Formation Of Microphase-separated Structure Research Articles

Phase behavior of mixtures of hard colloids and soft coarse-grained macromolecules.

Effective "soft" interactions between macromolecules such as polymers, amphiphilic dendrimers, and suitably designed DNA based dendritic molecules have been shown to be purely repulsive and non-diverging. We report the structure and phase behavior of a mixture of hard colloids and soft coarse-grained macromolecules. Through the use of Reference Interaction Site Model theory and molecular dynamics simulations we find that hard colloids and soft macromolecules act as depletants toward each other, generating a medium-induced effective attraction. This effective attraction leads to the formation of non-dispersed phases at high densities. At low and high fractions of hard colloids the system macrophase separates into two disparate regions of hard colloids and soft macromolecules. However, this system microphase separates into a hard-rich and soft-rich self-assembled domains at intermediate compositions. The formation of microphase separated structure in this system of isotropic, disconnected, and purely repulsive colloids is surprising and quite novel. This behavior is likely due to a softening of the interface between hard-rich and soft-rich self-assembled domains. Molecular dynamics simulations have revealed that the microphase separated state has an overall disordered bicontinuous morphology. The hard-rich domain forms an ordered FCC structure and the soft-rich domain forms a disordered cluster-fluid, making the structure simultaneously ordered and disordered.

Ultra-robust, self-healable and recyclable polyurethane elastomer via a combination of hydrogen bonds, dynamic chemistry, and microphase separation

Flexibility, robustness, transparency, and recyclability are critical to the application of self-healing polymer materials in the field of flexible electronics. However, integrating all the above properties remains a huge challenge to date. In this work, we put forward a facile strategy to prepare polyurethane (PU) elastomer with ultra-high strength and self-healing performance based on hydrogen bonds, disulfide dynamic chemistry, and microphase separation at the same time. Three different self-healing PUs were obtained by introducing disulfide bonds and different types of hydrogen bonds. A robust, transparent, and recyclable PU with amino-terminated chain extender (PUA) with fast and efficient self-healing performance was prepared. The mechanical and self-healing properties of the PUA were effectively balanced by the synergistic effect of reversible interaction of disulfide bonds and the formation of microphase separated structure. The results indicated that the PUA exhibited high transparency up to 90% and excellent mechanical property, e.g. the tensile strength and elongation at break can reach 37.10 MPa and 1080%, respectively. Meanwhile, it can achieve a high self-healing efficiency of 96.8% at 80 °C for 4 h and maintain 84% of the initial mechanical strength even after four times of recycling. Moreover, the colloid graphite/PUA flexible strain sensor was prepared by the combination of colloid graphite and PUA, which can accurately detect both large and tiny scale deformations.

High Temperature Polymer Electrolyte Membrane Achieved By Grafting Poly(1-vinylimidazole) on Polysulfone for Fuel Cell Applications

High temperature polymer electrolyte membranes with phosphoric acid doping are crucial materials of high temperature fuel cells. However, the evolution of the type membrane is suffering from the trade-off between proton conductivity and mechanical strength, because high proton conductivity requires high phosphoric acid doping level, which will reduce the mechanical properties due to the plasticization of phosphoric acid on polymer backbone. Here, a new strategy is employed to respond to the unresolved challenges by grafting poly(1-vinylimidazole) as phosphoric acid doping sites on polysulfone backbone via atom transfer radical polymerization. Then poly(1-vinylimidazole) grafted polysulfone membrane with different length of side chains is obtained and soaked in phosphoric acid to work as high temperature polymer electrolyte membrane. The tapping-mode AFM images and 1-D SAXS result of PA doped membrane suggest the formation of micro-phase separated structures, and the ionomer peaks shift from 1.34 nm-1 to 1.19 nm-1 with increasing the length of side chain, corresponding to d-spacing of 4.67 nm and 5.28 nm, respectively. Therefore, the prepared phosphoric acid doped membranes possess excellent proton conductivity of 127 mS cm-1 under 160 °C due to the structure, while mechanical properties are retained due to the reduction of plasticizing effect caused by the separation of phosphoric acid adsorption sites and polymer backbone, presenting an outstanding tensile strength of 7.94 MPa. Meanwhile, the impressive fuel cell performance with the membranes is gained, reaching a maximum peak power density of 559 mW cm-2 under 160 oC. More importantly, the work provides a new sight to solve the trade-off between proton conductivity and mechanical strength for phosphoric acid doped high temperature polymer electrolyte membranes. Figure 1

High temperature polymer electrolyte membrane achieved by grafting poly(1-vinylimidazole) on polysulfone for fuel cells application

