The nanostructures of strong and weak polyelectrolyte brushes in the ionic amphiphilic block copolymer monolayer at the air/water interface were investigated by in situ X-ray and neutron reflectometry. The hydrophilic layer under the water was found to be not a simple brush layer but a carpet/brush double layer structure when the hydrophilic chain is long enough and the brush density is high enough. The critical brush density and hydrophilic chain length for the transition between carpet only/carpet + brush structure transition were also found. The weak acid monolayer first expanded by addition of salt but was shrunk by further addition of salt. The strong acid monolayer was not affected by salt addition up to certain salt concentration around 10-1 M, but was shrunk by further addition of salt. These phenomena could be interpreted as due to the charged state of polyelectrolyte chains in the brush layer and the electrostatic repulsion between polymer brush chains in the brush layer.
The NMR imaging microscopy is a very useful means for obtaining non-destructively μm-scale spatial information on probe molecules in bulk matter. Using the 1H chemical shift NMR imaging microscopy, we successfully determined the spatial distribution of paramagnetic metal ions in polymer gel. Results showed that the chemical shift NMR imaging microscopy is a useful means for elucidating the spatial heterogeneous polymer gel network system. The three-dimensional NMR microscopy showed that a hundred long channel cavities with, μm-scale diameters are formed along the direction parallel to α-helix axis in the highly-oriented polypeptide gels. Further, the phase-separated structure of the poly (methyl methacrylate) (PMMA) /poly (styrene) (PS) blends at the order of several tens of μm has been reasonably elucidated by 3D NMR microscopy. Thus, 3D NMR microscopy is a very useful means for characterizing 3D structure of phase-separated polymer blends, along with X-ray microscopy.
Three-dimensional (3D) visualization of nanostructures by transmission electron micrography (TEM) combined with computerized tomography i. e. 3D-TEM is reviewed for soft materials such as nanofiller/rubber composites and block copolymers. Natural rubber (NR) mixed with carbon black (CB) or silica was subject to the measurements by bright-field technique, and 3D images showing the dispersion of them in the NR matrix were successfully obtained. From the images, several structural parameters were evaluated. Comparison of conductivity and 3D nanostructure of NR/CB composites suggests pseudo-network structure of CB through aggregation and agglomeration. Such network structure has been assumed from the mechanical behaviors of filled NR vulcanizates, and these 3D-TEM results finally enable us to picture the networks. Organic polymers are usually sensitive to electron irradiation and quite often have to be stained by a heavy metal; these conditions are not favorable to 3D-TEM measurements. Therefore, we have to be selective in choosing the samples. In spite of these limits, the technique is becoming more and more important, and it will be of much use for establishing nanotechnology of soft materials as an exact science.
A novel idea to extend the capability of an atomic force microscopy (AFM) to soft materials is proposed for the purpose of obtaining sample deformation and modulus distribution images as well as topographic image (nanorheology mapping). An immiscible polymer blend system, elongated natural rubber, and hair cross section are used as model samples. Further extension of this idea leads to tapping-mode force-distance curve analysis aiming at the acquisition of sample deformation information. A force modulation technique is also reviewed in terms of the future development of three-dimensional mechanical properties imaging by AFM, together with the above two techniques.
Recently, three-dimensional (3D) direct observations and analyses of polymer morphologies have drawn considerable attention because they not only offer intuitive understanding of the morphologies but also provide novel structural parameters that can never be obtained from other techniques. Together with the laser scanning confocal microscopy, transmission electron microtomography (TEMT) and X-ray computerized tomography allow 3D direct observations over a wide spatial range from nm to μm: The most sophisticated TEMT achieves the spatial resolution of less than 1 nm in the 3D reconstructed images. In the present paper, various applications of the 3D microscopy to polymer nano-structures, including microphase-separated structures of block copolymers (cylindrical- and gyroid-structures), polymer/clay and polymer/filler nano-composites, will be reported in order to demonstrate the wide and promising capabilities of the new technique. A novel experimental technique of TEMT, i. e. “dual-axis tomography”, is also reported.
