Mechanochromic Response of Poly(ethylene glycol) Methacrylate Hydrogel Encapsulated Crystalline Colloidal Arrays

Foulger, Stephen H.; Jiang, Ping; Lattam, Amanda C.; Smith, Dennis W.; Ballato, John

doi:10.1021/la010264e

Cited by 137 publications

(117 citation statements)

References 30 publications

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“…[12] Briefly, the film fabrication involves the following steps: Monodisperse crosslinked polystyrene particles dispersed in water and with a particle diameter of 150 nm were allowed to electrostatically self-assemble and then encapsulated in a photoinitiated free-radical-polymerized methacrylate functionalized poly(ethylene glycol) (PEG) hydrogel. [11] The water from the hydrogel was removed, and the stabilized arrays were reswollen in 2-methoxyethyl acrylate (MOEA). The incorporation of a small quantity of ethylene glycol dimethacrylate and the photoinitiator 2,2-diethoxyacetophenone (DEAP) into the reswollen system, with subsequent photopolymerization, resulted in a robust composite film.…”

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Dynamic Tuning of Organic Lasers with Colloidal Crystals

et al. 2006

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The prospect of an inexpensive organic laser which can dynamically (i.e., in real time) alter its lasing wavelength is desirable for a number of display and communication technologies. Extensive efforts have focused on developing liquid-crystalbased lasers which can exhibit emission tuning through the application of an external stimuli, such as a mechanical stress, a temperature variation, or a radiation exposure. [1][2][3][4] Polymeric-based lasers are especially interesting organic systems due to their low cost, stability, and ease of fabrication relative to liquid-crystal-based systems. To this end, tunable distributed-feedback (DFB) lasers, which rely on the dynamic variation of a grating in the gain medium, are of particular interest. Mechanically tunable DFB lasers have been fabricated by using an elastomeric substrate with an overlaid grating, where the straining of the substrate changes the period of the grating and the resulting lasing wavelength. [5] In addition, a phototunable organic DFB laser has recently been presented which utilizes an azopolymer that allows for the phototemplating of variable-period gratings. [6] Although these systems are promising, they often require an extensive synthetic effort to produce the gain medium or complicated interference lithography to form the grating. Lasers require two main elements for operation, an active material to provide optical gain and a resonator structure to provide optical feedback. One strategy to simplify the development of tunable organic lasers is to choose a laser design that decouples the resonator from the selection of the gain medium. In a conventional "external" resonator cavity design, an organic gain material is deposited onto a mirror and capped with a second mirror to form a cavity. The light generated in the active material is reflected between the two mirrors, and, if the reflectivity of the mirrors is sufficiently high and the active material has adequate optical gain to offset the sources of loss, the structure will begin to lase.The current effort focuses on the utilization of colloidal crystals to provide the required reflectivity in an external resonator cavity design. Previous efforts to fabricate lasers utilizing colloidal crystals have focused on the assembly of the particles into close-packed arrays through sedimentation, relying on non-specific particle-particle "hard sphere" packing to induce order. These close-packed crystals have typically been infiltrated with a laser dye and exhibited either random or DFB lasing. [7,8] The current approach utilizes charged polymeric colloidal particles that self-assemble through long-range electrostatic repulsive interactions to procure order. These ordered systems have been employed in the fabrication of opalescent films that exhibit a mechanochromic response (i.e., photonic crystals that exhibit a strain-induced variation of their rejection wavelength), [9][10][11][12][13] where the response has been attributed to an affine deformation of the lattice. This response is intimately tied to ...

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“…1b). [11] The total laser tuning range was 32 nm, with the intrinsic absorption of the gain medium (cf. inset of Fig.…”

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Dynamic Tuning of Organic Lasers with Colloidal Crystals

et al. 2006

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“…Fitting the dependence of the contraction in thickness with the strain along the film allows the Poisson ratio, ϳ 0.4, to be determined, comparable to similar elastomers. 12 Although strained photonic crystals have been measured before, [13][14][15] this is the first time to our knowledge that such a measurement has been carried out on an ordered composite material composed of hard spheres in an elastic absorbing matrix.…”

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Compact strain-sensitive flexible photonic crystals for sensors

