In this review, we highlight and discuss the effects of interfacial properties on the major mechanisms governing the aging of emulsions: flocculation, coalescence and Ostwald ripening. The process of ...emulsification is also addressed, as it is well recognized that the adsorption properties of emulsifiers play an important role on it.
The consolidated background on these phenomena is briefly summarised based on selected literature, reporting relevant findings and results, and discussing some criticalities. The typical experimental approaches adopted to investigate the above effects are also summarised, underlining in particular the role of adsorption at the droplet interface. Attention is paid to different types of surface-active species involved with emulsion production, including solid particles. The latter being of increasing interest in a wide variety of emulsions-related products and technologies in various fields. The possibility to stop the long term aging caused by Ostwald ripening in emulsions is also discussed, quantifying under which conditions it may occur in practice.
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•The effects of interfacial properties on the main mechanisms underlying the aging of emulsions are reviewed.•Suitable methodological approaches for the investigations of these effects are discussed.•Procedures to account for the surfactant depletion of the continuous emulsion phase, caused by the adsorption at the droplet interface, are reported. The necessity to apply these corrections is discussed on the basis of previous experimental studies.•A criterion to assess the practical possibility to stabilise Ostwald ripening in emulsions, based on the sole dilational rheology is derived.
The pandemic emergency determined by the spreading worldwide of the SARS-CoV-2 virus has focused the scientific and economic efforts of the pharmaceutical industry and governments on the possibility ...to fight the virus by genetic immunization. The genetic material must be delivered inside the cells by means of vectors. Due to the risk of adverse or immunogenic reaction or replication connected with the more efficient viral vectors, non-viral vectors are in many cases considered as a preferred strategy for gene delivery into eukaryotic cells. This paper is devoted to the evaluation of the gene delivery ability of new synthesized
bis-pyridinium surfactants with six methylene spacers, both hydrogenated and fluorinated, in comparison with compounds with spacers of different lengths, previously studied. Results from MTT proliferation assay, electrophoresis mobility shift assay (EMSA), transient transfection assay tests and atomic force microscopy (AFM) imaging confirm that pyridinium
surfactants could be a valuable tool for gene delivery purposes, but their performance is highly dependent on the spacer length and strictly related to their structure in solution. All the fluorinated compounds are unable to transfect RD-4 cells, if used alone, but they are all able to deliver a plasmid carrying an enhanced green fluorescent protein (EGFP) expression cassette, when co-formulated with 1,2-dioleyl-sn-glycero-3-phosphoethanolamine (DOPE) in a 1:2 ratio. The fluorinated compounds with spacers formed by six (FGP6) and eight carbon atoms (FGP8) give rise to a very interesting gene delivery activity, greater to that of the commercial reagent, when formulated with DOPE. The hydrogenated compound GP16_6 is unable to sufficiently compact the DNA, as shown by AFM images.
We investigate the interfacial dynamics of a 2D self-organized mixed layer made of silica nanoparticles interacting with phospholipid (DPPC) monolayers at the air/water interface. This system has ...biological relevance, allowing investigation of toxicological effects of nanoparticles on model membranes and lung surfactants. It might also provide bio-inspired technological solutions, exploiting the self-organization of DPPC to produce a non-trivial 2D structuration of nanoparticles. The characterization of interfacial dynamics yields information on the effects of NPs on the mechanical properties, important to improve performances of systems such as colloidosomes, foams, creams. For this, we combine micro-tracking in real-space with measurement in momentum-space via x-ray photon-correlation spectroscopy and Digital Fourier Microscopy. Using these complementary techniques, we extend the spatial range of investigation beyond the limits of each one. We find a dynamical transition from Brownian diffusion to an arrested state driven by compression, characterized by intermittent rearrangements, compatible with a repulsive glass phase. The rearrangement and relaxation of the monolayer structure results dramatically hindered by the presence of NPs, which is relevant to explain some the mechanical features observed for the dynamic surface pressure response of these systems and which can be relevant for the respiratory physiology and for future drug-delivery composite systems.
This review focuses on recent results obtained by synchrotron X-ray techniques applied to the characterization of interfacial systems, with main emphasis on flat interfaces and on colloidal systems. ...The techniques covered are, for structural determinations: X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and grazing incidence X-ray excited fluorescence (GIXF), while dynamics are investigated by X-ray photon correlation spectroscopy (XPCS) mainly in the grazing-incidence geometry (GIXPCS).
The systems reviewed are, in order of growing complexity, floating Langmuir monolayers, supported films of lipids and proteins, polymeric films, buried interfaces, colloidal systems and gels formed by colloids either in 3D or in the form of 2D interfacial layers. Recent results are critically discussed, and some interesting directions of development are outlined, having also in mind new technical developments such as X-ray free electron laser sources and micro-focused synchrotron beamlines.
