Microcapsules are attractive core-shell configurations for studies of controlled release, biomolecular sensing, artificial microbial environments, and spherical film buckling. However, the production of microcapsules with ultra-thin shells remains a challenge. Here we develop a simple and practical osmolarity-controlled swelling method for the mass production of monodisperse microcapsules with ultra-thin shells via water-in-oil-in-water (W/O/W) double-emulsion drops templating. The size and shell thickness of the double-emulsion drops are precisely tuned by changing the osmotic pressure between the inner cores and the suspending medium, indicating the practicability and effectiveness of this swelling method in tuning the shell thickness of double-emulsion drops and the resultant microcapsules. This method enables the production of microcapsules even with an ultra-thin shell less than hundreds of nanometers, which overcomes the difficulty in producing ultra-thin-shell microcapsules using the classic microfluidic emulsion technologies. In addition, the ultra-thin-shell microcapsules can maintain their intact spherical shape for up to 1 year without rupturing in our long-term observation. We believe that the osmolarity-controlled swelling method will be useful in generating ultra-thin-shell polydimethylsiloxane (PDMS) microcapsules for long-term encapsulation, and for thin film folding, buckling and rupturing investigation.

The automobile engine timing system is an important sub-transmission system, which transfers the high speed crankshaft rotation to the camshaft valve mechanism or auxiliary driving device (water pump, fuel pump) according to the strict phase relation. Compared with chain drive, synchronous belt timing system has obvious advantages in consumption, CO 2 emission reduction, noise reduction and friction reduction. Therefore, many scholars have studied the dynamics and meshing performance of the transmission system. Takagishi H, et al ( 2005) conducted dynamic simulation of the timing system based on multi-body dynamics, studied the meshing interference between the synchronous belt and the belt pulley, the contact stress and the load distribution on the belt and the dynamic response of the system, also evaluated the belt life and noise behavior by calculating the maximum contact load and vibration amplitude of the belt. Long S et al (2020) proposed a modeling method for general layout of synchronous belt drive system, established transmission models of synchronous belt, automatic tension pulley and pulleys, and proposed an iterative numerical algorithm to determine the dynamic response of the system. However, the low lifetime of synchronous belt restricted the application of synchronous belt timing system. Gajewski W (2006) proposed the non-circular pulley timing system to compensate the vibration of the system, by reducing the load peak of the system components, to increase the belt life, reduce noise, and improve the dynamic performance of the system. Sopouch M, et al ( 2007) utilized a multi-body dynamics approach to research the vibration characteristics of the timing system. For elliptical pulley timing system, compared with the circular pulley timing system, the amplitude of camshaft angle fluctuation, the maximum dynamic tension of the belt and the maximum transverse vibration amplitude of the belt are