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A bottom-up approach, the Langmuir–Blodgett technique, is used for the preparation of composite thin films of gold nanoparticles and polymers: poly-(styrene-b-2-vinylpyridine), poly-2-vinylpyridine, and polystyrene. The self-assembly of poly-(styrene-b-2-vinylpyridine) at the air–water interface leads to the formation of surface micelles, which serve as a template for the organization of gold nanoparticles into ring assemblies. By using poly-2-vinylpyridine in conjunction with low surface pressure, the distance between nanostructures can be increased, allowing for optical characterization of single nanostructures. Once deposited on a solid substrate, the preorganized gold nanoparticles are subjected to further growth by the reduction of additional gold, leading to a variety of nanostructures which can be divided into two categories: nanocrescents and circular arrays of nanoparticles. The optical properties of individual structures are investigated by optical dark-field spectroscopy and numerical calculations. The plasmonic behavior of the nanostructures is elucidated through the correlation of optical properties with structural features and the identification of dominant plasmon modes. Being based on a self-assembly approach, the reported method allows for the formation of interesting plasmonic materials under ambient conditions, at a relatively large scale, and at low cost. These attributes, in addition to the resonances located in the near-infrared region of the spectrum, make nanocrescents candidates for biological and chemical sensing. [ABSTRACT FROM AUTHOR]

The massive amplification of fluorescence signal observed upon hybridization of as few as five DNA molecules into self-assembled structures formed between a cationic polymer and DNA oligonucleotides is investigated. These superlighting polymer-DNA aggregates were studied by fluorescence spectroscopy, static and dynamic light scattering, and zeta potential measurements in order to characterize the aggregation behavior and to understand the processes involved during DNA detection. Multi-angle laser light scattering was also used to obtain the weight-average aggregate mass (AM), the aggregation number (Nagg), the radius of gyration (Rg), and the dissymmetry ratio (z). These results have been used, together with TEM imaging, to propose a suitable physical model for the aggregates.

Ferrofluids can be used to make deformable mirrors having highly interesting characteristics (e.g., extremely large strokes and low costs). Until recently, such mirrors were thought to be restricted to corrections of frequencies lower than 10 Hz, thus limiting their usefulness. We present counterintuitive results that demonstrate that the limiting operational frequency can be increased by increasing the viscosity of the ferrofluid. We tested the response of ferrofluids having viscosities as high as 494 cP, finding that they could allow an adaptive optics correction frequency as high as 900 Hz. We also demonstrate that we can counter the amplitude loss due to the high viscosity by overdriving the actuators. The overdriving technique combines high current, short duration pulses with ordinary driving step functions to deform the mirror. The integration of a FDM in a complete closed-loop adaptive optics system running at about 500 Hz thus appears to be a realistic goal in the near future. OCIS codes: 220.1000, 220.1080, 230.3810.

We describe a new technology for the fabrication of inexpensive high-quality mirrors. We begin by chemically producing a large number of metallic nanoparticles coated with organic ligands. The particles are then spread on a liquid substrate where they self-assemble to give optical quality reflective surfaces. Since liquid surfaces can be modified by a variety of means (e.g., rotation, electromagnetic fields), this opens the possibility of making a new class of versatile and inexpensive optical elements that can have complex shapes and that can be modified within short time scales. Interferometric measurements show optical quality surfaces. We have obtained reflectivity curves that show 80% peak reflectivities. We are confident that we can improve the reflectivity curves because theoretical models predict higher values. We expect nanoengineered liquid mirrors to be useful for scientific and engineering applications. The technology is interesting for large optics, such as large rotating parabolic mirrors, because of its low cost. Furthermore, because the surfaces of ferrofluids can be shaped with magnetic fields, one can generate complex, time-varying surfaces that are difficult to make with conventional techniques. OCIS codes: 000.3110, 240.6700, 260.3910, 350.1260.

The photoexcitation, relaxation, and optical erasure regimes of spiropyran- (SP-) doped polymer films were studied. Cellulose acetate, poly(vinyl acetate), and poly(methyl methacrylate) (PMMA) were used as host polymer matrices. We studied the character of the photoreaction for both coloring and bleaching processes. Reversible holographic recording in SP-PMMA films and the origin of the photochemical fatigue was studied upon repeated UV-visible irradiation cycles. [C] 2001 Optical Society of America

ABSTRACT A procedure for the fabrication of aluminum-coated reflective PDMS thin films having a low surface roughness and high reflectance is presented. Elastomer films are prepared by spin-coating on a sacrificial layer that permits subsequent release from the substrate. Appropriate surface treatments are established for the deposition of a thin, highly reflective metal coating. The composite membranes are deposited on an ethylene glycol based ferrofluid to fabricate a new ferrofluidic deformable mirror. Surface deformations of a few micrometers can be produced with low strength magnetic fields. The reflective elastomer membranes do not alter the rheological behavior of the ferrofluid in magnetic fields and thus offer new perspectives for the use of ferrofluidic mirrors in adaptive optics. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44542. [ABSTRACT FROM AUTHOR]