Jianying Wang

Microfluidic Fabrication and Thermoreversible Response of Core/Shell Photonic Crystalline Microspheres Based on Deformable Nanogels

Soft photonic crystals (PC) are more appealing due to the responsiveness of the building blocking-deformable nanoparticles to the external stimuli. In this report, we demonstrate, for the first time, the generation of soft core/shell PC microspheres through a combination of a microfluidic technique, encapsulation of well-ordered temperature responsive polymer nanogels suspension, and photopolymerization of a transparent shell resin. This strategy not only ensures the monodispersity of core/shell PC microspheres, but also precisely controls their size, shell thickness, and optical properties by simply adjusting the flow rate ratio and mass fraction of the nanogels. More interestingly, the intensity of the reflection spectra of the crystalline nanogel arrays in the core can be modulated reversibly by controlling the shell thickness or the temperature. As a result of their symmetric structure, the resulting PC microspheres exhibited excellent structural colors and photonic band gaps for normal incident light independent of the position on the spherical surface. Multifunctional PC microspheres can also be generated by simply dispersing functional species together with the nanogels. This core/shell PC microsphere with tunable shell thickness and reversible thermoresponse could be significant for potential applications in the fields of chemical/biological sensors, display, encoding, and optical switching.

Multiresponsive Hydrogel Photonic Crystal Microparticles with Inverse-Opal Structure

Hydrogel photonic crystal microparticles (HPCMs) with inverse-opal structure are generated through a combination of microfluidic and templating technique. Temperature and pH responsive HPCMs have firstly been prepared by copolymerizing functional monomers, for example, N-isopropylacrylamide (NIPAm) and methacrylic acid (MAA). HPCMs not only show tunable color variation almost covering the entire wavelength of visible light (above 150 nm of stop-band shift) by simply tailoring temperature or pH value of the solution, but also display rapid response (less than 1 min) due to the small volume and well-ordered porous structure. Importantly, the temperature sensing window of the HPCMs can be enlarged by controlling the transition temperature of the hydrogel matrix, and the HPCMs also exhibit good reversibility and reproducibility for pH response. Moreover, functional species or particles (such as azobenzene derivative or magnetic nanoparticles) can be further introduced into the hydrogel matrix by using post-treatment process. These functionalized HPCMs can respond to the UV/visible light without significantly influencing the temperature and pH response, and thus, multiresponsive capability within one single particle can be realized. The presence of magnetic nanoparticles may facilitate secondary assembly, which has potential applications in advanced optical devices.

Janus photonic crystal microspheres: centrifugation-assisted generation and reversible optical property.

A new strategy to prepare core/shell Janus photonic crystal (PC) microspheres with reversible optical spectrum property is demonstrated. The microfluidic technique was employed to generate the uniform core/shell PC microspheres containing nanogels aqueous suspension. Under centrifugal force, the nanogel particles homogeneously dispersed in the core of microspheres would aggregate in the half of the microspheres, leading to Janus PC microspheres with varied reflection spectra at the different side of the spheres. More interestingly, such Janus structure of PC microspheres and their reflection spectrum were significantly reversible when the centrifugation was employed and removed alternatively. In addition, due to the soft and thermal-responsive nature of the building blocks (e.g., nanogels), Janus structures and optical properties of the PC microspheres are highly influenced by the temperature, centrifugal speed, and time, providing the other parameters on the manipulation of properties of the PC microspheres. This strategy provides a new concept for the preparation of Janus PC microspheres with tunable structures and optical properties, which will find potential applications in the field of sensors, optical devices, barcodes, etc.

Encapsulation of pristine fullerene C60 within block copolymer micelles through interfacial instabilities of emulsion droplets

We report a facile and versatile strategy to encapsulate pristine fullerene (C60) within spherical or wormlike block copolymer micelles through interfacial instability of emulsion droplets. C60 and amphiphilic block copolymer polystyrene-b-poly(ethylene oxide) were firstly dispersed in chloroform. The resulting solution was emulsified with aqueous sodium dodecylsulfate solution by simply shaking it. The emulsion droplets were collected in an open container and the solvent was allowed to evaporate. During solvent evaporation, the emulsion droplets became unstable and broke into tiny droplets, i.e., interfacial instabilities occurred, triggering the formation of uniform spherical micelles with encapsulated fullerenes in the micellar cores. More interestingly, fullerene addition induced a morphological transition from cylindrical micelles to string-of-vesicles and then to spherical micelles with increasing fullerene contents of 5 wt%, 10 wt%, and 30 wt%, respectively. We show that the optical properties of the confined C60 molecules can be modified by varying the quantity of fullerenes in the micelles. In addition, poly(3-hexylthiophene) (P3HT) can be co-encapsulated with C60 into the micellar cores when P3HT was dissolved in the initial polymer solution prior to emulsification. Presence of C60 in the micellar cores induced fluorescence quenching of P3HT due to photoinduced energy transfer from electron-donating P3HT to electron-accepting C60 molecules. Hybrid micelles with well-controlled structures and components can be potentially useful in the area of photodynamic therapy and photovoltaics.

