We have no acknowledgements.

Caution: Please wear a lab-coat, gloves, and safety glasses and read material safety data sheets (MSDS) before use. All purchased materials have been used without further purification.
1. Preparation of Emulsions Consisting of Styrene/PFO/Aqueous SDS Solution Mixtures
<ol>
	<li>To prepare 5 mM of aqueous SDS solution, dissolve 14.5 mg of SDS in 10 mL of high-purity H2O. 
	NOTE: High-purity H2O has been used (resistivity (R) = 18 M&#937; cm, surface tension (&#947;) = 72.0 mN m-1 at 25 &#176;C).</li>
	<li>Add 1.5 g of styrene, 0.6 g of PFO, and 0.9 g of 5 mM of aqueous SDS solution to a 10 mL glass vial with a stir bar. 
	NOTE: In scanning confocal fluorescence microscopy observations, add 2.6 mg of coumarin 102 and 0.062 mg of calcein to the mixture.</li>
	<li>Stir the mixture for 60 min at 1,150 rpm under room temperature and then raise the temperature to 80 &#176;C.</li>
	<li>Stir the mixture for 60 min at 1,150 rpm and 80 &#176;C.</li>
</ol>
2. Fabrication of polymer particles using Emulsions Consisting of Styrene/PFO/Aqueous SDS Solution Mixtures
<ol>
	<li>Add 3.9 mg of potassium peroxodisulfate, 2 mg of pyrene, 1.5 g of styrene, 0.6 g of PFO, and 0.9 g of 5 mM of aqueous SDS solution to a 10 mL glass vial with a stir bar and seal it with a rubber septum.</li>
	<li>Deoxygenate the mixture by bubbling nitrogen gas through a syringe needle for 30 min. 
	Caution: Slowly flow the nitrogen gas to not generate a large amount of foam.</li>
	<li>To prepare the emulsion, stir the mixture for 60 min at 1,150 rpm and room temperature and then raise the temperature to 80 &#176;C.</li>
	<li>Stir the mixture for 30 min at 1,150 rpm and 80 &#176;C.</li>
	<li>Transfer the cloudy part (1.8 mL) in the resultant solution (3 mL) to the test tube and then add 30% aqueous ethanol solution to completely terminate the polymerization reaction.</li>
	<li>Sonicate (Power: 130 W, Frequency: 4.2 kHz) for 10 min to wash resultant polymer particles and then centrifuge for 10 min at 2300 x g.</li>
	<li>To obtain the polymer particles, remove the supernatant solution from the test tube.</li>
	<li>Add 3 mL of water to the resultant solids in the test tube. Sonicate (Power: 130 W, Frequency: 4.2 kHz) for 10 min and centrifuge for 10 min at 2300 x g. Remove the supernatant solution from the test tube.</li>
	<li>Repeat the washing procedure (Step 2.8) until foam is not generated from the supernatant solution. Evaporate water to obtain the solid of hollow polymer particles.</li>
</ol>
3. Preparation of microcapsules using the hollow polymer particles
<ol>
	<li>Add 1 mg of hollow polystyrene particles (step 2.9) and 4 mL of water to a 10 mL glass vial with a stir bar.</li>
	<li>Sonicate (Power: 130 W, Frequency: 4.2 kHz) for 10 min to disperse the hollow particles in water.</li>
	<li>Add 0.1 mL of toluene to the water dispersed the particles and then stir it for 1 h at 100 rpm under room temperature. Transfer the liquid to a test tube. 
	Caution: If the rotation per minute increases, the morphology of particles will deform.</li>
	<li>Centrifuge the liquid for 10 min at 2300 x g to isolate the microcapsules form it. Remove the supernatant solution from the test tube.</li>
</ol>

