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Journal Articles

Aspect-ratio-dependent phase transitions and concentration fluctuations in aqueous colloidal dispersions of charged platelike particles

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Fujita, Takako*; Nakato, Teruyuki*; Koizumi, Satoshi; Ota, Noboru*; Yagi, Naoto*; Hashimoto, Takeji

Physical Review E, 85(1), p.011403_1 - 011403_15, 2012/01

 Times Cited Count:19 Percentile:75.27(Physics, Fluids & Plasmas)

Phase transition of aqueous colloidal dispersions of charged plate-like particles of niobate nanosheets were investigated as a function of the aspect ratio ($$r_{rm asp}$$) and particle volume concentration ($$theta$$$$_{rm P}$$) by small-angle neutron scattering and small-angle X-ray scattering. The results elucidated the following three pieces of evidence: (1) the macroscopic phase separation of the dispersions into an isotropic phase and a liquid crystalline phase (LC) under the condition of (a) varying $$r_{rm asp}$$ at a constant $$theta$$$$_{rm P}$$ = 0.01, and of (b) varying $$theta$$$$_{rm P}$$ (0.01 $$leq$$ $$theta$$$$_{rm P}$$ $$leq$$ 0.025) at a constant $$r_{rm asp}$$ = 2.5$$times$$10$$^{-3}$$. (2) the $$r_{rm asp}$$-induced phase transition of the LC phase from a nematic phase to a highly periodic layered phase upon increasing r under the condition (a). (3) the LC phase having remarkable concentration fluctuations of the particles which are totally unexpected for the conventional lyotropic molecular LC but which are anticipated to be general for the plate-like colloidal particles.

Journal Articles

Hierarchical structure of niobate nanosheets in aqueous solution

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi; Koizumi, Satoshi; Nakato, Teruyuki*; Hashimoto, Takeji

Journal of Applied Crystallography, 40(s1), p.s101 - s105, 2007/04

 Times Cited Count:20 Percentile:85.6(Chemistry, Multidisciplinary)

no abstracts in English

Oral presentation

Small angle neutron scattering observation of liquid crystalline sol of niobate nanosheets

Miyamoto, Nobuyoshi; Yamaguchi, Daisuke; Nakato, Teruyuki*; Koizumi, Satoshi; Hashimoto, Takeji

no journal, , 

The structure of liquid crystalline sols of niobate nanosheets was observed by USANS, SANS, and USAXS as the function of the average lateral size L and the volume fraction $$phi$$ of the nanosheets. The nanosheets sols were obtained by a reaction of K$$_{4}$$Nb$$_{6}$$O$$_{17}$$ crystals with propylammonium followed by washing with water. The sol was ultrasonicated for 10-180 min and diluted to yield the series of the samples with different L and $$phi$$. At q$$>$$ 0.1, the peaks due to the lamellar structure of the liquid crystal were observed in the scattering curves. The basal spacing was ca. 40 nm, independent of L, at $$phi$$ = 3.6 vol % and it decreased with decreasing $$phi$$. The scattering curves at 0.01 $$<$$ q $$<$$ 0.1 depended largely on L, or the form factor of the nanosheets. At q $$<$$ 0.01 nm$$^{-1}$$, the power law of q$$^{-2.5}$$ was observed independent of L, indicating the presence of the liquid crystalline domains with mass fractal structure.

Oral presentation

Observation and analysis of the niobate nanosheet solution

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi; Koizumi, Satoshi; Nakato, Teruyuki*; Hashimoto, Takeji

no journal, , 

The exfoliated K$$_{4}$$Nb$$_{6}$$O$$_{17}$$ nanosheets in the aqueous solutions were observed by (ultra-) small-angle neutron and X-ray scattering (SANS, USANS and USAXS). A comprehensive measurement revealed the assembled structure of nanosheets in wide range of q, from 3$$times$$10$$^{-4}$$ nm$$^{-1}$$ to 1 nm$$^{-1}$$, where q is the magnitude of scattering vector. The details of liquid crystalline structure formed by [Nb$$_{6}$$O$$_{17}$$]$$^{4-}$$ nanosheets, which was reflected on the scattering at higher q region ($$>$$3$$times$$10$$^{-2}$$ (nm$$^{-1}$$)), largely depend on the nanosheet lateral dimension or its volume fraction. On the other hand, at lower q region ($$<$$1$$times$$10$$^{-2}$$ (nm$$^{-1}$$)), the scattering profile shows a power law scattering of which index is -2.5 regardless of the nanosheet lateral dimension or its volume fraction, suggesting that at large scale nanosheets take similar mass fractal distribution.

