Abstract
Single-particle fluorescence imaging is used to monitor dynamic processes that occur during patterned photopolymerization of liquid-crystalline monomers. A spatial gradient of chemical potential can be created at the border of bright and dark regions by structured illumination in the photopolymerization process, leading to mutual diffusion of polymers and monomers. Analysis of the fluorescence from single quantum dots doped into the monomers at minute concentrations enables visualization of highly directional flow from the illuminated region where the photopolymerization proceeds toward a masked unpolymerized region. This directional mass flow causes flow-induced orientation of the polymers that is subsequently fixed by completion of the polymerization reaction, resulting in a mesoscopic aligned area of the polymer film.
Highlights
The preparation of molecularly aligned structures is a fascinating topic from the standpoint of basic molecular physics and has tremendous technological significance for next-generation optoelectronic, photonic, mechanical, or biomedical materials and devices[1,2,3,4]
The mixture was dried in a vacuum oven, and the powder was deposited on an indium thin oxide (ITO)-covered microscope cover glass and heated on a hot stage above the melting point
The molten state was verified by a transmission microscope image and by monitoring free Brownian diffusion of the quantum dots (QDs) in epifluorescence mode
Summary
The preparation of molecularly aligned structures is a fascinating topic from the standpoint of basic molecular physics and has tremendous technological significance for next-generation optoelectronic, photonic, mechanical, or biomedical materials and devices[1,2,3,4]. Photoalignment processes have been developed that enable orientation of side-chain liquid-crystalline (LC) polymers, surfacegrafted polymers, or block copolymers[5,6]. Side-chain LC polymers offer a variety of alignment methods that take advantage of the technology developed for LC molecules by combining with photopolymerization techniques. The method uses spatially patterned unpolarized light to initiate photopolymerization and achieve molecular alignment in an area of a sample where a chemical potential gradient has been created by the presence of polymerized and unpolymerized regions[11,12,13,14]. The gradient is assumed to result in mass flow that aligns the precursor monomers and polymers. The concentration gradient and the following molecular alignment are restricted to a narrow area near the edge of bright and dark regions of the photomask.
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