Three-dimensional visualization of phase transition in polystyrene-block-polydimethylsiloxane thin film

Reticulation of Block Copolymer Nanostructures from Perforation

This work aims to examine a variety of metastable phases from the controlled self-assembly of a lamellae-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) and its blends with a PDMS homopolymer. Kinetically trapped phases including hexagonally perforated lamellae (HPL), double diamond (DD), and double gyroid (DG) can be obtained from the blends, making it feasible to investigate the transition mechanisms from perforation to reticulation for the formation of network phases (i.e., DD and DG) as evidenced by temperature-resolved small-angle X-ray scattering experiments. Most interestingly, on the basis of the 3D reconstruction of transmission electron microscopy (TEM) images (electron tomography), an epitaxial relationship between the [001] direction of HPL and the [111] direction for DG and DD phases for the transformations from HPL to DG and DD, respectively, can be clearly identified. Specifically, the 3D double networks of PDMS are initiated from the parallel PDMS layers with PS perforation, forming the topological building units for the gyroid (trigonal planar texture) and diamond (tetrapod texture) phases. As a result, this finding may fill up the lost parts of the morphological evolution from perforation to reticulation in terms of topological transformations.

Wetting transitions in adhesive surfaces of polystyrene: The petal effect

HYPOTHESIS

The petal effect is a well-known natural phenomenon in surface science and has served as inspiration for the creation of several materials with superhydrophobic qualities and high adhesion. As surface roughness has a crucial role in these properties, being able to modulate it could help us design materials at will. Capillary penetration frustrates diffusion and promotes large contact angles as well as high adhesion.

EXPERIMENTS

Polystyrene surfaces were created using the spin-coating technique. By varying the polymer concentration, the surface roughness was modified. To determine the roughness parameters, atomic force microscopy was used. We recorded advancing and receding contact angles using water and glycerol as test liquids to study contact angle hysteresis, the work of adhesion and the apparent surface energy, which was determined with the Chibowski and Perea-Carpio method. For the purpose of elucidating the wetting states, captive bubble experiments were conducted.

FINDINGS

Using an easy method, we create polystyrene surfaces with both superhydrophobicity and strong adhesion, where the roughness area factor regulates wetting transitions from Cassie-Baxter to Wenzel. The receding contact angle suggests capillary penetration, which we demonstrate by captive bubble experiments. In addition, a link was found between the surface roughness and apparent surface energy.

Study of the phase-transition behavior of (AB)3 type star polystyrene-block-poly(n-butylacrylate) copolymers by the combination of rheology and SAXS

A series of three-armed star polystyrene-block-poly(n-butylacrylate) copolymers (PS-b-PBA)3 were synthesized to study the phase-transition behavior of the copolymers. The order-to-disorder transition temperature has been determined by oscillatory at different temperatures and dynamic temperature sweep at a fixed frequency. Moreover, the micro-phase separation in the block copolymers has been evaluated by time–temperature superposition, while the free volume and the active energy of the copolymers have been calculated. Interestingly, active energy decreased with the increase in the molecular weight of the PBA components. To further determine the order-to-disorder transition temperature precisely, small angle X-ray scattering was performed at different temperatures. These results confirm that the chain mobility of the star-shaped copolymers is strongly dependent on the arm molecular weight of the star polymers, which will be beneficial for the processing and material preparation of the block copolymers.

Electron Crystallographic Investigation of Crystals on the Mesostructural Scale

The precise structural solution of crystals on a mesostructural scale is challenging due to the difficulties in obtaining electron diffraction and the complicated relationship between the crystal structure factors (CSFs) and the conventional underfocus phase-contrast transmission electron microscopy (TEM) images due to the large unit cell and the complex structures. Here, we present the structural investigation of mesostructured crystals via the combination of electron crystallographic Fourier synthesis and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that only relies on the mass-thickness contrast. The three-dimensional electrostatic potential is reconstructed from the amplitudes and phases extracted from the Fourier transforms of the corresponding HAADF-STEM images and merged into a set of CSFs. This method is verified on silica scaffolds following a shifted double-diamond surface network with space group I41/amd. The results indicate that electron crystallography reconstruction by HAADF-STEM images is more suitable and accurate in determining the structure in comparison with conventional TEM electron crystallography reconstruction. This approach transfers the contrast of mesostructured crystals to images more accurately and the relationship between the Fourier transforms of HAADF-STEM images and the CSFs is more intuitive. It shows great advantages for the structural solution of crystals on the mesostructural scale.