Current Opinion in Colloid & Interface Science最新文献

The membrane of Gram-negative bacteria (GNB) is especially robust due to the additional, unique, highly asymmetric outer membrane, with lipopolysaccharides (LPSs) as the main component. This LPS layer serves as a protective barrier against antibiotics, host immune responses, and other environmental stresses. However, constructing model membranes containing LPS that capture the structural asymmetry for fundamental studies of the GNB cell wall remains an open challenge. In this context, we discuss how recent physicochemical studies of Langmuir monolayers incorporating LPS help us better understand the elastic properties and structural integrity of model LPS bacterial membranes. The classic Langmuir–Blodgett trough has been used to reveal different lipid phase behaviors of monolayers containing LPS mutants with different molecular architectures to mimic the outer leaflet of the GNB outer membrane, shedding light on the underpinning molecular interactions. Permeation and penetration of antimicrobial peptides are shown to alter the viscoelastic properties of LPS monolayers. The LPS-containing Langmuir monolayer can also be transferred to a substrate as the outer leaflet of an asymmetric solid-supported bilayer, and we will discuss the limitations and potential optimization of this method. Finally, we highlight how different physicochemical methods can corroborate and contribute to unravelling the structural characteristics of model bacterial membranes.

Microbubble dispersions are now commonly deployed in industrial applications ranging from bioprocesses to chemical reaction engineering, at full scale. There are five major classes of microbubble generation devices that are scalable. In recent years, some of these approaches have been explicitly studied for the influence of wetting properties on microbubble performance, for which the major proxy is the bubble-size distribution. In this piece, the methodologies for inferring bubble-size distribution are explored, with several recent advances as well as their potential pitfalls. Subsequently, studies where microbubble generation has been under investigation for wetting effects are assessed and in some cases, those that were not allowed the deduction that wetting is a significant factor. Two particular studies are highlighted: (i) systematic variation of wetting effects within a venturi with removable walls substituted with coated walls of known contact angle with hydrodynamic cavitation induced microbubbles and (ii) variation of ionic liquids with staged fluidic oscillation before steady flow. The first study shows that even in scenarios where high inertial effects would be expected to dominate, wetting influences are significant. The second study shows that transient effects are strongly influenced by both imbibition into pores and surface wetting but that viscous resistance is always a key factor. From the exploration of these recent studies, specific recommendations are made about how to assess the influence of wetting in those mechanisms/devices where it has not been explicitly studied, via deduction from those mechanisms/devices where the effects are demonstrably significant and indeed in some cases, controlling. In study (ii), which is the first to blow micro/bubbles into ionic liquids, wetting and transient effects are reasonable for between 25% and 50% reduction in average bubble size, although up to 70% reduction is observable when viscous effects are dominant, relative to the control of steady flow with the same pressure drop. Indeed, staging transient operations shows both bubble-size reduction and increased volumetric throughput are simultaneously possible.

The wetting and dewetting of solid surfaces is ubiquitous in physical systems across a range of length scales, and it is well known that there are maximum speeds at which these processes are stable. Past this maximum, flow transitions occur, with films deposited on solids (dewetting) and the outer fluid entrained into the advancing one (wetting). These new flow states may be desirable, or not, and significant research effort has focused on understanding when and how they occur. Up until recently, numerical simulations captured these transitions by focussing on steady calculations. This review concentrates on advances made in the computation of the time-dependent problem, utilising dynamical systems theory. Facilitated via a linear stability analysis, unstable solutions act as ‘edge states’, which form the ‘point of no return’ for which perturbations from stable flow cease decaying and, significantly, show the system can become unstable before the maximum speed is achieved.

In surfactant solutions, the bulk hydrodynamic flow couples to extensional/compressional surface flows due to Marangoni stresses induced at the interface. With the increasing surfactant concentration, these Marangoni stresses can suppress the surface flows and lead to non-moving, retarded, surfaces. We review this phenomenon with special focus on the dynamic dewetting of a substrate pulled out of a pool of surfactant solution. In this case, the dewetting meniscus surface can be retarded (fully or partially) because of the appearance of surface tension gradients opposing the flow in the adjacent liquid. With an increasing flow velocity, the non-uniformity of the meniscus surface becomes stronger resulting in its separation on a mobile and an immobile part with a sharp transition between them. The presence of a non-uniform adsorption layer at the meniscus surface strongly complicates the dewetting dynamics which becomes dependent on the surfactant balance at the surface.

