Synthesis of Optically Complex,Porous, and Anisometric Polymeric Microparticles by Templating from Liquid Crystalline Droplets

It is demonstrated that aqueous dispersions of micrometer‐sized liquid crystal (LC) droplets provide the basis of a general and facile methodology for the templated synthesis of spherical and nonspherical polymeric microparticles with complex internal structure and porosity. Specifically, nematic droplets of reactive (RM257)/nonreactive mesogens with distinct internal configurations are prepared using a range of approaches, the reactive mesogens are photopolymerized, and then the nonreactive mesogens are extracted to yield polymeric particles. It is found that LC droplets exhibiting bipolar, radial, axial or preradial configurations template the formation of spindle‐shaped, spherical, spherocylindrical or tear‐shaped polymeric microparticles, respectively. Each type of microparticle exhibits distinct optical signatures indicating the presence of an internal LC‐templated, anisotropic polymer network. In addition, by using a microfluidic system to generate monodisperse LC droplets containing 10%–40% wt/wt of RM257, spindle‐shaped microparticles with tailored aspect ratios ranging from 2.4 to 1.2 are formed. The mass density of spherical microparticles templated from radial LC droplets can be tuned to range from 0.2 to 0.6 g cm^?3, revealing the introduction of porosity (confirmed by electron microscopy) with a volume‐average pore diameter of 39 ± 16 nm (obtained from nitrogen sorption isotherms).     

Polymer Microparticles with Controllable Surface Textures Generated through Interfacial Instabilities of Emulsion Droplets

A general and versatile route to prepare hierarchical polymer microparticles via interfacial instabilities of emulsion droplets is demonstrated. Uniform emulsion droplets containing hydrophobic polymers and n‐hexadecanol (HD) are generated through microfluidic devices. When organic solvent diffuses through the aqueous phase and evaporates, shrinking emulsion droplets containing HD and polystyrene (PS) will trigger interfacial instabilities to form microparticles with wrinkled surfaces. Interestingly, surface‐textures of the particles can be accurately tailored from smooth to high textures by varying the HD concentration and/or the rate of solvent evaporation. Moreover, composite particles can be generated by suspending different hydrophobic species to the initial polymer solutions. This versatile approach for preparing particles with highly textured surfaces can be extended to other type of hydrophobic polymers which will find potential applications in the fields of drug delivery, tissue engineering, catalysis, coating, and device fabrication.     

Biomimetic Miniaturized Platform Able to Sustain Arrays of Liquid Droplets for High‐Throughput Combinatorial Tests

The development of high‐throughput and combinatorial technologies is helping to speed up research that is applicable in many areas of chemistry, engineering, and biology. A new model is proposed for flat devices for the high‐throughput screening of accelerated evaluations of multiplexed processes and reactions taking place in aqueous‐based environments. Superhydrophobic (SH) biomimetic surfaces based on the so‐called lotus effect are produced, onto which arrays of micro‐indentations allow the fixing of liquid droplets, based on the rose‐petal effect. The developed platforms are able to sustain arrays of quasi‐spherical microdroplets, allowing the isolation and confinement of different combinations of substances and living cells. Distinct compartmentalized physical, chemical, and biological processes may take place and be monitored in each droplet. The devices permit the addition/removal of liquid and mechanical stirring by adding magnetic microparticles into each droplet. By facing the chip downward, it is possible to produce arrays of cell spheroids developed by gravity in the suspended droplets, with the potential to be used as microtissues in drug screening tests.     

Microfluidic Synthesis of Liquid Crystalline Elastomer Particle Transport Systems which Can Be Remote‐Controlled Magnetically

Here, the microfluidic synthesis of liquid crystalline elastomer (LCE) particles, which can be remote‐controlled magnetically and used as transport systems, is presented for the first time. Ferri‐magnetic, rod‐shaped Fe₃O₄ nanoparticles are functionalized with poly(methyl methacrylate) to make them compatible with organic LCE precursor compounds. Their influence on the LCE precursor alignment is studied and thermoresponsive as well as photoresponsive LCE microparticles containing 0–6 wt% Fe₃O₄ are synthesized with a microfluidic device. Thermal and photochemical actuations of these particles are investigated. Their magnetic addressability is studied with a recently developed magnetic setup, by which the particles can be guided on liquid surfaces in the centimeter range–but with a precision in the submillimeter range. This allows the performance of reversible light‐ or heat‐controlled actuations at desired positions. The potential of synthesized LCE particles as transport systems is demonstrated by the transport of plastic, textiles or copper, which can be pushed just due to magnetic forces or transported in general by taking advantage of the phase dependent “stickiness” of LCEs. These studies open doors to novel applications of LCEs as microrobots using magnetism as a control.     

