A Surfactant-Free and Shape-Controlled Synthesis of Nonspherical Janus Particles with Thermally Tunable Amphiphilicity.

A surfactant-free approach is proposed to synthesize nonspherical Janus particles with temperature-dependent wettability on hydrophobic surfaces. Sub-micrometer-sized particles comprising poly(styrene-co-divinylbenzene) core and a thermally responsive poly(N-isopropylacrylamide-co-methacrylic acid) shell are first synthesized to stabilize styrene droplets in water, producing a Pickering emulsion. Upon heating to 80 °C and subsequent addition of initiators to the aqueous phase, styrene droplets are polymerized and combine with the core-shell particles to construct dumbbell-shaped nonspherical particles. The shape of the nonspherical particles is controllable by adjusting the equilibrium time of the Pickering emulsion at 80 °C, which is conducted prior to polymerization. The mechanism of formation is discussed in more detail. Since molecular surfactants or stabilizers are not used during the synthesis, the present nonspherical particles well exhibit their own temperature-dependent amphiphilic characteristics. The aqueous dispersion containing the dumbbell-shaped particles alters its wettability on hydrophobic polymer surfaces according to temperature changes, demonstrating its temperature-dependent amphiphilicity change.

Understanding viscoelastic behavior of hybrid nanocellulose film based on rheological and electrostatic observation in blended suspension.

The effects of TEMPO-mediated oxidized cellulose nanofibril (TOCN) on the viscoelastic behavior and phase of cellulose nanocrystal (CNC) in suspension and film were investigated using polarized optical microscopy, rotational rheometry, and dynamic mechanical analysis. The sodium cation from TOCN changed the electrostatic state of CNC by screening the CNC surface charge. The volume inflation of TOCN locally increased the CNC concentration in the suspension. In turn, the CNC-CNC interactions increased the viscosity and the yield stress. Based on the experimental observation, the changing mechanisms of electrostatic state and particular interaction in the TOCN/CNC suspensions were suggested. In the hybrid film, the time dependency of complex moduli was changed owing to the different networking between CNCs and TOCNs. The CNC-CNC contacts easily collapsed by strain, while the TOCN-TOCN entanglements were slowly altered. This study provides a fundamental understanding of CNC behavior for optimizing processes and composite properties.