Oral presentation

Structure analysis of liquid crystalline nanosheet of niobate, 1

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi; Koizumi, Satoshi; Nakato, Teruyuki*; Hashimoto, Takeji

no journal, , 

no abstracts in English

Oral presentation

Hierarchical structure of nanosheet colloid observed by ultra-small-angle neutron scattering

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi; Koizumi, Satoshi; Nakato, Teruyuki*; Mayama, Hiroyuki*; Tsujii, Kaoru*; Hashimoto, Takeji

no journal, , 

no abstracts in English

Oral presentation

Observation of the self-assembled structure of the two-dimensional particles system

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Koizumi, Satoshi; Hashimoto, Takeji; Nakato, Teruyuki*; Mayama, Hiroyuki*; Tsujii, Kaoru*

no journal, , 

The hierarchical structures composed of two-dimensional particles were observed via ultra-small-angle scattering method. We have investigated two systems: (1) exfoliated K$$_{4}$$Nb$$_{6}$$O$$_{17}$$ nanosheet colloidal dispersion, (2) porous silica fabricated from alkylketene dimer template. Although the physical and chemical structures and properties are largely different in these two systems, a similar point to them is regarded as below. The thickness of the constituent particles is ranging from a few nanometers to several tens of nanometers. Various fractal-like power-law scattering were obtained in the ultra-small angle scattering region reflecting the difference in the self-assembly of the particles.

Oral presentation

Relation between mean lateral size and structure in the niobate nanosheet colloidal suspension

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Koizumi, Satoshi; Nakato, Teruyuki*; Hashimoto, Takeji

no journal, , 

The structure of niobate nanosheets in aqueous colloidal suspensions was investigated by small-angle neutron scattering (SANS). The nanosheet, obtained by the exfoliation of layered K$$_{4}$$Nb$$_{6}$$O$$_{17}$$ single crystal, has a regular thickness (d) of 1.8 nm, while lateral size (L) is variable from 100 nm to 10 $$mu$$m depending on the preparation process. Such an large aspect (i.e., L/d) ratio is peculiar to the nanosheet of K$$_{4}$$Nb$$_{6}$$O$$_{17}$$ crystal, and has never been obtained by other type of clay nanosheet. According to the SANS measurement, the aspect ratio of the nanosheet is deeply related to the regularity of the spacing between the nanosheet particles in the colloidal suspension. A comprehensive comparison between niobate nanosheets and other clay nanosheets is argued.

Oral presentation

Control of the lateral size and interparticle distance of niobate nanosheet colloid

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Koizumi, Satoshi; Nakato, Teruyuki*; Hashimoto, Takeji

no journal, , 

The structure of niobate nanosheet in aqueous colloidal suspension was investigated by small-angle neutron scattering. The nanosheet, obtained by the exfoliation of layered K$$_{4}$$Nb$$_{6}$$O$$_{17}$$ single crystal, has a regular thickness of 1.8nm, while its lateral size (L) is variable from 100nm to several $$mu$$m depending on the preparation process. The influence of L on the structure of the colloidal suspensions was examined in this study and following two results were elucidated. (1) when L was larger than 1$$mu$$m, the orientational order of nanosheet particles was prior to those of positional order, while (2) when L was smaller than 1$$mu$$m, the positional order of nanosheet particles was prior to those of orientational order. This is an intriguing example showing the fact that the structure of constituent nanosheet particles control the liquid crystalline nature of the colloidal suspensions.

Oral presentation

Formation of liquid crystalline phases in colloidal suspensions of K$$_{4}$$Nb$$_{6}$$O$$_{17}$$ nanosheet

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Koizumi, Satoshi; Nakato, Teruyuki*; Yagi, Naoto*; Hashimoto, Takeji

no journal, , 

Two new experimental evidences were obtained in lyotropic liquid crystalline (LC) phase behavior consisting of a model charged colloidal platelike particle system yielded from layered niobate crystal of K$$_{4}$$Nb$$_{6}$$O$$_{17}$$. Firstly, the effect of mean lateral size ($$overline{D}$$$$_{lat}$$) of the particle was examined at a constant volume fraction of the particle ($$phi$$) where a LC phase coexisted with an isotropic (I) phase. The coexisting LC phase was abruptly transformed from nematic to lamellar (L) as $$overline{D}$$$$_{lat}$$ was decreased. Secondly, the $$phi$$ dependence of the interparticle distance (d) was examined along the I-L transition. In the coexistence region, d showed nearly the same value between those two phases and varied with $$phi$$, being out of the usual lever rule.

Oral presentation

Liquid crystalline phases in colloidal suspensions of K$$_{4}$$Nb$$_{6}$$O$$_{17}$$ nanosheets

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Fujita, Takako*; Nakato, Teruyuki*; Koizumi, Satoshi; Yagi, Naoto*; Ota, Noboru*; Hashimoto, Takeji

no journal, , 

Formation of lyotropic liquid crystalline (LC) phase was observed on a charged colloidal platelike particle system yielded from layered niobate crystal of K$$_{4}$$Nb$$_{6}$$O$$_{17}$$. Firstly, the effect of mean lateral size (D) of the particle was examined at a constant volume fraction of the particle (.fai.) where a LC phase coexisted with an isotropic (I) phase. The coexisting LC phase was distinctly transformed from nematic to lamellar (L) as D was diminished. Secondly, the .fai. dependence of the interparticle distance (d) was examined along the I-L transition. In the coexistence region, d varied with .fai. and held nearly the same value between I and L phases, apparently deviating from gas-liquid condensation-type phase separation.

