Soft colloids have recently attracted great attention both in fundamental studies and applications thanks to their deformability, elasticity and interpenetrable nature, providing a very rich phenomenology. Among soft colloids, microgels, particles composed of chemically crosslinked polymer networks, are very enthralling due to their hybrid nature which combines the properties of polymers and colloids. Herein we focus on a colloidal suspension of poly(N-isopropylacrylamide) (PNIPAM) microgel [1] and on colloidal suspensions of interpenetrated polymer network (IPN) microgels made of PNIPAM and poly(acrylic acid) (PAAc) [2]. PNIPAM microgels change their affinity with the solvent as the temperature changes; the addition of the second network of PAAc makes IPN microgels sensitive also to pH. Moreover, these systems undergo to a phase transition passing from a liquid to an arrested state as a function of concentration. The study aims to verify the influence that different contents of N,N'-methylbisacrylamide (BIS), the crosslinker used to polymerize the PAAc network, have on the swelling behaviour, the dynamics and the viscoelastic properties of the systems. To this purpose, concentration, temperature and pH-dependence of the dynamic of four different IPN microgel solutions is carefully investigated through Dynamic Light Scattering (DLS) and rheology. The swelling behaviour of PNIPAM and IPN microgels is also studied performing molecular dynamics simulations. This in silico study on microgel particles is divided in three phases. As a first step the swelling behaviour of a microgel particle composed of single-network is studied. Then it is analysed how the swelling capability is affected by the introduction of a second neutral interpenetrated network that does not respond to temperature changes. Eventually the effects that a second charged network introduces on the swelling is investigated. Both experimental and simulation data allow to conclude that the different concentrations of BIS have a strong effect on the swelling capability of IPN microgels and on the softness of their structure. Particularly a higher concentration of BIS reduces the swelling capability of microgels particles as a function of temperature. Moreover, also the slowing down of the dynamics up to the formation of an arrested state is influenced by the BIS concentration. Results suggest that a higher concentration of BIS shifts the transition to an arrested state to higher concentrations of IPN solutio ns. These findings open the way to further investigation on the role that topological constrains have on the interactions between microgel particles and how they influence the transition to arrested states.

Modifying bitumens to improve their characteristics is one of the ways to increase road pavement durability reducing maintenance costs and environmental issues. In this study the structural and mechanical characteristics of a 50/70 bitumen modified by two different char samples are presented. The choice of char as bitumen modifier fulfils the recent needs for environmental protection. The two char samples come from the pyrolysis of Refuse Derived Fuel (RDF) and waste tyres (WT), respectively. They differ in composition and morphology and their production took place with different yields. Char-modified bitumens revealed increased shear modulus and resistance to mechanical stress as found by rheometry. Artificial aging of these char-modified bitumens unveiled that the bitumen modified by char from WT (WT-char) possessed a certain resilience against aging, with a reduced increase in rigidity upon aging. The anti-aging effect showed by WT-char was attributed to its higher carbon content, which confers higher compatibility with the bitumen chemical nature and presumably a more uniform dispersion within the bituminous structure thanks to the establishment of more effective interactions.

In its many applications, the Atomic Force Microscope (AFM) is a promising tool in cardiac mechanobiology because it can unravel the viscoelastic and mechano-dynamic properties of individual cardiomyocytes. However, the biophysical investigation of more accurate 3D models is hampered by commercial probes, which typically operate at the cell sub-compartmental resolution. We have previously shown how flat macro-probes can over-come these limitations by extending the AFM mechanical measurements to multicellular aggregates. Such macro-probes are fabricated by standard micromachining and carry a flat polymeric wedge to offset the AFM mounting tilt. Therefore, the AFM is upgraded to a micro-parallel plate rheometer with unmatched force range and sensitivity. In this article, we show how these macro-probes can be applied to reveal the global rheology of primary cardiomyocytes spheroids, by performing stress-relaxation tests. More importantly, we demonstrate that these macro-probes can be used as passive sensors capable of monitoring the spheroid beating force and beating pattern, and to perform a "micro-CPR" on the spheroid itself.