<ol>
	<li>Okubo, M., Fujibayashi, T., Terada, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+micron-sized,+monodisperse+polymer+particles+of+disc-like+and+polyhedral+shapes+by+seeded+dispersion+polymerization.">Synthesis of micron-sized, monodisperse polymer particles of disc-like and polyhedral shapes by seeded dispersion polymerization.</a> Colloid Polym Sci. 283 (7), 793-798 (2005).</li><li>Fujibayashi, T., Okubo, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+Thermodynamic+Stability+of+Micron-Sized,+Monodisperse+Composite+Polymer+Particles+of+Disc-like+Shapes+by+Seeded+Dispersion+Polymerization.">Preparation and Thermodynamic Stability of Micron-Sized, Monodisperse Composite Polymer Particles of Disc-like Shapes by Seeded Dispersion Polymerization.</a> Langmuir. 23 (15), 7958-7962 (2007).</li><li>Okubo, M., Fujibayashi, T., Yamada, M., Minami, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micron-sized,+monodisperse,+snowman/confetti-shaped+polymer+particles+by+seeded+dispersion+polymerization.">Micron-sized, monodisperse, snowman/confetti-shaped polymer particles by seeded dispersion polymerization.</a> Colloid Polym Sci. 283 (9), 1041-1045 (2005).</li><li>Xu, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+Monodisperse+Particles+by+Using+Microfluidics:+Control+over+Size,+Shape,+and+Composition.">Generation of Monodisperse Particles by Using Microfluidics: Control over Size, Shape, and Composition.</a> Angew Chem Int Ed. 44 (5), 724-728 (2005).</li><li>Serra, C. A., Chang, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic-Assisted+Synthesis+of+Polymer+Particles.">Microfluidic-Assisted Synthesis of Polymer Particles.</a> Chem Eng Tech. 31 (8), 1099-1115 (2008).</li><li>Higuchi, T., Yabu, H., Shimomura, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+preparation+of+hemispherical+polystyrene+particles.">Simple preparation of hemispherical polystyrene particles.</a> Colloids Surf A. 284, 250-253 (2006).</li><li>Sun, Z. Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonspherical+Colloidal+Crystals+Fabricated+by+the+Thermal+Pressing+of+Colloidal+Crystal+Chips.">Nonspherical Colloidal Crystals Fabricated by the Thermal Pressing of Colloidal Crystal Chips.</a> Langmuir. 21 (20), 8987-8991 (2005).</li><li>Deng, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+approach+to+the+construction+of+3-D+ordered+macrostructures+with+polyhedral+particles.">A novel approach to the construction of 3-D ordered macrostructures with polyhedral particles.</a> J Mater Chem. 18 (4), 408-415 (2008).</li><li>Hyuk Im, S., Jeong, U., Xia, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymer+hollow+particles+with+controllable+holes+in+their+surfaces.">Polymer hollow particles with controllable holes in their surfaces.</a> Nat Mater. 4 (9), 671-675 (2005).</li><li>Saito, N., Kagari, Y., Okubo, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Colloidal+Stabilizer+on+the+Shape+of+Polystyrene/Poly(methyl+methacrylate)+Composite+Particles+Prepared+in+Aqueous+Medium+by+the+Solvent+Evaporation+Method.">Effect of Colloidal Stabilizer on the Shape of Polystyrene/Poly(methyl methacrylate) Composite Particles Prepared in Aqueous Medium by the Solvent Evaporation Method.</a> Langmuir. 22 (22), 9397-9402 (2006).</li><li>Cai, P. -. j., Tang, Y. -. j., Wang, Y. -. t., Cao, Y. -. j. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+polystyrene+hollow+spheres+in+W/O/W+multiple+emulsions.">Fabrication of polystyrene hollow spheres in W/O/W multiple emulsions.</a> Mater Chem Phys. 124 (1), 10-12 (2010).</li><li>Liang, S. -. S., Chen, S. -. L., Chen, S. -. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diverse+macroporous+spheres+synthesized+by+multiple+emulsion+polymerization+for+protein+analyses.">Diverse macroporous spheres synthesized by multiple emulsion polymerization for protein analyses.</a> Chem Commun. 47 (29), 8385-8387 (2011).</li><li>Kondo, Y., Yoshino, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hybrid+fluorocarbon/hydrocarbon+surfactants.">Hybrid fluorocarbon/hydrocarbon surfactants.</a> Curr Opin Colloid Interface Sci. 10 (3-4), 88-93 (2005).</li><li>Takahashi, Y., Kondo, Y., Schmidt, J., Talmon, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-Assembly+of+a+Fluorocarbon-Hydrocarbon+Hybrid+Surfactant:+Dependence+of+Morphology+on+Surfactant+Concentration+and+Time.">Self-Assembly of a Fluorocarbon-Hydrocarbon Hybrid Surfactant: Dependence of Morphology on Surfactant Concentration and Time.</a> J Phys Chem B. 114 (42), 13319-13325 (2010).</li><li>Takahashi, Y., Nasu, Y., Aramaki, K., Kondo, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unusual+viscoelastic+behavior+of+aqueous+solutions+of+fluorocarbon-hydrocarbon+hybrid+surfactant+and+its+morphological+transformations.">Unusual viscoelastic behavior of aqueous solutions of fluorocarbon-hydrocarbon hybrid surfactant and its morphological transformations.</a> J Fluor Chem. 145, 141-147 (2013).</li><li>Yoshino, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Syntheses+of+Hybrid+Anionic+Surfactants+Containing+Fluorocarbon+and+Hydrocarbon+Chains.">Syntheses of Hybrid Anionic Surfactants Containing Fluorocarbon and Hydrocarbon Chains.</a> Langmuir. 11 (2), 466-469 (1995).</li><li>Zarzar, L. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamically+reconfigurable+complex+emulsions+via+tunable+interfacial+tensions.">Dynamically reconfigurable complex emulsions via tunable interfacial tensions.</a> Nature. 518 (7540), 520-524 (2015).</li></ol>

We have nothing to disclose.

