Deep eutectic solvents have shown the ability to promote the self-assembly of surfactants in solution. However, some differences have been found compared with self-assembly in pure water and other polar organic solvents. The behaviour of alkyltrimethylammonium bromides in choline chloride:glycerol deep eutectic solvent has been studied by means of surface tension, X-ray and neutron reflectivity and small-angle neutron scattering. The surfactants were found to remain surface active and showed comparable critical micelle concentrations to the same surfactants in water. Our scattering studies demonstrate that these surfactants form globular micelles with ellipsoidal shape in solution. The size, shape and aggregation number of the aggregates were found to vary with the chain length of the surfactant. Specific solvent-headgroup interactions were not found in this system, unlike those we have previously postulated for anionic surfactants in choline chloride deep eutectic solvents.

We investigate the reversible, binary gelation of poly(N-isopropylacrylamide) (pNIPAM) microgels in the presence of triblock-copolymer (PEO–PPO–PEO type) surfactant. Confocal microscopy highlights that both polymers are present in the gel network.

Colloidal gels constitute an important class of materials found in many contexts and with a wide range of applications. Yet as matter far from equilibrium, gels exhibit a variety of time-dependent behaviours, which can be perplexing, such as an increase in strength prior to catastrophic failure. Remarkably, such complex phenomena are faithfully captured by an extremely simple model—‘sticky spheres’. Here we review progress in our understanding of colloidal gels made through the use of real space analysis and particle resolved studies. We consider the challenges of obtaining a suitable experimental system where the refractive index and density of the colloidal particles is matched to that of the solvent. We review work to obtain a particle-level mechanism for rigidity in gels and the evolution of our understanding of time-dependent behaviour, from early-time aggregation to ageing, before considering the response of colloidal gels to deformation and then move on to more complex systems of anisotropic particles and mixtures. Finally we note some more exotic materials with similar properties.

We investigate the degradation behaviour of a triblock-copolymer surfactant made from polyethylene oxide (PEO) and polypropylene oxide (PPO) (PEO-PPO-PEO), highlighting how the aggregation behaviour of this polymer in water alters with ageing. Samples aged at room temperature were compared to samples degraded using accelerated ageing at elevated temperatures. We find that large mass losses occurred to the polymer surfactant which resulted in a change in the aggregation behaviour, with larger, rod-like or planar aggregates forming at longer degradation times. We look at how this change in aggregation behaviour changes the formulation stability of these polymers, specifically, the interaction of the polymer surfactant with poly(N-isopropylacrylamide) microgels. It is known that these species associate and form gels at elevated temperatures. This paper highlights how commonly used polymeric surfactants can degrade over time, resulting in dramatic changes to aggregation behaviour and therefore, formulation properties.

We investigate the temperature dependent phase behaviour of mixtures of poly(Nisopropylacrylamide) (pNIPAM) microgel colloids and a triblock copolymer (PEO-PPO-PEO) surfactant, which undergoes micellisation. Gelation in these systems results from an increase in temperature. Here we alter the heating rate and observe that the mechanism for aggregation changes from one of depletion of the microgels by the micelles at low temperatures to association of the two species at high temperatures. We use this to access multiple structures at one microgel concentration. Samples with a micelle concentration above 7 wt% were found to demix into phases rich and poor in microgel particles at temperatures below 33 • C, under conditions where the microgels particles are partially swollen. Under rapid heating full demixing is bypassed and gel networks are formed instead. The temperature history of the sample therefore allows for kinetic selection between different final structures, which may be metastable.

We investigate the temperature-dependent phase behavior of mixtures of poly(N-isopropyl­acrylamide) (pNIPAM) microgel colloids and a triblock copolymer (PEO–PPO–PEO) surfactant. Usually, gelation in these systems results from an increase in temperature. Here we investigate the role of the heating rate, and surprisingly, we find that this causes the mechanism of aggregation to change from one which is driven by depletion of the microgels by the micelles at low temperatures to the association of the two species at high temperatures. We thus reveal two competing mechanisms for attractions between the microgel particles which can be controlled by changing the heating rate. We use this heating-rate-dependent response of the system to access multiple structures for the same system composition. Samples were found to demix into phases rich and poor in microgel particles at temperatures below 33 °C, under conditions where the microgels particles are partially swollen. Under rapid heating full demixing is bypassed, and gel networks are formed instead. The temperature history of the sample, therefore, allows for kinetic selection between different final structures, which may be metastable.