Magnetic and Transparent Composites by Linking Liquid Crystals to Ferrite Nanoparticles through Covalent Networks

The fabrication of transparent, flexible, and optically homogeneous magnetic composites containing ferrite (Fe₃O₄) nanoparticles, liquid crystals (LCs), and siloxane backbones is reported. The transparent magnets are achieved by covalently bonding LCs to the siloxane backbones and then linking them to dopamine‐functionalized ferrite nanocrystals. They exhibit simultaneous high transparency and strong magnetic properties. A remarkable feature of these films is that the surface morphology of the LC‐attached ferrite films can be tuned by an external magnetic field, demonstrating a striped surface in the direction of the field. We show that the LC‐attached film can act as an alignment layer to orient LCs, enabling the development of LC alignment surfaces on the basis of these nanomagnet–LC polymer composites.     

Thermosensitive Molecular,Colloidal, and Bulk Interactions Using a Simple Surfactant

Efficient use of (nano)particle self‐assembly for creating nanostructured materials requires sensitive control over the interactions between building blocks. Here, a very simple method for rendering the interactions between almost any hydrophobic nano‐ and microparticles thermoswitchable is described and this attraction is characterized using colloid probe atomic force microscopy (CP‐AFM). In a single‐step synthesis, a thermoresponsive surfactant is prepared that through physical adsorption generates a thermosensitive brush on hydrophobic surfaces. These surface layers can reversibly trigger gelation and crystallization of nano‐ and microparticles, and at the same time can be used to destabilize emulsions on demand. The method requires no chemical surface modification yet is universal, reproducible, and fully reversible.     

Optically Active Spherical Polyelectrolyte Brushes with a Nanocrystalline Magnetic Core

The unique properties of magnetic nanocrystals have triggered intensive research towards their effective functionalization and application in many technological fields. Although synthesis of magnetic colloids is being thoroughly studied, there is limited knowledge on the synthesis, characterization, and properties of magnetic polyelectrolyte spherical brushes. In the present work, the preparation of such hybrids and the subsequent formation of stable aqueous colloids are described. The core of the spherical brush consists of a magnetic γ‐Fe₂O₃ nanocrystallite (faceted but mostly spherical‐like) with a mean diameter of 17 nm. The bioadhesive polyelectrolyte poly(sodium 4‐styrene sulfonate), forming the surrounding brush layer, was proven to be an effective covalently modifying macromolecule for the iron oxide surface, as Fourier transform IR spectroscopy revealed. Several observations on colloidal aspects are discussed and are successfully explained by models and experiments describing polyelectrolyte brushes with a soft polymeric core. Finally, the hybrids exhibit their multifunctional character and their technological importance by combining in a single and soluble product with magnetic and nonlinear optical properties.     

Magnetocontrollable Droplet and Bubble Manipulation on a Stable Amphibious Slippery Gel Surface

Smart manipulation of liquid/bubble transport has garnered widespread attention due to its potential applications in many fields. Designing a responsive surface has emerged as an effective strategy for achieving controllable transport of liquids/bubbles. However, it is still challenging to fabricate stable amphibious responsive surfaces that can be used for the smart manipulation of liquid in air and bubbles underwater. Here, amphibious slippery surfaces are fabricated using magnetically responsive soft poly(dimethylsiloxane) doped with iron powder and silicone oil. The slippery gel surface retains its magnetic responsiveness and demonstrates strong affinity for bubbles underwater but shows small and switching resistance forces with the water droplets in air and bubbles underwater, which is the key factor for achieving the controllable transport of liquids/bubbles. On the slippery gel surface, the sliding behaviors of water droplets and bubbles can be reversibly controlled by alternately applying/removing an external magnetic field. Notably, compared with slippery liquid‐infused porous surfaces, the slippery gel surface demonstrates outstanding stability, whether in air or underwater, even after 100 cycles of alternately applying/removing the magnetic field. This surface shows potential applications in gas/liquid microreactors, gas–liquid mixed fluid transportation, bubble/droplet manipulation, etc.     

