Yuya Shinohara

Synergy Effect on Morphology Switching: Real-Time Observation of Photo-Orientation of Microphase Separation in a Block Copolymer†

The dynamic motions of molecular assemblies are essential in biological systems and in some functional materials and devices. For technical applications, the liquid crystal (LC) display is a typical example; LC displays are based on the dynamic alignment switching of LC molecules driven by an electric field. Over the past two decades, significant research efforts have led to the establishment of a light-driven alignment method for LC materials. When linearly polarized light (LPL) irradiates an LC polymer film that contains a rod-like photochromic unit such as azobenzene (Az), the mesogenic groups reorient in a cooperative way to a nonexcitable direction, specifically, the direction orthogonal to the electric vector (E) of the actuating polarized light. The mesogenic units can be further reoriented by irradiating with LPL from another E direction. On the other hand, macroscopic actuators consisting of photochromic LC polymers have recently become an active area of research. They show large and reversible shape deformations in response to light. The cooperative motions of LC units within the aligned materials lead to macroscopic deformations. Some bending deformations reflect the direction of the LPL used for the irradiation. 9] Despite the accumulated knowledge concerning the previously discussed light-driven materials, photoresponsive systems that have an intermediate “mesoscopic” feature size (typically 10–100 nm) remain an underexplored area. Such structures are readily available by the microphase separation (MPS) of block copolymers. These size regions are expected to play important roles in the development of lowcost processes that exceed the limitations of ordinary photolithography. 13] Thus, numerous investigations have been conducted to manipulate the mesostructures of block copolymers. 13] However, the efforts to date have mostly been limited to the construction of static fixed structures attained by directed assembly using for example patterned surfaces, mechanical flow, electric fields, or magnetic fields. Only a few attempts have been made to alter the MPS structure by external stimuli. Herein, the dynamic reorientation process of an MPS mesostructure was pursued under application of external electric fields 22] using in situ scanning probe microscopy and synchrotron X-ray scattering measurements. The elucidation of the light-induced reorientation processes of the MPS morphology of a block copolymer remains a challenging problem. Our previous experiments have shown that a diblock copolymer, which consists of polystyrene and an LC Azcontaining polymer block, is able to alter the orientation of an MPS cylinder structure (distance between the cylinders: ca. 32 nm) of coiled polystyrene domains in response to LPL. Herein we report time-resolved in situ measurements of the photoinduced alignment changes of both smectic LC Az layers and a mesoscopic coiled polymer domain array by Xray scattering from a synchrotron radiation source. The strong cooperative motions between the hierarchies of the constituents of photoresponsive molecules and mesoscopic MPS domains are revealed by this approach. In our previous work on a polystyrene-based polymer (glass transition temperature (Tg) of polystyrene = 102 8C), the photoalignment procedure required both LPL irradiation and annealing followed by successive slow cooling; real-time monitoring was therefore not feasible. In the present study, a newly synthesized Az LC block copolymer containing poly(butyl methacrylate) (PBMA, Tg = 20 8C) instead of polystyrene was employed (Figure 1 a; P5Az10MA43-bPBMA70). This diblock copolymer formed the amorphous cylinders in the Az LC block matrix in the MPS structure, as determined by small-angle X-ray scattering measurements (Supporting Information, Section S3-3). The LC phases and thermal properties of P5Az10MA43-b-PBMA70 were evaluated using differential scanning calorimetry (DSC), thermal optical polarized microscopy, and X-ray diffraction measurements (Supporting Information, Section S3-2). P5Az10MA43b-PBMA70 exhibited a Tg of 55 8C, which is identical to that of the P5Az10MA homopolymer. This result indicates that the PBMA and Az LC blocks were phase-separated from each [*] Prof. S. Nagano Nagoya University Venture Business Laboratory, Precursory Research for Embryonic Science and Technology (PRESTO) Furo-cho, Chikusa, Nagoya, 464-8603 (Japan) E-mail: snagano@apchem.nagoya-u.ac.jp

Hydrophobic Molecules Infiltrating into the Poly(ethylene glycol) Domain of the Core/Shell Interface of a Polymeric Micelle: Evidence Obtained with Anomalous Small-Angle X-ray Scattering

Polymeric micelles have been extensively studied as nanoscale drug carriers. Knowing the inner structure of polymeric micelles that encapsulate hydrophobic drugs is important to design effective carriers. In our study, the hydrophobic compound tetrabromocathecol (TBC) was chosen as a drug-equivalent model molecule. The bromine atoms in TBC act as probes in anomalous small-angle X-ray scattering (ASAXS) allowing for its localization in the polymeric micelles whose shape and size were determined by normal small-angle X-ray scattering (SAXS). Light scattering measurements coupled with field flow fractionation were also carried out to determine the aggregation number of micelles. A core-corona spherical model was used to explain the shape of the micelles, while the distribution of bromine atoms was explained with a hard-sphere model. Interestingly, the radius of the spherical region populated with bromine atoms was larger than the one of the sphere corresponding to the hydrophobic core of the micelle. This result suggests that the TBC molecules infiltrate the PEG hydrophilic domain in the vicinity of the core/shell interface. The results of light scattering and SAXS indicate that the PEG chains at the shell region are densely packed, and thus the PEG domain close to the interface has enough hydrophobicity to tolerate the presence of hydrophobic compounds.

