Colloidal Objects Research Articles

Structural Rheology in the Development and Study of Complex Polymer Materials.

The progress in polymer science and nanotechnology yields new colloidal and macromolecular objects and their combinations, which can be defined as complex polymer materials. The complexity may include a complicated composition and architecture of macromolecular chains, specific intermolecular interactions, an unusual phase behavior, and a structure of a multi-component polymer-containing material. Determination of a relation between the structure of a complex material, the structure and properties of its constituent elements, and the rheological properties of the material as a whole is the subject of structural rheology-a valuable tool for the development and study of novel materials. This work summarizes the author's structural-rheological studies of complex polymer materials for determining the conditions and rheo-manifestations of their micro- and nanostructuring. The complicated chemical composition of macromolecular chains and its role in polymer structuring via block segregation and cooperative hydrogen bonds in melt and solutions is considered using tri- and multiblock styrene/isoprene and vinyl acetate/vinyl alcohol copolymers. Specific molecular interactions are analyzed in solutions of cellulose; its acetate butyrate; a gelatin/carrageenan combination; and different acrylonitrile, oxadiazole, and benzimidazole copolymers. A homogeneous structuring may result from a conformational transition, a mesophase formation, or a macromolecular association caused by a complex chain composition or specific inter- and supramolecular interactions, which, however, may be masked by macromolecular entanglements when determining a rheological behavior. A heterogeneous structure formation implies a microscopic phase separation upon non-solvent addition, temperature change, or intense shear up to a macroscopic decomposition. Specific polymer/particle interactions have been examined using polyethylene oxide solutions, polyisobutylene melts, and cellulose gels containing solid particles of different nature, demonstrating the competition of macromolecular entanglements, interparticle interactions, and adsorption polymer/particle bonds in governing the rheological properties. Complex chain architecture has been considered using long-chain branched polybutylene-adipate-terephthalate and polyethylene melts, cross-linked sodium hyaluronate hydrogels, asphaltene solutions, and linear/highly-branched polydimethylsiloxane blends, showing that branching raises the viscosity and elasticity and can result in limited miscibility with linear isomonomer chains. Finally, some examples of composite adhesives, membranes, and greases as structured polymeric functional materials have been presented with the demonstration of the relation between their rheological and performance properties.

Out-of-equilibrium interactions and collective locomotion of colloidal spheres with squirming of nematoelastic multipoles

Many living and artificial systems show similar emergent behavior and collective motions on different scales, starting from swarms of bacteria to synthetic active particles, herds of mammals, and crowds of people. What all these systems often have in common is that new collective properties like flocking emerge from interactions between individual self-propelled or driven units. Such systems are naturally out-of-equilibrium and propel at the expense of consumed energy. Mimicking nature by making self-propelled or externally driven particles and studying their individual and collective motility may allow for deeper understanding of physical underpinnings behind collective motion of large groups of interacting objects or beings. Here, using a soft matter system of colloids immersed into a liquid crystal, we show that resulting so-called nematoelastic multipoles can be set into a bidirectional locomotion by external oscillating electric fields. Out-of-equilibrium elastic interactions between such colloidal objects lead to collective flock-like behaviors emerging from time-varying elasticity-mediated interactions between externally driven propelling particles. Repulsive elastic interactions in the equilibrium state can be turned into attractive interactions in the out-of-equilibrium state under applied external electric fields. We probe this behavior at different number densities of colloidal particles and show that particles in dense dispersions collectively select the same direction of a coherent motion due to elastic interactions between near neighbors. In our experimentally implemented design, their motion is highly ordered and without clustering or jamming often present in other colloidal transport systems, which is promising for technological and fundamental-science applications, like nano-cargo transport, out-of-equilibrium assembly, and microrobotics.

Qualitatively and Quantitatively Different Configurations of Nematic-Nanoparticle Mixtures.

