soft matter

Ordering Dynamics of Soft Matter

1) Static and Dynamic Structures in Ordering of Soft Micelles
2) Dynamics of order-order transitions in surfactant assemblies
3) Shear induced morphology transition of surfactant assemblies
4) Ordering process in the induction period of crystallization of polymer
5) Polymer crystallization from ultra-thin film

Structure Formation of Soft Matter Complex System
1) Morphology transition of molecular assemblies induced by guest particles
2) Morphology transition of membranes induced by polymer confinement
3) Depletion interaction in rod particle and semi-flexible polymer mixture

Ordering Dynamics of Soft Matter

１) Static and Dynamic Structures in Ordering of Soft Micelles

1-1 The crystallization of spherical particles is one of the most fundamental first-order phase transitions. The static and dynamic structures of hard spheres in the crystallization have been well understood. By introducing soft inter-particle interactions, the static and dynamic structures are significantly modified. For example, surfactant micelles show the non-close-packed lattice, body centered cubic (BCC) and A15 (Kelvin polygons) lattice in the phase diagram and characteristic slow dynamics in the fluid and crystal phases. We have investigated the static and dynamic structures in ordering of soft micelles using light scattering, X-ray scattering, neutron scattering and rheology measurements.
[Related papers]
Static and Dynamic Structures of Spherical Nonionic Surfactant Micelles during the Disorder-Order Transition
M. Imai, I. Yoshida, T. Iwaki, and K. Nakaya
J. Chem. Phys. 122, 044906 (2005)
Diffusion of surfactant micelles in fluid and crystal phases
M. Imai, M. Kurimoto, F. Matsuura, Y. Sakuma, and T. Kawakatsu
Soft Matter, accepted (DOI:10.1039/C2SM07122C)

2）Dynamics of order-order transitions in surfactant assemblies

1-2 The surfactant molecule composed of the hydrophilic and the hydrophobic groups forms various self-assemblies in water, such as micelle, lamellae, cylinder, gyroid and so on. We have investigated the phase transition dynamics between the ordered phases especially focus on the pre-transition and the intermediate structures. Prior to the lamellar to gyroid transition, a least stable fluctuation mode appears in lamellar membrane and then the intermediate hexagonal perforated lamellar structure is stabilized. The perforated lamellar structure transform to the gyroid keeping a geometrically epitaxial relationship. Such a characteristic intermediate structures are a unique feature of phase transitions of soft matter.
[Related papers]
Kinetic Pathway of Lamellar -> Gyroid Transition: Pretransition and Transient States.
M. Imai, A. Saeki, T. Teramoto, A. Kawaguchi, K. Nakaya, T. Kato, and K. Ito
J. Chem. Phys. 115, 10525 (2001).
Dynamical Nature of Least Stable Fluctuation Modes of Lamellar Structure Observed in a Nonionic Surfactant/Water System
M. Imai, K. Nakaya, T. Kawakatsu, and H. Seto
J. Chem. Phys. 119, 8103-8111 (2003).
Kinetic pathway to double gyroid structure
M. Imai, K. Sakai, M. Kikuchi, K. Nakaya, A. Saeki, and T. Teramoto
J. Chem. Phys. 122, 214906(1-10)(2005).

３）Shear induced morphology transition of surfactant assemblies

Since the surfactant assemblies are stabilized by relatively weak interactions, they easily deform their morphologies when subjected to external fields, such as a shear field. When we apply the shear field to the anisotropic lamellar assemblies, the planar membranes often transform to the isotropic multilamellar vesicles (onions) with two dimensional hexagonally close-packed configuration. We have investigated the shear-induced ordering of onions in a nonionic surfactant (C12E4) system using a small-angle light scattering and a small-angle X-ray scattering technique.
[Related papers]
Shear-Induced Ordering of Lamellar and Gyroid Structures Observed in a Nonionic Surfactant System.
M. Imai, K. Nakaya, and T. Kato
European Physical Journal E, 5, 391-402 (2001).
Order-disorder transition of nonionic onions under shear flow
Y. Suganuma, M. Imai, T. Kato, U. Olsson, and T. Takahashi
Langmuir 26, 7988-7995 (2010).

