Many applications that utilise wireless sensor networks (WSNs) require essentially secure communication. However, WSNs suffer from some inherent weaknesses because of restricted communication and hardware capabilities. Key management is the crucial important building block for all security goals in WSNs. Most existing researches tried to assign keys assuming homogeneous network architecture. Recently, a few key management models for heterogeneous WSNs have been proposed. In this study, the authors propose a dynamic key management framework based on elliptical curve cryptography and signcryption method for heterogeneous WSNs. The proposed scheme has network scalability and sensor node (SN) mobility especially in liquid environments. Moreover, both periodic authentication and a new registration mechanism are proposed through prevention of SN compromise. The authors analyse some of the more seminal hierarchical heterogeneous WSN key management schemes and compare them with the proposed scheme. On comparing the proposed scheme with the more seminal hierarchical heterogeneous WSN key management schemes, the proposed framework individually proves to be better in terms of communication, computation and key storage.