The rheology of the polymer matrix plays a crucial role in determining the quality of thermoplastic laminates. To highlight this aspect, we prepared laminates based on polyamide 11 (PA11), a bio-based matrix with tricky rheology, and basalt fiber fabrics. The PA11 viscosity rapidly increases over time due to degradation phenomena. Samples were prepared by two procedures differing in terms of duration and intensity of the hot compaction step. Morphological analyses revealed that the fast procedure ensures a better impregnation of the fabrics, with a substantial reduction of the volume of voids (1%, against 9% of the slow procedure). This reflects in considerable increases of the flexural modulus (ca. + 20%) and strength (ca. + 60%) and a significant reduction the extent of impact damage. This study provides useful guidelines for a correct selection of the processing parameters based on the knowledge of the rheological behavior of the polymer matrix.

Oleogels are a class of solid-fat mimetics that contain a large fraction of oil. Most of these materials have low stiffness and poor oil-binding capacity at commercially viable concentrations, which limits their application in the food and cosmetic industries. To improve their mechanical behavior, we exploited the concepts of particulate-filled materials by developing oil-continuous monoglyceride composites reinforced with crystalline cellulose of various sizes. Cellulose was used as the reinforcing filler material due to its strength, biodegradability, and abundance. The composites gradually stiffened and became more brittle with a progressive increase of the cellulose weight fraction as the maximum packing fraction of fillers approached. This was manifested as an increase in the viscoelastic moduli and yield stress, consistent with the size of the filler. Based on differential scanning calorimetry, X-ray diffraction, X-ray scattering analyses, and microscopic analyses, the inert surface of crystalline celluloses provided a solid substrate for the crystallization of monoglycerides, favoring the lamellar stacking of monoglyceride molecules during the composite oleogel formation regardless of the cellulose size. The present study suggests that cellulose is a suitable bio-based filler material to obtain mechanically strong oleogels suitable for high-shear applications e.g., in food and pharmaceutical industries.

We present mesoscale numerical simulations of Rayleigh-Bénard (RB) convection in a two-dimensional model emulsion. The systems under study are constituted of finite-size droplets, whose concentration is systematically varied from small (Newtonian emulsions) to large values (non-Newtonian emulsions). We focus on the characterisation of the heat transfer properties close to the transition from conductive to convective states, where it is well known that a homogeneous Newtonian system exhibits a steady flow and a time-independent heat flux. In marked contrast, emulsions exhibit non-steady dynamics with fluctuations in the heat flux. In this paper, we aim at the characterisation of such non-steady dynamics via detailed studies on the time-averaged heat flux and its fluctuations. To quantitatively understand the time-averaged heat flux, we propose a side-by-side comparison between the emulsion system and a single-phase (SP) system, whose viscosity is suitably constructed from the shear rheology of the emulsion. We show that such local closure works well only when a suitable degree of coarse-graining (at the droplet scale) is introduced in the local viscosity. To delve deeper into the fluctuations in the heat flux, we furthermore propose a side-by-side comparison between a Newtonian emulsion (i.e., with a small droplet concentration) and a non-Newtonian emulsion (i.e., with a large droplet concentration), at fixed time-averaged heat flux. This comparison elucidates that finite-size droplets and the non-Newtonian rheology cooperate to trigger enhanced heat-flux fluctuations at the droplet scales. These enhanced fluctuations are rooted in the emergence of space correlations among distant droplets, which we highlight via direct measurements of the droplets displacement and the characterisation of the associated correlation function. The observed findings offer insights on heat transfer properties for confined systems possessing finite-size constituents.

The phase behaviour of soft colloids has attracted great attention due to the large variety of new phenomenologies emerging from their ability to pack at very high volume fractions. Here we report rheological measurements on interpenetrated polymer network microgels composed of poly(Nisopropylacrylamide) (PNIPAM) and polyacrylic acid (PAAc) at fixed PAAc content as a function of weight concentration. We found three different rheological regimes characteristic of three different states: a Newtonian shear-thinning fluid, an attractive glass characterized by a yield stress, and a jamming state. We discuss the possible molecular mechanisms driving the formation of these states.