４）Ordering process in the induction period of crystallization of polymer

1-4 During an induction period of the polymer crystallization, randomly entangled polymer chains forms the regular aligned crystals with the critical size. During the induction period of crystallization of poly(ethylene terephthalate), the coupling of density and orientation fluctuations play an important role, thus the parallel ordering of polymer segments occurs due to the increase of the polymer chain rigidity. After the parallel ordered domains grow to a certain size, the packing of polymer segments, polymer crystallization, starts. We made clear the role of the induction period using light, X-ray and neutron scattering techniques.
[Related papers]
Structural Formation of Poly(ethylene terephthalate) during the Induction Period of Crystallization 1. -Ordered Structure Appearing before Crystal Nucleation -
M.Imai, K. Mori, T. Mizukami, K. Kaji and T. Kanaya
Polymer 33, 4451-4456, (1992).
Structural Formation of Poly(ethylene terephthalate) during the Induction Period of Crystallization 2. -Kinetic Analysis based on the theories of phase separation -
M.Imai, K. Mori, T. Mizukami, K. Kaji and T. Kanaya
Polymer 33, 4457-4462, (1992).
Orientaion Fluctuations of Poly(ethylene terephthalate) during the Induction Period of Crystallization
M. Imai, K. Kaji and T. Kanaya
Physical Review Letters 71, 4162-4165, (1993).
Ordering Process in the Induction Period of Crystallization of Poly(ethylene terephthalate)
M. Imai, K. Kaji, T. Kanaya and Y. Sakai
Physical Review B 52, 12696-12704 (1995)

Structure Formation of Soft Matter Complex System

１) Morphology transition of molecular assemblies induced by guest particles
Soft matter forms characteristic mesoscopic assemblies, which are stabilized by a delicate balance between the entropic and the enthalpic interactions. By doping guest particles, the additional entropic interaction originated from the translational entropy of guest particles induces structural transitions. We have investigated various morphology transitions of soft matter complex systems induced by addition of guest particles.
[Related papers]
Inter-lamellar interactions modulated by addition of guest components
M. Imai, R. Mawatari, K. Nakaya, and S. Komura
Eur. Phys. J. E. 13, 391-400 (2004).
Lamellar to Micelle Transition of Nonionic Surfactant Assemblies Induced by Addition of Colloidal Particles
Y. Suganuma, N. Urakami, R. Mawatari, S. Komura, K. Nakaya-Yaegashi and M. Imai
J. Chem. Phys. 129, 134903(1-10) (2008).
Shape Deformation of Giant Vesicles Encapsulating Charged Colloidal Particles
Y. Natsume, O. Pravaz, H. Yoshida1, and M. Imai
Soft Matter 6 5359-5366 (2010).

２) Morphology transition of membranes induced by polymer confinement

By confining polymer chain in nano-meter-sized space separated by surfactant membrane, the membrane changes their morphology to optimize the conformational entropy of polymer chains or the specific interaction between surfactant and polymer. For example, microemulsion droplets can confine the polymer chains inside of the closed nano-space by selecting the solubility of the polymer to the solvent. In such a strongly confined system, we observed a series of morphology transitions of microemulsion droplets as a function of the degree of polymer confinement. In addition we observed a unique morphology transition when the polymer undergoes a sol-gel transition inside the nano-space.
[Related papers]
Polymer-Confinement-Induced Nematic Transition of Microemulsion Droplets
K. Nakaya, M. Imai, S. Komura, T. Kawakatsu, and N. Urakami
Europhysics Letters,71, 494-500 (2005).
Effects of Grafted Polymer Chains on Lamellar Membranes
T. Masui, M. Imai, K. Nakaya and T. Taniguchi
J. Chem. Phys. 124, 074904 (1-12) (2006).
Molecular dynamics simulation for morphological change of water-in-oil microemulsion droplets induced by addition of polymer chains
T. Kurokawa, N. Urakami, K. Nakaya-Yaegashi, A. Sakashita, M. Imai, and T. Yamamoto
Soft Matter 7, 7504-7510 (2011).

３）Depletion interaction in rod particle and semi-flexible polymer mixture

The most familiar entropic interaction induced by the guest particles is the depletion interaction, i.e. attractive interaction between host particles. Thus, by overlapping the depletion zone surrounding the host particles the guest particles obtain large free volume. The increase of the free volume raises the translational entropy of guest particles, but at the expense of lowering the entropy of mixing. In the case of rod particle and semi-flexible polymer mixture, the rods start to aggregate at the very dilute concentration (less than 0.1 mg/ml), which is an extreamly enhanced depletion effect.
[Related papers]
The Isotropic-Nematic Transition and the Phase Separation of the Tabacco Mosaic Virus Particles with Polysaccharide
N. Urakami, M. Imai, Y. Sano and M. Takasu
J. Chem. Phys. 111, 2322-2328 (1999).
Polysaccharides Induced Crystallization of TMV Particles
M. Imai, N. Urakami, A. Nakamura, R. Takada, R. Oikawa and Y. Sano
Langmuir 18, 9918-9923 (2002).
The Dependence of Sphere Size on the Phase Behaviors for the Mixture of Rods and Spheres.
N. Urakami and M. Imai
J. Chem. Phys. 119, 2463-2470 (2003).