| POLYMERS Vol.70 No.8 |
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COVER STORY
Visualization of Force |
| COVER STORY: Highlight Reviews |
| Measuring Forces/Stresses Inside a Developing Embryo | Kaoru SUGIMURA |
| <Abstract> Biopolymers, such as actin filaments and nuclear lamina, are responsible for force generation and mechanotransduction in cells. The measurement of force and stress in vivo is essential to understand how cell mechanics lead to precise tissue patterning and deformation during development. In this review, I introduce the principles, advantages, and limitations of the methods used to measure force and stress in vivo, with emphasis on force sensors that are closely related to polymer chemistry. Finally, I discuss the future directions of interdisciplinary research that combines polymer chemistry and life science. Keywords: Mechanics / Development / Morphogenesis / FRET |
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| Effects of Polymer Deformation and Relaxation on Flow Characteristics | Ruri HIDEMA, Hiroshi SUZUKI |
| <Abstract> Addition of little amounts of polymers to Newtonian fluid drastically changes the flow characteristics such as sudden increase of relaxation time, elastic instability in a micro channel, and turbulent drag reduction. This is due to deformation and relaxation of polymers in fluids. In this article, we introduce recent researches that focus on behaviours of polymers in an extensional flow, effects of polymers on extensional rheology of the solution, and turbulent drag reduction. Keywords: Rheology / Complex Fluids / Extensional Flow / Drag Reduction / Microfluidics |
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| COVER STORY: Topics and Products |
| Low Friction Polymer Additives for Oil-Based/Water-Based Lubrication | Shinji YAMADA |
| <Abstract> Recent nanotribological studies on the polymer additives which are useful to obtain low-friction surfaces in oil-based and water-based lubrication are described. The surface forces apparatus (SFA) technique was used to investigate the sliding film structures and friction properties of polymer additives adsorbed on mica surfaces from their oil-based/water-based solutions. By using the optical technique of the SFA (fringes of equal chromatic order, FECO), we measured the thickness of intervening lubricant films with the resolution of 0.1 nm simultaneously with the friction measurements. The results enabled us to discuss the molecular structures and sliding conformations that are suitable for reducing friction in boundary lubrication of oil-based/water-based systems. Keywords: Polymer Additive / Nanotribology / Boundary Lubrication / Surface Forces Apparatus |
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| Emissive Polymer Chemosensors that are Capable of Visualizing Pressures | Kotoe NAKASHA, Gaku FUKUHARA |
| <Abstract> External stimulus-responsive polymers serve as great promises for wide applications in material science and practical diagnosis. In particular, pressure is one of the most ubiquitous external stimuli and can cause changes in polarity and viscosity of solvents used. Recently, hydrostatic pressure, or isotropic mechanical force, has attracted much attention in the fields of mechanochemistry and mechanobiology. We have also demonstrated the hydrostatic pressure-control concept. In this review, we want to highlight our recent studies on emissive polymer chemosensors controlled by hydrostatic pressure. Keywords: Chemosensors / Hydrostatic Pressure / Pyrene / Aggregation-Induced Emission / Peptide / Polystyrene / Spectroscopy |
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| Fluorescent Force Probe for Evaluating Nanoscale Stress Concentration of Polymers | Ryota KOTANI, Shohei SAITO |
| <Abstract> Understanding nanoscale force transmission in pico-to-nanoNewton range is important in polymer physics. While physical approaches have limitations to analyze local force distribution in condensed environments, chemical doping of force probe is promising. However, there are demanding requirements to probe the local force without structural damage, which corresponds to the force range below covalent bond scission (nanoNewton) and over thermal fluctuation (picoNewton). Here we report a conformationally flexible dual fluorescent force probe with 100-picoNewton threshold that realizes ratiometric analysis on nanoscale force distribution in stretched polymer chain network. Without changing original polymer properties, the force distribution has been reversibly monitored in real time. Chemical control of the probe location demonstrated that local stress concentration is twice more biased at crosslinkers than main chains particularly in a strain-hardening region. Due to the sensitive response, proportion of the stressed force probe was estimated more than 100 times higher than activation ratio of conventional mechanophores. Keywords: Force Probe / Mechanophore / Polymer Physics / Rheology / Stress Concentration / Polyurethane / Fluorescent Probe / FLAP |
