A nozzle arrangement for an inkjet printer. the nozzle arrangement comprising a substrate assembly defining an inlet channel; a nozzle chamber wall and a roof wall collectively positioned on the substrate assembly to define a nozzle chamber in fluid communication with the inlet channel, the roof wall defining an ejection port in fluid communication with the nozzle chamber; a thermal actuator mounted to the substrate assembly and extending into the nozzle chamber to terminate in a free end, the thermal actuator comprising a pair of actuating members spaced apart to form a gap, one of the actuating members being connected to an electrical supply; a heat sink assembly positioned in the gap between the pair of actuating members; and a sealing structure provided between an end of the thermal actuator mounted to the substrate and an end of the thermal actuator terminating in the nozzle chamber, the sealing structure permitting movement of the thermal actuator therein and inhibiting fluid leakage from the nozzle chamber via surface tension.