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

https://doi.org/10.1103/PhysRevE.85.011403

Phase transition of aqueous colloidal dispersions of charged plate-like particles of niobate nanosheets were investigated as a function of the aspect ratio () and particle volume concentration () 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 at a constant = 0.01, and of (b) varying (0.01 0.025) at a constant = 2.510. (2) the -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.

Combined SANS, SEC, NMR, and UV-Vis studies of simultaneous living anionic copolymerization process; Simultaneous elucidation of propagating living chains at three different length scales

Zhao, Y.; Tanaka, Hirokazu*; Miyamoto, Nobuyoshi*; Koizumi, Satoshi; Hashimoto, Takeji

Macromolecules, 42(5), p.1739 - 1748, 2009/04

https://doi.org/10.1021/ma8017519

Living anionic polymerization of methyl methacrylate controlled by metal-free phosphazene catalyst as observed by small-angle neutron scattering, gel-permeation chromatography and UV-visible spectroscopy

Miyamoto, Nobuyoshi; Inoue, Yoshihisa*; Koizumi, Satoshi; Hashimoto, Takeji

Journal of Applied Crystallography, 40(s1), p.s568 - s572, 2007/04

https://doi.org/10.1107/S0021889807009673

no abstracts in English

Aggregation behavior of polyisoprene chain ends during living anionic polymerization as investigated by time-resolved small-angle neutron scatting

Miyamoto, Nobuyoshi; Yamauchi, Kazuhiro*; Hasegawa, Hirokazu*; Hashimoto, Takeji; Koizumi, Satoshi

Physica B; Condensed Matter, 385-386(1), p.752 - 755, 2006/11

https://doi.org/10.1016/j.physb.2006.06.053

The living anionic polymerization processes of isoprene and styrene in benzene- initiated by -butyl lithium were studied by in-situ small-angle neutron scattering (SANS) and time-resolved molecular weight () measurement by gel permeation chromatography (GPC). In the course of the polymerization of isoprene ( = 5300 g mol), the small angle scattering increased with the reaction time . The molecular weight and its time-change, determined by GPC, is crucial to quantitatively analyze time-resolved SANS measurements; we were able to determine association number uniquely as a function of . Upon termination of the living polymerization, SANS profile greatly changed: the scattering intensity in the intermediate -region (0.2 1.0 nm) remarkably decreased, indicating disaggregation of the living ends upon the termination. Also, strong upturn in the low-q region appeared (q 0.1 nm) due to the generation of colloidal LiOH or LiO(CH), which are insoluble in benzene. Detailed data and analyses of isoprene and styrene systems will be given in the 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 KNbO 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.

In-situ observation of living anionic polymerization process by simultaneous measurements of small angle neutron scattering and UV-vis spectroscopy

Miyamoto, Nobuyoshi; Inoue, Yoshihisa*; Koizumi, Satoshi; Hashimoto, Takeji

no journal, , 

no abstracts in English

In-situ and time-resolved observation of living anionic polymerization process

Miyamoto, Nobuyoshi; Koizumi, Satoshi; Hashimoto, Takeji

no journal, , 

no abstracts in English

In situ and real-time observation of living anionic polymerization process and polymerization-induced self-assembly of polyisoprene-b-polystyrene-d8

Zhao, Y.; Miyamoto, Nobuyoshi*; Koizumi, Satoshi; Hashimoto, Takeji

no journal, , 

In-situ and real-time observation of simultaneous living anionic polymerization process of isoprene (I) and styrene-d8 (S) in benzene-d6 as a solvent with sec-buthyllithium as an initiator into polyisoprene-block-polystyrene-d8 and the polymerization-induced self-assembling structures was carried out by a combination of UV-vis spectroscopy, gel permission chromatography (GPC), nuclear magnetic resonance (NMR) and Small-angle Neutron Scattering (SANS) experiments. The results revealed three time regions with time. In region 1, Only PI blocks were growing. In region 2, PS segments were formed and tapered structures were observed. In region 3, PS blocks were growing rapidly, and polymerization-induced microphase separation was observed.

In-situ and real-time observation of living anionic polymerization process and polymerization-induced self-assembly of polyisoprene-b-polystyrene-d8

Zhao, Y.; Miyamoto, Nobuyoshi; Koizumi, Satoshi; Hashimoto, Takeji

no journal, , 

The simultaneous living anionic copolymerization of isoprene (I) and styrene-d8 (S) monomers, initiated by sec-butyllithium in benzene-d6, was investigated by means of time-resolved SANS, UV-Vis spectroscopy, SEC, and NMR. The results revealed the 3 time regions. In region 1, random copolymers rich in isoprene (80 wt%) were synthesized. SANS intensity was weak and almost time-independent, and UV-vis absorbance at 450 nm was very weak. In region 2, styrene-d8-rich random block sequences were formed to result in the block copolymers. A broad scattering peak appeared in SANS, aggregation number changed from 4 to 2 at the end of this region. In region 3, the remaining S underwent a rapid polymerization into polystyrene (PS), leading to the formation of P(I-ran-S)-block-P(S-ran-I)-block-PS. Polymerization-induced disorder-to-order transition and order-to-order transition from hex-cylinder to lamella occurred.

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 KNbO single crystal, has a regular thickness of 1.8nm, while its lateral size (L) is variable from 100nm to several 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 1m, the orientational order of nanosheet particles was prior to those of positional order, while (2) when L was smaller than 1m, 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.