Oral presentation

Interparticle distance between the sheet-like niobate particles in the lamellar-forming colloidal dispersion

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Fujita, Takako*; Nakato, Teruyuki*; Koizumi, Satoshi; Ota, Noboru*; Yagi, Naoto*; Hashimoto, Takeji

no journal, , 

The lyotropic lamellar phase in colloidal suspension has been well established in the recent work of the exfoliated inorganic phosphatoantimonate crystal. Here we report the other distinct lamellar phase formed in the colloidal suspension of hexaniobate "nanosheet", which is coexistent with an isotropic phase. This colloidal system clearly shows that not only the degree of orientational order but also that of positional order are quite different between upper isotropic phase and bottom lamellar phase. However, a definite interparticle correlation does exist in the isotropic phase and the difference in the mean interparticle distance (d) between lamellar and isotropic phases turned out rather small. All those pieces of experimental evidence suggest that the coexisting isotropic-lamellar phases is not attributed to the sedimentation of the nanosheet particles by the gravity but arisen as a result of ordering process of nanosheet particles by getting over the random thermal force of Brownian motion.

Oral presentation

SANS and SAXS observation on the layered-structure-forming nanosheet colloid

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Fujita, Takako*; Nakato, Teruyuki*; Koizumi, Satoshi; Ota, Noboru*; Yagi, Naoto*; Hashimoto, Takeji*

no journal, , 

The lyotropic lamellar phase in colloidal suspension has been well established in the recent work of the exfoliated inorganic phosphatoantimonate crystal. Here we report the other distinct lamellar phase formed in the colloidal suspension of hexaniobate nanosheet, which is coexistent with an isotropic phase. It is clear that not only the degree of orientational order but also that of positional order are quite different between upper isotropic phase and bottom lamellar phase. However, a definite interparticle correlation does exist in the isotropic phase and the difference in the mean interparticle distance between lamellar and isotropic phases turned out rather small. All those pieces of experimental evidence suggest that the coexisting isotropic-lamellar phases is not attributed to the sedimentation of the nanosheet particles by the gravity but arisen as a result of ordering process of nanosheet particles by getting over the random thermal force of Brownian motion.

Oral presentation

Anisotropic shape and power law behavior of the scattering peak observed on the layered phase of colloidal platelike particles

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Nakato, Teruyuki*; Koizumi, Satoshi*; Ota, Noboru*; Yagi, Naoto*; Hashimoto, Takeji; Kawakatsu, Toshihiro

no journal, , 

The line shape of the scattering peaks from the layered phase of colloidal plate-like particles, which consist of niobate single layer crystal (often referred as "nanosheet"), was intensively examined in this study and a distinct anisotropy was found for the power law behavior of the peak intensity with respect to the q$$_{z}$$ and q$$_{x}$$ directions. Namely, the power law exponent of the peak intensity for q$$_{x}$$-direction was nearly double of that for q$$_{z}$$-direction. This experimental piece of evidence was at least qualitatively in agreement with Caille s prediction. In this study, the Caille' s formula was numerically integrated and the two-dimensional calculated scattering pattern was obtained. The q-behavior of the calculated scattering pattern is naturally similar to those of theoretical analysis and obtained experimental data.

Oral presentation

Analysis of highly periodic scattering data from a colloidal dispersion of plate-like particles

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Nakato, Teruyuki*; Koizumi, Satoshi*; Ota, Noboru*; Yagi, Naoto*; Hashimoto, Takeji; Kawakatsu, Toshihiro*

no journal, , 

A highly periodic morphology of liquid crystalline (LC) phase formed in the aqueous colloidal dispersions of charged plate-like particles of niobate nanosheets was investigated by small-angle scattering method. The scattering profile was examined by line shape analysis and compared with calculation based on the Caille's formula. Qualitatively, an agreement between the experimental data and calculation (or theory) was obtained for the anisotropic decay of the peak intensity between the radial direction and that of perpendicular to the radial direction. Further quantitative comparison is under progress.

Oral presentation

Scattering analysis for highly oriented colloidal dispersion consisting of sheet-like inorganic particles

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Nakato, Teruyuki*; Koizumi, Satoshi*; Ota, Noboru*; Yagi, Naoto*; Hashimoto, Takeji; Kawakatsu, Toshihiro

no journal, , 

Self-assembled structures of aqueous colloidal dispersions of niobate nanosheets having a uniform thickness of d = 1.6 nm and an average lateral dimension of L = 650 nm, hence an extremely large nominal aspect ratio (L/d) of $$sim$$400 were studied by micro-beam synchrotron small-angle X-ray scattering (SAXS). The results elucidated highly orientated, periodic layered liquid crystalline phase exhibiting a multiple-order scattering peaks. The line-profiles of the multiple-order peaks were analyzed in the directions both parallel and perpendicular to the one-dimensional stacks of the nanosheets for each order of the peaks. The results were compared with the formula based on harmonic approximation. An experimental problem associated with effects of orientation distributions of the stacks on the line profile analyses was quantitatively examined.

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