The return of a forgotten polymer—Polycaprolactone in the 21st century

Nanosphere lithography (NSL) is an inexpensive, simple to implement, inherently parallel, high throughput, materials general nanofabrication technique capable of producing an unexpectedly large variety of nanoparticle structures and well-ordered 2D nanoparticle arrays. This article describes our recent efforts to broaden the scope of NSL to include strategies for the fabrication of several new nanoparticle structural motifs and their characterization by atomic force microscopy. NSL has also been demonstrated to be well-suited to the synthesis of size-tunable noble metal nanoparticles in the 20−1000 nm range. This characteristic of NSL has been especially valuable for investigating the fascinating richness of behavior manifested in size-dependent nanoparticle optics. The use of localized surface plasmon resonance (LSPR) spectroscopy to probe the size-tunable optical properties of Ag nanoparticles and their sensitivity to the local, external dielectric environment (viz., the nanoenvironment) is discussed in...

Nanosphere Lithography: A Versatile Nanofabrication Tool for Studies of Size-Dependent Nanoparticle Optics

Chemical sensors respond to the presence of a specific analyte in a variety of ways. One of the most convenient is a change in optical properties, and in particular a visually perceptible colour change. Here we report the preparation of a material that changes colour in response to a chemical signal by means of a change in diffraction (rather than absorption) properties. Our material is a crystalline colloidal array of polymer spheres (roughly 100 nm diameter) polymerized within a hydrogel that swells and shrinks reversibly in the presence of certain analytes (here metal ions and glucose). The crystalline colloidal array diffracts light at (visible) wavelengths determined by the lattice spacing, which gives rise to an intense colour. The hydrogel contains either a molecular-recognition group that binds the analyte selectively (crown ethers for metal ions), or a molecular-recognition agent that reacts with the analyte selectively. These recognition events cause the gel to swell owing to an increased osmotic pressure, which increases the mean separation between the colloidal spheres and so shifts the Bragg peak of the diffracted light to longer wavelengths. We anticipate that this strategy can be used to prepare 'intelligent' materials responsive to a wide range of analytes, including viruses.

Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials

Temperature-sensitive aqueous microgels.

Polymer microspheres for controlled drug release

Two switchable, mesoscopically periodic materials were created by combining crystalline colloidal array (CCA) self-assembly with the temperature-induced volume phase transition of poly(N-isopropylacrylamide) (PNIPAM). Body-centered-cubic CCAs of hydrated, swollen PNIPAM particles Bragg-diffract infrared, visible, and ultraviolet light weakly, whereas arrays of compact shrunken particles diffract efficiently. A tunable diffracting array was also created by embedding a CCA of polystyrene spheres within a PNIPAM hydrogel that swells and contracts with temperature; thus the array lattice constant varies with temperature, and the diffracted wavelength was thermally tunable across the entire visible spectrum. These materials may find applications in many areas of optics and materials science.

https://science.sciencemag.org/content/sci/274/5289/959.full.pdf

Thermally Switchable Periodicities and Diffraction from Mesoscopically Ordered Materials

Devices that comprise novel, mesoscopically periodic materials that combine crystalline colloidal array (CCA) self-assembly with the temperature ined volume phase transitions of various materials, preferably poly(N-isopropylacrylamide) (PNIPAM) are disclosed. In one embodiment, a PNIPAM CCA is formed in an aqueous media and contained within cell means. In another embodiment, a CCA of charged particles is formed and polymerized in a PNIPAM hydrogel. Methods for making these devices are also disclosed. The devices of the present invention are useful in many applications including, for example, optical switches, optical limiters, optical filters, display devices and processing elements. The devices are further useful as membrane filters. All of these devices have the feature of being tunable in response to temperature. Devices that change diffracted wavelength in response to pressure are also disclosed.

Method of using thermally switchable optical devices

Devices that comprise novel, mesoscopically periodic materials that combine crystalline colloidal array (CCA) self assembly with the temperature induced volume phase transistions of various, materials, preferably poly (N-isopropylacrylamide) (PNIPAM) are disclosed. In one embodiment, a PNIPAMCCA is formed in an aqueous media (14) and contained within cell means (16). In another embodiment, a CCA of charged particles (12) is formed and polymerized in a PNIPAM hydrogel. Methods for making these devices are also disclosed. The devices of the present invention are useful in many applications including, for example, optical switches, optical limiters, optical filters, display devices and processing elements. The devices are further useful as membrane filters. All of these devices have the feature of being tunable in response to temperature. Devices that change diffracted wavelength in response to pressure are also disclosed.

Hari B. Sunkara

Papers

Thermally Switchable Periodicities and Diffraction from Mesoscopically Ordered Materials

Method of using thermally switchable optical devices

Thermally switchable optical devices

Crystalline colloidal array compositions

Thermisch schaltbare optische materialen