Cellular electrets polymer is a new ferroelectret material exhibiting large piezoelectricity and has attracted considerable attentions in researches and industries. Property characterization is very important for this material and current investigations are mostly on macroscopic properties. In this work, we conduct nanoscale piezoelectric and ferroelectric characterizations of cellular polypropylene (PP) films using piezoresponse force microscopy (PFM). First, both the single-frequency PFM and dual-frequency resonance-tracking PFM testings were conducted on the cellular PP film. The localized piezoelectric constant d₃₃ is estimated to be 7–11pC/N by correcting the resonance magnification with quality factor and it is about one order lower than the macroscopic value. Next, using the switching spectroscopy PFM (SS-PFM), we studied polarization switching behavior of the cellular PP films. Results show that it exhibits the typical ferroelectric-like phase hysteresis loops and butterfly-shaped amplitude loops, which is similar to that of a poly(vinylidene fluoride) (PVDF) ferroelectric polymer film. However, both the phase and amplitude loops of the PP film are intensively asymmetric, which is thought to be caused by the nonzero remnant polarization after poling. Then, the D-E hysteresis loops of both the cellular PP film and PVDF film were measured by using the same wave form as that used in the SS-PFM, and the results show significant differences. Finally, we suggest that the ferroelectric-like behavior of cellular electrets films should be distinguished from that of typical ferroelectrics, both macroscopically and microscopically.

Heterogeneous composite flooding has performed well with regard to enhanced oil recovery after polymer flooding in recent years. In order to significantly increase oil recovery, the development parameters should be designed differently for each well. However, it is difficult to rapidly allocate development parameters through the lowering of computational costs. Therefore, the authors of this paper carried out research to clarify the main controlling factors of parameter allocation. Firstly, the numerical simulation domain was separated into several regions, with injection wells and production wells at the center of each region. The statistical parameters of each region were calculated. Then, the water injection rate, liquid production rate, and chemical agent concentration were allocated based on the proportion of statistical parameters in each region. A large number of development schemes were designed by combining different injection and production allocations that were calculated based on each statistical parameter. Finally, the development performance of each scheme was simulated and analyzed. The statistical parameters corresponding to the best performance scheme were regarded as the main controlling factors of heterogeneous composite flooding after polymer flooding. These results showed that the main controlling factors for the allocation of the water injection rate were pore volume and permeability variation coefficient. The main controlling factors for liquid production rate were the remaining oil saturation, formation coefficient, and reservoir pressure. The main controlling factors for chemical agent concentration were pressure and permeability variation coefficient. These findings concerning the main factors controlling development parameter allocation were validated by practical application in several well groups of an actual reservoir model. This study provides references for improving heterogeneous composite flooding performance for post-polymer flooding reservoirs in the future.

V-shaped microcantilevers exhibit high sensitivity and low stiffness characteristics, making them suitable for use as atomic force microscopy probes that enable high-resolution surface imaging and nanomechanical characterization of soft biological samples in liquid environments. However, due to the complex geometry of the V-shaped microcantilever and the effects of fluid–structure coupling and nonlinear tip–sample interactions when operating in liquids, it is generally difficult to study its dynamic characteristics analytically. This study establishes a computational framework based on the finite difference method (FDM) to analyze the dynamic response of a V-shaped microcantilever in liquids by equivalently modeling fluid effects as added mass and damping. The resonance frequencies and the time-varying displacement of the V-shaped microcantilever are calculated and compared with those obtained by the finite element method to validate the accuracy and efficiency of FDM. The effects of the cantilever–sample separation, the free amplitude, and the sample modulus on the dynamic responses of the V-shaped microcantilever are further analyzed. Results demonstrate that nonlinear tip–sample interactions excite higher harmonics, amplified by internal resonance of higher modes. Reducing free amplitude or employing phase imaging enhances measurement sensitivity in liquids. This method offers a computationally efficient tool for dynamic analysis and structural optimization of V-shaped microcantilevers in fluid environments.

Bimodal amplitude modulation atomic force microscopy (AM-AFM) is widely used in nanoscale topography and mechanical property imaging for a variety of materials. In this paper, the stability of the amplitude/phase spectroscopy curves and the imaging contrast in bimodal AM-AFM for different mode combinations are investigated computationally in ambient air. The results show that with the second mode amplitude used for topography feedback on a stiff material, the amplitude/phase spectroscopy would probably undergo volatile fluctuation, leading to unstable imaging. With the third mode amplitude set for topography imaging, it would be difficult for the feedback to maintain the prescribed amplitude since a large cantilever position variation is required for different sample moduli. With the first mode amplitude set for topography feedback, the amplitude and the phase of the second mode vary monotonically with sample modulus or viscosity in comparison with the third or the fourth mode, which is suitable for compositional contrast imaging. These results would provide useful guidelines for optimum imaging in bimodal AFM measurements.