The emulsions containing Janus droplets of styrene and PFO were obtained above 10 wt% of the weight fraction of aqueous SDS concentration and any weight fraction of styrene and PFO. When the various weight-fractions of the emulsions containing the Janus droplets have been polymerized for 30 min, the hollow polystyrene particles can be obtained for all composition. These results indicate that the protocol demonstrated here is simple. In addition, the diameter, hole size, and hole volume of the hollow polystyrene particles can be controlled by the polymerization time in the method described here.
We suggest the following mechanism for the fabrication of the hollow polystyrene particles. Janus oil droplets consisting of styrene and PFO formed in the O/W emulsions containing mixtures of aqueous SDS solution, styrene, and PFO at 80 &#176;C. PFO droplets are located on the surface of styrene droplets. Since KPS, an initiator of the polymerization, is soluble in the water phase, the polymerization will progress at the interface of the styrene/aqueous SDS solution. Styrene in the ternary emulsions was polymerized to polystyrene at 80 &#176;C, whereas PFO, having no polymerizable groups, remained in the emulsions at that temperature. After the polymerization was terminated, a hole on the polystyrene particle was formed by removal of PFO. Therefore, the hollow cup-type polystyrene particles having a hole on the surface were fabricated atany weight fraction of styrene and PFO and all polymerization times.
Adding a small amount of toluene to the hollow polystyrene particles fabricated by radical polymerization for 90 min brings about sealing the holes on the hollow polystyrene particles. This phenomena is consistent with that reported by Hyuk et al.9. The capsulation method can contain an aqueous material in the particles.
In this article, we have demonstrated a fabrication method of hollow polymer particles using Janus oil droplets consisting of styrene and PFO, which are mutually immiscible. The preparation method of non-spherical polymer particles has already been studied because of their potential use in various applications. This strategy using Janus oil droplets of hydrocarbon oil and fluorocarbon oil will apply to the fabrication of non-spherical polymer particles from various types of monomer and drug delivery system.

While spherical polymer particles have been widely used in various industrial applications, it is well-known that dimple particles, hemispheres, disks, and ellipsoids, have been prepared by seeded polymerizations1,2,3, photo-polymerization of non-spherical monomer droplets using microreactor with specific geometries4,5, self-organization using reprecipitation of polymers6, and deformation of spherical polymer particles by mechanical external forces7,8. In particular, hollow polymer particles with micrometer-size have been fabricated by evaporation of a good solvent from spherical polymer particles swollen by the solvent9,10 and polymerization using multiple emulsions11,12.
In this work, we focus on the usage of mutual immiscibility of hydrocarbon and fluorocarbon oils in the fabrication of polymer particles. Hybrid surfactants have a hydrocarbon chain and a fluorocarbon chain in the molecule. Previously, we have reported the unique properties of hybrid surfactants that are not observed in conventional surfactants13,14,15. We have also studied emulsions using hydrocarbon oil, fluorocarbon oil, and aqueous surfactant solution, which are mutually immiscible16. However, there are very few studies of the emulsions17. These studies have described the morphology of oil droplets consisting of hydrocarbon oil and fluorocarbon oil in aqueous surfactant solutions.
Here, we show a detailed protocol of the fabrication of hollow polymer particles by radical polymerization using oil droplets in emulsions consisting of hydrocarbon oil, fluorocarbon oil, and aqueous sodium dodecylsulfate (SDS) solutions. We suggest a new strategy, which is different from conventional methods, for the preparation of non-spherical polymer particles. This method can simply fabricate the hollow polymer particles in a short time. In addition, the protocol of the preparation of microcapsules through the hollow polymer particles is shown.

<table><tbody><tr><td>&lt;strong&gt;Material&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Sodium dodecylsulfate, 95.0%</td><td>Wako Pure Chemical Industries, Ltd.</td><td>192-08672</td><td></td></tr><tr><td>Styrene, 99.0%</td><td>Tokyo Chemical Industry Co. Ltd.</td><td>S0095</td><td></td></tr><tr><td>Perfluorooctane, 99%</td><td>Fluorochem Ltd.</td><td>8706</td><td></td></tr><tr><td>Coumarin 102, 97.0%</td><td>Tokyo Chemical Industry Co. Ltd.</td><td>C2267</td><td></td></tr><tr><td>Calcein</td><td>Dojindo Molecular Technologies, Inc.</td><td>C001</td><td></td></tr><tr><td>Potassium peroxodisulfate, 98.0%</td><td>Kanto Chemical Co., Inc.</td><td>32375-30</td><td></td></tr><tr><td>Pyrene, 97.0%</td><td>Wako Pure Chemical Industries, Ltd.</td><td>167-05302</td><td></td></tr><tr><td>Ethanol, 99.5%</td><td>Kanto Chemical Co., Inc.</td><td>14033-00</td><td></td></tr><tr><td>Toluene, 99.5%</td><td>Kanto Chemical Co., Inc.</td><td>40180-00</td><td></td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Scanning Electron Microscope</td><td>Hitachi High-Technologies Corporation</td><td>S-4800</td><td></td></tr><tr><td>Scanning Transmission Electron Microscope</td><td>Hitachi High-Technologies Corporation</td><td>S-4800</td><td></td></tr><tr><td>Ultrasonic cleaner</td><td>Branson Ultrasonics, Emerson Japan, Ltd.</td><td>Model 3510</td><td></td></tr><tr><td>Centrifuge</td><td>AS ONE Corporation</td><td>CN-1050</td><td></td></tr></tbody></table>

