## 1 Introduction  
Injection molding technology has become one of the main methods of mass polymer material molding due to the advantages of its short molding cycle, low-cost, and high precision [1; 2; 3]. However, with the wide application of polymer parts with micro-nano structure features, higher molding requirements are put forward. In CIM, the retention phenomenon and the condensation layer effect at the nanostructure make the cavity filling insufficient [4], and the replication capability of the product is poor. Therefore, it is particularly difficult to produce nanostructure products by the CIM method. Molding nanostructures parts with a good replication capability is developing into a hot research topic [5; 6; 7; 8; 9]. [PERSON] et al. made characteristic structures smaller than 100 nm on an optical disk for the first time by using injection molding technology, which improves storage space [10]. [PERSON] et al. studied the effect of injection rate, mold temperature, melt temperature, and other process parameters on the filling of nanostructures [11]. With the continuous development of RHCM technology in recent years, the mold temperature can be precisely controlled, and the mold cavity temperature can be rapidly heated to near polymer T\({}_{\mathrm{g}}\) until rapid cooling during the late packing stage [12]. [PERSON] and [PERSON] et al. used rapid heating technology to heat the mold surface, and nanostructures with a higher replication rate were obtained [13; 14]. However, it is difficult to directly characterize the evolution process of the polymer molecular chain-filling morphology in the mold cavity and the molecular mechanism of nanostructure replication capabilities under limited experimental conditions. In recent years, molecular simulation methods have been applied to study the microscopic mechanism, such as the fluidity of polymer molecular chains [15], the interfacial diffusion of multilayer polymer films [16], the simulation analysis of nanoimprint lithography technology [17], polymer glass transition [18], nanoinjection molding [19; 20], and so on. [PERSON] et al. used PMMA as research materials, applied molecular dynamics method to study the polymer filling into nanocavity by injection molding, and elucidated the effects of molecular weight and cavity size on the filling behavior and final replication quality of nanostructures [19]. Furthermore, they also applied molecular dynamics method to study the interfacial interaction and joining properties of PP-Al hybrid structures in nanoinjection molding [20]. The molecular simulation technique can be used not only to explain the macroscopic experimental phenomenon from the microscopic perspective, but also visually to analyze the filling dynamic process in the nanostructures, which is difficult to observe due to the limitation of experimental equipment at the molecular size.  
In this paper, based on the molecular dynamics method, the interface model between the PC and nickel mold insert was established by using amorphous long- and short-chain polycarbonates as research materials. Firstly, glass transition temperatures of different PC systems were studied to determine their mold temperature in RHCM. Then, the nanostructure molding mechanism of long and short-chain polymer systems in CIM and RHCM was discussed, and the filling morphology evolution in nanostructures and the reason for the high-low filling rate were analyzed to provide a theoretical basis for further improving the replication capability of nanostructures and improving the quality of nanostructure parts.