We consider the influence of different nanoparticles or micrometre-scale colloidal objects, which we commonly refer to as particles, on liquid crystalline (LC) orientational order in essentially spatially homogeneous particle-LC mixtures. We first illustrate the effects of coupling a single particle with the surrounding nematic molecular field. A particle could either act as a "dilution", i.e., weakly distorting local effective orientational field, or as a source of strong distortions. In the strong anchoring limit, particles could effectively act as topological point defects, whose topological charge q depends on particle topology. The most common particles exhibit spherical topology and consequently act as q = 1 monopoles. Depending on the particle's geometry, these effective monopoles could locally induce either point-like or line-like defects in the surrounding LC host so that the total topological charge of the system equals zero. The resulting system's configuration is topologically equivalent to a crystal-like array of monopole defects with alternating topological charges. Such configurations could be trapped in metastable or stable configurations, where the history of the sample determines a configuration selection.

Colloidal Objects in Biomedicine: Modern Trends and Prospects

Colloidal Objects in Biomedicine: Modern Trends and Prospects

Colloidal Objects in Biomedicine: Modern Trends and Prospects

This review presents historical retrospective on the development of biomedicine as a science and indicates the role of colloidal objects, as well as contains the summary of the reviews and research articles included in the special issue.

Colloidal Manipulation through Plasmonic and Non‐plasmonic Laser‐Assisted Heating

AbstractIn spite of the long‐term awareness of the conversion of light to heat even in materials with low absorption coefficient via the photothermal effect and consequent usage of the effect to evaluate thermo‐optic properties of the materials, only recently has the thermal field created via photon‐to‐phonon conversion been exploited for manipulation of colloidal objects as well as living cells. As compared to conventional direct photon‐assisted manipulation via optical tweezers, the optothermal manipulation technique employs much lower optical source power and can manipulate particles over a long range. In this review, the working mechanisms, concepts, and applications of a series of recently established optothermal techniques are discussed for the manipulation of diverse species including micro/nanoparticles, biological cells, molecules, and micelles in various fluidic environments. The physical mechanism of the optical manipulation that relies on the coordinated action of thermal convection, Marangoni convection, thermophoresis, thermoelectricity, depletion attraction, and thermo‐osmotic flow is discussed in detail. With their low‐power operation, diverse functionalities, and simple optics employed, optothermal manipulation techniques are increasingly finding a wide range of applications in colloidal science, life sciences, materials science, and nanoscience, as well as in the developments of colloidal functional devices and nanomedicine.

Modular assembly of microswimmers with liquid compartments.

Artificial microswimmers, i.e. colloidal scale objects capable of self-propulsion, have garnered significant attention due to their central role as models for out of equilibrium systems. Moreover, their potential applications in diverse fields such as biomedicine, environmental remediation, and materials science have long been hypothesized, often in conjunction with their ability to deliver cargoes to overcome mass transport limitations. A very efficient way to load molecular cargoes is to disperse them in a liquid compartment, however, fabricating microswimmers with multiple liquid compartments remains a significant challenge. To address this challenge, we present a modular fabrication platform that combines microfluidic synthesis and sequential capillarity-assisted particle assembly (sCAPA) for microswimmers with various liquid compartments. We demonstrate the synthesis of monodisperse, small polymer-based microcapsules (Ø = 3-6μm) with different liquid cargoes using a flow-focusing microfluidic device. By employing the sCAPA technique, we assemble multiple microcapsules into microswimmers with high precision, resulting in versatile microswimmers with multiple liquid compartments and programmable functionalities. Our work provides a flexible approach for the fabrication of modular microswimmers, which could potentially actively transport cargoes and release them on demand in the future.

Using Cluster Theory to Calculate the Experimental Structure Factors of Antibody Solutions

Monoclonal antibody solutions are set to become a major therapeutic tool in the years to come, capable of targeting various diseases by clever design of their antigen binding site. However, the formulation of stable solutions suitable for patient self-administration typically presents challenges, as a result of the increase in viscosity that often occurs at high concentrations. Here, we establish a link between the microscopic molecular details and the resulting properties of an antibody solution through the characterization of clusters, which arise in the presence of self-associating antibodies. In particular, we find that experimental small-angle X-ray scattering data can be interpreted by means of analytical models previously exploited for the study of polymeric and colloidal objects, based on the presence of such clusters. The latter are determined by theoretical calculations and supported by computer simulations of a coarse-grained minimal model, in which antibodies are treated as Y-shaped colloidal molecules and attractive domains are designed as patches. Using the theoretically predicted cluster size distributions, we are able to describe the experimental structure factors over a wide range of concentration and salt conditions. We thus provide microscopic evidence for the well-established fact that the concentration-dependent increase in viscosity is originated by the presence of clusters. Our findings bring new insights on the self-assembly of monoclonal antibodies, which can be exploited for guiding the formulation of stable and effective antibody solutions.

