Authors: S.V. Kazakov
Affilation: Pace University, United States
Pages: 463 - 466
Keywords: hydrogel, fiber core, photoplymerization, swelling/shrinking, kinetics
The ultimate goal of the research is to fabricate a cylindrical polymer network (hydrogel) on the side-surface (not the distal end) of an optical fiber core and characterize spectroscopically its swelling/de-swelling ability in response to different stimuli. It was demonstrated that an optical fiber with open side surface of its core connected to a spectrometer is an apparatus for polymerization and analytical device in one. As a result of the kinetic study of photopolymerization by the light passing through the fiber core, it was found that evanescent waves scattered on the successively formed polymer layers led to a cylindrical film formation around fiber core. Surprisingly, the hydrogel layer was significantly thicker than the penetration depth of evanescent field out of the fiber core, which is typically about few tenth of wavelength. Two kinetic processes were measured and analyzed: (1) swelling of the poly–N–(isopropylacrylamide) (PNIPA) hydrogel film during its dry-wet transition on the fiber core, and (2) collapsing of the temperature sensitive PNIPA hydrogel layer supported by the fiber core in the course of a solubility phase transition. An interesting phenomenon was unexpectedly discovered: the PNIPA cross-linked network photopolymerized around the fiber core begins to absorb the light of different spectral composition from the core above the Lower Critical Solution Temperature (LCST) of the polymer used. Herein, for PNIPA hydrogel layer, ultraviolet began to absorb at LCST~32C, as temperature elevated, the spectral range of absorbed light expanded more and more to the visible and near infrared domains. A cylindrical polymer network of nanometer size is a prerequisite for a supported 2D-single macromolecule. A light emitting polymer, cross-linked around a fiber core, is a starting point for designing an optically pumped organic laser.