Anomalistic Self-Assembled Phase Behavior of Block Copolymer Blended with Organic Derivative Depending on Temperature

Amphiphilic Pluronic block copolymers have attracted great attention in a broad spectrum of potential applications due to the excellent phase behaviors in an aqueous solution, and many efforts have been made to investigate their phase behaviors under various external conditions. With a variety of external conditions, however, the closed looplike phase behaviors of a Pluronic block copolymer in an aqueous solution have not been reported yet. Herein, we report the closed looplike (CLL) phase behavior of a Pluronic P65 triblock copolymer blended with an organic derivative, 5-methylsalicylic acid (5mS), in aqueous solution, which is very unique for block copolymers. As the 5mS concentration increases, the isotropic to ordered phase or back to isotropic phase transition temperature is decreased while the number of closed loops is increased to two. To the best of our knowledge, this is the first demonstration of a CLL phase transition of a Pluronic block copolymer in an aqueous solution, which is readily applicable to optical devices such as optical sensors or optoelectronics, and nanotemplates for a highly ordered superlattice. Furthermore, this provides new insight into the understanding on the phase behavior of a Pluronic block copolymer blended with additives

Small-Angle Neutron Scattering Study on Defect-Controlled Polymer Networks

Tetra-PEG gels are classified to near-“ideal” networks with significantly low inhomogeneities, which were confirmed by small-angle neutron scattering (SANS). In this study, we systematically introduced two types of defects into Tetra-PEG gels and investigated effects of defects on structure. First, we prepared defect-rich networks by simply reducing prepolymer concentration, and observed the evolution of network structure by time-resolved SANS during gelation process. In this case, both the scattering intensity and the correlation length increased with reaction time in the ϕ < ϕ* region, while they scarcely changed in the ϕ > ϕ* region. Here, ϕ and ϕ* are the polymer volume fractions at observation and that at chain-overlap concentration, respectively. Second, we prepared “<i>p</i>-tuned” Tetra-PEG gels by tuning the reaction probability, <i>p</i>, and soaked them in water to expose the inhomogeneities. It was revealed that SANS profiles of as-prepared gels did not change noticeably, while those of swollen gels systematically changed with decreasing <i>p</i>. On the basis of these results, we discuss the relationship between the defects of polymer network and inhomogeneities by using simple schematic pictures of polymer network

Fabrication and Structural Characterization of Module-Assembled Amphiphilic Conetwork Gels

Structural analysis of inhomogeneity-free poly­(ethylene glycol)–poly­(dimethyl­siloxane) (PEG–PDMS) amphiphilic conetwork gels has been performed by the complementary use of small-angle X-ray and neutron scattering. Because of the hydrophobicity of PDMS units, the PEG–PDMS gels exhibit a microphase-separated structure in water. Depending on the volume fraction of PDMS, the microphase-separated structure varies from core–shell to lamellar. The obtained X-ray and neutron scattering profiles are reproduced well using a core–shell model together with a Percus–Yevick structure factor when the volume fraction of PDMS is small. The domain size is much larger than the size of individual PEG and PDMS unit, and this is explained using the theory of block copolymers. Reflecting the homogeneous dispersion conditions in the as-prepared state, scattering peaks are observed even at a very low PDMS volume fraction (0.2%). When the volume fraction of PDMS is large, the microphase-separated structure is lamellar and is demonstrated to be kinetically controlled by nonequilibrium and topological effects

SANS and DLS Study of Tacticity Effects on Hydrophobicity and Phase Separation of Poly(<i>N</i>‑isopropylacrylamide)

The tacticity effect on phase separation process of poly­(<i>N</i>-isopropylacrylamide) (PNiPAM) aqueous solutions was investigated by dynamic light scattering (DLS) and small angle neutron scattering (SANS) measurements. SANS measurement revealed that hydrophobicity of PNiPAM consisting of meso- and racemo-isomers increased with increasing the meso-content. This result is in accordance with the result of the previous experimental and simulation study on NiPAM dimers (DNiPAM) and trimers (TNiPAM) [Katsumoto, Y.; J. Phys. Chem. B 2010, 114, 13312−13318, and Autieri, E.; J. Phys. Chem. B 2011, 115, 5827–5839]; i.e., meso-diad is more hydrophobic than racemo-diad. In addition, a series of scattering experiments revealed that the ratio of meso-diad does not affect the static structure or the shrinking behavior of a single chain, but strongly affects the aggregation behavior. The PNiPAMs with low meso-content suddenly associate around the phase separation temperature, while that of the high meso-content gradually aggregate with increasing temperature. We propose that phase transition behavior of PNiPAM aqueous solutions can be controlled by changing the stereoregularity of the polymer chain

Structural Study on the UCST-Type Phase Separation of Poly(<i>N</i>‑isopropylacrylamide) in Ionic Liquid

Upper critical solution temperature (UCST)-type phase separation behavior and its conformational change of well-defined poly­(<i>N</i>-isopropylacrylamide) (pNIPAm) in deuterated room-temperature ionic liquid (IL), 1-ethyl-3-methylimidazolium bis­(trifluoromethanesulfonyl)­amide (<i>d</i>₈-[C₂mIm⁺]­[TFSA^–]), were investigated by means of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) measurements. From the temperature dependence of time-averaged scattering intensity obtained by DLS, it was found that the cloud points of pNIPAm/<i>d</i>₈-[C₂mIm⁺]­[TFSA^–] solutions increased with molecular weight (<i>M</i>_w) and concentration. In addition, it was found that there are two relaxation modes of pNIPAm in the IL solutions. From SANS measurements, the radius of gyration, <i>R</i>_g, and the Flory–Huggins interaction parameter, χ, were evaluated as a function of temperature during the phase separation