Nanoporous Polymeric Periodic Structures Fabricated by Emulsion-assisted Holographic Patterning
- PDF / 1,555,773 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 219 Views
1228-KK11-02
Nanoporous Polymeric Periodic Structures Fabricated by Emulsion-assisted Holographic Patterning Vincent K.S. Hsiao1 and Wei-Ting Chang2 1 Department of Applied Materials and Optoelectronic Engineering, National Chi Nan University No 1, University Rd. Puli, Nantou Hsien, 54561, Taiwan 2 Department of Applied Chemistry, National Chi Nan University No 1, University Rd. Puli, Nantou Hsien, 54561, Taiwan ABSTRACT We report a new technique of creating a nanoporous polymeric nanostructure by photopatterning emulsions generated from a formamide (polar phase) and an acrylate-monomer (nonpolar phase). Formamide is a highly polar solvent that forms well dispersed, non-aqueous emulsion droplets within the monomer-containing nonpolar phase before holographic patterning. Photochemically initiated polymerization of the nonpolar phase (acrylate monomer) forces the formation of ordered formamide emulsions defined by the holographic interference. Evaporation of the formamide from the ordered structure yields a periodic structure with high optical reflectivity and a wide reflection bandwidth. The average size and the size distribution of formamide droplets in the photopolymer fluid must be controlled to fabricate a periodic structure with high reflectivity. Furthermore, we found that the addition of sodium dioctyl sulfosuccinate (AOT) surfactant helps to stabilize the formamide emulsion which further facilitates the formation of the ordered nanopores with uniform size. INTRODUCTION The nature of emulsion (oil and water dispersions) which generates the micro- or nanomicelles depends on the solubility of “water” in “oil” or vice versa. With suitable surfactant or detergent, “microemulsion” dispersion may be well stabilized in the non-aqueous mixture [1]. The colloidal self-assembling of opal or inverse-opal structure has shown a very promising way to generate ordered structure, such as photonic crystal (PC). Photonic crystal needs a periodic modulation of dielectric constant that creates a stop bandwidth in which certain wavelength of photon is “trapped” inside the periodic structure while others are passed out. In the system of holographic photopolymerization the first demonstration was the pure photopolymer (monomer) as a starting material to produce periodic index modulation [2]. Later with adding the non-reactive fluid, liquid crystal (LC), into monomer syrup the applications of the periodic structure were extended. The phase separation between the photopolymer and LC generates LC/polymer lamella that the period can be controlled by the holographic interference patterning. The fabrication process is well known as the holographic polymer dispersed liquid crystal (H-PDLC) technique [3]. One-step, large area and simple fabrication in the formation of one dimensional (1D) periodic structure or Bragg reflection grating can be achieved. The index modulation between each layer is the result of the index difference between LC (nave=1.61) and polymer (nave=1.51). Since the LC is not well dissolved in the monomer syrup, the LC d
Data Loading...
