Photonic water dynamically responsive to external stimuli

Abstract

Fluids that contain ordered nanostructures with periodic distances in the visible-wavelength range, anomalously exhibit structural colours that can be rapidly modulated by external stimuli. Indeed, some fish can dynamically change colour by modulating the periodic distance of crystalline guanine sheets cofacially oriented in their fluid cytoplasm. Here we report that a dilute aqueous colloidal dispersion of negatively charged titanate nanosheets exhibits structural colours. In this ‘photonic water', the nanosheets spontaneously adopt a cofacial geometry with an ultralong periodic distance of up to 675 nm due to a strong electrostatic repulsion. Consequently, the photonic water can even reflect near-infrared light up to 1,750 nm. The structural colour becomes more vivid in a magnetic flux that induces monodomain structural ordering of the colloidal dispersion. The reflective colour of the photonic water can be modulated over the entire visible region in response to appropriate physical or chemical stimuli.

Iridescence in nematics: Photonic liquid crystals of nanoplates in absence of long-range periodicity

“…In particular, lamellar structure is one of the most studied designs for fabricating photonic materials of 2D building blocks due to the structural similarity to natural nacre and pearls (18). For example, several lamellar 2D monolayers, including graphene oxide and titanium oxide nanosheets (19,20), have been developed into colorful PLCs. By contrast, forming visible color by nematic structure is notoriously difficult due to the lack of long-range periodicity in most nematic phases.…”

“…In consequence of smaller order parameter (i.e., less crystalline), the nematic phase may allow higher flexibility and larger directional diffusivity (24,25), and thus is promising for dynamic chemical/biological sensing, which would be complementary to existing photonic materials with prolonged response to stimuli (26,27). In addition, as lamellar structure requires high monodispersity in nanoplate thickness, toxic chemicals or strong oxidizers are often necessary to prepare monolayers during exfoliation (19,20,28), while the less-ordered nematic structure may circumvent such requirement (29). Despite these advantages, however, developing a photonic structure based on achiral nematic phase remains a formidable task, as the nematic…”

Influence of Substrate Wettability on Colloidal Assembly

“…Colloidal crystals [1][2][3][4] has aroused wide research attention owing to its fascinating light manipulation properties and important application in sensing [5][6][7][8][9][10][11][12][13][14][15][16][17][18], detecting [19][20][21][22], catalytic [23,24] and some special optic devices [25][26][27][28][29][30][31][32]. Colloidal crystals are generally fabricated from the well-ordered assembly of the monodispersed latex particles or infiltrating the functional materials into the template and subsequent template removal (the typical fabrication process for the inverse opals).…”

Extra‐Large Mechanical Anisotropy of a Hydrogel with Maximized Electrostatic Repulsion between Cofacially Aligned 2D Electrolytes

“…After these works,h owever,w en oticed that the electrostatic repulsion between as-prepared TiNSs were largely attenuated by excess amount of free ions (tetramethylammonium hydroxide,Q + OH À ;F igure 1b), which were employed for the exfoliation of TiNSs ( Figure S1 in the Supporting Information). [11] Therefore,w ee nvisioned that much more anisotropic hydrogels could be obtained by using the aqueous dispersion of extensively washed TiNSs enabling larger electrostatic repulsion (Figure 1d,i ). In the present work, we successfully enhanced the anisotropic parameter of the hydrogel from 3.0 to 18 by simply lowering the free-ion concentration (Figure 2c and f) and demonstrated as uperb ability of the hydrogel for seismic isolation (Figure 3).…”

“…In this study,w eu sed TiNSs of the same quality employed for our previous studies [9] as precursors for the anisotropic hydrogels;h owever, TiNSs were extensively washed by repeated centrifugation (Figure 1d,i ) according to our previous report ( Figure S2). [11] After wash-ing, the concentration of free ions ([Q + OH À ]) in the TiNS dispersion ([TiNS] = 0.8 wt %) decreased from~10 mm to 0.3 mm.S mall-angle X-ray scattering (SAXS) measurements of the TiNS dispersion with different [Q + OH À ]v alues,i n conjunction with the theoretical calculation using the Derjaguin-Landau-Verwey-Overbeek (DLVO)t heory (Figure S3), [12] proved that the lowering [Q + OH À ]e nhances the electrostatic repulsion between TiNSs,t hereby increasing TiNS distance ( Figure S4).…”