Characterization of two-dimensional ultra-small- angle X-ray scattering apparatus for application to rubber filled with spherical silica under elongation

Two-dimensional ultra-small-angle X-ray scattering (2D-USAXS) apparatus at SPring-8 has been characterized. 2D-USAXS is a promising tool to study the structural change of the hierachical aggregate structure of fillers such as carbon black and silica particles in rubber. The aggregate structure of fillers is key to understanding the reinforcement effects which fillers show in rubber. We have applied 2D-USAXS to rubber filled with spherical silica particles and proved it to be a powerful technique.

Upgrade of the small angle X-ray scattering beamlines at the Photon Factory

BL-10C and BL-15A at the Photon Factory, which became operational in 1982, are some of the oldest small angle X-ray scattering beamlines in the world. Recently, both beamlines were upgraded for two-dimensional (2D) SAXS-WAXS experiments. A wide-area imaging plate (IP) detector and a fast-readout flat panel (FP) detector were installed at BL-10C and BL-15A, respectively. Preliminary experiments of both systems showed promising results.

Microscopic structural evolution during the liquid-liquid transition in triphenyl phosphite

Recently the liquid?liquid transition (LLT) was found in a molecular liquid, triphenyl phosphite, which allows us to follow the kinetics of the transformation of one liquid to another. Here we investigate the microscopic structural change during the LLT by means of time-resolved synchrotron x-ray scattering measurements. We confirm that during spinodal-decomposition-type transformation a new peak corresponding to a particular intermolecular phosphor?phosphor distance emerges and grows with time. This indicates that short-range order develops in the liquid during LLT. We show that the short-range order does not represent the crystalline structure, but the locally favoured structure. We found that the temporal increase of the intensity of this peak, i.e., the fraction of locally favoured structures, is proportional to that of the heat released during the transformation. This means that the formation of locally favoured structures is the origin of the heat release. This is consistent with the proposal that the order parameter governing LLT is the number density of locally favoured structures. This yields a valuable insight into the nature of the ordering in the liquid?liquid transition.

Structural analysis of single wool fibre by scanning microbeam SAXS

The technique of scanning microbeam small-angle X-ray scattering (SAXS) has been applied to investigate the inhomogeneity in the nanostructure of a single bilateral wool fibre in relation to two types of cortices, the so-called orthocortex and paracortex, which are located at the outer side and the inner side of the curved fibre, respectively. On the basis of the equatorial scattering intensity profiles from both experiments and simulation, the inhomogeneity in the mean IF (intermediate filament)-IF distance, IF diameter and IF orientation, corresponding to the structural difference between the orthocortex and the paracortex in bilateral wool fibre, has been quantitatively obtained.

Pinhole-type two-dimensional ultra-small-angle X-ray scattering on the micrometer scale

A pinhole-type ultra-small-angle X-ray scattering set-up that enlarges the accessible q-range to 0.25 µm−1 is described.

Composition dependence of the micellar architecture made from poly(ethylene glycol)-block-poly(partially benzyl-esterified aspartic acid).

Poly(ethylene glycol)-block-poly(partially benzyl-esterified aspartic acid), denoted by PEG-P(Asp(Bzl)), is one of the most examined blockcopolymers for drug carriers. However, little is known about fundamental physical properties. Nine samples of PEG-P(Asp(Bzl)) with different benzylation fractions (F(Bzl)) and aspartic chain lengths (DP(Asp)) were synthesized, and the aggregation number (N(agg)), core radius (R(C)), and other structural parameters were determined with combination of light scattering and synchrotron X-ray small-angle scattering. The major factor to determine N(agg) and R(C) was found to be F(Bzl), i.e., the hydrophobic nature of the core, even though F(Bzl) was changed in the relatively small composition range from 66 to 89 mol %. When we compared the data for the same F(Bzl), the scaling theory was consistent with the core chain length dependence of both core and micelle sizes. The overcrowding nature of the tethered PEG chains on the micelles was increased about 1.3-2.9 times with increasing N(agg) compared with the unperturbed state in solutions.

Indirectly illuminated X-ray area detector for X-ray photon correlation spectroscopy

An indirectly illuminated X-ray area detector is employed for X-ray photon correlation spectroscopy (XPCS). The detector consists of a phosphor screen, an image intensifier (microchannel plate), a coupling lens and either a CCD or CMOS image sensor. By changing the gain of the image intensifier, both photon-counting and integrating measurements can be performed. Speckle patterns with a high signal-to-noise ratio can be observed in a single shot in the integrating mode, while XPCS measurement can be performed with much fewer photons in the photon-counting mode. By switching the image sensor, various combinations of frame rate, dynamic range and active area can be obtained. By virtue of these characteristics, this detector can be used for XPCS measurements of various types of samples that show slow or fast dynamics, a high or low scattering intensity, and a wide or narrow range of scattering angles.

Two-dimensional pattern reverse Monte Carlo method for modelling the structures of nano-particles in uniaxial elongated rubbers

Two-dimensional pattern reverse Monte Carlo (2D pattern RMC) analysis is performed to model the structures of nano-particles in uniaxially elongated rubbers using two-dimensional patterns of structure factor of the nano-particles obtained by time-resolved two-dimensional ultra-small angle x-ray scattering. Four spot patterns are observed for a large elongation ratio and the shapes change with increasing elongation ratio. We performed the 2D pattern RMC method for the uniaxial system in order to make a model of the structures from the two-dimensional structure factors. The preliminary results of the 2D pattern RMC analysis of the two-dimensional structure factors of silica particles in a uniaxially elongated styrene-butadiene rubber are presented.