Pattern Formation in Homogeneous Polymer Solutions Induced by a Continuous-Wave Visible Laser

Sigel, R.; Fytas, George; Vainos, N.A.; Pispas, Stergios; Hadjichristidis, Nikos

doi:10.1126/science.1071930

Cited by 42 publications

(46 citation statements)

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“…For example, in colloidal suspensions, this can be accomplished through optical radiation forces capable of manipulating particle concentration and molecular kinetics at the mesoscopic level 2,7,11,12 . In principle, such optically induced processes can be exploited for initiating and regulating chemical reactions, for sorting different species of nanoparticles, and for influencing diffusion and osmotic pressure effects, to mention a few These issues can be addressed by first considering how the particle polarizability is related to optical nonlinearities that are solely mediated by radiation pressure effects.…”

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confidence: 99%

Optical Nonlinearities and Enhanced Light Transmission in Soft-Matter Systems with Tunable Polarizabilities

et al. 2013

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2Controlling light transport in soft-matter systems could be crucial in many and diverse fields of science and technology. For example, in colloidal suspensions, this can be accomplished through optical radiation forces capable of manipulating particle concentration and molecular kinetics at the mesoscopic level 2,7,11,12 . In principle, such optically induced processes can be exploited for initiating and regulating chemical reactions, for sorting different species of nanoparticles, and for influencing diffusion and osmotic pressure effects, to mention a few These issues can be addressed by first considering how the particle polarizability is related to optical nonlinearities that are solely mediated by radiation pressure effects. In general, a particle displays a positive polarizability (PP) whenever its refractive index exceeds that of the background medium, while in the converse case its polarizability is negative (NP). As indicated in several studies Fig. 1(c)], one could synthesize soft-matter systems with a tunable polarizability, optimized nonlinear response, and enhanced light transmission.In this study, we experimentally demonstrate a new class of synthetic colloidal suspensions capable of exhibiting negative polarizabilities. This is accomplished in a stabilized mixture of Polytetrafluoroethylene (PTFE) particles in a glycerin-water solution. We show that by judiciously introducing NP particles in conventional PP colloidal suspensions, the resulting "mixed" polarizability can be fine-tuned, thereby enabling us to modify the nonlinear response of these systems. In particular,we observe robust propagation and up to a fourfold-enhanced transmission of an optical beam when traversing an NP suspension as compared to that in a typical PP suspension. Such light penetration through otherwise strong scattering environment is attributed to the interplay between optical forces and 4 self-activated transparency effects while no thermal effect is involved. Our experimental observations are in agreement with a previously derived thermodynamic model that takes into account the interplay between the optical intensity and the osmotic pressure in the presence of particle-particle interactions 19 .These findings may pave the way towards synthesizing soft-matter systems with customized optical nonlinearities that can enable an intensity-dependent reduction in scattering losses.To understand light-particle dynamics in colloidal dispersions, we first consider the optical gradient force that typically dominates the interaction process. To first order, this component of the optical force is given 2,16 by = ∇ /4, where I is the optical intensity and α is the polarizability of the particle. In the dipole regime, = 3 ( − 1)/( + 2), where V is the particle's volume, = / is a measure of the contrast between the refractive index of the particle and that of the background fluid . Therefore, PP dielectric particles with > ( > 0) will be attracted towards

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confidence: 99%

Optical Nonlinearities and Enhanced Light Transmission in Soft-Matter Systems with Tunable Polarizabilities

et al. 2013

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“…No entanto, a fala que descreve os especializados métodos de organização e construção de estruturas descritas como complexas, harmoniosas, ornadas e perfeitas (Forró, 2000;Niemeyer, 2002;Buriak, 2004;Arslan et al, 2005;Ruiz et al, 2008;Liu, Yan, 2009;Lai et al, 2012;Service, 2005a) contrasta com aquela de que os métodos ainda não estão perfeitamente constituídos, e que a nanotecnologia traz riscos e precisa ter seus objetivos e instrumentos melhor estabelecidos e padronizados (Sigel et al, 2002;Bai, 2005;Service, 2005e;Holden, 2007).…”

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“…A nanotecnologia por vezes produz métodos e produtos mais caros (Bohannon, 2005); difíceis de alcançar e mais difíceis de operar (Travesset, 2011), com resultados inesperados (Sigel et al, 2002) e propriedades e consequências desconhecidas (Service, 2004b;Hopkins et al, 2005;Hurtley, Szuromi, 2006). Estes aspectos são bem menos abordados e pormenorizados do que as potenciais aplicações dos nanoderivados.…”

Section: Perfeição X Riscounclassified

Nanotecnociência e Humanidade

Pyrrho¹,

Schrram²

2016

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A navegação consulta e descarregamento dos títulos inseridos nas Bibliotecas Digitais UC Digitalis, UC Pombalina e UC Impactum, pressupõem a aceitação plena e sem reservas dos Termos e Condições de Uso destas Bibliotecas Digitais, disponíveis em https://digitalis.uc.pt/pt-pt/termos.Conforme exposto nos referidos Termos e Condições de Uso, o descarregamento de títulos de acesso restrito requer uma licença válida de autorização devendo o utilizador aceder ao(s) documento(s) a partir de um endereço de IP da instituição detentora da supramencionada licença.Ao utilizador é apenas permitido o descarregamento para uso pessoal, pelo que o emprego do(s) título(s) descarregado(s) para outro fim, designadamente comercial, carece de autorização do respetivo autor ou editor da obra. Na medida em que todas as obras da UC Digitalis se encontram protegidas pelo Código do Direito de Autor e Direitos Conexos e demais legislação aplicável, toda a cópia, parcial ou total, deste documento, nos casos em que é legalmente admitida, deverá conter ou fazer-se acompanhar por este aviso.

