We study structure and dynamics of polymer systems in a wide spatial scale from nm to mm and in a time scale from ps to ms using neutron, X-ray and light scattering as well as optical microscope and AFM to understand their properties and functions.
We performed these structure and dynamics studies from basic science viewpoint as well as applications. Our recent interests are focused on polymer crystallization, glass transition, polyelectrolytes, polymer gels and polymers in confinement. In the following we introduce some results obtained in our laboratory.
In Japan we will have first neutron beam in J-PARC in spring, 2008, which is a big accelerator facility including neutron, muon, and other elementary particle physics. We aim to establish new soft-matter science using quantum beam such as J-PARC neutron and Spring-8 (SR facility) X-ray.
Polymer Crystallization and Higher Order Structure
We are investigating polymer crystallization process to elucidate the formation mechanism using scattering methods such as X-ray, neutron and light and microscope technique such as optical microscope, AFM and electron microscope. Now we are interested in polymer crystallization mechanism via intermediate states between amorphous and crystal states.
Glass Transition of Polymers
Glass transition is still a mysterious problem in condensed matter physics as well as polymer physics because viscosity or relaxation time (of a-process) increases more than 10 orders of magnitude near the glass transition temperature Tg without discontinuous structure changes. We study dynamics of glass-forming polymers in glassy state as well as near glass transition temperature using quasielastic and inelastic neutron scattering and dynamics light scattering. In glassy state we focus on Boson peak as well as picosecond fast process, and near glass transition we investigate the a-process. In addition we also study the long-range density fluctuations (or Fischer cluster) in glass-forming polymers using static and dynamic light scattering.
Hierarchic Structure of Polymer Gels
and Formation Mechanism
Polymer gels are very familiar to human being in daily life, which are often found in foods, animals and plants. In order to develop synthetic gels with high performance and high functionality such as drug delivery system and artificial muscle extensive studies have been performed on various kinds gels. Our group is focusing on poly(vinyl alcohol) (PVA) gels because it is water-soluble and biocompatible, and investigating the hierarchic structure in a wide spatial scale from A to mm using neutron and light scattering and optical microscope. Dynamics of PVA gels are also studied using neutron spin-echo technique to understand response of the gels to external stimulations.
Structure of Polyelectrolyte Solutions
Polyelectrolyte has many electrical charges on it and shows characteristic features due to electrostatic interactions which are never seen in neutral polymers. One of the most interesting features of polyelectrolyte solutions is increase in reduced viscosity as the concentration decreases. It was thought in the former time that it was caused by extension of polyelectrolyte chains due to electrostatic repulsive force. This is written in many textbooks. We revealed for the first time that the former interpretation was wrong but it is caused by electrostatic repulsive force between polyelectrolytes.
Dynamics and Phase Separation in Confinement
Properties of polymers in confinement such as thin films and porous media are very different from those in bulk. We are studying dynamics of glass-forming polymers in thin film in a range between 5 to 500 nm using neutron and X-ray reflectivity and quasielastic neutron scattering. In addition we also study phase separation and dewetting in polymer blend thin films using neutron reflectivity, light scattering, AFM and optical microscope.
Development of Apparatus
We develop neutron spectrometers as well as laboratory apparatuses for progress in our researches.
- Ultra-fast temperature jump apparatus
- Light scattering apparatus with confocal principle
- Neutron spin-echo spectrometer
- Inverted geometry neutron TOF spectrometer
Researches in Future
Creation of New Softmatter Science by Quantum Beam
We have made progress in softmatter science, especially in polymers using neutron and SR X-ray, and often given final answers to some scientific problems. In Japan we have SR facilities such as Photo Factory in Tsukuba and Spring-8 in Nishiharima, and will have intense pulse neutron beam from J-PARC (1 Mw) in spring 2008. In USA similar pulse neutron facility SNS has already provided first beam, and ISIS in England will complete the second target station for pulse neutron near future. Softmatter science is one of the next scientific targets in these facilities. Our group also wants to create new softmatter science using new neutron beam as well as SR X-ray based on the previous results obtained in our laboratory by neutron and SR X-ray. In the following we show future directions and some previous results of softmatter science by neutron and SR X-ray.
- Mesoscopic Structure of Softmatter and Formation Process
Structure study by small-angel neutron and X-ray is one of the most important subjects in softmatter science to elucidate hierarchic structure in a wide spatial scale from A to mm in-situ measurements. In neutron scattering experiments we can see specific molecules or specific parts of molecules using deuterium labeling method. We have already studied polymer crystallization process, glassy structure, polymer gels, polymer micelles, polyelectrolytes using small-angle neutron scattering
- Slow Dynamics of Softmatter
Structure of softmatter is formed on delicate balance between enthalpy and entropy. In order to understand the response of softmatter to external stimulations we have to study the dynamics. We have investigated dynamics of glass-forming materials polymer gels, polymer micelles, polyelectrolyte solutions.
- Surface and Interface Structure of Softmatter and Dynamics
Properties of softmatter are very much influenced by surface and interface structure. Surface and interface structure studies are essential to understand the softmatter properties. We have already studied structure and dynamics of polymer thin films and phase separation and dewetting of polymer blend thin films using X-ray and neutron reflectivity and quasielastic neutron scattering.