Cellulose‐Based Microparticles for Magnetically Controlled Optical Modulation and Sensing

Abstract

Responsive materials with birefringent optical properties have been exploited for the manipulation of light in several modern electronic devices. While electrical fields are often utilized to achieve optical modulation, magnetic stimuli may offer an enticing complementary approach for controlling and manipulating light remotely. Here, the synthesis and characterization of magnetically responsive birefringent microparticles with unusual magneto‐optical properties are reported. These functional microparticles are prepared via a microfluidic emulsification process, in which water‐based droplets are generated in a flow‐focusing device and stretched into anisotropic shapes before conversion into particles via photopolymerization. Birefringence properties are achieved by aligning cellulose nanocrystals within the microparticles during droplet stretching, whereas magnetic responsiveness results from the addition of superparamagnetic nanoparticles to the initial droplet template. When suspended in a fluid, the microparticles can be controllably manipulated via an external magnetic field to result in unique magneto‐optical coupling effects. Using a remotely actuated magnetic field coupled to a polarized optical microscope, these microparticles can be employed to convert magnetic into optical signals or to estimate the viscosity of the suspending fluid through magnetically driven microrheology.

Cellulose through the Lens of Microfluidics: A Review

“…The scheme on the left makes microbeads using a T-section design, whereas the diagram on the right is for flow focusing for production of Janus particles. Reproduced with permissions from [267][268][269][270].…”

“…Display technologies, microrheological studies, and camouflaging devices might all benefit from these capabilities. A sample of the results [269] of using a magnetic field to guide microparticle size production in depicted in Figure 7b. To make the microparticle (CNC-laden) impressionable to magnetic fields, CNC building blocks were mixed with a small concentration of iron oxide nanoparticles.…”

Anisotropic Microparticles from Microfluidics

“…Very recently, Hausmann and colleagues presented a kind of anisotropic microparticles made from cellulose and superparamagnetic iron oxide nanoparticles. 21 These anisotropic particles were found with magnetic response birefringence and idiosyncratic magnetic optical character for optical modulation and sensing. To be specific, the birefringence property was obtained by adjusting cellulose nanocrystals inside the particles during the stretching process, whereas the magnetic response was achieved by appending superparamagnetic nanoparticles to the original template.…”

“…[15][16][17][18] Due to their special morphologies and complex components, anisotropic particles are capable of breaking through the limitation of general isotropic particles and combining different functions within a single particle entity, which is suggestive of their unpredicted and untapped potential in a host of fields, including display, sensing, drug delivery, cell culture, and so on. [19][20][21][22][23][24] For example, anisotropic particles, which are light composite materials that exhibit particular mechanical properties, have been designed by making use of the reinforcing capacity of fiber and platelets. 25 In addition, cell transportation and oriented release could be realized by taking advantage of crescent structures.…”

Adaptive Nanoparticle‐Polymer Complexes as Optical Elements: Design and Application in Nanophotonics and Nanomedicine

“…External magnetic field coupled with a polarized optical microscope allowed conversion of magnetic into optical signals. [ 136 ]…”