Formation of hybrid core–shell microgels induced by autonomous unidirectional migration of nanoparticles

This Communication describes a facile strategy for the fabrication of inorganic nanoparticle (NP)-loaded hybrid core–shell microgels. The formation of core–shell microgels constitutes a novel mechanism in which the ionic-crosslinking of charged polymers (e.g., alginate) drives the unidirectional migration of NPs towards the centre of droplets. This versatile strategy allows the encapsulation of inorganic NPs with different sizes, shapes and surface properties in the core of the microgels in a single step.

Uniform Core–Shell Photonic Crystal Microbeads as Microcarriers for Optical Encoding

We demonstrate a rapid and robust method to fabricate uniform core-shell photonic crystal (PC) microbeads by the microfluidic and centrifugation-redispersion technique. Colored crystalline colloidal arrays (CCAs) were first prepared through centrifugation-redispersion approach by self-assembly of polystyrene-poly(N-isopropylacrylamide) (PS-PNIPAm) core/shell nanoparticles (NPs). Different from the conventional NPs (e.g., charged PS or PNIPAm NPs), PS-PNIPAm NPs could easily self-assemble into well-ordered CCAs by only one purification step without laborious pretreatment (e.g., dialysis or ion exchange) or slow solvent-evaporation process. The CCAs is then encapsulated into a transparent polymer shell with functional groups (e.g., copolymer of ETPTA and butyl acrylate (BA)), triggering the formation of core-shell PC microbeads which can be used as optical encoding microcarriers. Importantly, this technique allows us to produce core-shell PC microbeads in a rapid and robust way, and the optical reflections of the PC microbeads appear highly stable to various external stimuli (e.g., temperature, pH value, and ionic strength) relying on the features of the CCAs core and protection of the polymer shell. Moreover, various probe biomolecules (e.g., proteins, antibodies, and so on) can be easily linked on the surface of the core-shell PC microbeads owing to the hydrophilic modification induced by the hydrolysis of BA on the microbead surface, enabling the multiplex biomolecular detection.

Fabrication of porous polymer microparticles with tunable pore size and density through the combination of phase separation and emulsion-solvent evaporation approach

A facile and versatile route to prepare porous polymer microparticles with tunable pore size and density through the combination of phase separation and emulsion-solvent evaporation method is demonstrated. When volatile organic solvent (e.g., chloroform) diffuses through the aqueous phase containing poly(vinyl alcohol) (PVA) and evaporates, n-hexadecane (HD) and polystyrene (PS) in oil-in-water emulsion droplets occur to phase separate due to the incompatibility between PS and HD, ultimately yielding microparticles with porous structures. Interestingly, density of the pores (pore number) on the shell of microparticles can be tailored from one to hundreds by simply varying the HD concentration and/ or the rate of solvent evaporation. Moreover, this versatile approach for preparing porous microparticles with tunable pore size and density can be applied to other types of hydrophobic polymers, organic solvents, and alkanes, which will find potential applications in the fields of pharmaceutical, catalyst carrier, separation, and diagnostics.

Reprogrammable ultra-fast shape-transformation of macroporous composite hydrogel sheets

In this communication, we report a composite macroporous hydrogel sheet that can rapidly transform into multiple 3D shapes in response to near-infrared (NIR) light on demand. The transformation relies on the photo-thermal-induced asymmetric shrinking of the hydrogel material, which is further verified by finite element modeling.

Light-triggered generation of multifunctional gas-filled capsules on-demand

A combination of a microfluidic technique and laser-triggered reactions has been developed to fabricate functional gas-filled capsules (GFCs) on-demand with applications such as a pressure sensor. This method involves (i) the generation of monodispersed alginate microcapsules containing ammonium bicarbonate (AB) as gas resource and gold nanorods as a heating resource, in a microfluidic device; and (ii) the near-infrared light-triggered generation of gases from the AB-containing microcapsules and simultaneous encapsulation of the gases in an alginate shell to produce GFCs. Various functional substances such as dyes, quantum dots, and magnetic nanoparticles can be introduced into the shell of the GFCs to impart the system with multifunctionality. We further demonstrated the use of the GFCs as pressure sensors capable of sensing the variation in the pressure of environment.

Er:YAG fractional laser as a percutaneous absorption promoter for controlled delivery of antibody in vitro

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