Computational Chemistry‐Guided Design of Selective Chemoresponsive Liquid Crystals Using Pyridine and Pyrimidine Functional Groups

Computational chemistry‐guided designs of chemoresponsive liquid crystals (LCs) with pyridine or pyrimidine groups that bind to metal‐cation‐functionalized surfaces to provide improved selective responses to targeted vapor species (dimethylmethylphosphonate (DMMP)) over nontargeted species (water) are reported. The LC designs against experiments are tested by synthesizing 4‐(4‐pentyl‐phenyl)‐pyridine and 5‐(4‐pentyl‐phenyl)‐pyrimidine and quantifying LC responses to DMMP and water. Consistent with the computations, pyridine‐containing LCs bind to metal‐cation‐functionalized surfaces too strongly to permit a response to either DMMP or water whereas pyrimidine‐containing LCs undergo a surface‐driven orientational transition in response to DMMP without interference from water. The computation predictions are not strongly dependent on assumptions regarding the degree of coordination of the metal ions but are limited in their ability to predict LC responses when using cations with mostly empty d orbitals. Overall, this work identifies a promising new class of chemoresponsive LCs based on pyrimidine that exhibits enhanced tolerance to water, a result that is important because water is a ubiquitous and particularly challenging chemical interferent in chemical sensing strategies based on LCs. The work also provides further evidence of the transformative utility of computational chemistry methods to design LC materials that exhibit selective orientational responses in specific chemical environments.     

Repeated Transfer of Colloidal Patterns by Using Reversible Buckling Process

The reversible nature of buckling is employed to repeatedly transfer colloids assembled in buckling patterns to flat surfaces. The cycle of colloidal loading–transfer–buckling is repeatedly carried out to fabricate the same colloidal patterns. The key to success is the reduction in the amplitude of the buckling patterns to a few nanometers as well as the recovery of initial buckling patterns after repeated stretching. The reduced buckling amplitude by poststretching or thermal annealing embosses the colloids assembled in the trenches of the buckling patterns, which enables the transfer regardless of the size, species, or layer thickness of the particles. This report demonstrates various transferred patterns composed of colloidal crystals, fluorescence hydrogel colloids, Au nanoparticles, and iron oxide magnetic particles. Since the process does not require surface modification of the colloids, it can be used to fabricate any colloidal patterns.     

Rapid and Controllable Digital Microfluidic Heating by Surface Acoustic Waves

Fast and controllable surface acoustic wave (SAW) driven digital microfluidic temperature changes are demonstrated. Within typical operating conditions, the direct acoustic heating effect is shown to lead to a maximum temperature increase of about 10 °C in microliter water droplets. The importance of decoupling droplets from other on‐chip heating sources is demonstrated. Acoustic‐heating‐driven temperature changes reach a highly stable steady‐state value in ≈3 s, which is an order of magnitude faster than previously published. This rise time can even be reduced to ≈150 ms by suitably tailoring the applied SAW‐power excitation profile. Moreover, this fast heating mechanism can lead to significantly higher temperature changes (over 40 °C) with higher viscosity fluids and can be of much interest for on‐chip control of biological and/or chemical reactions.     

Template‐Assisted Self‐Assembly of Spherical Colloids into Complex and Controllable Structures

Colloidal aggregates with well‐controlled sizes, shapes, and structures have been fabricated by dewetting aqueous dispersions of monodispersed spherical colloids across surfaces patterned with two‐dimensional arrays of relief structures (or templates). The capability and feasibility of this approach have been demonstrated with the organization of polymer latex or silica beads into homo‐aggregates, including circular rings; polygonal and polyhedral clusters; and linear, zigzag, and spiral chains. It was also possible to generate hetero‐aggregates in the configuration of HF and H₂O molecules that contained spherical colloids of different sizes, compositions, densities, functions, or a combination of these features. These uniform, well‐defined aggregates of spherical colloids are ideal model systems to investigate the aerodynamic, hydrodynamic, and optical properties of colloidal particles characterized by non‐spherical shapes and/or complex topologies. They can also serve as a new class of building blocks to generate hierarchically self‐assembled structures that are expected to exhibit interesting features valuable to areas ranging from condensed matter physics to photonics.     

