Nanotech 1-4

How big is a nanometer

1 × 10^-9 m

Why do nanomaterials and their respective bulk counterparts exhibit different properties

• Surfaces at the nanoscale play a large role in the properties of materials.

• Quantum effects dominate the properties of materials at the nanoscale

• High surface-area-to-volume ratio of nanomaterials compared with their bulk counterparts

Charcoal has _____ electrical conductivity and carbon nanotubes have _____ electrical conductivity

low ; high

SAV ratio or the surface area per unit volume of a cube ____ as the
dimensions of the cube _____.

increases ; decreases

What is the S.I unit for SAV ratio?

m^-1

Surfaces with a ___ surface energy have ____ contact angle, and
they exhibit poor wetting

low ; high

Titanium dioxide exhibits photocatalytic behavior when exposed to _____.

ultraviolet light

Self-cleaning property is dependent on ____, _____ and ______

• contact area between liquid droplet and the surface

• Contact angle of the liquid

• Sliding angle (i.e. minimum inclination angle needed for droplet to slide off the surface)

Why do composites containing nanomaterials outperform composites made of bulk materials?

There is increased matrix-reinforcement interface at the nanoscale due to the size effect.

What are photocatalytic nanomaterials

nano-sized particles which work as a catalyst in the presence of sunlight, which do not change themselves or being consumed in a chemical reaction.

Photocatalytic stage

When UV light activates a material like titanium dioxide (TiO₂), producing reactive radicals (like OH• and O₂⁻) that break down organic dirt, bacteria, and pollutants on the surface.

Superhydrophilic stage

After UV activation, the surface becomes superhydrophilic, meaning water spreads out evenly across it instead of forming droplets — this helps rinse off the loosened dirt easily with water.

Superhydrophobic self cleaning approach

• Very high static water contact angle

• very low sliding angle

Superhydrophilic self cleaning approach

• Surface able to spread water to wash/carry away the dirt

• Coating (i.e. TiO2) can chemically break down absorbed dirt in sunlight

Why is abalone shell stiff, strong and tough

Stiff

• Closely packed, layered nanostructure of aragonite platelets

Strong

• Interlocks function as physical obstacles to the relative movement of aragonite platelets

Tough

• Arrest and deflection of cracks by the soft organic adhesive layer

Crack propagation through a brittle material is accompanied by a _____ spreading of crack with _____ plastic deformation.

rapid ; little

Effect of _____ material found in composite with brittle and ductile materials is to provide ______, making it difficult for cracks to propagate

ductile ; crack deflection