Solvophobicity-Driven Mesoscale Structures: Stabilizer-Free Nanodispersions.

Solvophobicity-driven mesoscale structures that lack any stabilizers are perhaps the most common spontaneously formed stable colloidal objects (particles, droplets). In spite of this, they have been significantly overlooked for a long time and the knowledge on solvophobicity-driven mesoscale structures (SDMSs) is rather limited. Here, we follow up on our previous work on mesoscale solubility [Rak, D.; Sedlák, M. On the Mesoscale Solubility in Liquid Solutions and Mixtures. J. Phys. Chem. B 2019, 123, 1365-1374. 10.1021/acs.jpcb.8b10638] and aim at providing a fully consistent picture of the nature, formation, and stability of SDMSs. We investigate both aqueous and nonaqueous mixtures, showing that this phenomenon is universal and not limited to aqueous systems. An experimental regime diagram is constructed as a function of the concentration of the solvophobic component and the solvophobicity strength given by mixtures of various organic solvents. Aqueous mixtures are investigated using well-defined ternary systems comprising water, ethanol (or other organic solvents), and a series of linear alkanes serving as hydrophobes. This investigation covers unique long-time monitoring of SDMS stability (up to three years). Another parameter studied in detail is the temperature of the mixture. SDMSs are characterized in terms of their shape and size distributions obtained using orthogonal techniques. Last but not least, we bring some insights into the SDMS surface zeta potential─the key quantity behind the stability of SDMSs. We investigate zeta potential as a function of the mixture composition, pH, and temperature.

Langmuir‐Blodgett Assembly to order Nanoparticles and Colloidal Objects

Bottom-up assembly of nanoparticles and colloidal objects pose a formidable challenge when processing devices. Speed, compatibility with various materials, defect tolerance and cost effectiveness are among the desired properties of a suitable nanoscale assembly process. In this regard, the Langmuir‐Blodgett (LB) technique is a highly sought-after candidate which aids in arranging a large number of nanostructures on solid surfaces. This mini-review aims to provide a concise account on the LB technique and four distinct ways of how it allows to assemble systems made of nanoparticles and colloidal objects: namely, close-packed nanoparticle superlattices by compression, micrometer scale nanoparticle fingering patterns by dip coating, single nanoparticle lines by stick-slip deposition and one-step patterning of aligned nanowire arrays.

Confinement-induced accumulation and de-mixing of microscopic active-passive mixtures

Understanding the out-of-equilibrium properties of noisy microscale systems and the extent to which they can be modulated externally, is a crucial scientific and technological challenge. It holds the promise to unlock disruptive new technologies ranging from targeted delivery of chemicals within the body to directed assembly of new materials. Here we focus on how active matter can be harnessed to transport passive microscopic systems in a statistically predictable way. Using a minimal active-passive system of weakly Brownian particles and swimming microalgae, we show that spatial confinement leads to a complex non-monotonic steady-state distribution of colloids, with a pronounced peak at the boundary. The particles’ emergent active dynamics is well captured by a space-dependent Poisson process resulting from the space-dependent motion of the algae. Based on our findings, we then realise experimentally the de-mixing of the active-passive suspension, opening the way for manipulating colloidal objects via controlled activity fields.