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| Cellulose-Based Cholesteric Liquid Crystalline Elastomers for Visualization of Mechanical Stress and Strain | Kenichiro HAYATA, Naoto IWATA, Seiichi FURUMI |
| <Abstract> Cellulose is the most abundant natural polymer on the Earth. Hydroxypropyl cellulose (HPC) derivatives are known to exhibit cholesteric liquid crystal (CLC) phase with visible Bragg reflection. Although the viscous CLCs of HPC derivatives show the changes in reflection color by mechanical compression, the changed reflection colors are not stable due to the molecular reorientation by diffusion. On the other hand, we successfully prepared the CLC elastomer (CLCE) films of crosslinked HPC derivatives with a capability to reversibly change the reflection colors by a compression-release process. Very recently, we have developed the CLCE films with high flexibility fabricated by new types of HPC derivatives, which thereby enable the reversible reflection color changes by not only compression, but also a stretch process. Finally, we demonstrated the visualization of both tension and strain by the CLCE films. Therefore, our cellulose-based CLCE films with capabilities to visualize mechanical stress and strain can be potentially applicable to a wide variety of industrial fields in the future. Keywords: Cellulose / Cholesteric Liquid Crystal / Elastomer / Stretch / Bragg Reflection / Visualization / Mechanical Stress / Strain |
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| Development of Mechano-Optical Sensing Materials for Polymer Robotics | Kyohei HISANO, Osamu TSUTSUMI |
| <Abstract> Strain sensors are a key component to develop next-generation robots – the soft robot. For such applications, the electronic sensing using flexible electronic materials are continuing to be at the forefront of the sensing technology. Recently, the optical sensing systems have attracted much attention because of their noninvasivity, sensitivity, and spatio-temporal resolution. Here, we introduce the trend in strain sensors, and propose a potential application of chiral-nematic liquid crystal elastomers. Indeed, there is remarkable maturity in the development of numerous stimuli-responsive liquid crystal elastomers. However, the control of the recovery process after the stimuli removal has not enjoyed comparable growth. Interestingly, our materials design concept of layering the elastomers with other materials allows us to arbitrary tune the rate of the recovery process in both macroscopic deformation and microscopic molecular orientation. Based on the concept, we have suceeded to fabricate a mechano-optical sensor with high sensitivity and high spatio-temporal resolution. This concept would open a pathway to control the recovery process in various stimuli-responsive liquid crystal elastomers. Keywords: Chiral-Nematic Liquid Crystal / Liquid Crystal Elastomer / Soft Elasticity / Strain Sensor / Soft Robot |
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| Polymer Science and I: A Personal Account |
| Physics Never Ends | Naoyuki SAKUMICHI |
| <Abstract> I am researching gel physics at the Sakai-Chung group using “tetra gels,” which have controllable and homogenous networks. With the help of Prof. Sakai, Prof. Chung, Dr. Katashima, and students, we create new physics one after another. The physics of polymer gels never ends. |
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| Front-Line Polymer Science |
| Structure and Dynamics of Macromolecules Observed by Terahertz Spectroscopy | Hiromichi HOSHINA |
| <Abstract> In this paper, polymer spectroscopy in the terahertz (THz) frequency region is reviewed. Due to the recent development of the THz spectroscopic technique, observation of polymer spectra in a lower frequency region has become much easier. THz vibrational spectra reflect intermolecular vibrational motion. Especially, crystalline polymers show characteristic vibrational bands in the THz region, which can be used for the quantitative analysis of polymer crystallinity and crystal structure. Interestingly, polymers with hydrogen bonds show characteristic bands in the frequency region of 2-4 THz. Water adsorption is also a good research target for THz polymer spectroscopy, because small amounts of bound water drastically changes the spectra. Dynamics of bound water in the polymer sample is studied by THz spectroscopy combined with ab initio molecular dynamics simulation. THz spectroscopy provides rich information about structure and dynamics of polymers, and is expected to become a novel tool for polymer science. Keywords: Terahertz Spectroscopy / Polymer / Hydrogen Bonding / Bound Water / Dynamics |
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