preparation of hollow polystyrene particles and microcapsules by radical polymerization of janus droplets consisting of hydrocarbon and fluorocarbon oils

In this article, we have demonstrated a method for producing hollow particles and microcapsules using oil droplets consisting of hydrocarbon oil (styrene) and fluorocarbon oil (perfluoro-n-octane, PFO) in aqueous surfactant (sodium dodecylsulfate, SDS) solutions. Since fluorocarbon oils are immiscible with hydrocarbon oils, the two oils are separated. Emulsions are prepared by stirring styrene/PFO/aqueous SDS solution mixtures at 80 &#176;C. The type of emulsions and the morphology of droplets in the emulsions are observed by light microscope and scanning confocal fluorescence microscope. It is found that oil droplets with Janus-type morphologies consisting of mutually immiscible styrene and PFO are formed in aqueous SDS solutions. Polystyrene particles are fabricated by radical polymerization of the ternary mixtures of styrene/PFO/aqueous SDS solution at 80 &#176;C. The morphologies of the polystyrene are confirmed by scanning electron microscopy and scanning transmission electron microscopy observations. These observations show the preparation of hollow polystyrene particles with a single hole on the surface. To our knowledge, this method is a novel strategy using the immiscibility of hydrocarbon and fluorocarbon oils. The hollow particles can also be applied to the preparation of microcapsules.

Light and scanning confocal fluorescence microscopy observations were performed to determine the morphology and composition of droplets in the emulsions consisting of styrene, PFO, and 5 mM aqueous SDS solution (Figure 1). Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) observations showed the formation of hollow particles and microcapsules (Figure 2).
The DIC and confocal fluorescence microscopy images of emulsions consisting of ternary mixtures of styrene/PFO/aqueous SDS solution indicate that the continuous phase is aqueous SDS solution, because green fluorescence corresponding to calcein was observed in the continuous phase, and therefore, oil-in-water type emulsions are formed (Figure 1a and 1b). These images also show that the oil droplets consist of styrene and PFO, which are mutually immiscible. The DIC and confocal fluorescence microscopy images of emulsions containing coumarin 102 reveal that a PFO droplet is located at the interface between water and a styrene droplet. The ternary mixtures of styrene, PFO, and aqueous SDS solution at 5 mM form emulsions containing Janus oil droplets, which consist of styrene and PFO.
The SEM and STEM images of polymer particles fabricated by the radical polymerization of the emulsions of styrene/PFO/5 mM aqueous SDS solution show the preparation of hollow non-spherical polystyrene particles with a hole on the surface (Figure 2a and 2b). The formation rate, diameter, and hole size of the hollow polystyrene particles are evaluated by observing 200 particles through SEM and STEM. The averaged diameter estimated from SEM observations is 1.3 &#181;m. The size is consistent with the diameter of the polymer particles estimated from dynamic light scattering measurements. The formation rate is approximately 100%. The averaged hole-size and volume of the hole in the hollow particles are 0.8 &#177; 0.4 &#181;m and 0.9 &#177; 0.4 &#181;m3, respectively. Therefore, the hollow polystyrene particles having a 0.8 &#181;m hole were fabricated by radical polymerization of Janus droplets containing styrene in the emulsions.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56922/56922fig1.jpg" /> 
Figure 1. Morphologies of droplets in emulsions consisting of styrene, PFO, and 5 mM aqueous SDS solution. (a) Differential interference contrast (DIC) and (b) confocal fluorescence microscopy images of the emulsions containing aqueous fluorescent calcein. (c) DIC and (d) confocal fluorescence microscopy images of the emulsions containing oil-soluble fluorescent coumarin 102. <a href="https://cloudflare.jove.com/files/ftp_upload/56922/56922fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56922/56922fig2.jpg" /> 
Figure 2. Morphologies of hollow polystyrene particles and microcapsules fabricated using emulsions consisting of styrene, PFO, and 5 mM aqueous SDS solution. (a) SEM and (b) STEM images of the hollow polystyrene particles. (c) SEM and (d) STEM images of the microcapsules. <a href="https://cloudflare.jove.com/files/ftp_upload/56922/56922fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Preparation of Hollow Polystyrene Particles and Microcapsules by Radical Polymerization of Janus Droplets Consisting of Hydrocarbon and Fluorocarbon Oils at J