Cryogenic transmission electron microscopy for observation of monomer protrusions that emerge during formation of dumbbell-shaped polymer colloids

Anisotropic particles exhibit directional interactions resulting in a rich phase behavior. Considerable efforts have thus been invested in guiding particle synthesis into an anisotropic direction. Dumbbell-shaped polymer particles are one of the most remarkable examples. They result from phase separation during seeded polymerization. The underlying mechanism and thermodynamic principles are understood from its proximal end. Segregation of monomer and seed particle results in a monomer protrusion attached to the seed. Polymerization of the protrusion finally yields particles with two bulb-shaped halves. Little attention has been paid to an investigation of transient states, namely the formation of liquid protrusions grown from monomer-swollen seeds. This study demonstrates that cryogenic transmission electron microscopy is an excellent tool for mapping transient states within colloidal objects. Swelling of polymer particles and formation of liquid protrusions mediated by a surface coating on the seeds is explored for styrene and methyl-methacrylate at different temperatures and monomer-to-seed volume ratios.Graphical

Membrane Phase Drives the Assembly of Gold Nanoparticles on Biomimetic Lipid Bilayers.

In recent years, many efforts have been devoted to investigating the interaction of nanoparticles (NPs) with lipid biomimetic interfaces, both from a fundamental perspective aimed at understanding relevant phenomena occurring at the nanobio interface and from an application standpoint for the design of novel lipid–nanoparticle hybrid materials. In this area, recent reports have revealed that citrate-capped gold nanoparticles (AuNPs) spontaneously associate with synthetic phospholipid liposomes and, in some cases, self-assemble on the lipid bilayer. However, the mechanistic and kinetic aspects of this phenomenon are not yet completely understood. In this study, we address the kinetics of interaction of citrate-capped AuNP with lipid vesicles of different rigidities (gel-phase rigid membranes on one side and liquid-crystalline-phase soft membranes on the other). The formation of AuNP–lipid vesicle hybrids was monitored over different time and length scales, combining experiments and simulation. The very first AuNP–membrane contact was addressed through molecular dynamics simulations, while the structure, morphology, and physicochemical features of the final colloidal objects were studied through UV–visible spectroscopy, small-angle X-ray scattering, dynamic light scattering, and cryogenic electron microscopy. Our results highlight that the physical state of the membrane triggers a series of events at the colloidal length scale, which regulate the final morphology of the AuNP–lipid vesicle adducts. For lipid vesicles with soft membranes, the hybrids appear as single vesicles decorated by AuNPs, while more rigid membranes lead to flocculation with AuNPs acting as bridges between vesicles. Overall, these results contribute to a mechanistic understanding of the adhesion or self-assembly of AuNPs onto biomimetic membranes, which is relevant for phenomena occurring at the nano–bio interfaces and provide design principles to control the morphology of lipid vesicle–inorganic NP hybrid systems.

Fabrication of pH-degradable supramacromolecular microgels with tunable size and shape via droplet-based microfluidics

This study presents a versatile method to synthesize stimuli-responsive microgels with supramolecular cross-links exhibiting tunable size and shape via droplet-based microfluidics. The natural polyphenol tannic acid (TA) is used to cross-link poly(N-vinylcaprolactam) (PVCL) chains in aqueous droplets by the formation of hydrogen bonds and hydrophobic interactions between the phenolic groups of TA and the carbonyl group and the hydrophobic segments of lactam ring of PVCL chains. The obtained microgels exhibit diameters in the range of 130–150µm in swollen state in aqueous solution. Synthesized microgels exhibit pH-responsive behavior: at low pH microgels deswell and shrink due to the protonation of phenolic groups and enhanced hydrophobic interactions; at high pH microgels swell and disintegrate due to the deprotonation of phenolic groups and destruction of hydrogen bonds with PVCL chains. Additionally, we present supramacromolecular microgels in cylindrical shape with different aspect ratios using a new design of microfluidic chip by varying flow rates at high concentration of the prepolymerized precursor combined with rapid pH-triggered on-chip gelation. Furthermore, developed synthesis methodology allows on-chip encapsulation of colloidal objects into large supramacromolecular microgels during the cross-linking step. The complete and fast release of objects by pH-triggered degradation indicates that the pH-responsive supramacromolecular microgels can be used for controlled loading/release of various payloads, like probiotics. Moreover, cell studies of L929 fibroblast clearly show the biocompatibility of the microgels.

