Wang-Eun Lee

Fluorescent Actuator Based on Microporous Conjugated Polymer with Intramolecular Stack Structure

IO N Artifi cial smart materials that respond to external stimuli, such as heat, light, chemicals, and electric fi elds, have recently attracted considerable attention for applications to actuators and sensors. [ 1 ] An wide range of conjugated polymers have been developed as functional active materials not only for soft actuation but also for optical sensing. [ 1h , 2 ] To our best knowledge, however, there are no reports on conjugated polymers showing a simultaneous optical output signal and actuation behavior. The actuation of soft materials in response to chemical stimuli is based on a reversible expansion/contraction in volume. [ 3 ]

Remarkable Change in Fluorescence Emission of Poly(diphenylacetylene) Film via in situ Desilylation Reaction: Correlation with Variations in Microporous Structure, Chain Conformation, and Lamellar Layer Distance

Fluorescence (FL) emission properties, microporous structures, energy-minimized chain conformations, and lamellar layer structures of the silicon-containing poly(diphenylacetylene) derivative of p-PTMSDPA before and after desilylation were investigated. The nitrogen-adsorption isotherms of p-PTMSDPA film before and after desilylation were typical of type I, indicating microporous structures. The BET surface area and pore volume of the p-PTMSDPA film were significantly reduced after the desilylation reaction, simultaneously, its FL emission intensity remarkably decreased. The theoretical calculation on both model compounds of p-PTMSDPA and its desilylated polymer, PDPA, showed a remarkable difference in chain conformation: The side phenyl rings of p-PTMSDPA are discontinuously arranged in a zig-zag pattern, while the PDPA is continuously coiled in a helical manner. The lamellar layer distance (LLD) in the p-PTMSDPA film significantly decreased after the desilylation reaction.

Positive-/negative-, erasable-/immobilized-, mono-/multi-color fluorescence image patterning of molecular-scale porous polymer film via a microcontact printing method using various chemical inks.

Fluorescent image patterns of a substituted acetylene polymer film with a large FFV were successfully obtained by a µCP method using several kinds of chemical ink compounds. PO and SCA generated positive-type fluorescent image patterns. On the other hand, an ethanolic solution of DNT generated a negative-type fluorescent image pattern due to a significant quenching effect. An NMP solution of NR gave a two-color image pattern due to an intermolecular energy transfer from PTMSDPA to NR.

Fluorescence Response of Conjugated Polyelectrolyte in an Immiscible Two-Phase System via Nonelectrostatic Interaction with Surfactants.

This paper reports a unique fluorescence (FL) response and diverse applications of conjugated polyelectrolyte (CPE) through nonelectrostatic interaction with appropriate (bio)surfactants in an immiscible two-phase system. A sulfonated microporous conjugated polymer (SMCP) with a conformation-variable intramolecular stacked structure was used as the CPE film. Despite the extremely high hydrophilicity, the SMCP film responded significantly to the hydrophobic circumstances, either physicochemically or electronically, in the presence of water-in-oil (w/o)-type nonionic surfactants with appropriate hydrophile-lipophile balance (HLB) values. The polymer film became fully wet with hydrophobic solvents due to the addition of small amounts of (bio)surfactant to reveal remarkable FL emission enhancement and chromism. Microcontact and inkjet printing using the SMCP film (or SMCP-adsorbed paper) and the surfactant solution as substrate and ink, respectively, provided high-resolution FL images due to the distinctive surfactant-induced FL change (SIFC) characteristic. Moreover, the additional electrostatic interaction of SMCP film with oppositely charged surfactants further enhanced the FL emission. Our findings will help comprehensive understanding of the nonelectrostatic SIFC mechanism of CPEs and development of novel SIFC-active materials.

Charge transfer dye-based PHEMA hydrogel sensor: its fluorescence responses to pH, metal ion, and humidity

Poly(2-hydroxyethylmethacrylate) (PHEMA) is one of the most well known synthetic hydrogels. In this study, PHEMA gel containing a charge transfer dye was synthesized using a copolymerization method. This polymer gel swelled appropriately in water with a swelling ratio (Q) of approximately 1.0, and swelled significantly in aprotic polar solvents, such as DMF and DMSO, with Q values of >8.0, whereas it never swelled in nonpolar solvents. The fluorescence (FL) emission band of the hydrogel polymer showed a red shift exclusively in water, whereas it showed a blue shift in the other solvents tested. The emission band also shifted to shorter wavelengths with increasing proton activity (with decrease in pH) or iron cation concentration, and the FL intensity increased gradually. The FL intensity also decreased significantly with increasing absolute humidity.Graphical AbstractA charge transfer dye-based PHEMA gel was synthesized using a copolymerization method. The FL emission band of the hydrogel polymer showed a red shift exclusively in water. The emission band shifted to shorter wavelengths with increasing in proton activity or iron cation concentration and the FL intensity gradually increased. The FL intensity deceased significantly with increasing absolute humidity.

One-Step Synthesis of Hollow Dimpled Polystyrene Microparticles by Dispersion Polymerization

The design and preparation of hollow nonspherical microparticles are of great significance for their potential applications, but the development of a facile synthetic method using only one production step remains a great challenge. In the current work, a new template-free method based on dispersion polymerization was successfully developed to produce anisotropic hollow polystyrene (PS) microparticles in a single step. In the synthesis, ammonium persulfate (APS) played a critical role in the formation and growth of highly uniform and stable hollow PS microparticles. By varying the concentration of APS and that of the stabilizer used, polyvinylpyrrolidone, we were able to control the average size of the PS particles and their degree of concavity. Based on our results and observations, a plausible mechanism for formation of these unusually shaped PS microparticles was proposed.