Interplay between cubic and hexagonal phases in block copolymer solutions

Temperature-Selective Self-Assembled Superlattices of Gold Nanoparticles Driven by Block Copolymer Template Guidance

Self-assembly of nanoparticles (NPs) into highly ordered structure can enhance their electronic and optical properties that provide great potential applications such as nanoelectronics and nanophotonics. However, the self-assembly of NPs upon external stimuli was still mainly continuous and irreversible, making various potential applications of NPs difficult. Herein, the self-assembled superlattices of gold nanoparticles (AuNPs) with a temperature-selective response had been investigated by using the amphiphilic block copolymer as a template. The AuNPs in the block copolymer template, which has the closed looplike phase behavior upon heating, self-assembled into the highly ordered body centered cubic (BCC) or face centered cubic (FCC) structures at a specific temperature region that means a temperature-selective responsiveness. The formation of highly ordered self-assembled superlattices (BCC or FCC symmetries) of AuNPs with the closed looplike phase behavior was controlled by the additive and temperature. This study is the first demonstration for temperature-selective response of the cooperative self-assembly of AuNPs in the block copolymer template.

Calculation of scattering-patterns of ordered nano- and mesoscale materials

Analytical expressions for the scattering patterns of ordered nano- and mesoscopic materials are derived and compared to measured scattering patterns. Ordered structures comprising spheres (fcc, bcc, hcp, sc, and bct), cylinders (hex and sq), lamellae (lam) and vesicles, as well as bicontinuous cubic structures (Ia3d, Pn3m, and Im3m) are considered. The expressions take into account unit cell dimensions, particle sizes and size distributions, lattice point deviations, finite domain sizes, orientational distributions, core/shell-structures as well a variety of peak shapes. The expressions allow to quantitatively describe, model and even fit measured SAXS and SANS-patterns of ordered or oriented micellar solutions, lyotropic phases, block copolymers, colloidal solutions, nanocomposites, photonic crystals, as well as mesoporous materials.

Rheological response and dynamics of the amphiphilic diamond phase from kinetic lattice–Boltzmann simulations

The purpose of the present paper is to report on the first computational study of the dynamical and rheological response of a self-assembled diamond mesophase under Couette flow in a ternary mixture composed of oil, water and an amphiphilic species. The amphiphilic diamond mesophase arises in a wide range of chemical and biological systems, and a knowledge of its rheological response has important implications in materials science and biotechnological applications. The simulations reported here are performed using a kinetic lattice–Boltzmann method. Lyotropic liquid crystals exhibit characteristic rheological responses in experiments that include shear-banding and a non-Newtonian flow curve as well as viscoelasticity under oscillatory shear. Their behaviour under steady and oscillatory shear is correctly reproduced in our simulations. On cessation of shear, as the morphology returns to the diamond phase, the relaxation of the stress response follows a stretched-exponential form for low initial strain rates.

Order causes secondary Bragg peaks in soft materials

Highly ordered soft materials exhibit Bragg peaks that cannot be indexed assuming homogeneous crystal structures. Their origin has been attributed to changes in the crystal structure that are induced by the ordering process such as by application of external fields. This would restrict the use for the generation of highly ordered nano- and microstructured materials where a homogeneous crystal structure is a key requirement. Here, we demonstrate that these Bragg peaks are an inherent property of homogeneous ordered soft materials related to the finite coherence of their crystalline lattice. Their consideration allows a detailed and quantitative analysis of the diffraction patterns of seemingly unrelated materials such as lyotropic liquid-crystalline phases, mesoporous materials, colloidal dispersions, block copolymers, electrorheological fluids and photonic crystals. It further enables us to develop a concise picture of order, line density, field-induced orientation and epitaxial relations for soft-material lattices.

Transient Solidlike Behavior near the Cylinder/Disorder Transition in Block Copolymer Solutions

A nearly symmetric polystyrene-block-polyisoprene diblock copolymer dissolved at a concentration of 40% in styrene-selective solvents exhibited a cylinder-to-disorder transition upon heating. The solvents used were diethyl phthalate (DEP) and 75:25 and 50:50 mixtures of DEP with di-n-butyl phthalate (DBP). In DEP, the most styrene-selective of the three solvents, rheological measurements indicated a distinct plateau in the temperature-dependent elastic modulus across the 8 degrees C interval above the order-disorder transition temperature, T(ODT) = 116 degrees C. Previous small-angle neutron scattering measurements in this regime indicated the equilibrium phase to be a liquidlike solution of approximately spherical micelles. An isothermal frequency sweep in this regime indicated a very long relaxation time. Annealing eventually led to the recovery of liquidlike rheological response, over a time scale of hours. Qualitatively similar phenomena were also observed in 75:25 DEP/DBP and 50:50 DEP/DBP solutions, except the fact that the temperature window of the transient response is narrow and the time scale for the recovery diminishes significantly. Neither small-angle X-ray scattering nor static birefringence gave any clear signature of the transient structure. The structure that leads to the transient rheological response is attributed to micellar congestion due to the slow relaxation of anisotropic micelles into an equilibrium distribution of micelles. Possible origins of the remarkable solvent selectivity dependence are also discussed.