A two-step strategy for delivering particles to targets hidden within microfabricated porous media.

The delivery of small particles into porous environments remains highly challenging because of the low permeability to the fluids that carry these colloids. Even more challenging is that the specific location of targets in the porous environment usually is not known and cannot be determined from the outside. Here, we demonstrate a two-step strategy to deliver suspended colloids to targets that are "hidden" within closed porous media. The first step serves to automatically convert any hidden targets into soluto-inertial "beacons," capable of sustaining long-lived solute outfluxes. The second step introduces the deliverable objects, which are designed to autonomously migrate against the solute fluxes emitted by the targets, thereby following chemical trails that lead to the target. Experimental and theoretical demonstrations of the strategy lay out the design elements required for the solute and the deliverable objects, suggesting routes to delivering colloidal objects to hidden targets in various environments and technologies.

Sustainable Removal of Microplastics and Natural Organic Matter from Water by Coagulation-Flocculation with Protein Amyloid Fibrils.

Water contamination is a global threat due to its damaging effects on the environment and human health. Water pollution by microplastics (MPs), dissolved natural organic matter (NOM), and other turbid particles is ubiquitous in water treatment. Here, we introduce lysozyme amyloid fibrils as a novel natural bio-flocculant and explore their ability to flocculate and precipitate the abovementioned undesired colloidal objects. Thanks to their positively charged surface in a very broad range of pH, lysozyme amyloid fibrils show an excellent turbidity removal efficiency of 98.2 and 97.9% for dispersed polystyrene MPs and humic acid (HA), respectively. Additionally, total organic carbon measurements confirm these results by exhibiting removal efficiencies of 93.4 and 61.9% for purifying water from dispersed MPs and dissolved HA, respectively. The comparison among amyloid fibrils, commercial flocculants (FeCl3 and polyaluminumchloride), and native lysozyme monomers points to the superiority of amyloid fibrils at the same dosage and sedimentation time. Furthermore, the turbidity of pristine and MP-spiked wastewater and lake water decreased after the treatment by amyloid fibrils, validating their coagulation-flocculation performance under natural conditions. All these results demonstrate lysozyme amyloid fibrils as an appropriate natural bio-flocculant for removing dispersed MPs, NOM, and turbid particles from water.

Improving the Activity of DNA-Encoded Sensing Elements through Confinement in Silk Microcapsules.

Assembling synthetic bioparts into simplified artificial cells holds tremendous promise for advancing studies into the synthesis, biosensing, and delivery of biomolecules. Currently, the most successful techniques for encapsulation of the transcription-translation machinery exploit compartmentalization in liposomal vesicles. However, improvements to these methods may increase permeability to polar molecules, functionalization of the membrane with biologically active elements, and encapsulation efficiency. Microcapsules prepared via templated layer-by-layer (LbL) assembly using natural polymers have the potential to resolve some of the hurdles associated with liposomes. Here, we introduce a design for immobilizing DNA templates encoding translationally activated riboswitches and RNA aptamers into microcapsules prepared from regenerated silk fibroin protein. Adjusting several key parameters such as the presence of a polymer primer, concentration of silk protein, and DNA loadings during LbL assembly resulted in biocompatible, semipermeable, DNA-laden microcapsules. To preserve bioactivity, DNA was immobilized inside of the capsule membrane, which not only promoted stability during long-term storage at ambient conditions but also improved output response from spatially confined DNA-encoded sensing elements (SEs). Multiple copies of mRNA and GFPa1 protein were synthesized upon activation with specific analytes during in vitro transcription/translation reactions, demonstrating that selective permeability of silk microcapsules was essential for the diffusion of components of the cell-free system inside of the capsules. Further functionalization of capsule shells with gold nanoparticles (AuNPs) and antibodies (IgG) demonstrated the applicability of microcompartmentalized colloidal objects carrying SEs for remote sensing and/or targeted delivery. In the future, multifunctional, biocompatible silk-based microcapsules loaded with different RNA sensors can help advance the design of multiplexed biosensors tracking multiple biomarkers in complex media.