Pursiainen

Baumberg

Ryan

et al. 2005

Applied Physics Letters

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A promising fabrication route to produce absorbing flexible photonic crystals is presented, which exploits self-assembly during the shear processing of multi-shelled polymer spheres. When absorbing material is incorporated in the interstitial space surrounding high-refractive-index spheres, a dramatic enhancement in the transmission edge on the short-wavelength side of the band gap is observed. This effect originates from the shifting optical field spatial distribution as the incident wavelength is tuned around the band gap, and results in a contrast up to 100 times better than similar but nonabsorbing photonic crystals. An order-of-magnitude improvement in strain sensitivity is shown, suggesting the use of these thin films in photonic sensors. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2032590͔ Synthesis of three-dimensional ͑3D͒ photonic crystals based on synthetic opals has been well developed over the past decade, 1-3 with a particular focus on in-filling with highrefractive-index media to create true 3D band gaps.1,4 However, the application of 3D photonic crystals has been restricted compared to the advanced technology built on twodimensional photonic crystals fabricated from patterned planar waveguides.5-7 Here we present an alternative approach to fabricating useful photonic crystals based on the extrusion self-assembly of low-contrast flexible photonic nanomaterials. Tuning of the band gaps with angle and strain is clearly observed in these films. However, as is typical in polymer-based photonic crystals, the dielectric nanostructures exhibit a low on/off contrast at the edges of the Bragg scattering peaks making their incorporation into sensors problematic. We show that by introducing an absorbing material into the surroundings of the polymer spheres ͑which is very easy to achieve in this process͒, the transmission contrast can be increased by a factor of Ͼ100, leading to prospective applications in compact vibration and thermal sensors. We analyze this behavior in terms of the optical field distribution on either side of the band gap, and show that absorbing 3D photonic crystals inherently improve on the performance of absorbing one-dimensional ͑1D͒ photonic crystals ͑Bragg mirrors͒.Our sample precursors consist of hard polystyrene ͑PS͒ cores, covered by a poly͑methylmethacrylate͒ ͑PMMA͒ interlayer, and a polyethylacrylate ͑PEA͒ shell. Self-assembly processes occur during the shearing by uniaxial compression of the precursor melt resulting in fcc crystallization of the PS-PMMA cores, with the soft PEA shell material filling the spaces between the PS-PMMA lattice sites thus forming an elastic film. Hence the ͑111͒ plane of the fcc lattice is parallel to the sample surface. A detailed description of the precursors and the manufacturing is reported elsewhere. 8 The final samples used here are disks with a diameter of 10 cm and a thickness of around 250 m ͓Fig. 1͑a͔͒.Angle-dependent reflection measurements were carried out to identify the final lattice pitch and average refractive index. Monoch...

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“…Many photonic gel materials, with a relatively broad range of colour tunability have been developed 5,11,12 . However, the reported response time of these materials, ranging from several seconds to a few hours, is much slower than the video rate 12,[14][15][16] .…”

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Mechano-actuated ultrafast full-colour switching in layered photonic hydrogels

et al. 2014

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Photonic crystals with tunability in the visible region are of great interest for controlling light diffraction. Mechanochromic photonic materials are periodically structured soft materials designed with a photonic stop-band that can be tuned by mechanical forces to reflect specific colours. Soft photonic materials with broad colour tunability and fast colour switching are invaluable for application. Here we report a novel mechano-actuated, soft photonic hydrogel that has an ultrafast-response time, full-colour tunable range, high spatial resolution and can be actuated by a very small compressive stress. In addition, the material has excellent mechanical stability and the colour can be reversibly switched at high frequency more than 10,000 times without degradation. This material can be used in optical devices, such as full-colour display and sensors to visualize the time evolution of complicated stress/strain fields, for example, generated during the motion of biological cells.

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Mechanochromic Response of Poly(ethylene glycol) Methacrylate Hydrogel Encapsulated Crystalline Colloidal Arrays

Cited by 137 publications

References 30 publications

Dynamic Tuning of Organic Lasers with Colloidal Crystals

Dynamic Tuning of Organic Lasers with Colloidal Crystals

Compact strain-sensitive flexible photonic crystals for sensors

Mechano-actuated ultrafast full-colour switching in layered photonic hydrogels

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