Preparation of Hollow Polystyrene Particles and Microcapsules by Radical Polymerization of Janus Droplets Consisting of Hydrocarbon and Fluorocarbon Oils

A protocol for the fabrication of hollow polymer particles and microcapsules by radical polymerization using emulsions consisting of styrene, perfluoro-n-octane, and aqueous SDS (sodium dodecylsulfate) solution is presented.

In this article, we have demonstrated a method for producing hollow particles and microcapsules using oil droplets consisting of hydrocarbon oil (styrene) ...

preparation-hollow-polystyrene-particles-microcapsules-radical

Universidad de Cartagena UDEC

Research

JoVE Journal

Chemistry

9.9K Views.  Tokyo University of Science. A protocol for the fabrication of hollow polymer particles and microcapsules by radical polymerization using emulsions consisting of styrene, perfluoro-n-octane, and aqueous SDS (sodium dodecylsulfate) solution is presented.

Video: Preparation of Hollow Polystyrene Particles and Microcapsules by Radical Polymerization of Janus Droplets Consisting of Hydrocarbon and Fluorocarbon Oils

Synthesis of Poly(N-isopropylacrylamide) Janus Microhydrogels for Anisotropic Thermo-responsiveness and Organophilic/Hydrophilic Loading Capability

Janus microparticles are compartmentalized particles with differing molecular structures and/or functionality on each of their two sides. Because of this unique property, Janus microparticles have been recognized as a new class of materials, thereby attracting a great deal of attention from various research fields. The versatility of these microparticles has been exemplified through their uses as building blocks for self-assembly, electrically responsive actuators, emulsifiers for painting and cosmetics, and carriers for drug delivery. This study introduces a detailed protocol that explicitly describes a synthetic method for designing novel Janus microhydrogels composed of a single base material, poly(N-isopropylacrylamide) (PNIPAAm). Janus microdroplets are firstly generated via a hydrodynamic focusing microfluidic device (HFMD) based on the separation of a supersaturated aqueous NIPAAm monomer solution and subsequently polymerized through exposure to UV irradiation. The resulting Janus microhydrogels were found to be entirely composed of the same base material, featured an easily identifiable compartmentalized morphology, and exhibited anisotropic thermo-responsiveness and organophilic/hydrophilic loading capability. We believe that the proposed method introduces a novel hydrogel platform with the potential for advanced synthesis of multi-functional Janus microhydrogels.

Synthesis of PolyN-isopropylacrylamide Janus Microhydrogels for Anisotropic Thermo-responsiveness and Organophilic/Hydrophilic Loading Capability

We present a protocol to synthesize Janus microhydrogels composed entirely of the same base material, poly(N-isopropylacrylamide) (PNIPAAm), with a clearly compartmentalized structure base on the phase separation of a supersaturated NIPAAm monomer solution. The synthesized Janus microhydrogels show unique properties such as anisotropic thermo-responsiveness and organophilic/hydrophilic loading capability.

Janus microparticles are compartmentalized particles with differing molecular structures and/or functionality on each of their two sides. Because of this ...

Using Polystyrene-block-poly(acrylic acid)-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are encapsulated in polystyrene-block-poly(acrylic acid) (PSPAA) shells and then used as monomers for their self-assembly. Spherical PSPAA micelles upon acid treatment are known to assemble into cylindrical micelles. Exploiting this tendency, the core-shell nanoparticles are induced to aggregate, coalesce, and then transform into long chains. When more than one type of nanoparticles are used, random and block &#8220;copolymers&#8221; of nanoparticles can be obtained. Detailed procedures are reported for the PSPAA encapsulation of nanoparticles, homo- and co-polymerization of the core-shell nanoparticles, separation and purification of the resulting nanoparticle chains. Transformations of single-line chains into double- and triple-line chains are also presented. The synergy between the polymer shell and the embedded nanoparticles leads to an unusual chain-growth polymerization mode, giving long nanoparticle chains that are distinct from the products of the traditional step-growth aggregation process.

Using Polystyrene-block-polyacrylic acid-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We report protocols for &#8220;polymerizing&#8221; various types of polymer-encapsulated metal nanoparticles into long chains of &#8220;homo-&#8220; and &#8220;co-polymers&#8221;.

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are ...