Surface‐Initiated Redox Route to Hollow MnO2 Nanostructures

AbstractNanostructured MnO2 are gaining great research interest because of their wide applications ranging from optical and electronic devices to energy storage and catalysis. However, the formation of a well‐defined MnO2 coating on the surface of various colloidal objects has been challenging due to surface incompatibility. Here, we report a unique and robust surface‐initiated redox route to the controlled deposition of MnO2 on colloidal particles, which can be employed to produce high‐quality hollow MnO2 nanoshells and a variety of MnO2 coated nanocomposites. Colloidal resorcinol formaldehyde (RF) resin spheres serve as both reducing agents and sacrificial templates to initiate the controlled deposition of MnO2 on their surfaces. Further, the RF resin can also be coated on the surface of other colloidal nanostructures to allow overcoating of MnO2 through the redox reaction and produce nanocomposites such as SiO2@MnO2 and Au@MnO2. The size and thickness of the MnO2 nanoshells can be tuned precisely to induce resonant Mie scattering, leading to bright colorations that can shift reversibly in response to the changes in the refractive index of the surroundings.

Аналог постоянной Планка для коллоидной системы

Based on the assumption of the instability of the colloidal state caused by the movement of charged particles, we previously obtained equations characterizing the structure of the colloid: a Schrödinger-type equation that defines the redistribution of thermal and potential energy in the colloid and a material equation – the diffusion equation with the Liesegang operator, which is connected directly with the substance, allowing find breaks in structures caused by vibrations of electrically charged particles. Such effects for colloidal chemical manifestations are called macroscopic quantum effects. That is, macroscopic quantum effects are a combination of phenomena in which the characteristic features of quantum mechanics are directly manifested in the behavior of macroscopic, for example, colloidal objects. As a rule, the behavior of macroscopic objects contains a large number of atoms and is described with high accuracy by the equations of classical physics, which do not include the characteristic quantum value – the constant bar. Based on the equations constructed by the authors, which are the equations of plasma hydrodynamics, a mathematical model is created that reduces the colloidal system to an equation similar to the Schrödinger equation and calculates a certain constant that is an analogue of the Planck constant for macroscopic colloidal systems and computes the constant of this equation , which is equal in magnitude . It differs significantly in magnitude from the Planck constant, because it characterizes the already complex macroscopic quantum oxyhydrate colloidal system.

Toward a Spatiotemporal Model of Oxidation in Lipid Dispersions: A Hypothesis‐Driven Review

AbstractUnsaturated lipids are prone to get oxidized through a sequence of reactions known as lipid oxidation. From a phenomenon considered at the beginning as a mere chemical process and described by the triptych of initiation, propagation, and termination, the vision of lipid oxidation has progressively evolved to further integrate the physical dimension of the phenomenon. Despite tremendous research efforts, however, this sequence of reactions is not yet well understood, especially in lipid dispersions where many facts are still inexplicable and unpredictable under the current paradigm. Here, the aim is to suggest that the main reason why a better understanding has not already been achieved is that the reactional network is not yet organized in a coherent spatiotemporal framework. The novel concepts and hypotheses proposed in this article may help redirecting a significant part of research efforts toward the establishment of a spatially and temporally resolved model of oxidation in dispersed lipids.Practical Application: Predicting how oxidation spreads in lipid dispersions represents a goal of crucial importance for academia but also for industry. Such prediction models would indeed greatly help food manufacturers prevent oxidation by using the most adapted antioxidative strategies for their specific products. To achieve such an objective, it is proposed that the first thing to do is to go beyond the extremely reductive and narrow framework in which this chemical process has been locked in. Indeed, while lipid dispersions are composed of a multitude of lipid colloids, researchers usually consider oxidation at the sole level of an individual droplet or membrane. Instead, lipid oxidation is advocated as a dynamic trafficking of chemical species within large communities of different colloidal objects such as droplets, membranes, or micelles dispersed in water—a system that dubbed “colloidal ecosystem”. This might represent a scale complementary to the scales of individual colloids or molecules that were the sole consideration so far to try to represent lipid oxidation. Only then can one hope to effectively apply modeling and “omics” approaches, as is explained in more details in this article.