Capture of Soft Particles on Electrostatically Heterogeneous Collectors: Brushy Particles

This work investigated how particle softness can influence the initial adhesive capture of submicrometer colloidal particles from flow onto collecting surfaces. The study focused on the case dominated by potential attractions at the particle periphery (rather than, for instance, steric stabilization, requiring entropically costly deformations to access shorter-range van der Waals attractions.) The particles, “spherical polyelectrolyte brushes” with diameters in the range of 150–200 nm depending on the ionic strength, consisted of a polystyrene core and a corona of grafted poly­(acrylic acid) chains, producing a relatively thick (20–40 nm) negative brushy layer. The adhesion of these particles was studied on electrostatically heterogeneous collecting surfaces: negatively charged substrates carrying flat polycationic patches made by irreversibly adsorbing the poly-l-lysine (PLL) polyelectrolyte. Variation in the amount of adsorbed PLL changed the net collector charge from completely negatively charged (repulsive) to positively charged (attractive). Adjustments in ionic strength varied the range of the electrostatic interactions. Comparing capture kinetics of soft brushy particles to those of similarly sized and similarly charged silica particles revealed nearly identical particle capture kinetics over the full range of collecting surface compositions at high ionic strengths. Even though the brushy particles contained an average of 5 vol % PAA in the brushy shell, with the rest being water under these conditions, their capture was indistinguishable from that of similarly charged rigid spheres. The brushy particles were, however, considerably less adherent at low ionic strengths where the brush was more extended, suggesting an influence of particle deformability or reduced interfacial charge. These findings, that the short time adhesion of brushy particles can resemble that of rigid particles, suggest that for bacteria and cell capture, modeling the cells as rigid particles can, in some instances, be a good approximation

Ionic Strength-Responsive Binding between Nanoparticles and Proteins

Electrostatic interaction is a strong, dominant nonspecific interaction which was extensively studied in protein–nanoparticle (NP) interactions [Lounis, F. M.; J. Phys. Chem. B 2017, 121, 2684−2694; Tavares, G. M.; Langmuir 2015, 31, 12481–12488; Antonov, M.; Biomacromolecules 2010, 11, 51–59], whereas the role of hydrophobic interaction arising from the abundant hydrophobic residues of globule proteins upon protein–NP binding between the proteins and charged nanoparticles has rarely been studied. In this work, a series of positively charged magnetic nanoparticles (MNPs) were prepared via atom transfer radical polymerization and surface hydrophobicity differentiation was achieved through postpolymerization quaternization by different halohydrocarbons. The ionic strength- and hydrophobicity-responsive binding of these MNPs toward β-lactoglobulin (BLG) was studied by both qualitative and quantitative methods including turbidimetric titration, dynamic light scattering, and isothermal titration calorimetry. Judged from the critical binding pH and binding constant for MNP–BLG complexation, the dependence of binding affinity on surface hydrophobicity exhibited an interesting shift with increasing ionic strength, which means that the MNPs with higher surface hydrophobicity exhibits weaker binding affinity at lower ionic strength but stronger affinity at higher ionic strength. This interesting observation could be attributed to the difference in ionic strength responsiveness for hydrophobic and electrostatic interactions. In this way, the well-tuned binding pattern could be achieved with optimized binding affinity by controlling the surface hydrophobicity of MNPs and ionic strength, thus endowing this system with great potential to fabricate separation and delivery system with high selectivity and efficiency

Recoverable Platinum Nanocatalysts Immobilized on Magnetic Spherical Polyelectrolyte Brushes

Recoverable platinum nanocatalysts immobilized on magnetic spherical polyelectrolyte brushes (MSPB) were synthesized and characterized by high resolution transmission electron microscope (HRTEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). High catalytic activity was found by photometrically monitoring the reduction of 4-nitrophenol by NaBH₄ in the presence of MSPB-Pt composites. An excellent stability and recyclability of catalyst was observed after consecutive eight runs following by external magnetic-separation and redispersion. This novel approach provides an excited potential application in preparation of recyclable metal nanocatalysts with high activity

Multi-Stimuli-Responsive Amphiphilic Assemblies through Simple Postpolymerization Modifications

