chemistry - separate chemistry 2: bulk & surface properties of matter including nanoparticles (9.35 - 9.39)

9.35 size of nanoparticles vs sizes of atoms & molecules

few hundred atoms

1-100nm

larger than atoms (e.g. oxygen atom 0.1nm diameter)

larger than simple molecules

(smaller than cells)

9.36 properties & uses of nanoparticulate materials - sunscreens

large SA:volume ratio

titanium dioxide: in bulk = white solid; absorbs harmful UV radiation from sunlight (may cause cancer)

nanoparticulate titanium dioxide: transparent - very small particles; absorbs harmful UV radiation

useful for almost-invisible sunscreens

9.36 properties & uses of nanoparticulate materials - catalysts

large SA:volume ratio

stain-resistant clothes treated with nanoparticulate materials stay clean - nanoparticles catalyse breakdown of dirt

9.37 risks associated with nanoparticulate materials

may pose hazards to human health & environment

small size: breathed in; pass through cell-surface membranes

large SA:volume ratio: catalyse harmful reactions; carry toxic substances bound to surfaces

risks hard to determine - modern nanoparticulate materials not in use for long

composite material definition

mixture of 2 or more materials

combined to produce material with improved properties

9.38 physical properties of glass ceramics

transparent

hard, brittle

poor heat & electrical conductors

(windows, bottles)

9.38 physical properties of clay ceramics

opaque

hard, brittle

poor heat & electrical conductors

(bricks, porcelain)

9.38 physical properties of polymers

transparent/translucent/opaque

tough/ductile

poor heat & electrical conductors

(plastic bags, bottles)

9.38 physical properties of composites

mixture of 2/more materials

combined to produce material with improved properties

e.g. fibreglass = glass fibres + polymer resin

• glass fibres: brittle, low density, high tensile strength

• polymer resin: hardwearing, not strong

• fibreglass: lightweight, strong, tough

9.38 physical properties of metals

shiny

good heat & electrical conductors

(cars, bridges, electrical cables)

9.39 why do properties of material make it suitable for given use?

e.g. electrical cables:

• metal is suitable - good electrical conductor, ductile

• polymer is unsuitable - poor electrical conductor

(use 9.38)