Porosity at Different Structural Levels in Human and Yak Belly Hair and Its Effect on Hair Dyeing.

Yak belly hair was proposed as a cheap substitute for human hair for the development of hair dyes, as its chemical composition closely resembles human hair in Raman spectroscopy. The absence of melanin in yak belly hair also leads to a strong reduction of fluorescence in Raman measurements, which is advantageous for the investigation of the effectivity of hair dyes. To assess the suitability for replacing human hair, we analyzed similarities and differences of both hair types with a variety of methods: Raman spectroscopy, to obtain molecular information; small-angle X-ray scattering to determine the nanostructure, such as intermediate filament distance, distance of lipid layers and nanoporosity; optical and scanning electron microscopy of surfaces and cross sections to determine the porosity at the microstructural level; and density measurements and tensile tests to determine the macroscopic structure, macroporosity and mechanical properties. Both types of hair are similar on a molecular scale, but differ on other length scales: yak belly hair has a smaller intermediate filament distance on the nanoscale. Most striking is a higher porosity of yak belly hair on all hierarchical levels, and a lower Young's modulus on the macroscale. In addition to the higher porosity, yak belly hair has fewer overlapping scales of keratin, which further eases the uptake of coloring. This makes, on the other hand, a comparison of coloring processes difficult, and limits the usefulness of yak belly hair as a substitute for human hair.

Glycol-modified silanes: novel possibilities for the synthesis of hierarchically organized (hybrid) porous materials.

The preparation of porous hierarchical architectures that have structural features spanning from the nanometer to micrometer and even larger dimensions and that exhibit certain functionalities is one of the new challenging frontiers in materials chemistry. The sol-gel process is one of the most promising synthesis routes toward such materials because it not only offers the possibility to incorporate organic functions into the porous host but also offers the possibility to deliberately tailor the pore structure. In this Account, the opportunities given by the application of novel diol-modified silanes are discussed for the synthesis of hierarchically organized inorganic and also inorganic-organic porous monoliths.

Particles coming together: electron centers in adjoined TiO2 nanocrystals.

To include particle attachment and porosity of nanostructured materials in the discussion of their electronic properties is critical to our understanding of charge transfer across grain boundaries. We report the condensation of isolated TiO(2) nanocrystals via the application of a simple hydration-dehydration cycle. After contact with water and subsequent removal of adsorbed water, these nanocrystals form a mesoporous structure with altered properties as compared with the original material: first, the energy needed for defect formation is substantially reduced, and second, electron paramagnetic resonance measurements reveal the presence of polarizable conduction band electrons not detectable in samples which have not been in contact with water.