Reconfigurable assembly of charged polymer-modified Janus and non-Janus particles: from half-raspberries to colloidal clusters and chains

What is the role of PEO chains in the assembly of core-corona supraparticles in aqueous dispersions?

Hypothesis The assembly of core-corona supraparticles in aqueous dispersions has been regularly assisted by auxiliary monomers/oligomers which modify the individual particles with, e.g., surface grafting of polyethylene oxide (PEO) chains or other hydrophilic monomers. However, this modification complicates the preparation and purification procedures and increases potential upscaling efforts. Hybrid polymer-silica core-corona supracolloids could be more simply assembled if the PEO chains from surfactants, typically used by default as polymer stabilizers, concomitantly act as assembly promotors. The supracolloids assembly could therefore be more easily achieved without requiring particles functionalization or post-purification steps. Methods The self-assembly of supracolloidal particles prepared with PEO-surfactant stabilized (Triton X-405) and/or PEO-grafted polymer particles is compared to differentiate the roles of the PEO chains in the assembly of core-corona supraparticles. Using time-resolved dynamic light scattering (DLS) and cryogenic transmission electron microscopy(cryo-TEM), the effect of concentration of PEO chains (from surfactant) on the kinetics and dynamics of supracolloids assembly is investigated. Self-consistent field (SCF) lattice theory was used to numerically study the distribution of PEO chains at the interfaces present in the supracolloidal dispersions. Findings The PEO based surfactant can be used as assembly promoter of core-corona hybrid supracolloids due to its amphiphilic nature and via establishing hydrophobic interactions. The concentration of the PEO surfactant, and especially the PEO chains distribution over the different interfaces, crucially affect the supracolloids assembly. A simplified pathway for preparing hybrid supracolloidal particles with a well-controlled corona coverage over polymer cores is presented.

Four-Level Structural Hierarchy: Microfluidically Supported Synthesis of Polymer Particle Architectures Incorporating Fluorescence-Labeled Components and Metal Nanoparticles

Hierarchical assemblies of functional polymer particles are promising due to their surface as well as physicochemical properties. However, hierarchical composites are complex and challenging to form due to the many steps necessary for integrating different components into one system. Highly structured four-level composite particles were formed in a four-step process. First of all, gold (Au) nanoparticles, poly(methyl methacrylate) (PMMA) nanoparticles, and poly(tripropylene glycol diacrylate) (poly-TPGDA) microparticles were individually synthesized. By applying microfluidic techniques, polymer nano- and microparticles were formed with tunable size and surface properties. Afterwards, the negatively charged gold nanoparticles and PMMA particles functionalized with a positively charged surface were mixed to form Au/PMMA assemblies. The Au/PMMA composites were mixed and incubated with poly-TPGDA microparticles to form ternary Au/PMMA/poly-TPGDA assemblies. For the formation of composite-containing microparticles, Au/PMMA/poly-TPGDA composites were dispersed in an aqueous acrylamide-methylenebisacrylamide solution. Monomer droplets were formed in a co-flow microfluidic device and photopolymerized by UV light. In this way, hierarchically structured four-level composites consisting of four different size ranges─0.025/0.8/30/1000 μm─were obtained. By functionalizing polymer nano- and microparticles with different fluorescent dyes, it was possible to visualize the same composite particle under two different excitation modes (λ_ex = 395-440 and λ_ex = 510-560 nm). The Au/PMMA/poly-TPGDA composite-embedded polyacrylamide microparticles can be potentially used as a model for the creation of composite particles for sensing, catalysis, multilabeling, and biomedical applications.

Reconfigurable assembly of colloidal motors towards interactive soft materials and systems

Due to the highly flexible reconfiguration of swarms, collective behaviors have provided various natural organisms with a powerful adaptivity to the complex environment. To mimic these natural systems and construct artificial intelligent soft materials, self-propelled colloidal motors that can convert diverse forms of energy into swimming-like movement in fluids afford an ideal model system at the micro-/nanoscales. Through the coupling of local gradient fields, colloidal motors driven by chemical reactions or externally physical fields can assembly into swarms with adaptivity. Here, we summarize the progress on reconfigurable assembly of colloidal motors which is driven and modulated by chemical reactions and external fields (e.g., light, ultrasonic, electric, and magnetic fields). The adaptive reconfiguration behaviors and the corresponding mechanisms are discussed in detail. The future directions and challenges are also addressed for developing colloidal motor-based interactive soft matter materials and systems with adaptation and interactive functions comparable to that of natural systems.

