in polar solvents, in which the refractive index and density can be controlled precisely, and whose interactions are tunable using controlled living radical polymerisation methods, illustrated in Fig. 1. Fluorinated methacrylate polymers, such as poly(trifluoroethyl methacrylate), have relatively low refractive indices, n ≤ 1.415, yet a very large density, ρ ∼ 1.538 g/ml. Conversely, aliphatic methacrylate polymers have densities that decreases with the length of the alkyl group: ρ∼ methyl methacrylate >ethyl methacrylate >t-butyl methacrylate, but exhibit relatively high refractive indices, nPMMA ≈ 1.495. Combining these two types of monomers at different molar ratios yields a copolymer of which density and refractive index can be tuned; a similar strategy to tune the refractive index of the PMMA system was reported previously29. Here we choose a combination of trifluoroethyl methacrylate (TFEMA) and tert-butyl methacrylate (tBMA). Homopolymers of each exhibit the following properties: PTFEMA [ρ = 1.53 g/ml, n = 1.4185] and PtBMA [ρ = 1.022 g/ml, n = 1.4630]. The dispersion copolymerization of TFEMA and tBMA yields particles with a very low size polydispersity, typically CV ≤ 5% (Fig. 2, see SI). The particle size can be tuned precisely from a ∼ 0.55 μm–8 μm by changing the type and amount of cosolvent and by the monomer volume fraction charged during dispersion polymerization, see Fig. 3. At a ratio of 28:72 of TFEMA:tBMA, by volume, particles have a relatively low density, ρ = 1.16 g/ml, refractive index, n = 1.452, and high glass transition temperature, Tg ∼ 86 °C as measured by differential scanning calorimetry while in the suspending solution. This comonomer ratio is specifically chosen to refractive index and density match the colloids to a mixture of polar solvents, formamide and sulfolane.

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.