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The rheological behavior of human semen is overlooked and essentially unexplored in the scientific literature. Here, we provide the first quantitative experimental evidence that post-liquafaction normospermic human semen behaves as a viscoelastic fluid and the shear moduli can be scaled according to the weak-gel model.

Emulsions are ubiquitous in many consumer products, including food, cosmetics and pharmaceuticals. Whilst their macroscopic characterisation is well-established, understanding their microscopic behaviour is very challenging. In our previous work we investigated oil-in-water emulsions by studying the effect of water on structuring and dynamics of such systems. In the present work, we investigate the effect of surfactant concentration on microstructure and diffusion within the water-in-oil emulsion system by using low-field pulsed-field gradient (PFG) NMR studies carried out with a benchtop NMR instrument, in conjunction with optical imaging. The results reveal that at high surfactant concentration the formation of smaller droplets gives rise to a third component in the PFG NMR attenuation plot, which is mostly attributed to restricted diffusion near the droplet boundaries. In addition, structuring effects due to increase in surfactant concentration at the boundaries could also contribute to further slowing down water diffusion at the boundaries. As the surfactant concentration decreases, the average droplet size becomes larger and both restriction and structuring effects at the droplet boundaries become less significant, as suggested by the PFG NMR plot, whereby the presence of a third diffusion component becomes less pronounced.

Hydrogels have been successfully employed as analogues of the extracellular matrix to study biological processes such as cells' migration, growth, adhesion and differentiation. These are governed by many factors, including the mechanical properties of hydrogels; yet, a one-to-one correlation between the viscoelastic properties of gels and cell fate is still missing from literature. In this work we provide experimental evidence supporting a possible explanation for the persistence of this knowledge gap. In particular, we have employed common tissues' surrogates such as polyacrylamide and agarose gels to elucidate a potential pitfall occurring when performing rheological characterisations of soft-materials. The issue is related to (i) the normal force applied to the samples prior to performing the rheological measurements, which may easily drive the outcomes of the investigation outside the materials' linear viscoelastic regime, especially when tests are performed with (ii) geometrical tools having unbefitting dimensions ( i.e. , too small). We corroborate that biomimetic hydrogels can show either compressional stress softening or stiffening, and we provide a simple solution to quench these undesired phenomena, which would likely lead to potentially misleading conclusions if they were not mitigated by a good practice in performing rheological measurements, as elucidated in this work.

Concentrated aqueous solutions of surfactants, often referred to as pastes, experience complex phase and rheology changes upon dissolution in water, which is a typical step in the production of liquid detergents. During the dilution process, depending on water content, surfactant molecules can arrange in different morphologies, such as lamellar or cubic and hexagonal structures. These phases are characterized by different physico-chemical properties, such as viscosity or diffusivity, which lead to non-simple transport mechanisms during the dissolution process. In this work, we investigate the dissolution of concentrated Sodium Lauryl Ether Sulfate (SLES) pastes in water under quiescent conditions by coupling different experimental techniques. A thorough rheological characterization of the system showed non-monotonic changes of several orders of magnitude in its viscosity and viscoelastic moduli as a function of water content. Time-lapse microscopy allowed us to image the dynamic evolution of the phase changes as water penetrated in a disk-shaped sample (with the same geometry used in rheological tests). Numerical simulation, based on a simple diffusion-based multi-parameter model is shown to describe satisfactorily SLES dissolution data.

Although the phase behavior of emulsions has been thoroughly investigated, the effect of flow on emulsion morphology, which is relevant for many applications, is far from being fully elucidated. Here, we investigate an emulsion based on two common nonionic surfactants in a range of water concentration where complex and diverse microstructures are found at rest, such as multilamellar and bicontinuous phases. In spite of such complexity, once subjected to shear flow, all the emulsions investigated are characterized by thinning filaments which eventually break up into a concentrated suspension of micro-sized water-based droplets dispersed in a continuous oil phase. The so-formed droplets tend to align in string-like structures. The emulsions exhibit a yield stress, whose value can be estimated by the plug-core velocity profiles in pressure-driven capillary flow, thus providing evidence of weakly attractive interdroplet interactions. The latter are consistent with droplet clustering and percolation observed at rest. These results can also be relevant to the flow behavior of other liquid-liquid systems, such as polymer blends, where the flow-induced microstructure is under debate as well.

Gelatin gels are increasingly involved in many industrial applications due to several advantages including cost efficiency and biocompatibility. Generally, their production requires the use of aqueous solvents, which cause significant swelling, due to the ability of solvent molecules to penetrate through the gel microstructure and increase its volume. Since swelling mechanisms and their effect on the gel structure are not fully understood, further investigations are required. In this work, we combine macroscopic measurements of the swelling ratio (SR) with Nuclear Magnetic Resonance (NMR) and Confocal Laser Scanning Microscopy (CLSM) to investigate changes in the gelatin structure as a function of both polymer concentration and swelling time. SR values increase as a function of time until a maximum is reached and then show a slight drop for all the gelatin concentrations after 24 h swelling time, probably due to a network relaxation process. NMR allows determination of mass transport and molecular dynamics of water inside the gelatin pores, while CLSM is used to visualize the penetration of tracers (polystyrene microbeads) with a diameter much larger than the gel pores. Structural parameters, such as average pore size and tortuosity, are estimated. In particular, the pore size decreases for higher polymer concentration and increases during swelling, until reaching a maximum, and then dropping at longer times. The penetration of tracers provides evidence of the heterogeneity of the gel structure and shows that single microcarriers can be loaded in gelatin gels upon swelling.