We developed a method for virtual imaging experiments on the real three-dimensional structures obtained by 3D experiments. We add the imaging interface to the software “Gourmet, ”which is the platform of the OCTA system. Using this interface, we can convert the real structure to the initial structure for several simulators on OCTA. We can convert the structure from the data obtained by 3D confocal microscopy, 3D transmission electon microscopy, and X-ray computer tomography images. As one example of this study, we applied this method to the deformation problem of blend structure using the simulator “MUFFIN” in OCTA system. We can perform the simulation for the operation of the shear, uniaxial compresion, and uniaxial elongation, and we can obtain the clear images of the deformed structures on the real structures.
A quadrangular prism specimen made of a block copolymer nanostructure (a ‘prism-shaped’ section) was observed in three dimensions (3D) by transmission electron microtomography (TEMT) over as wide a tilt range as possible. A cross section of the prism-shaped section was 200 nm on each side. For comparison, a conventional ultra-thin section having the same thickness as the prism-shaped section was employed. The image quality of the projections taken at a high tilt angle, e. g. 60°, of the prism-shaped section was better than that of the ultra-thin section because its effective thickness was thinner than the ultra-thin section at the same tilt angle. As a result, the projections at very high tilt angles, e. g. ±75°, can be used for the 3D reconstruction in the case of prism-shaped sections, while those at such high tilt angles obtained from the ultra-thin section become so blurred that they may not be appropriate for use in the reconstruction. By use of a prism-shaped section, the contrast of the reconstructed image was significantly enhanced. The elongation of the images along the optical axis of microscope due to the Missing Wedge was also considerably reduced in the case of the prism-shaped section.
We made a 3D median filter to remove noises and to smooth out the 3D image obtained by electron tomography and we examined its effectiveness. We applied the filter to the 3D reconstructed data obtained for the cylindrical microdomain structure of a SIS triblock copolymer by using an ordinary conventional electron microscope and showed that a clear 3D image could be obtained.
Co-continuous morphology with a controllable spatial gradient of characteristic length scales was generated by utilizing photopolymerization and photo-cross-linking reactions for polystyrene/poly (methyl methacrylate) interpenetrating polymer networks (IPNs). The resulting morphology was observed in situ by using a confocal laser scanning microscope (LCSM) with contrast enhanced by fluorescence of fluorescein labeled on PS chains. The IPNs were synthesized from a PS/MMA monomer mixture containing small amounts of photoinitiator and crosslinker for the PMMA network formation. PS networks were, on the other hand, produced via photodimerization of anthracene. Both the PMMA and PS networks were simultaneously produced by irradiation with 365 nm ultraviolet (uv) light. The light intensity was used as a driving force to control the gradient of the characteristic length scales of the spinodal structures resulting from the two networking reactions. It was found that a gradient of co-continuous structure was produced by irradiation using strong uv intensity (0.10 mW/cm2), whereas a uniform co-continuous morphology without gradient was obtained upon irradiation with a weak intensity (0.01mW/cm2). The 3-dimensional phase morphology was constructed from the images obtained at different depths along the direction of irradiation. These preliminary results indicate that polymers with a co-continuous gradient can be generated and controlled by the methods described in this study.
Monodisperse polystyrene (PS) particle multilayers with coherent structure were constructed by Langmuir-Blodgett (LB) method. The reflectance spectra of the particle multilayers with various incident angles indicated that the constructed particle multilayers showed a typical optical character of the conventional multilayers having different refractive indices. It was suggested that the particle multilayer could be treated as a multilayer constructed by polymer layer and air layer. The fact was strongly supported by a simulation of the corresponding model, which was designed for analyzing optical characterization of the particle multilayer. The refractive index of the particle multilayer with nickel ion was also discussed by simulation, suggesting that a theoretical designing of the particle multilayer with various refractive indices would be possible. It was also suggested that coordination of metal ion on the surface of the particle would be enhanced its contribution to increasing the refractive index.