A strategy to construct different stimuli-responsive polymers from postpolymerization modifications of a single polymer scaffold via thiol–disulfide exchange has been developed. Here, we report on a random copolymer that enables the design and syntheses of a series of dual or multi-stimuli-responsive nanoassemblies using a simple postpolymerization modification step. The reactive functional group involves a side chain monopyridyl disulfide unit, which rapidly and quantitatively reacts with various thiols under mild conditions. Independent and concurrent incorporation of physical, chemical, or biologically responsive properties have been demonstrated. We envision that this strategy may open up opportunities to simplify the synthesis of multifunctional polymers with broad implications in a variety of biological applications

Organic Amine-Mediated Synthesis of Polymer and Carbon Microspheres: Mechanism Insight and Energy-Related Applications

A general organic amine-mediated synthesis of polymer microspheres is developed based on the copolymerization of resorcinol, formaldehyde, and various organic amines at room temperature. Structure formation and evolution of colloidal microspheres in the presence of polyethylenimine are monitored by dynamic light scattering measurements. It is found that the colloidal clusters are formed instantaneously and then experience an anomalous shrinkage–growth process. This should be caused by two different reaction pathways: cross-linking inside the microspheres and step-growth polymerization of substituted resorcinol on the microsphere surface, leading to the formation of core–shell heterogeneous structures as confirmed by TEM observation and XPS analysis. A formation mechanism of polymer microspheres is provided based on the aggregation of polyethylenimine/resorcinol–formaldehyde (PEI-RF) self-assembled nuclei, which is apparently different from the conventional Stöber process. Furthermore, nitrogen-doped carbon microspheres are prepared by the direct carbonization of these polymer microspheres, which exhibit microporous BET surface areas of 400–500 m² g^–1, high nitrogen contents of 5–6 wt %, and a good CO₂ adsorption capacity up to 3.6 mmol g^–1 at 0 °C. KOH activation is further employed to develop the porous texture of carbon microspheres without sacrificing the spherical morphology. The resultant activated carbon microspheres exhibit small particle size (<80 nm), high BET surface areas of 1500–2000 m² g^–1, and considerable nitrogen content of 2.2–2.0 wt %. When used as the electrode materials for supercapacitors, these activated carbon microspheres demonstrate a high capacitance up to 240 F g^–1, an unprecedented rate performance and good cycling performance

Encapsulation of Quantum Dot Clusters in Stimuli-Responsive Spherical Polyelectrolyte Brushes

Novel fluorescence-labeled spherical polyelectrolyte brushes consisting of a fluorescent polystyrene (PS) nanocomposite core and a poly­(acylic acid) (PAA) brush shell were successfully prepared. Quantum dots (QDs) were well confined in the PS core through hybrid emulsion polymerization. PAA chains were then grafted onto the surface of the fluorescent PS core to form a brush structure through photoemulsion polymerization. The obtained fluorescent spherical polyelectrolyte brushes are highly pH sensitive in addition to their excellent dispersibility in water. Fluorescent nanoclusters were introduced into spherical polyelectrolyte brushes to acquire high sensitive detection in the applications of spherical polyelectrolyte brushes as catalyst tracer, as biosensor, and in protein coding

Preparation of Superhydrophobic Magnetic Cellulose Sponge for Removing Oil from Water

It is still a challenging global task for oil/water separation. Here we fabricate superhydrophobic magnetic cellulose sponge (SMCE) that can be used to separate free oil/water mixtures and surfactant-stabilized W/O emulsions. The simple modification includes only two steps: a thin layer of ferroferric oxide (Fe₃O₄) was coated on cellulose sponge surface via codeposition method, and subsequently magnetic cellulose sponge was modified with hexadecyltrimethoxysilane, which could react with Fe₃O₄ or hydroxyl groups of cellulose. The purpose of coating Fe₃O₄ is to increase the roughness of the surface and recycle the sample by magnetic force. SMCE could separate oil–water mixtures with a high separation efficiency and good reusability. The sample is green, low cost, and environmental friendly, which makes it a promising candidate to be used in oil–water separation

Resin from Liaohe Heavy Oil: Molecular Structure, Aggregation Behavior, and Effect on Oil Viscosity