Textured and Hierarchically Constructed Polymer Micro- and Nanoparticles

Microfluidic techniques allow for the tailored construction of specific microparticles, which are becoming increasingly interesting and relevant. Here, using a microfluidic hole-plate-device and thermal-initiated free radical polymerization, submicrometer polymer particles with a highly textured surface were synthesized. Two types of monomers were applied: (1) methylmethacrylate (MMA) combined with crosslinkers and (2) divinylbenzene (DVB). Surface texture and morphology can be influenced by a series of parameters such as the monomer–crosslinker–solvent composition, surfactants, and additives. Generally, the most structured surfaces with the simultaneously most uniform particles were obtained in the DVB–toluene–nonionic-tensides system. In a second approach, poly-MMA (PMMA) particles were used to build aggregates with bigger polymer particles. For this purpose, tripropyleneglycolediacrylate (TPGDA) particles were synthesized in a microfluidic co-flow arrangement and polymerized by light- irradiation. Then, PMMA particles were assembled at their surface. In a third step, these composites were dispersed in an aqueous acrylamide–methylenebisacrylamide solution, which again was run through a co-flow-device and photopolymerized. As such, entities consisting of particles of three different size ranges—typically 0.7/30/600 µm—were obtained. The particles synthesized by both approaches are potentially suitable for loading with or incorporation of analytic probes or catalysts such as dyes or metals.

Protein-like particles through nanoprecipitation of mixtures of polymers of opposite charge

HYPOTHESIS

Polymer nanoparticles (NPs) have a very high potential for applications notably in the biomedical field. However, synthetic polymer NPs cannot yet concurrence the functionalities of proteins, their natural counterparts, notably in terms of size, control over internal structure and interactions with biological environments. We hypothesize that kinetic trapping of polymers bearing oppositely charged groups in NPs could bring a new level of control and allow mimicking the surfaces of proteins.

EXPERIMENTS

Here, the assembly of mixed-charge polymer NPs through nanoprecipitation of mixtures of oppositely charged polymers is studied. Two series of copolymers made of ethyl methacrylate and 1 to 25 mol% of either methacrylic acid or a trimethylammonium bearing methacrylate are synthesized. These carboxylic acid or trimethylammonium bearing polymers are then mixed in different ratios and nanoprecipitated. The influence of the charge fraction, mixing ratio of the polymers, and precipitation conditions on NP size and surface charge is studied.

FINDINGS

Using this approach, NPs of less than 25 nm with tunable surface charge from +40 mV to -40 mV are assembled. The resulting NPs are sensitive to pH and certain NP formulations have an isoelectric point allowing repeated charge reversal. Encapsulation of fluorescent dyes yields very bright fluorescent NPs, whose interactions with cells are studied through fluorescence microscopy. The obtained results show the potential of nanoprecipitation of oppositely charged polymers for the design of NPs with precisely tuned surface properties.

Self-Assembly of Colloidal Molecules Based on Host-Guest Chemistry and Geometric Constraints

The preparation of colloidal molecules (CMs), that is, clusters of colloids with a defined aggregation number and configuration, is of continued and significant interest in colloid chemistry and materials science and numerous interactions have been utilized to drive their (self-)assembly. However, only very few reports are available on the assembly of CMs based on host-guest chemistry. In this paper, we investigate the assembly of like-charged silica particles into well-defined, core-satellite AB_n-type CMs in water, mediated by host-guest interactions and geometric constraints. Exploiting the inherent dynamics of noncovalent attraction and making use of a soft polymer shell to enhance multivalent host-guest interactions, we successfully synthesized AB₃, AB₄, and AB₆ CMs by selecting the appropriate size ratio of satellite to core particles.