BaCe0.65Zr0.20Y0.15O3-8-Ce0.85Gd0.15O2-8 (BCZ20Y15-GDC15) is currently one of the most studied composites for applications as dense ceramic membranes for H-2 purification and membrane reactors. However, the efficiency of the structure represents a crucial issue to be solved for its practical uses. In this work the optimization of suitable slurries for the manufacturing of green asymmetric BCZ20Y15-GDC15 structures by mu-extrusion 3D-printing was investigated. The effect of the composition and rheological behavior on the stability and printability of the slurries was evaluated. Then, optimized slurries with different solid content were printed by a home-made mu-extrusion 3D printer through a step by step process: smooth and defect-free as-printed asymmetric structures with planar architecture were obtained. (c) 2020 Elsevier B.V. All rights reserved.

We investigate the rheology of strain-hardening spherical capsules, from the dilute to the concentrated regime under a confined shear flow using three-dimensional numerical simulations. We consider the effect of capillary number, volume fraction and membrane inextensibility on the particle deformation and on the effective suspension viscosity and normal stress differences of the suspension. The suspension displays a shear-thinning behaviour that is a characteristic of soft particles such as emulsion droplets, vesicles, strain-softening capsules and red blood cells. We find that the membrane inextensibility plays a significant role on the rheology and can almost suppress the shear-thinning. For concentrated suspensions a non-monotonic dependence of the normal stress differences on the membrane inextensibility is observed, reflecting a similar behaviour in the particle shape. The effective suspension viscosity, instead, grows and eventually saturates, for very large inextensibilities, approaching the solid particle limit. In essence, our results reveal that strain-hardening capsules share rheological features with both soft and solid particles depending on the ratio of the area dilatation to shear elastic modulus. Furthermore, the suspension viscosity exhibits a universal behaviour for the parameter space defined by the capillary number and the membrane inextensibility, when introducing the particle geometrical changes at the steady state in the definition of the volume fraction.

Lipid layers are considered among the first protective barriers of the human body against pollutants, e.g., skin, lung surfactant, or tear film. This makes it necessary to explore the physico-chemical bases underlying the interaction of pollutants and lipid layers. This work evaluates using a pool of surface-sensitive techniques, the impact of carbon black and fumed silica particles on the behavior of Langmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The results show that the incorporation of particles into the lipid monolayers affects the surface pressure-area isotherm of the DPPC, modifying both the phase behavior and the collapse conditions. This is explained considering that particles occupy a part of the area available for lipid organization, which affects the lateral organization of the lipid molecules, and consequently the cohesion interactions within the monolayer. Furthermore, particles incorporation worsens the mechanical performance of lipid layers, which may impact negatively in different processes presenting biological relevance. The modification induced by the particles has been found to be dependent on their specific chemical nature. This work tries to shed light on some of the most fundamental physico-chemical bases governing the interaction of pollutants with lipid layers, which plays an essential role on the design of strategies for preventing the potential health hazards associated with pollution.

Fractal analysis can be properly applied to complex structures, like physical and chemical networks formed by particles or polymers, when they exhibit self-similarity over an extended range of length scales and, hence, can be profitably used not only for their morphological characterization but also for individuating possible relationships between morphology and mechanisms of aggregation and crosslinking, as well as between morphology and physical properties. Several experimental methods are available to determine the fractal dimension of gel networks, including various scattering techniques and microscopies, permeability measurements and rheology. The present study regards the self-assembly kinetics of High Methoxyl Pectin (HMP) solutions with different pectin and sucrose concentrations investigated by rheological measurements to highlight the effects of pectin and sucrose concentrations on the gel point and to evaluate the degree of compactness of the incipient gel networks through an interpretation of the viscoelastic response at the sol-gel transition

Hypothesis: Multi-component supramolecular hydrogels are gaining increasing interest as stimuli-responsive materials. To fully understand and possibly exploit the potential of such complex systems, the hierarchical structure of the gel network needs in-depth investigations across multiple length scales. We show that a thorough structural and rheological study represents a crucial pillar for the exploitation of this class of functional materials. Experiments: Supramolecular hydrogels are prepared by self-assembly of hexadecyltrimethylammonium bromide (CTAB) and azobenzene-4,4?-dicarboxylic acid (AZO) in alkaline aqueous solution. The CTAB/AZO concentration was varied from ? = 0.25 to 4 wt% keeping the CTAB:AZO molar ratio fixed at 2:1. The systems were thoroughly studied through a combination of X-ray scattering, microscopy, rheological and spectroscopic analyses. Findings: The CTAB/AZO solutions form a self-supporting gel with nanofibrillar structure below ~30 °C. The critical gelation concentration is ? = 0.45 wt%. Above this threshold, the gel elasticity and strength increase with CTAB/AZO content as ~(?-?). The hydrogels exhibit self-healing ability when left at rest after a stress-induced damage. Moreover, the light-induced isomerization of the AZO moieties provides the gel with light-responsiveness. Overall, the multi-stimuli responsiveness of the studied CTAB/AZO hydrogels makes them a solid starting point for the development of sensors for mechanical vibrations and UV/visible light exposure.