Resin accounts for over 30% of the composition of Liaohe heavy crude oil and can result in severe difficulties in oil recovery and transportation. To determine the structure of the resin extracted from Liaohe heavy oil, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, elemental analysis, Fourier-transform IR spectroscopy, and NMR spectroscopy were employed to determine the chemical structure of the resin. The results showed that the resin molecule is composed of anthracene, two cycloalkanes, and six alkyl chains grafted on the cyclic-structure core. UV–visible spectroscopy, turbidity measurements, dynamic light scattering, optical microscopy, and scanning electron microscopy were used to observe the resin aggregation behavior upon addition of a poor solvent. The effect of the resin on the rheology of model oils was investigated systematically. The π–π interactions among resin molecules impose a critical impact on the assembly of the resins. The quantum mechanics calculations revealed that there are two low-well depths of interaction energy when two resin molecules approach, which implies that the bending and branching structure of the resin aggregates may originate from the staggered stacking of the resin molecules. These findings can improve our understanding of the resin aggregation behavior and thus enlighten the solution to the flowing problem during recovery and transportation of heavy oil with a high resin content

Facile Preparation of AIE-Active Fluorescent Nanoparticles through Flash Nanoprecipitation

Flash nanoprecipitation (FNP) is an easily scalable and fast processing method for the preparation of nanoparticles (NPs) with simple vortex equipment. By using the FNP method, fluorescent NPs are prepared in less than 1 s in a multi-inlet vortex mixer, in which hydrophobic aggregation-induced emission (AIE)-active dye of EDP is incorporated within the biocompatible block copolymer poly­(ethylene glycol)-<i>b</i>-poly­(ε-caprolactone) for EDP NP assembly. The formulation parameters of stream velocity, dyes, and loading and concentration in FNP are optimized. The sizes of the NPs ranged from 20 to 60 nm with a ratio change of mixed solvents. As a control, an aggregation-caused quenching (ACQ) molecule of BDP was also synthesized for BDP NPs. To gain insight into the effect of the polymer on the aggregation state of hydrophobic dyes, the preparation of EDP and BDP NPs without block copolymer was also investigated. Apparently, the sizes of the NPs display large distributions without an amphiphilic block copolymer as the engineering template, suggesting that the block of polymers plays a key role in tuning the aggregation state of encapsulated dyes in FNP processes. Moreover, the peak shifts of dye with different microenvironments also confirmed the successful encapsulation of fluorescent dye in the NP cores. Finally, by externally applied forces in the FNP method, the engineered assembly of AIE-active fluorescent NPs possessing a narrow size distribution with desirable fluorescence properties was obtained. These features provide the possibility of rapidly constructing controllable AIE-active fluorescent NPs as biomedical tracers

Facile Preparation of AIE-Active Fluorescent Nanoparticles through Flash Nanoprecipitation

Flash nanoprecipitation (FNP) is an easily scalable and fast processing method for the preparation of nanoparticles (NPs) with simple vortex equipment. By using the FNP method, fluorescent NPs are prepared in less than 1 s in a multi-inlet vortex mixer, in which hydrophobic aggregation-induced emission (AIE)-active dye of EDP is incorporated within the biocompatible block copolymer poly­(ethylene glycol)-<i>b</i>-poly­(ε-caprolactone) for EDP NP assembly. The formulation parameters of stream velocity, dyes, and loading and concentration in FNP are optimized. The sizes of the NPs ranged from 20 to 60 nm with a ratio change of mixed solvents. As a control, an aggregation-caused quenching (ACQ) molecule of BDP was also synthesized for BDP NPs. To gain insight into the effect of the polymer on the aggregation state of hydrophobic dyes, the preparation of EDP and BDP NPs without block copolymer was also investigated. Apparently, the sizes of the NPs display large distributions without an amphiphilic block copolymer as the engineering template, suggesting that the block of polymers plays a key role in tuning the aggregation state of encapsulated dyes in FNP processes. Moreover, the peak shifts of dye with different microenvironments also confirmed the successful encapsulation of fluorescent dye in the NP cores. Finally, by externally applied forces in the FNP method, the engineered assembly of AIE-active fluorescent NPs possessing a narrow size distribution with desirable fluorescence properties was obtained. These features provide the possibility of rapidly constructing controllable AIE-active fluorescent NPs as biomedical tracers