Phosphoric acid (PA)-doped high temperature polymer electrolyte membranes (HT-PEMs) are crucial materials for HT-PEM fuel cells (HT-PEMFCs). However, the development of HT-PEMs suffers from the trade-off between proton conductivity and mechanical strength. High proton conductivity requires a high doping level of PA, and PA acts as a plasticizer that reduces the mechanical properties. Here, a new strategy is employed to address the unresolved challenges; the strategy is to graft poly(1-vinylimidazole) as PA doping sites on the polysulfone backbone. This is achieved via atom transfer radical polymerization. High proton conductivity is achieved because of the formation of micro-phase separated structures, and the mechanical properties are retained because of the reduced plasticizing effect, which is caused by the separation of PA adsorption sites and the polymer backbone. The prepared PA-doped membranes have excellent proton conductivity of 127 mS cm−1 at 160 °C and outstanding tensile strength of 7.94 MPa. Meanwhile, single H2-O2 cell performance with the optimized membrane is impressive, reaching a peak power density of 559 mW cm−2 at 160 °C. More importantly, this work provides new insight into solving the trade-off between proton transport and mechanical strength for PA-doped HT-PEMs.

Calorimetric studies of PEO-b-PMMA and PEO-b-PiPMA diblock copolymers synthesized via atom transfer radical polymerization

Poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) and poly(ethylene oxide)-b-poly(isopropyl methacrylate) (PEO-b-PiPMA) diblock copolymers of different block ratios have been synthesized using atom transfer radical polymerization with functionalized PEO monomethylether as macroinitiator. The phase separation between the constituent blocks of the copolymers has been investigated by differential scanning calorimetry (DSC). In PEO-b-PMMA, the constituent blocks are completely miscible irrespective of their molar mass and block ratios. This behaviour remains the same for PEO-b-PiPMA with ≤15% PEO fraction; phase separation could only be observed for PEO-b-PiPMA with higher PEO content. These observations are supported by results of atomic force microscopy studies of films of two copolymers with comparable molecular weight and PEO fraction (≥24% PEO); a very well developed lamellar morphology was only observed for PEO-b-PiPMA, while the block domains were randomly dispersed in PEO-b-PMMA. Interestingly, the phase separation behaviour in PEO-b-PMMA with >30% PEO fraction has been found to be strongly dependent on its processing and thermal history. On the contrary, phase separation in PEO-b-PiPMA BCPs with ≥24% PEO fraction has not been affected by its processing or thermal history. Results indicate that the use of a block-selective solvent for the precipitation of the diblock copolymer promotes the formation of microphase separated structures even for copolymers with miscible blocks. The findings are relevant for ongoing attempts to utilize the microphase separation of such polymers to obtain well-defined nanoporous membranes and other materials.

Formation of Microphase-Separated Structure in a Triblock Copolypeptide LB Film

Formation of Microphase-Separated Structure in a Triblock Copolypeptide LB Film

A new way to control particle morphology in heterophase polymerizations

The formation of microphase separated structures in the confined space of latex particles is reported. Three different systems are investigated: emulsion polymerizations started either with polymeric radicals or with persulfate in the presence of ionic chain transfer agents, aqueous dispersions of well defined polystyrene model oligomers with sulfonate end groups, and miniemulsion polymerization in the presence of large amounts of preformed polymer in the droplets. In any of these cases microphase separation leads to the formation of inhomogeneities in the particles. Electron microscopy, atomic force microscopy, and X-ray absorption microscopy show identical structures and hence prove that the inhomogeneities already exit in the dispersed state.

Physical Gelation of Nematic Liquid Crystals with Amino Acid Derivatives Leading to the Formation of Soft Solids Responsive to Electric Field.

4′-heptyloxybiphenyl (7OCB), have been physically gelled due to the formation of hydrogen-bonded networks comprised of amino acid derivatives. The mixtures of nematic liquid crystals and amino acid derivatives exhibit thermoreversible three states, isotropic, isotropic gel, and nematic liquid-crystalline gel, through the phase change of each of components. The gel states are induced by the formation of microphase-separated structures and transition properties of liquid-crystalline solvents in the network structures are maintained. The anisotropic gels of 5CHB can respond to electric fields in polyimide-coated liquid crystal cells. The existence of a small amount of gelling agents has great effects on the electro-optic properties. Acceleration of response behavior of the nematic liquid crystal has been achieved by such physical gelation.

Physically crosslinked elastomers prepared from oligomeric polyolefins with mesogenic units

Two ABA-type liquid crystalline oligomers were newly synthesized, where A was a mesogenic group and B was polyolefin whose molecular mass was 2470. The A segment was prepared from p-hydroxyl benzoic acid and terephalic acid. The elastomeric films, whose moduli at 20% elongation were 0.4–1.0 MPa, were obtained by solution casting of the ABA-type oligomers. Dynamic mechanical analysis and differential scanning calorimetry measurement showed the glass transition of amorphous polyolefin segments, the melting of mesogenic groups, and the meso-to-isotropic transition of liquid crystalline phase. The formation of microphase-separated structures was confirmed by a small-angle X-ray scattering (SAXS) measurement. The presence of hexagonal cylinder domains, which were attributed to the aggregation of mesogenic groups in the polyolefin matrix, was also detected by SAXS. These liquid crystalline oligomers showed anisotropy under the crossed Nicoles, and the textures were observed to be nematic. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2247–2253, 2000