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Use of macromonomers as reactive stabilizers in mini-emulsion polymerization

Use of macromonomers as reactive stabilizers in mini-emulsion polymerization

A mini-emulsion polymerization is a variation on the more conventional emulsion polymerization process in that in the ideal scenario latex particles are formed by monomer droplet nucleation. The monomer droplets are turned into polymer particles. The trick to achieve this is to shrink monomer emulsion droplets to sub-micrometer diameters. For this two ingredients are key, one is a lyophobe, a compound that dissolves in the monomer droplet but does not like to partition into the continuous phase, here water. Typically n-hexadecane is used. This compound suppresses coarsening, also called Ostwald ripening, of the droplets by providing an Osmotic counter pressure. The other essential ingredient is a surfactant which aids to stabilize the large combined surface area of the droplets and keeps then from colliding and fusing (colloidal stability).

The use of molecular surfactants, however, can have negative impacts when the polymer latex is used in formulations and applications as the surfactant can migrate. For example in a clear coating it could lead to uptake of water, causing the transparent coating to become opaque, a phenomenon known as water whitening.

Autonomous electricity-free "icy road" warning signs

Autonomous electricity-free "icy road" warning signs

We set out to develop a prototype for “icy road” warning signs which was able to operate autonomously without the use of electricity, and which could be easily placed onto existing road features, such as street boundary pillars and road safety barriers.

The number of road accidents in the UK under frosty or icy conditions runs in the thousands. Our concept would aid to reduce these numbers, without the introduction of a digital, and thus electric, infrastructure.

The results from our studies are now published open access in the Journal of Materials Chemistry C from the Royal Society of Chemistry. The conceptual road sign application is a multi-lamellar flexible strip.

A temperature triggered response in the form of an upper critical solution temperature (UCST) type phase separation targeted near the freezing point of water manifests itself through light scattering as a clear-to-opaque transition. It is simultaneously amplified by an enhanced photoluminescence effect.

What happens to particle size distributions when making reactive surfactants and polymer colloids by emulsion polymerization?

What happens to particle size distributions when making reactive surfactants and polymer colloids by emulsion polymerization?

When we synthesize polymer colloids by emulsion polymerization, molecular surfactants are often employed. These are required to keep the polymer latex particles dispersed in the water phase, so that they do not clump together, a phenomenon known as coagulation. Keeping polymer dispersions stable is especially important in end applications, such as waterborne coatings and adhesives.

A downside of the use of surfactant molecules is that they can desorb from the surface of the latex particles. This makes the particles colloidally unstable, and they coagulate. This can be disastrous in product formulations, such as water-based paints which have many components. Another downside of this mobility of the surfactant molecules is that they can migrate in the final coating, once applied on a substrate. This leads to deterioration of the properties of the coated film.