Thermodynamics of deformation of latex blend coatings and its implications for tailoring their properties

Acrylic-based latex blend coatings, comprising a hard (T-g = 45 degrees C) and soft (T-g = -5 degrees C) phases are evaluated in terms of the total energy they absorb before failure in a tensile test. Simultaneous measurement of the work and heat of deformation using a novel technique of differentia gas pressure stretch calorimetry enables an estimate of change in their internal energy by application of the first law of thermodynamics. As the hard phase content of the blend is increased from 0-100%, its stiffness and tenacity increase, while the toughness (i.e., the energy to failure) undergoes a maximum at an intermediate composition. A partitioning of the mechanical work into heat and internal energy over the complete range of blend composition highlights the result that a simultaneous maximization of the heat dissipation and energy absorption is necessary to maximize blend toughness. This provides a new framework in which the properties of blend systems can be tailored in terms of their stiffness and toughness to design improved coatings.