Uniformly Shaped Poly(p‐phenylenediamine) Microparticles: Shape‐controlled Synthesis and Their Potential Application for the Removal of Lead Ions from Water

A novel method for the shape‐controlled synthesis of uniformly‐shaped poly(p‐phenylenediamine) (PpPD) microparticles with different morphologies under ambient condition has been developed using HAuCl₄ as an oxidant and poly(N‐vinylpyrrolidone) (PVP) as a surfactant. The results demonstrate that the morphologies of these microparticles can be varied from symmetrical spindle‐like to diamond‐like, centrosymmetric leaf‐like, and parallelogram‐like by tuning the concentration of reactants and their molar ratios. The length of these microparticles varies from 6 to 8 µm while the width can be tuned from 2 to 4 µm. The results demonstrate that PVP as a surfactant only plays a role in controlling the morphology of the polymer particles but has no influence on the polymer structures. UV‐Vis absorption spectroscopy shows the formation of a complex between polymer ligands and lead ions by detection of new absorption peaks. Even though the as‐prepared PpPD microparticles are only partly soluble, they still show an adsorptive affinity for lead ions.     

3D-Printed Underwater Super-Oleophobic Shark Skin toward the Electricity Generation through Low-Adhesion Sliding of Magnetic Nanofluid Droplets

Sustainable energy supply by converting mechanical to electric energy is critical for flexible electronic technologies, soft robots, and biomedical applications. The development of magnetoelectric conversion approaches requires new strategies with lightweight, small, and portable features. To address this need, an underwater magnetic nanofluid droplet-based generator (UMNDG) is designed to convert the mechanical energy of sliding droplets to electricity. The UMNDG consists of four parts: 3D-printed underwater superoleophobic surface bioinspired by shark skin, oily magnetic nanofluid droplets, bottom coil, and magnetic part. By improving the manufacturing parameters of 3D-printed shark skin, underwater superoleophobic and low-adhesion surfaces can be fabricated, allowing for the magnetic nanofluid droplets to slide upon the surfaces freely. When the magnetic nanofluid droplets slide/leave the bottom coil/magnet region, the magnetic flux passes through the coil changes, yielding the generation of electricity. Maxwell simulation is used to study related working mechanism. Finally, a ladder-type setup consisting of four UMNDGs is assembled in series, enabling to trigger the lighting of a LED bulb by continuous sliding of magnetic nanofluid droplets. Such a setup design may find use in a wide range of applications, from flexible electronic technologies to bio-inspired materials that interface with magnetic nanofluid systems.     

One‐Step Formulation of Protein Microparticles with Tailored Properties: Hard Templating at Soft Conditions

Formulation of therapeutic proteins into particulate forms is a main strategy for site‐specific and prolonged protein delivery as well as for protection against degradation. Precise control over protein particle size, dispersity, purity, as well as mild preparation conditions and minimal processing steps are highly desirable. It is, however, hard to fit all these criteria with conventional preparation techniques. Here a one‐step hard‐templating synthesis of microparticles composed of functional, non‐denatured protein is reported. The method is based on filling porous CaCO₃ microtemplates with the protein near to its isoelectric point (pI) followed by pH‐ or EDTA‐mediated dissolution of the tempplates. In principle, a wide variety of proteins can be converted into microparticles using this approach. The main requirement is an overlap of the protein insolubility and a template solubility for a certain parameter (here pH or EDTA). Here the formulation of insulin particles is studied in detail and it is shown that particles consisting of high molecular weight protein (catalase) can also be prepared. In this context, the synthesis of CaCO₃ templates with controlled size, the mechanism of the protein microparticle formation and mechanical properties of the microparticles are discussed. For the first time, the fabrication of mesoporous monodispersed CaCO₃ microtemplates with identical porocity but tuned diameter from 3 to 20 μm is demonstrated. The protein particle diameter can be adjusted by choosing the appropriate template size that is critical for successful pulmonary delivery of insulin. As a first step towards insulin delivery, the in vitro release of insulin at physiological conditions is studied.     

Facile Methods to Coat Polystyrene and Silica Colloids with Metal

To avoid the complex core surface functionalization or pretreatment that is necessary in order to coat latex and silica colloids with a uniform, complete metal shell, the solvent‐assisted route has been explored to prepare a complete metal (Ag or Au) shell with controlled thickness on polystyrene (PS) colloids and the electroless plating approach, based on electrostatic attraction, has been explored to prepare a complete silver shell with controlled thickness on silica colloids. Without any additional surface treatment, the as‐prepared complex core–shell colloids can be crystallized directly into long‐range‐ordered structures with photonic bandgaps, as reported here for the first time. These ordered structures may find potential applications as substrates or physical systems for the enhancement of Raman scattering studies, besides applications as photonic crystals. The optical plasmon resonance of the composite core–shell colloids changes with metal shell thickness, the wavelength varying over hundreds of nanometers. Our coating routes are facile and versatile, and can be extended to coat PS and silica colloids with any other metal whose ion or complex can be reduced in solution.     