The rheology of pressure-driven flows of two-dimensional dense monodisperse emulsions in neutral wetting microchannels is investigated by means of mesoscopic lattice Boltzmann simulations, capable of handling large collections of droplets, in the order of several hundreds. The simulations reveal that the fluidization of the emulsion proceeds through a sequence of discrete steps, characterized by yielding events whereby layers of droplets start rolling over each other, thus leading to sudden drops of the relative effective viscosity. It is shown that such discrete fluidization is robust against loss of confinement, namely it persists also in the regime of small ratios of the droplet diameter over the microchannel width. We also develop a simple phenomenological model which predicts a linear relation between the relative effective viscosity of the emulsion and the product of the confinement parameter (global size of the device over droplet radius) and the viscosity ratio between the disperse and continuous phases. The model shows excellent agreement with the numerical simulations. The present work offers new insights to enable the design of microfluidic scaffolds for tissue engineering applications and paves the way to detailed rheological studies of soft-glassy materials in complex geometries.

Mucus is a biomaterial with peculiar, gel-like viscoelastic properties, and bearing different functionalities, depending on the different mucosae it covers. It is clear that these functionalities have to stay effective throughout the in vivo broad range of physiological pH values at which the mucus is exposed. We sought here to determine the effect of pH on the rheological properties of ex vivo mucus. We demonstrate that viscoelastic properties of gastric mucus are quite "stable" to pH changes, in marked contrast with the pH sensitivity of purified mucin gels. We also find that the rheological features of porcine gastric mucus are reversible when the system is first alkalized up to solubilization (pH > 8.5) and then re-acidified to its initial pH value.

Agar is a natural polymer commonly used in various fields of application ranging from cosmetics to the food industry. In particular, for over forty years agar gels have been used in the field of conservation of Cultural Heritage where they are considered as one of the main well-performing tools in cleaning procedures. In the present work, the relation between the chemical composition and the mechanical strength of four different agar hydrogels was evaluated by comparing the results obtained via pyrolysis-gas chromatography/mass spectrometry and rheological characterization. Agar composition was studied by means of a pyrolysis-gas chromatography/mass spectrometry approach in order to differentiate the anhydrous, galactose and glucose units. Pristine agar gels, gels after double annealing, and gels with and without chelating agent were studied by means of amplitude, frequency and time sweep rheological tests to evaluate all the preparation approaches commonly used by conservators, also taking into account changes in the transparency via UV-vis spectroscopy. A high percentage of anhydrous units in the polymer backbone was found to provide superior mechanical stiffness to the pristine hydrogels, even if it did not seem to affect their long-term stability. The annealing process significantly improved the rheological response of galactose-rich agar hydrogels being able to promote the establishment of additional crosslinking points, whereas the additive presence showed to improve the hydrogel stiffness owing to a more structured polymer network. Moreover, the progressive reduction of the impurities and/or network defects within the hydrogels occurring due to the annealing process slightly increased the transparency of the hydrogels, which is an important aspect for applications in the conservation of Cultural Heritage.

We employ Diffusing Wave Spectroscopy (DWS) to characterize microscopic structure, internal dynamics and rheological properties of a paradigmatic emulsion formed by water and dodecane stabilized by the anionic surfactant Sodium Dodecyl Sulfate (SDS). We focus on ageing and stability in the regime of low surfactant concentration, well below the Critical Micellar Concentration (CMC). In the long-time ageing regimes differentiate in stable and unstable, depending on surfactant concentration. For the stable case, ageing affects the dynamics following a power law with an exponent independent on surfactant concentration, presumably related to the late stages of the water drainage process. On the contrary, at constant ageing, the dependence of the dynamics from surfactant concentration shows a slowdown, corresponding to a maximum in the bulk shear mechanical modulus, around [SDS]=2mM which is reminiscent of a similar maximum found by drop tensiometry in the dilational modulus of the single interface. This suggests a consistent picture of the mechanisms (de)stabilizing the emulsion, explained in terms of elementary process at the interface. These results show furthermore that DWS can be a reliable diagnostic for the study of the aging and of the mechanical properties of concentrate emulsions. This might be relevant to control stability of emulsions when a low concentration of surfactant is desired, e.g. for economical or environment reasons.

