Time-resolved synchrotron small-angle X-ray scattering (SAXS) studies were performed to investigate the unseeded formation and growth of colloidal calcium carbonate particles. Equimolar aqueous solutions of CaCl2·2H2O and Na2CO3 were rapidly mixed in a stopped-flow apparatus, and SAXS data were recorded using an image-intensified CCD detector. It is shown that SAXS allows studying those processes in situ, with a very good time resolution. It can provide unsurpassed real-time information about the particle size, shape, polydispersity, inner structure, and density. In these studies, well-defined, spherical CaCO3 particles with colloidal dimensions up to ca. 270 nm and a remarkable uniformity in size could be observed. After a short nucleation period, the number density of the growing spheres remains constant. From the evaluation of the absolute scattering intensities, the particle mass density could be determined to be ca. 1.62 g/cm3, which is considerably lower than the density of the crystalline modifications. Our data thus point to the formation of colloidal, amorphous particles that are a precursor modification of the thermodynamically stable calcite. It was found that these particles are isolated and do not form larger aggregates. Upon lowering the concentration of the educts, particle formation and growth are considerably slowed and smaller particles are being formed.

We report on the synthesis and the properties of side-chain liquid-crystal polymer (LCP) brushes attached to silicon oxide surfaces. The polymer monolayers have been generated at the surface of the substrate in situ following a “grafting-from” procedure. The mesogenic group of the LC brushes consists of a phenylbenzoate moiety linked to the methacrylate main chain via a flexible spacer. The thickness of the brush and the grafting density of the surface-attached polymer molecules can be controlled by adjusting the monomer concentration during brush growth and the reaction time of the polymerization, respectively. LC brushes with a thickness of up to 200 nm in the dry, solvent-free state have been obtained. The transition temperatures between the nematic and the isotropic state have been studied and compared to those of spin-cast films of the same polymer. The optical textures are investigated as a function of layer thickness, temperature, and sample history. The textures exhibit a strong memory effect in the sense that the exact same texture reappears after isotropization by heating or solvent exposure and returning to the nematic state.

The molecular orientation at the surface of polyimide (PI) alignment layers used for liquid crystal displays has been determined using X-ray absorption spectroscopy (NEXAFS). The second moments of the orientation distribution function obtained from a detailed analysis reveal that, upon rubbing, the PI substrates develop biaxiality and an inclination of a few degrees. For a nematic liquid crystal (LC) in contact with these alignment layers, the pretilt angle was determined and revealed a weak correlation with buffing strength.

TitleCoaxial electrospun cellulose-core fluoropolymer-shell fibrous membrane from recycled cigarette filter as separator for high performance lithium-ion battery Permalink https://escholarship.org/uc/item/9gc5x56wJournal ACS Sustainable Chemistry and Engineering, 3(5)