The synthesis and thermal expansion of metal coatings containing phase change material (PCM) prepared by electrolytic deposition were investigated. Such a composite combines the thermomechanical properties of the PCM with the high thermal conductivity of the metal, and can be used as a thermal actuator material. This study used paraffin as the PCM and copper as the metal matrix. The paraffin was first microencapsulated by emulsion polymerization to obtain microcapsules with a diameter of 1 - 5 mu m containing 90 vol% paraffin to facilitate the incorporation of paraffin in copper by electrocodeposition. The microcapsules were added to a copper sulfate bath up to a concentration of 500 g/L. The electrocodeposition was performed at room temperature with a current density between 2 and 5 A dm(-2). These composites were examined by scanning electron microscopy, differential scanning calorimetry, and vertical dilatometry. Coatings with 40 vol % of microcapsules and a heat capacity of 12 kJ kg(-1) during phase transformation were obtained. The thermal expansion of the composite showed a sharp increase in a small temperature range above the melting point. Although this behavior is ideal for thermal actuators, the effect decreased by thermal cycling. This remarkable thermomechanical behavior is explained by a thermoelastoplastic model for two-phase composites. (c) 2006 The Electrochemical Society.