Bubbles coated/encapsulated with a shell composed of polymers, lipids, lipopolymers,
proteins, surfactants, or a combination of these are called coated/encapsulated bubbles (EBs). EBs
have a large number of applications in the field of medical science, for targeted drug delivery as
contrast agents for ultrasound medical imaging, for biofilm removal, sonochemistry, and so on. Over
the past two decades, several shell models have been proposed as corrections to the Rayleigh-Plesset
equation to study the mechanics of EBs. For an EB suspended in a fluid, the interface between the gasencapsulation and encapsulation-liquid carries sufficient interface energy that significantly affects the
mechanics and cannot be neglected. However, the influence of this interface energy on EB dynamics
is not well studied in the existing EB models. Since these EBs are of a few microns radius, the effect or
significance of interface energy becomes more dominant. We propose an interface energy-based
model within the framework of continuum mechanics to study the EB dynamics.
Notably, the proposed interface energy model considers these interface effects through
interface strain and bending rigidity. The requirement of fictitious and natural configurations
introduced by interface effects in the present model helps to understand the physical aspects of EB
dynamics. The proposed model naturally induces residual stress field into the bulk of the bubble, with
possible expansion/shrinkage from a stress-free configuration to a natural equilibrium configuration.
We have shown that the negative dynamic interface tension associated with interface bending rigidity
is favorable for the EB dynamics. The coupled effect of interface strain and curvature term observed
is new and plays a dominant role in the compression dominant behavior of encapsulated bubble. Using
constrained optimization based on compression dominant bubble behavior, a better fit of the
experimental data is obtained to estimate the interface and material parameters independent of the
initial bubble radius. The proposed model also provides an important direction towards the estimation
of initial size-dependent interface and material properties of EBs with interesting future developments.