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“…Laser beams with polarization perpendicular to the direction of writing and the alignment of liquid crystals, produce snake-shaped patterns at an intermediate scan rate [2][3][4][5]. In comparison to one-photon absorption, in recent decades, two-photon (TP) lithography has emerged as a promising technique for direct laser writing, for its capacity to fabricate fine and well formed patterns, as well as three-dimensional structures, microscaled in size and nanoscaled in resolution [6,7].…”

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“…Composited by spreading submicrometer-sized liquid crystal (LC) droplets in a polymer matrix, PDLCs have shown both electrical and optical tunabilities, and have been applied to a variety of applications in optical devices from light switches, phase modulators, holographic gratings, to flat panel displays. Depending on the profile of writing beam and interplay among photoinduced polymerization, phase separation morphologies, and diffusion mechanism of monomer molecules, different structures like gratings, waveguides, and broken stripes are demonstrated [2][3][4][5]. In comparison to one-photon absorption, in recent decades, two-photon (TP) lithography has emerged as a promising technique for direct laser writing, for its capacity to fabricate fine and well formed patterns, as well as three-dimensional structures, microscaled in size and nanoscaled in resolution [6,7].…”

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confidence: 99%

Tunable pattern transitions in a liquid-crystal-monomer mixture using two-photon polymerization

Jisha

Hsu²,

Lin

et al. 2012

Opt. Lett.

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Through two-photon lithographic processes, we report experimentally and numerically a series of photoinduced tunable polymerization patterns in shapes from straight channel, serpentine curve, to periodic grating when an ultrashort femtosecond laser pulse directly writes in a liquid-crystal-monomer mixture along a line for different scanning speeds. Laser beams with polarization perpendicular to the direction of writing and the alignment of liquid crystals, produce snake-shaped patterns at an intermediate scan rate [2][3][4][5]. In comparison to one-photon absorption, in recent decades, two-photon (TP) lithography has emerged as a promising technique for direct laser writing, for its capacity to fabricate fine and well formed patterns, as well as three-dimensional structures, microscaled in size and nanoscaled in resolution [6,7]. Commercially available photopolymerizable monomers are generally transparent to infrared light and allow a deeper penetration, which makes them excellent candidates for two-photon polymerization (TPP). Although TP direct laser writing has been widely used for local alignment of LCs in predetermined structures like gratings, it has not been directly used to demonstrate transition of written patterns. Such transitional patterns have been observed in several hydrodynamic systems exhibiting symmetry-braking instabilities, resulting in patterns like coiling, buckling of jets, and meandering [8][9][10]. In this work, by scanning the laser along a straight line, formation and transition of various structures in the form of straight waveguide, serpentine patterns, and microgratings are demonstrated experimentally, through the TPP lithography in PDLCs by varying only the scanning speed of the laser. The direction of polarization of the writing beam plays an important role in the formation of curved structures, for which an original sinusoidally modulated laser intensity is transferred into a curved serpentine shape. Optical images taken from parallel and perpendicular analyzers reveal the reorientation of LCs, and a theoretical model with the introduction of convection flow is developed to explain these observed symmetry-breaking structures. The experimental setup for the fabrication is illustrated in Fig. 1. The LC-monomer mixture consisting of 30 wt. % of nematic LC E7 [11,12], 69.4 wt. % monomer NOA65 (Norland), 0.5 wt. % photoinitiator Rose bengal (Oregon medical laser center), and 0.1 wt. % of dye bis (2,4,6-trimethylbenzoy) phenylphosphine oxide (Ciba: Irgacure 819) is sandwiched between two glass slides with a separation of 30 μm. The glass surfaces are treated with DMOAP (N, N-dimethyl-Noctadecyl-3-aminopropyl-trimethoxysilyl chloride 6), in order to let the LC molecules stay in a hometropically

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Pattern Formation in Homogeneous Polymer Solutions Induced by a Continuous-Wave Visible Laser

Cited by 42 publications

References 14 publications

Optical Nonlinearities and Enhanced Light Transmission in Soft-Matter Systems with Tunable Polarizabilities

Optical Nonlinearities and Enhanced Light Transmission in Soft-Matter Systems with Tunable Polarizabilities

Nanotecnociência e Humanidade

Tunable pattern transitions in a liquid-crystal-monomer mixture using two-photon polymerization

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