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Research

Organic polymer particles have mainly been used in the form of film in paint and adhesive industrial sections. In addition to usage in the form of the film, there have been increasing interests in using the polymer particles in their particulate form. The polymer particles have been used as absorbents, ion-exchangers, affinity bioseparators, drug and enzyme carriers, viscosity modifiers, support materials, calibration standards, and functional beads for medical diagnostics. The latex particles have also found their applications as emulsion, foam and liquid marble stabilizers.

Our research activities are devoted to synthesis, characterization and application of advanced functional polymer latex particles with controlled surface/bulk chemistries, morphology, size and size distribution including conducting polymer particles, nanocomposite particles and stimuli-responsive polymer particles. Furthermore, the advanced polymer particles are used as stabilizers for fluid-fluid dispersion systems such as emulsions, foams and liquid marbles. Our researches have been conducted based on polymer chemistry and interfacial chemistry.

Synthesis of functional polymer-based particles

Various methods, such as emulsion polymerization, dispersion polymerization, seed polymerization, suspension polymerization and Pickering emulsion method, are utilized to synthesize functional polymer particles with controlled surface/bulk chemistries, morphology, size and size distribution.

1）Organic-inorganic nanocomposite particles

Conducting polymer-noble metal nanocomposites can be synthesized by a one-step chemical oxidative polymerization using metal salts, such as tetrachloroaurate, silver nitrate and palladium(II) chloride, as an oxidant. In 2006, we discovered a simple route to conducting polymer-noble metal nanocomposites in a form of colloidal particles by aqueous chemical oxidative dispersion polymerization. We have extended this discovery to include conducting polymer-noble metal nanocomposite-coated materials. It has been confirmed that the nanocomposite-based materials can work as effective catalysts for various organic reactions.

  • Journal of Materials Chemistry A 1(14), 4427-4430 (2013)
  • Langmuir 28(5), 2436–2447 (2012)
  • Catalysis Letters 141, 1097-1103 (2011)
  • Langmuir 26(9), 6230-6239 (2010)
  • Synthetic Metals 160, 1433-1437 (2010)
  • Journal of Materials Chemistry 17, 3777-3779 (2007)

2）Core-shell particles

Polymer particles with core-shell morphology have functions: (1) protection of core component from external stimuli, (2) controlled release of core component by external stimuli, (3) systematic introduction of functions into core and shell parts and so on. In our group, we have been developing seeded polymerization method and biomineralization method to synthesize functional core-shell particles.

  • Polymer 70, 77-87 (2015)
  • Journal of Colloid and Interface Science 430, 47-55 (2014)
  • Chemical Communications 46, 7217-7219 (2010)
  • Colloids and Surfaces B: Biointerfaces 78, 193–199 (2010)
  • Chemistry of Materials 19, 2435-2445 (2007)
  • Chemistry of Materials 18, 2758-2765 (2006)
  • Langmuir 22, 4923-4927 (2006)

3）Emulsifier-free particles (Ramsden/Pickering emulsion route)

Ramsden/Pickering emulsions are solid particle-stabilized emulsions in the absence of any molecular surfactant, where solid particles adsorbed to an oil-water interface [Ramsden, W. Proc Roy Soc. 1903, 72, 156.; Pickering, S. U. J. Chem. Soc. 1907, 91, 2001.]. In 2009, we describe the first fabrication of nanoparticle-coated polymeric microspheres by the evaporation of the oil from the Ramsden/Pickering-type organic solution of polymer-in-water emulsions. Neither molecular surfactant, polymeric stabilizer nor animal-originated materials such as collagen were used in this method, and this emulsion route is expected to be suitable for biomaterial application.

  • Langmuir 28 (25), 9405–9412 (2012)
  • Acta Biomaterialia 7, 821-828 (2011)
  • Langmuir 26(17), 13727-13731 (2010)
  • Langmuir 25(17), 9759-9766 (2009)

4）Hairy particles

Hairy particles are defined as the particles which carry grafted linear polymer chains having high affinity with the dispersing media on their surface. In our group, we utilized dispersion polymerization route (polymerization-induced phase separation method) toward polymer latex particles carrying hair with functions such as stimuli-responsive and biocompatible characters.

  • Langmuir 35(21), 6993-7002 (2019)
  • Macromolecules 45 (6), 2863–2873 (2012)
  • Journal of Polymer Science Part A: Polymer Chemistry 49(7), 1633-1643 (2011)
  • Polymer 51, 6240-6247 (2010)
  • Journal of Polymer Science Part A: Polymer Chemistry 47, 3431-3443 (2009)
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Emulsions stabilized with solid particles (Emulsion engineering)

We have designed, synthesized and evaluated several new classes of so-called 'Ramsden/Pickering' emulsifiers for the preparation of emulsions. It has been known for over a century that various finely divided solids can be used to stabilize either water-in-oil or oil-in-water emulsions. Recently increasing attention has been focused on organic (polymer)-based particles, since in principle these systems allow the particle wettability to be precisely tuned and also offer the possibility of triggered demulsification if stimulus-responsive polymers are incorporated. We have examined organic particles including nanocomposite particles, stimulus-responsive hairy particles and protein.