Catalytic and Light‐Driven ZnO/Pt Janus Nano/Micromotors: Switching of Motion Mechanism via Interface Roughness and Defect Tailoring at the Nanoscale

The first models of mesoporous ZnO/Pt Janus micromotors that show fuel‐free and light‐powered propulsion depending on the interface roughness are shown. Two models of ZnO semiconducting particles with distinct surface morphologies and pore structures are synthesized by self‐aggregation of primary nanoparticles and nanosheets into nanoscale rough and smooth microparticles, respectively. The self‐assembled nanosheet model (smooth) provides a large surface for the formation of a continuous Pt layer with strong adherence, whereas the discontinuous Pt species take place inside the inter‐nanoparticles pores in the self‐assembled nanoparticle model (rough). The effects of the interface, surface porosity, defect, and charge transfer on the light‐powered motion for both well‐designed mesoporous ZnO/Pt Janus micromotors are investigated and compared to find the underlying propulsion mechanisms. The degradation of two model pollutants is demonstrated as a proof‐of‐concept application of these carefully engineered Janus micromotors. In this work, it is shown that by discreet material fabrication together with semiconductor/metal interface charge transport interpretation, it would be possible to develop new light‐driven Janus micromotors based on other photocatalysts containing active surfaces such as TiO₂.     

Doxorubicin Nanocarriers Based on Magnetic Colloids with a Bio‐polyelectrolyte Corona and High Non‐linear Optical Response: Synthesis,Characterization, and Properties

Magnetic drug nanocarriers are synthesized following an arrested mineralization of magnetic spinel iron oxides in the presence of the biopolymer of sodium carboxymethylcellulose. Based on the experimental results, the polyelectrolyte corona probably attains a brushlike configuration around the magnetic particles. The inner core of these colloids may be constituted of polymer‐associated nanocrystallites, forming nanogel colloids. The hybrid colloids are endowed with a high loading capacity for the anticancer agent doxorubicin and pronounced pH responsiveness. They also display a dramatic increase in non‐linear optical response as compared to previous studies of similar materials. Furthermore, as cell studies indicate, the blank nanocarriers are cytocompatible and the drug retains its activity after loading in the nanocarriers.     

pH‐Responsive Catalytic Janus Motors with Autonomous Navigation and Cargo‐Release Functions

The fabrication of multifunctional polymeric Janus colloids that display catalytically driven propulsion, change their size in response to local variations in pH, and vary cargo release rate is demonstrated. Systematic investigation of the colloidal trajectories reveals that in acidic environments the propulsion velocity reduces dramatically due to colloid swelling. This leads to a chemotaxis‐like accumulation for ensembles of these responsive particles in low‐pH regions. In synergy with this chemically defined accumulation, the colloids also show an enhancement in the release rate of an encapsulated cargo molecule. Together, these effects result in a strategy to harness catalytic propulsion for combined autonomous transport and cargo release directed by a chemical stimulus, displaying a greater than 30 times local cargo‐accumulation enhancement. Lactic acid can be used as the stimulus for this behavior, an acid produced by some tumors, suggesting possible eventual utility as a drug‐delivery method. Applications for microfluidic transport are also discussed.     

Circular Gold Nanodisks with Synthetically Tunable Diameters and Thicknesses

2D or pseudo‐2D plasmonic Au nanocrystals, such as circular Au nanodisks, possess unique plasmonic properties. Circular Au nanodisks not only possess two large surfaces with circular symmetry but also exhibit the wide tunability for their plasmon resonance. However, the lack of effective synthetic methods for producing size‐tunable and monodispersed circular Au nanodisks hinders further studies on their properties and applications. Herein, the synthesis of uniformly sized circular Au nanodisks with synthetically tunable diameters and thicknesses is reported. By performing mild anisotropic oxidation on pregrown Au nanoplates with different thicknesses, the thicknesses of the obtained nanodisks are varied from ≈10 nm to ≈50 nm. The nanodisk diameters are tailored from ≈50 nm to ≈150 nm by controlling the oxidation time. Moreover, both homodimers and heterodimers made of circular Au nanodisks are constructed using molecular linkers. They exhibit rich plasmon modes. In particular, dark multipolar plasmon resonance modes can be excited and observed in the asymmetric heterodimers. Such circular Au nanodisks with controllable sizes, large atomically flat surfaces, and a dominant dipolar plasmon mode are ideal building blocks for constructing plasmonic assemblies and plasmon‐coupled systems with desired plasmonic properties and functions.