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•This is a review of recent results obtained in the last years by synchrotron radiation.•Techniques: reflectivity (XRR) grazing incidence diffraction (GIXRD) fluorescence (GIXF) photon correlation (XPCS, GI-XPCS)•Systems: floating Langmuir monolayers, supported films, gels and colloids either in 3D or as 2D interfacial layers
The development of very efficient and safe non-viral vectors, constituted mainly by cationic lipids bearing multiple charges, is a landmark for in vivo gene-based medicine. To understand the effect ...of the hydrophobic chain's length, we here report the synthesis, and the chemico-physical and biological characterization, of a new term of the homologous series of hydrogenated
bispyridinium surfactants, the 1,1'-bis-dodecyl-2,2'-hexane-1,6-diyl-bispyridinium chloride (GP12_6). Moreover, we have collected and compared the thermodynamic micellization parameters (cmc, changes in enthalpy, free energy, and entropy of micellization) obtained by isothermal titration calorimetry (ITC) experiments for hydrogenated surfactants GP12_6 and GP16_6, and for the partially fluorinated ones, FGP
(where
is the spacer length). The data obtained for GP12_6 by EMSA, MTT, transient transfection assays, and AFM imaging show that in this class of compounds, the gene delivery ability strictly depends on the spacer length but barely on the hydrophobic tail length. CD spectra have been shown to be a useful tool to verify the formation of lipoplexes due to the presence of a "tail" in the 288-320 nm region attributed to a chiroptical feature named ψ-phase. Ellipsometric measurements suggest that FGP6 and FGP8 (showing a very interesting gene delivery activity, when formulated with DOPE) act in a very similar way, and dissimilar from FGP4, exactly as in the case of transfection, and confirm the hypothesis suggested by previously obtained thermodynamic data about the requirement of a proper length of the spacer to allow the molecule to form a sort of molecular tong able to intercalate DNA.
A procedure for the optimization of a 3C–SiC buffer layer for the deposition of 3C–SiC/(001) Si is described. After a standard carbonization at 1125°C, SiH4 and C3H8 were added to the gas phase while ...the temperature was raised from 1125°C to the growth temperature of 1380°C with a controlled temperature ramp to grow a thin SiC layer. The quality and the crystallinity of the buffer layer and the presence of voids at the SiC/Si interface are related to the gas flow and to the heating ramp rate. In order to improve the buffer quality the SiH4 and C3H8 flows were changed during the heating ramp. On the optimized buffer no voids were detected and a high-quality 1.5μm 3C–SiC was grown to demonstrate the effectiveness of the described buffer.
•A procedure for the optimization of a 3C–SiC buffer layer for the deposition of 3C–SiC/(001) Si is presented.•Buffer layer quality and voids at interface depends on the gas flow and heating ramp rate. Lower ramp heating rate yield the best results.•On the optimized buffer very few density of voids were detected.•High-quality 1.5μm 3C–SiC was grown to demonstrate the effectiveness of the described buffer.
Controlled phase separation in a polymer film, with subsequent morphology rearrangement on the micro-scale, provides novel perspectives in smart materials. Based on our experience on supramolecularly ...compatibilised polymer blends consisting of polystyrene and poly(butyl methacrylate), we demonstrate here physical segregation of the blend in the solid state by the application of an electrochemical stimulus. The thereby occurring changes in film morphology, namely the appearance of voids and grains, have been characterised by atomic force microscopy in spin coated and in Langmuir-Schaefer deposited films.
We present an overview of recent advances in stimuli-responsive nanostructures for medicine and drug delivery aiming at improving the efficacy and minimizing side effects of cancer therapies. We ...focus on two complementary system: Self-Lighted Photodynamic Therapy (SLPDT), and magnetic systems for hyperthermia and for controlled drug release. SPLDT, also known as X-ray triggered PDT, bases on hybrid nanostructures such as functionalized SiC/SiOx nanowires and CeF3/ZnO nanostructures. We emphasize the importance of discriminating the various Reactive Oxygen Species (ROS) produced, i.e., singlet oxygen, peroxide, superoxide, and hydroxyl radicals, which have different effects on cells and different therapeutic efficacy. Singlet oxygen is quantified by an ad hoc NIR fluorimeter. SLPDT can be usefully complemented by smart systems responsive to magnetic fields. As examples, we discuss the use of superparamagnetic iron oxide nanoparticles for magnetic hyperthermia and magnetic nanocapsules for triggered drug release. Finally, we highlight promising directions for future developments.
Complex interfaces, such as vesicles and biological membranes, and interface-dominated systems, such as foams and emulsions, are central to a vast range of naturally occurring and synthetic ...materials. In order to characterize their dynamics, it is necessary to cover a wide range of length and time scales. This can only be done by a combination of different techniques. We review here recent results and discuss new trends focusing on two class of techniques: correlation spectroscopies and microscopies, highlighting some examples of their combined use.
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•In complex interfaces and interface-dominated systems, dynamics impact a wide range of technologies.•To characterize dynamics, a combination of techniques spanning a large range of space and time scales is needed.•Synergy between microscopy, direct accessing dynamics, and spectroscopy, which is superior in terms of statistics.•New results expected from the application of optical Monte Carlo methods to DWS.•New results expected from upcoming coherent x-ray beams (upgraded synchrotrons, XFELs) accessing fast dynamics.•A wealth of new microscopy techniques recently developed, thanks to new fast image processing hardware and software.
The control of the behavior of oil in water emulsions requires deeper investigations on the adsorption properties of the emulsion stabilizers at the interfaces, which are fundamental to explain the ...(de)stabilization mechanisms. In this work, we present an extensive study on oil-in-water emulsions stabilized by sodium dodecyl sulfate (SDS) below its critical micellar concentration. Dynamic tensiometry, dilational rheology, and electrical conductivity measurements are used to investigate the adsorption properties at the droplet interface, whereas the aging of the respective emulsions was investigated by monitoring the macroscopic thickness of the emulsion layer, by microimaging and dynamic light scattering (DLS) analysis, to get information on the drop size distribution. In addition, the droplet coalescence is investigated by a microscopy setup. The results of this multitechnique study allow deriving a coherent scenario where the adsorption properties of this ionic surfactant relate to those of the emulsion, such as, for example, the prevention of droplet coalescence and the presence of other mechanisms, such as Ostwald ripening, responsible for the emulsion aging.
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