All-optical modulation by continuous wave light using two-color excited-state absorption at visible wavelengths.

We demonstrated all-optical modulation with a nonlinear medium, i.e., indigo carmine, an aromatic conjugated structure with delocalized π-electrons, using non-high power continuous wave light for pump and probe of different visible wavelengths. Pump-induced probe transmission increase occurred through absorption saturation of probe light by pump-induced linear and nonlinear absorption including two-color excited-state absorption (ESA). The two-color ESA occurred only when both pump light and probe light co-propagated through a medium, leading to nearly pump power-independent increase in probe transmission for appropriately chosen wavelengths of pump and probe light, given the optical transition structure of electronic energy levels in the medium.

Water-Induced Crystal Transition and Accelerated Relaxation Process of Polyamide 4 Chains in Microfibers.

Microplastics have recently been identified as one of the major contributors to environmental pollution. To design and control the biodegradability of polymer materials, it is crucial to obtain a better understanding of the aggregation states and thermal molecular motion of polymer chains in aqueous environments. Here, we focus on melt-spun microfibers of a promising biodegradable plastic, polyamide 4 (PA4), with a relatively greater number density of hydrolyzable amide groups, which is regarded as an alternative to polyamide 6. Aggregation states and thermal molecular motion of PA4 microfibers without/with a post-heating drawing treatment under dry and wet conditions were examined by attenuated total reflectance-Fourier transform infrared spectroscopy and wide-angle X-ray diffraction analysis in conjunction with dynamic mechanical analysis. Sorbed water molecules in the microfibers induced the crystal transition from a meta-stable γ-form to a thermodynamically stable α-form via activation of the molecular motion of PA4 chains. Also, the post-drawing treatment caused a partial structural change of PA4 chains, from an amorphous phase to a crystalline phase. These findings should be useful for designing PA4-based structural materials applicable for use in marine environments.

Design of a Bioinert Interface Using an Amphiphilic Block Copolymer Containing a Bottlebrush Unit of Oligo(oxazoline).

We designed an amphiphilic block copolymer, poly(methyl methacrylate)-block-poly[oligo(2-ethyl-2-oxazoline) methacrylate] (PMMA-b-P[O(Ox)MA]), suitable for bioinert coating. Angular-dependent X-ray photoelectron spectroscopy and neutron reflectivity measurements revealed that the outermost surface of a dried film of PMMA-b-P[O(Ox)MA] was covered with the PMMA block-rich layer. Once the film came into contact with water, the P[O(Ox)MA] bottlebrush block was segregated toward the water interface. This structural rearrangement in the outermost region of the film resulted in the formation of the swollen oligo(oxazoline) layer with excellent bioinertness in terms of the suppression of serum protein adsorption and NIH3T3 fibroblast adhesion.