Neutron scattering techniques provide detailed information on the structure of and dynamics occurring within materials across multiple length and time scales. When combined with traditional characterisation techniques used in food materials science, they can generate unique insight and understanding that can assist in the development of new and improved ingredients and formulations. This review describes recent examples of the application of neutron scattering techniques across a broad range of food hydrocolloids as well as outlining future opportunities in the field.

Lyotropic non-lamellar liquid crystalline (LLC) nano-self-assemblies (including cubosomes and hexosomes) are attractive versatile platforms for the encapsulation and delivery of drugs and nutritional molecules. This is due to their unique structural features and architectural arrangements that afford loading of small molecules and macromolecules having different physicochemical properties with high efficiency. Considering the reported health-promoting effects of long-chain omega-3 polyunsaturated fatty acids (ω-3 PUFAs) and their precursors ω-3 PUFA monoacylglycerols; here, we focus on physicochemical and biological properties of a new family of non-lamellar LLC nanoparticles assembled either from binary mixtures of phosphatidylglycerol and three types of ω-3 PUFAs, or from single ω-3 PUFA monoacylglycerols. We discuss recent progress in understanding their complexity, pH sensitivity, and structural tunability, as well as highlight their potential applications in health and medicine.

Wetting plays a crucial role in achieving efficient condensation in applications such as atmospheric water harvesting, air conditioning and refrigeration, and thermal power plants. Despite decades of research, the industrial implementation of dropwise condensation, which is often superior to filmwise condensation, has been limited, mostly due to the poor durability of promoter coatings and the challenge of achieving dropwise condensation for non-aqueous working fluids. Both areas have seen noteworthy advancements over the past few years, some of which we highlight in this review article. For example, recognizing that contact angle hysteresis, not contact angles per se, are responsible for enabling dropwise condensation, ultra-smooth liquid-like polymer coatings and lubricant-infused surfaces were developed for use with water and non-aqueous working fluids. There are also several new developments for passive and active droplet removal. Advances in coating durability include a better understanding in the failure mechanisms and physics-informed designs of new coating processes and chemistries.

Wetting of solid surfaces by liquid deposition, contact dispensing, drop transfer, collision of wet particles, or during coating processes is often accompanied by the formation of liquid bridges between two or more solid substrates. They appear in many applications, like material science, microfluidics, biomedical, chemical, or aerospace engineering, and different fields of physics. In this study, the flows accompanying lifting of a Hele-Shaw cell, stretching or shearing of a liquid bridge, as well as liquid bridge flows observed during printing processes and other important applications, are briefly reviewed. Such flows are governed by surface tension, inertia, stresses associated with the liquid rheology, and forces caused by the substrate's wettability. Instabilities of liquid bridges lead to the formation of finger-like structures on the substrate or the appearance of cavities at the wetted region of the wall. The time required for jet pinch-off also determines the residual liquid volume on both solid bodies.

In recent years, a growing understanding of the underlying mechanisms of autoinflammatory and autoimmune disease has enabled significant advances in biomaterial therapeutics for their treatment and prevention. Drug-free or immune-active polymeric materials are of particular interest due to their chemical tunability, multifaceted mechanisms of action, and potential to offer alternatives to conventional treatments. While in many cases the relationships between polymer physicochemical properties and the immune processes they influence are context-dependent and require further clarity, several concepts are emerging that can be applied in the design of anti-inflammatory materials. This review highlights recent work that investigates these relationships, as well as work that applies them to immunomodulatory biomaterials for the treatment or prevention of autoimmune and autoinflammatory diseases.

Protein nanocages used as emulsion stabilizing colloidal particles are opening possibilities to the design of novel delivery systems for food, pharmaceutical and cosmetic applications. Protein nanocage-stabilized emulsions are able to co-deliver hydrophilic and hydrophobic compounds. The surface chemistry of the particles is one of the factors that determines their ability to stabilize the emulsion. Hence, the importance in developing strategies to rationally tailor the nanocage surface chemistry. This contribution summarizes recent advances in protein nanocage Pickering emulsions and the methods used to modify the nanocages. It discusses future strategies that may allow the modification of protein nanocages based on current knowledge of Pickering emulsions and protein nanocage engineering technology. The characterization methods for the investigation of these protein nanocages and nanocage stabilized emulsions are described. Finally, the applications of protein nanocages for nutrient delivery in the gastrointestinal tract will be discussed. This contribution provides a perspective for future work on protein nanocage stabilized emulsions.