Tailoring and understanding the mechanical properties of nanoparticle-shelled bubbles.

One common approach to generate lightweight materials with high specific strength and stiffness is the incorporation of stiff hollow microparticles (also known as bubbles or microballoons) into a polymeric matrix. The mechanical properties of these composites, also known as syntactic foams, greatly depend on those of the hollow microparticles. It is critical to precisely control the properties of these bubbles to fabricate lightweight materials that are suitable for specific applications.

Ellipsoidal particles encapsulated in droplets.

Using hydrodynamic focusing, we encapsulated polystyrene ellipsoidal particles in water droplets dispersed in an immiscible, continuous phase of light mineral oil. The axisymmetric shape of the drop partially encapsulating an elongated particle was computed as a function of the particle aspect ratio, droplet volume, and contact angle. When the droplet volume is within a certain range, pinned (partially engulfed) and fully engulfed equilibrium configurations coexist.

Beauty of lotus is more than skin deep: highly buoyant superhydrophobic films.

We develop highly buoyant superhydrophobic films that mimic the three-dimensional structure of lotus leaves. The high buoyancy of these structure stems from mechanically robust bubbles that significantly reduce the density of the superhydrophobic films. These highly buoyant superhydrophobic films stay afloat on water surface while carrying a load that is more than 200 times their own weight.

Using shape anisotropy to toughen disordered nanoparticle assemblies.

Assemblies of disordered nanoparticles constitute an important class of materials that have numerous applications in energy conversion and storage, electronics, photonics, and sensing. One major roadblock that limits the widespread utilization of disordered nanoparticle assemblies (DNAs) is their poor damage tolerance; they fracture under small loads and, thus, have low toughness. The absence of fundamental understanding on the mechanical behavior and failure mechanism of disordered nanoparticle assemblies makes it even more challenging to develop new strategies to toughen these structures without compromising their mechanical strength.

Avoiding cracks in nanoparticle films.

A new method utilizing subsequent depositions of thin crack-free nanoparticle layers is demonstrated to avoid the formation of cracks within silica nanoparticle films. Using this method, films can be assembled with thicknesses exceeding the critical cracking values. Explanation of this observed phenomenon is hypothesized to mainly arise from chemical bond formation between neighboring silica nanoparticles.

Mechanical reinforcement of nanoparticle thin films using atomic layer deposition.

Thin films composed of nanoparticles exhibit synergistic properties, making them useful for numerous advanced applications. Nanoparticle thin films (NTFs), however, have a very low resistance to mechanical loading and abrasion, presenting a major bottleneck to their widespread use and commercialization. High-temperature sintering has been shown to improve the mechanical durability of NTFs on inorganic substrates; however, these high-temperature processes are not amenable to organic substrates.