Fig. 1. Frying an egg on a hot pan, achieved by enabling the diffusion of phases but disabling the diffusion of concentrations.We introduce a unified particle framework which integrates the phase-field method with multi-material simulation to allow modeling of both liquids and solids, as well as phase transitions between them. A simple elastoplastic model is used to capture the behavior of various kinds of solids, including deformable bodies, granular materials, and cohesive soils. States of matter or phases, particularly liquids and solids, are modeled using the nonconservative Allen-Cahn equation. In contrast, materials-made of different substances-are advected by the conservative Cahn-Hilliard equation. The distributions of phases and materials are represented by a phase variable and a concentration variable, respectively, allowing us to represent commonly observed fluid-solid i nteractions. T he d ynamics o f a m ulti-phase, multimaterial system are governed by a unified Helmholtz free-energy density. This framework provides the first method in computer graphics capable of modeling a continuous interface between phases. It is versatile and can be readily used in many scenarios challenging to simulate. Examples are provided to demonstrate the capabilities and effectiveness of this approach.