Lung surfactant is a complex mixture of lipids and proteins which plays a major role in the respiratory cycle. This makes necessary to understand the effects of different external factors or agents, for example, inhaled particles, as a potential source of alteration of the normal physiological response of lung surfactant. However, in most cases, in vivo studies are difficult to perform, and preliminary studies based in model systems are required. Films of lipids or mixtures of lipids and proteins at the water-vapor interface are accounted as one of the most useful methodologies for initial assessments of the potential toxicity of inhaled particles. Thus, the study of the modifications induced by the incorporation of colloidal particles in the interfacial properties of layers mimicking some of the physicochemical features of lung surfactant might provide a first evaluation of the risks and hazards associated with the inhalation of particulate matter. Considering the importance of particles in technology and industry, it is mandatory to develop strategies providing information about toxicological aspects of these widespread materials. This review focuses its interest on the recent advancements on the application of studied bases on monolayers at the fluid interface as preliminary assay for deepening on a complex situation with biological interest.

The aim of this research is to deepen the knowledge of the role of friction on the dynamics of granular media; in particular the friction angle is taken into consideration as the physical parameter that drives stability, motion and deposition of a set of grains of any nature and size. The idea behind this work is a question: is the friction angle really that fundamental and obvious physical parameter which rules stability and motion of granular media as it seems from most works which deal with particle dynamics? The experimental study tries to answer this question with a series of laboratory tests, in which different natural and artificial granular materials have been investigated in dry condition by means of a tilting flume. The characteristic friction angles, both in deposition (repose) and stability limit (critical) conditions, were measured and checked against size, shape, density and roughness of the considered granular material. The flume tests have been preferred to "classical" geotechnical apparatuses (e.g. shear box) since the flume experimental conditions appear closer to the natural ones of many situations of slope stability interest (e.g. a scree slope). The results reveal that characteristic friction angles depend on size and shape of grains while mixtures of granules of different size show some sorting mechanism with less clear behaviour.

In this paper, the role of solvent characteristics on the rheological and physicochemical properties of organogels was investigated using different techniques. Vegetable oils, such as rice, sunflower and castor oil were used as solvents, for producing organogels with monoglycerides of fatty acids or a mixture of fatty alcohols (policosanol) as gelators. Moreover, two non-edible oils (silicon and paraffin oil) were also used for analysing the properties of solvents completely different in nature with respect to the edible ones, for a better interpretation of the given results. Organogels were investigated from a rheological point of view and through a microscopic analysis, given by polarised light (POM) and atomic force (AFM) microscopy, and X-rays to study the crystallinity of the system. The IR technique was used to analyse the intermolecular interactions, resulting in interesting information about the effect of oil polarity on the driving forces promoting structuration. This investigation showed that when solvents of a similar chemical nature are used, their physical properties, mainly oil polarity, are strictly related to the properties of the organogel, such as the onset of crystallisation temperature, the stiffness of the final material and its crystallinity. Anyway, these physical parameters seem insufficient to describe properly the role of solvents when oils of a different chemical nature are compared.

Organic material deposition by gravure printing is a promising pathway for the realization of large area flexible electronic devices. Nevertheless, in order to achieve high performance it is required to improve the electronic ink printability, operating on the fluid dynamic mechanisms involved during the process. In this work, this issue has been faced working on ink characteristics for a conductive and a dielectric material. The suitable ink features have been defined studying the influence on the printability of the different forces that act in the fluid during the printing process, using an experimental approach. Properly defined ink formulations have been printed, considering different shapes and dimensions of the cells on the gravure cliche to fit the ink features. The printing outcomes have been compared and analysed through the evaluation of several significant fluid dynamic parameters and the rheological characterization of the materials. Finally, exploiting the results of this study, high performance fully printed organic thin film transistors have been realized.