Hydrophilic colloidal properties of latexes

Latex-modified mortar and concrete have a markedly improved water retention over ordinary cement mortar and concrete. The water retention is dependent on the polymer-cement ratio. The reasons for this can probably be explained in terms of the hydrophilic colloidal properties of latexes themselves and the inhibited water evaporation due to the filling and sealing effects of impermeable polymer films formed. Accordingly, a sufficient amount of water required for cement hydration is held in the mortar and concrete and, for most latex-modified systems, dry cure is preferable to wet or water cure. This is also examined in Sec. 2.1. 

The colloidal properties of latex products are of great importance from both academic and industrial points of view. Some representative charaeteristics include the particle size and particle size distribution, the particle surface charge density (or zeta potential), the particle surface area covered by one stabilizer molecule, the conformation of the hydrophilic polymer physically adsorbed or chemically couplet onto the particle surface, the type and concentration of functional groups on the particle surface, the particle morphology, the optical and rheological properties and the colloidal stability. 

Other types of surfactants are the polymeric (steric) stabilisers, such as partially hydrolysed polyvinyl acetate. Also oligomeric species formed in situ, when SO radicals react with some monomer units in the aqueous phase, will have surface active properties, and can even form a colloidally stable latex Electrosteric stabilisers combine steric and electrostatic functionalities for example, inclusion of acrylic acid in a recipe results in chains with blocks comprised largely of poly(acrylic acid) which for in the aqueous phase, then pick up enough hydrophobic monomer to enter the particle and continue polymerisation in the particle interior. The hydrophilic component remains in the aqueous phase and provides colloidal stability both sterically and, imder the appropriate conditions of pH, electrostatically. This mode of stabilisation is very common in surface coatings, because it gives excellent freeze-thaw stability. 

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