Yang-Kyoo Han

Photo-responsive Polymers and their Applications to Optical Memory

We synthesized photo-responsive azo polymers from novel malonic ester and silicate ester monomers having two symmetrical azobenzene groups in the side chain. The possibility of their applications as reversible data storage media was investigated utilizing optical data recording techniques. As a result, the azo polymers had very excellent stability and resolution of the stored data as well as the sensitivity to pump beam. The polymeric thin films also could be used as erasable digital data materials for a practical use by an Ar ion pulse laser (pulse width: 10 μs). In addition, the polymeric thick films (500–1000 μm) from new monomer and methyl methacrylate showed good angular selectivity for holographic memory by using optical two wave mixing technique.

Synthesis of new erasable optical data storage polymers and their applications

Abstract Novel liquid crystalline malonic ester monomer was synthesized from malonyl dichloride and disperse red 1, a photoresponsive group. The monomer was polymerized with 1,6-dibromohexane, 1,8-dibromooctane, 1,10-dibromodecane, 1,12-dibromododecane, α,α ′ -dibromo- p -xylene, α,α ′ -dibromo- m -xylene, or α,α ′ -dibromo- o -xylene in the presence of sodium hydride to give seven kinds of novel poly(malonic esters) with two symmetrical photoresponsive groups in the side chain. The resulting polymer films were found to be excellent as reversible optical information recording media for data storage and retrieval through a trans – cis isomerization of azobenzene group by Ar laser irradiation. The sensitivity of data recording was dependent not only on the thickness of the polymeric thin film but also on the intensity of laser beam.

Long-Range Ordered Self-Assembly of Novel Acrylamide-Based Diblock Copolymers for Nanolithography and Metallic Nanostructure Fabrication

Novel acrylamide-based hard-soft hybrid block copolymers generate high-quality nanolithographic patterns satisfying high-resolution, long-range ordering, low defect density, moderate etch selectivity, and easy pattern transfer onto a substrate. The resulting patterns can also be used as a scaffold for metallic nanostructures such as aligned nanowires and nanomeshes with extraordinary structural regularity.

Polymer Thin Films Containing Azo Dye for Rewritable Media

The writing and erasing properties of azo-dye-doped polymer thin films at a blue wavelength were investigated. The optically induced birefringence in the polymer film due to a linearly polarized light can be utilized for digital optical data storage. The dependence of the contrast of a stored pattern on temperature was examined to estimate the thermal stability of the polymer films. Bits could be written and erased by irradiation of the linearly and circularly polarized laser beam, respectively.

Efficient formation of surface relief grating on azopolymer films by gold nanoparticles

This paper reports a method for the efficient formation of surface relief grating (SRG) on azopolymer films in which gold nanoparticles are dispersed. The height and shape of the SRG, which were formed by a two-beam interference technique, were found to be dependent on the content of gold nanoparticles. The optimum concentration of gold nanoparticles for the efficient formation of SRG was confirmed by atomic force microscopy (AFM), and the height of SRG at the content of 0.06 wt % was about 2.2 times higher than that of pure azopolymer film without gold nanoparticles. This is due to the field enhancement effect derived from the localized plasmon excitations of gold nanoparticles dispersed in the azopolymer film.

Novel mechanism of fast relaxation of photo-induced anisotropy in a poly(malonic esters) containing p-cyanoazobenzene

The relaxation behavior of photo-induced anisotropy has been investigated in a side-chain liquid crystalline(LC) poly(malonic ester) (PCN). Abnormal phenomenon, increment of the induced birefringence, in decaying process was observed just after the pumping beam polarized perpendicularly to the recording beam was illuminated in the relaxation process. This is difficult to explain using the present models, the thermal cis-trans isomerization or the free volume effect for the relaxation process. We suggest a new model considering the elastic force between the side-chain and the backbone in the polymeric film. According to our model, the backbone can be reoriented together with the side-chain, and fast relaxation is associated with the elastic force.

Synthesis of New Poly (Malonic Ester) Containing Disperse Red 1 and its Applications to Optical Data Storage

Abstract New poly(malonic ester) with two symmetrical azobenzene groups was synthesized by the reaction of novel liquid crystalline malonic ester monomer with disperse red 1 with 1,6-dibromohexane. The resulting polymer was found to be excellent as reversible optical information recording media for data storage and retrieval through a trans-cis isomerization of the azobenzene units by Ar laser irradiation and thermal process.

Preparation and Application of Poly(Vinyl Alcohol) Microcapsules Containing Azo Dye

Abstract Poly(vinyl alcohol) microcapsules containing disperse red 1 (DR1), a photoresponsive group, were prepared by a phase separation method (coacervation). The structure of PVA microcapsules was a core/shell type microsphere with DR1 used as a core material encapsulated with PVA. From a SEM analysis, the particle size was in the range of 2–6 μm. We also investigated the possibility of the application of the microcapsules as optical switching device media.

Synthesis of New Poly(Silicate Esters) with Disperse Red 1 and Their Application as Optical Data Storage Materials

Abstract New silicate ester monomer was synthesized by the reaction of 3-methacryloxypropylmeth-yldichlorosilane with disperse red 1 in methylene chloride. The monomer was polymerized with a radical initiator to produce the corresponding homopolymer and copolymers. These polymers were found to be excellent as reversible optical information recording media for data storage and retrieval through a trans-cis isomerization of the azobenzene groups by Ar laser irradiation.

Surface relief grating formation on an azo-polymer

Two types of photo-induced gratings, birefringence and surface relief gratings, were formed on an azo polymer film when two orthogonal circularly polarized writing beams irradiated the film. All the diffracted beams from the gratings were measured during irradiation and the surface relief height inscribed on the film was measured by using atomic force microscope (AFM) after the irradiation. The transmitted beam intensities were calculated using a Jones matrix for two gratings. The phase differences for the two gratings were separately determined by fitting the experimental results to the theory. Next, the changes of the phase differences of two gratings were measured in-situ using an exact equations. The results from this method agreed with previous one. The phase difference between two gratings was measured. The phase difference between two gratings converged on about 45 degrees in our case. Diffraction efficiency measurement and analysis revealed that the two gratings were independent of each other and that the mechanisms for the two gratings were different.