  • Polymers 8, 62 (2016)
  • RSC Advances 4(61), 32534-32537 (2014)
  • Langmuir 29, 5457-5465 (2013)
  • Journal of Colloid and Interface Science 338, 222-228 (2009)
  • Journal of Colloid and Interface Science 315, 287-296 (2007)
  • Langmuir 22, 6818-6825 (2006)
  • Langmuir 22, 2050-2057 (2006)

Foams stabilized with solid particles (Foam engineering)

Gas-in-liquid foams occur as intermediates or end-products in diverse industrial sectors, including food manufacturing, cosmetic formulations, and personal care products, as well as in the synthesis of porous materials. In order to prevent macroscopic phase separation of the gas and liquid, ionic or nonionic surfactants or polymeric stabilizers (including proteins), which adsorb to gas-liquid interfaces, are usually added. In addition to these molecular-level foam stabilizers, it has been known that finely divided particles can stabilize liquid foams by adsorbing to gas-liquid interfaces. We are working on fabrication and characterization of functional foams/bubbles stabilized with polymer latex particles.

【Review】
  • Current Opinion in Colloid & Interface Science 50, 101380 (2020)
  • Polymer Journal 51, 1081-1101 (2019)
  • Langmuir 33, 7365-7379 (2017)
【Original article】
  • Langmuir 34(3), 933-942 (2018) [Highlights from the Langmuir Editorial Advisory Board]
  • Soft Matter 12, 4794-4804 (2016)
  • Soft Matter 11, 9099-9106 (2015)
  • Chemistry Letters 44(6), 773-775 (2015)
  • Soft Matter 11 (3), 572-579 (2015)
  • Langmuir 27(21), 12902-12909 (2011)
  • Langmuir 23, 8691-8694 (2007)
  • Langmuir 23, 11381-11386 (2007)
  • Journal of the American Chemical Society 128, 7882-7886 (2006)
  • Langmuir 22, 7512-7520 (2006)
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Liquid droplet stabilized with solid particles (Liquid marble, Dry liquid)

Liquid marbles [Aussilious, P.; Quéré, D. Nature 2001, 411, 924.], which are typically millimeter-sized water droplets stabilized by adsorbed particles at gas-liquid interfaces, have attracted increasing attention in view of their potential applications in cosmetics, pharmaceuticals and home & personal care products. These liquid-in-gas dispersed systems are usually prepared using relatively hydrophobic particles that adsorb at the gas-liquid interface. Most of the literature is concerned with surface-modified lycopodium powder, hydrophobic silica particles or carbon black although there have also been a few examples of polymer latexes being used as ‘liquid marble’ stabilizers. In principle, such synthetic particles should be particularly attractive for preparing liquid marbles, since they can be readily designed with specific surface chemistries (and hence wettability) using various functional monomers. Moreover, it is possible to confer stimulus-responsive character, which is more difficult to achieve using inorganic particles. We are working on fabrication and characterization of functional liquid marbles stabilized with polymer latex particles.

【Review】
  • Polymer Journal 51, 1081-1101 (2019)
  • Accounts of Materials & Surface Research 4(2), 61-68 (2019)
  • Advanced Functional Materials 26(40), 7206-7223 (2016)
【Original article】
  • Advanced Materials Interfaces (2020) DOI:10.1002/admi.202001573
  • Langmuir 36(44), 13274-13284 (2020)
  • Langmuir 36(10), 2695-2706 (2020)
  • Advanced Functional Materials 29(25), 1808826 (2019) [Highlighted in Nature, NewScientist, NHK]
  • Langmuir 34(17), 4970-4979 (2018)
  • Materials Horizons 3, 47-52 (2016) [Highlighted in Chemistry World, NewScientist, Yahoo top news]
  • Soft Matter 11, 7728-7738 (2015)
  • Langmuir 30(11), 3051–3059 (2014)
  • Langmuir 27(13), 8067-8074 (2011)
  • Soft Matter 6, 635-640 (2010)
  • Journal of the American Chemical Society 131, 5386-5387 (2009)

Particulate materials in nature

Some aphids that live in the leaf galls of the host plant are known to fabricate liquid marbles consisting of honeydew and wax particles as an inner liquid and a stabilizer, respectively. We study the liquid marbles fabricated by the galling aphids, Eriosoma moriokense, based on chemistry and physical chemistry.

  • Langmuir 35, 6169-6178 (2019)
  • Konchu to Shizen 55(7), 5-8 (2020)

Delivery and release of materials based on soft dispersed systems

Controlling and powering the locomotion of small objects is a fascinating research topic. We study on motion control of small objects (including liquid marbles and bubbles) in a remote manner on a water surface by Marangoni flow induced by a simple near-infrared laser or sunlight. Using light as an external stimulus allows for the control of the position, area, timing, direction and velocity of delivery. This approach makes it possible to not only transport the materials but also to release them at a specific place and time, as controlled by external stimuli.

  • Polymer 212, 123295 (2020)
  • Polymer Journal 52, 589-599 (2020)
  • European Polymer Journal 132, 109723 (2020)
  • Langmuir 36(25), 7021-7031(2020)
  • Polymer Journal 51, 761-770 (2019)
  • RSC Advances 9, 8333-8339 (2019)
  • Macromolecules 52(2), 708-717 (2019) [Highlighted in Asahi Shimbun]
  • Polymer 148, 217-227 (2018)
  • ACS Applied Materials & Interfaces 9(38), 33351-33359 (2017) [Highlighted in NIKKEI]
  • Polymer Chemistry 8, 2609-2618 (2017)
  • Advanced Functional Materials 26, 3199-3206 (2016) [Highlighted in Nature Photonics, NewScientist]

Advanced polymeric films

Air-water interface can be used as a place to give regularity and asymmetry to materials. We are working on the synthesis of Janus-type composite colloidal crystal films at air-water interface.

  • Angewandte Chemie International Edition 51, 9809-9813 (2012)
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