High Throughput Single-cell and Multiple-cell Micro-encapsulation

Microfluidic encapsulation methods have been previously utilized to capture cells in picoliter-scale aqueous, monodisperse drops, providing confinement from a bulk fluid environment with applications in high throughput screening, cytometry, and mass spectrometry. We describe a method to not only encapsulate single cells, but to repeatedly capture a set number of cells (here we demonstrate one- and two-cell encapsulation) to study both isolation and the interactions between cells in groups of controlled sizes. By combining drop generation techniques with cell and particle ordering, we demonstrate controlled encapsulation of cell-sized particles for efficient, continuous encapsulation. Using an aqueous particle suspension and immiscible fluorocarbon oil, we generate aqueous drops in oil with a flow focusing nozzle. The aqueous flow rate is sufficiently high to create ordering of particles which reach the nozzle at integer multiple frequencies of the drop generation frequency, encapsulating a controlled number of cells in each drop. For representative results, 9.9 &mu;m polystyrene particles are used as cell surrogates. This study shows a single-particle encapsulation efficiency Pk=1 of 83.7% and a double-particle encapsulation efficiency Pk=2 of 79.5% as compared to their respective Poisson efficiencies of 39.3% and 33.3%, respectively. The effect of consistent cell and particle concentration is demonstrated to be of major importance for efficient encapsulation, and dripping to jetting transitions are also addressed. 
Introduction 
Continuous media aqueous cell suspensions share a common fluid environment which allows cells to interact in parallel and also homogenizes the effects of specific cells in measurements from the media. High-throughput encapsulation of cells into picoliter-scale drops confines the samples to protect drops from cross-contamination, enable a measure of cellular diversity within samples, prevent dilution of reagents and expressed biomarkers, and amplify signals from bioreactor products. Drops also provide the ability to re-merge drops into larger aqueous samples or with other drops for intercellular signaling studies.1,2 The reduction in dilution implies stronger detection signals for higher accuracy measurements as well as the ability to reduce potentially costly sample and reagent volumes.3 Encapsulation of cells in drops has been utilized to improve detection of protein expression,4 antibodies,5,6 enzymes,7 and metabolic activity8 for high throughput screening, and could be used to improve high throughput cytometry.9 Additional studies present applications in bio-electrospraying of cell containing drops for mass spectrometry10 and targeted surface cell coatings.11 Some applications, however, have been limited by the lack of ability to control the number of cells encapsulated in drops. Here we present a method of ordered encapsulation12 which increases the demonstrated encapsulation efficiencies for one and two cells and may be extrapolated for encapsulation of a larger number of cells.
To achieve monodisperse drop generation, microfluidic "flow focusing" enables the creation of controllable-size drops of one fluid (an aqueous cell mixture) within another (a continuous oil phase) by using a nozzle at which the streams converge.13 For a given nozzle geometry, the drop generation frequency f and drop size can be altered by adjusting oil and aqueous flow rates Qoil and Qaq. As the flow rates increase, the flows may transition from drop generation to unstable jetting of aqueous fluid from the nozzle.14 
When the aqueous solution contains suspended particles, particles become encapsulated and isolated from one another at the nozzle. For drop generation using a randomly distributed aqueous cell suspension, the average fraction of drops Dk containing k cells is dictated by Poisson statistics, where Dk = &lambda;k exp(-&lambda;)/(k!) and &lambda; is the average number of cells per drop. The fraction of cells which end up in the "correctly" encapsulated drops is calculated using Pk = (k x Dk)/&Sigma;(k' x Dk'). The subtle difference between the two metrics is that Dk relates to the utilization of aqueous fluid and the amount of drop sorting that must be completed following encapsulation, and Pk relates to the utilization of the cell sample. As an example, one could use a dilute cell suspension (low &lambda;) to encapsulate drops where most drops containing cells would contain just one cell. While the efficiency metric Pk would be high, the majority of drops would be empty (low Dk), thus requiring a sorting mechanism to remove empty drops, also reducing throughput.15
Combining drop generation with inertial ordering provides the ability to encapsulate drops with more predictable numbers of cells per drop and higher throughputs than random encapsulation. Inertial focusing was first discovered by Segre and Silberberg16 and refers to the tendency of finite-sized particles to migrate to lateral equilibrium positions in channel flow. Inertial ordering refers to the tendency of the particles and cells to passively organize into equally spaced, staggered, constant velocity trains. Both focusing and ordering require sufficiently high flow rates (high Reynolds number) and particle sizes (high Particle Reynolds number).17,18 Here, the Reynolds number Re =uDh/&nu; and particle Reynolds number Rep =Re(a/Dh)2, where u is a characteristic flow velocity, Dh [=2wh/(w+h)] is the hydraulic diameter, &nu; is the kinematic viscosity, a is the particle diameter, w is the channel width, and h is the channel height. Empirically, the length required to achieve fully ordered trains decreases as Re and Rep increase. Note that the high Re and Rep requirements (for this study on the order of 5 and 0.5, respectively) may conflict with the need to keep aqueous flow rates low to avoid jetting at the drop generation nozzle. Additionally, high flow rates lead to higher shear stresses on cells, which are not addressed in this protocol. The previous ordered encapsulation study demonstrated that over 90% of singly encapsulated HL60 cells under similar flow conditions to those in this study maintained cell membrane integrity.12 However, the effect of the magnitude and time scales of shear stresses will need to be carefully considered when extrapolating to different cell types and flow parameters. The overlapping of the cell ordering, drop generation, and cell viability aqueous flow rate constraints provides an ideal operational regime for controlled encapsulation of single and multiple cells.
Because very few studies address inter-particle train spacing,19,20 determining the spacing is most easily done empirically and will depend on channel geometry, flow rate, particle size, and particle concentration. Nonetheless, the equal lateral spacing between trains implies that cells arrive at predictable, consistent time intervals. When drop generation occurs at the same rate at which ordered cells arrive at the nozzle, the cells become encapsulated within the drop in a controlled manner. This technique has been utilized to encapsulate single cells with throughputs on the order of 15 kHz,12 a significant improvement over previous studies reporting encapsulation rates on the order of 60-160 Hz.4,15 In the controlled encapsulation work, over 80% of drops contained one and only one cell, a significant efficiency improvement over Poisson (random) statistics, which predicts less than 40% efficiency on average.12
In previous controlled encapsulation work,12 the average number of particles per drop &lambda; was tuned to provide single-cell encapsulation. We hypothesize that through tuning of flow rates, we can efficiently encapsulate any number of cells per drop when &lambda; is equal or close to the number of desired cells per drop. While single-cell encapsulation is valuable in determining individual cell responses from stimuli, multiple-cell encapsulation provides information relating to the interaction of controlled numbers and types of cells. Here we present a protocol, representative results using polystyrene microspheres, and discussion for controlled encapsulation of multiple cells using a passive inertial ordering channel and drop generation nozzle.

