Soft materials such as rubber materials consist of hierarchical structures and their rich variety of mechanical properties originate from the structures and the correlation among hierarchies. Here we discuss hierarchy in static and dynamic aspects in rubber materials.

We developed a novel straining holder for polymeric materials that is capable of applying large tensile deformation to specimens and performing high-angle tilt for electron tomography. A sample cartridge with a variety of polymeric materials, such as microtomed thin sections of bulk specimens and solvent-cast thin films, can be mounted on the holder. The holder has the following features: large tensile deformation (800 μm) with a large field of view (800×200 μm before the deformation), easy to follow the same field of view and a high tilt angle (±75°) during tensile observations. The strain on the specimen can be applied as large as 26, at least one order of magnitude larger than the predecessor desigined for metallic materials. We demonstrated that deformation processes of isoprene rubber containing silica nanoparticles with this tensile holder.

Terahertz (THz) radiation, which exists between microwave and infrared electromagnetic region, has characteristics of penetration without any destruction into materials like radio wave and X ray. This merit enables us to expect that the THz light is useful for non-destructive inspection of industrial products such as plastics and polymers including rubbers. Our research group is investigating possibilities of estimation of various rubber conditions using THz time-domain spectroscopy (THz-TDS). In this article, what kind of information we could obtained inside rubber products by THz radiation is focused and explained based on our previous and new unpublished experimental results.

Atomic force microscopy (AFM) offers nanometer-scale mapping of materials’ properties. Especially our modified AFM called as ‘nanorheological AFM’ enables to measure the accurate frequency-dependent storage modulus, loss modulus, and loss tangent (tanδ) over a wide frequency range from 1.0 Hz to 20 kHz at same temperature, in addition to controlling a wide temperature range from -10 to 30 °C, so that we can undergo the viscoelastic maps of mechanical properties over 6 orders frequency.

In this report, consequently, the values of dynamic properties obtained by nanorheological AFM can be compared with those using bulk dynamic mechanical analysis (DMA) measurements. The peak frequency and values of tanδ obtained for silica-filled styrene-butadiene rubber (SBR) nicely corresponded to those of bulk DMA measurements. The loss tangent mapping and its histogram showed interfacial regions around silica particle has lower loss tangent than that of SBR rubber matrix. We have succeeded in quantitatively measuring the frequency dependence of inhomogeneity in rubber component nearby silica interface for the first time.

The performance of a polymer composite material, in which inorganic fillers are dispersed, is closely related to the aggregation states and dynamics of polymer chains at the interface with the filler. In this short review, we first introduce the relaxation behavior of polymer chains in thin films supported on solid substrates, suggesting that the surface and interfacial dynamics are faster and slower than that in the bulk. Then, aggregation states and dynamics of rubbery chains as well as glassy ones are directly discussed on the basis of the interfacial sensitive vibrational spectroscopy. We clearly demonstrate that chains at the substrate interface can be hardly relaxed even at a temperature being far above the bulk glass transition temperature. Finally, we try to combine this knowledge with the viscoelastic properties of bulk composite materials composed of a rubbery polymer and an inorganic filler.