Combining monodisperse drop generation with inertial ordering of cells and particles, we describe a method to encapsulate a desired number of cells or particles in a single drop at kHz rates. We demonstrate efficiencies twice exceeding those of unordered encapsulation for single- and double-particle drops.

Microfluidic encapsulation methods have been previously utilized to capture cells in picoliter-scale aqueous, monodisperse drops, providing confinement ...

Bioengineering

Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins with the synthesis of a hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) homopolymer using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under mild visible light irradiation (&#955; = 460 nm, 0.7 mW/cm2), this macro-chain transfer agent (macro-CTA) in the presence of a ruthenium based photoredox catalyst, Ru(bpy)3Cl2 can be chain extended with a second monomer to form a well-defined block copolymer in a process known as Photoinduced Electron Transfer RAFT (PET-RAFT). When PET-RAFT is used to chain extend POEGMA with benzyl methacrylate (BzMA) in ethanol (EtOH), polymeric nanoparticles with different morphologies are formed in situ according to a polymerization-induced self-assembly (PISA) mechanism. Self-assembly into nanoparticles presenting POEGMA chains at the corona and poly(benzyl methacrylate) (PBzMA) chains in the core occurs in situ due to the growing insolubility of the PBzMA block in ethanol. Interestingly, the formation of highly pure worm-like micelles can be readily monitored by observing the onset of a highly viscous gel in situ due to nanoparticle entanglements occurring during the polymerization. This process thereby allows for a more reproducible synthesis of worm-like micelles simply by monitoring the solution viscosity during the course of the polymerization. In addition, the light stimulus can be intermittently applied in an ON/OFF manner demonstrating temporal control over the nanoparticle morphology.

This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins ...

Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by &#960;-&#960; Stacking Interactions

In this study, an amphiphilic copolymer that includes a core-forming block with phenyl groups was synthesized by living anionic polymerization of phenyl glycidyl ether (PheGE) on methoxy-polyethylene glycol (mPEG-b-PPheGE). Characterization of the copolymer revealed a narrow molecular distribution (PDI &#60; 1.03) and confirmed the degree of polymerization of mPEG122-b-(PheGE)15. The critical micelle concentration of the copolymer was evaluated using an established fluorescence method with the aggregation behavior evaluated by dynamic light scattering and transmission electronic microscopy. The potential of the copolymer for use in drug delivery applications was evaluated in a preliminary manner including in vitro biocompatibility, loading and release of the hydrophobic anti-cancer drug doxorubicin (DOX). A stable micelle formulation of DOX was prepared with drug loading levels up to 14% (wt%), drug loading efficiencies &#62; 60% (w/w) and sustained release of drug over 4 days under physiologically relevant conditions (acidic and neutral pH, presence of albumin). The high drug loading level and sustained release is attributed to stabilizing &#960;-&#960; interactions between DOX and the core-forming block of the micelles.

The key steps of living anionic polymerization of phenyl glycidyl ether (PheGE) on methoxy-polyethylene glycol (mPEG-b-PPheGE) are described. The resulting block copolymer micelles (BCMs) were loaded with doxorubicin 14% (wt%) and sustained release of drug over 4 days under physiologically relevant conditions was obtained.

In this study, an amphiphilic copolymer that includes a core-forming block with phenyl groups was synthesized by living anionic polymerization of phenyl ...

Grafting Multiwalled Carbon Nanotubes with Polystyrene to Enable Self-Assembly and Anisotropic Patchiness

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a free-radical polymerization strategy to enable the modulation of the nanotube surface properties and produce supramolecular self-assembly of the nanostructures. First, a selective hydroxylation of the pristine nanotubes through a biphasic catalytically mediated oxidation reaction creates superficially distributed reactive sites at the sidewalls. The latter reactive sites are subsequently modified with methacrylic moieties using a silylated methacrylic precursor to create polymerizable sites. Those polymerizable groups can address further polymerization of styrene to produce a hybrid nanomaterial containing PS chains grafted to the nanotube sidewalls. The polymer-graft content, amount of silylated methacrylic moieties introduced and hydroxylation modification of the nanotubes are identified and quantified by Thermogravimetric Analysis (TGA). The presence of reactive functional groups hydroxyl and silylated methacrylate are confirmed by Fourier Transform Infrared Spectroscopy (FT-IR). Polystyrene-grafted carbon nanotube solutions in tetrahydrofuran (THF) provide wall-to-wall collinearly self-assembled nanotubes when cast samples are analyzed by transmission electron microscopy (TEM). Those self-assemblies are not obtained when suitable blanks are similarly cast from analogous solutions containing non-grafted counterparts. Therefore, this method enables the modification of the nanotube anisotropic patchiness at the sidewalls which results into spontaneous auto-organization at the nanoscale.

A procedure for the synthesis of polystyrene-grafted multiwalled carbon nanotubes using successive chemical modification steps to selectively introduce the polymer chains to the sidewalls and their self-assembly via anisotropic patchiness is presented.

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

Engineering

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Synthesis of Monodisperse Cylindrical Nanoparticles via Crystallization-driven Self-assembly of Biodegradable Block Copolymers

The production of monodisperse cylindrical micelles is a significant challenge in polymer chemistry. Most cylindrical constructs formed from diblock copolymers are produced by one of three techniques: thin film rehydration, solvent switching or polymerization-induced self-assembly, and produce only flexible, polydisperse cylinders. Crystallization-driven self-assembly (CDSA) is a method which can produce cylinders with these properties, by stabilizing structures of a lower curvature due to the formation of a crystalline core. However, the living polymerization techniques by which most core-forming blocks are formed are not trivial processes and the CDSA process may yield unsatisfactory results if carried out incorrectly. Here, the synthesis of cylindrical nanoparticles from simple reagents is shown. The drying and purification of reagents prior to a ring-opening polymerization of &#949;-caprolactone catalyzed by diphenyl phosphate is described. This polymer is then chain extended by methyl methacrylate (MMA) followed by N,N-dimethyl acrylamide (DMA) using reversible addition&#8722;fragmentation chain-transfer (RAFT) polymerization, affording a triblock copolymer that can undergo CDSA in ethanol. The living CDSA process is outlined, the results of which yield cylindrical nanoparticles up to 500 nm in length and a length dispersity as low as 1.05. It is anticipated that these protocols will allow others to produce cylindrical nanostructures and elevate the field of CDSA in the future.

Crystallization-driven self-assembly (CDSA) displays the unique ability to fabricate cylindrical nanostructures of narrow length distributions. The organocatalyzed ring-opening polymerization of &#949;-caprolactone and subsequent chain extensions of methyl methacrylate and N,N-dimethyl acrylamide are demonstrated. A living CDSA protocol that produces monodisperse cylinders up to 500 nm in length is outlined.

The production of monodisperse cylindrical micelles is a significant challenge in polymer chemistry. Most cylindrical constructs formed from diblock ...

Photochemical Initiation Of Radical Polymerization Reactions

Source: David C. Powers, Tamara M. Powers, Texas A&#38;M
In this video, we will carry out the photochemically initiated polymerization of styrene to generate polystyrene, which is an important commodity plastic. We will learn the fundamentals of photochemistry and use simple photochemistry to initiate radical polymerization reactions. Specifically, in this module we will examine the photochemistry of benzoyl peroxide and its role as a photo-initiator of styrene polymerization reactions. In the described experiments, we will investigate the role of wavelength, photon absorption, and excited state structure on the efficiency (measured as quantum yield) of photochemical reactions.

Source: David C. Powers, Tamara M. Powers, Texas A&#38;M
In this video, we will carry out the photochemically initiated polymerization of styrene to ...