Lecture 14 - Nanocomposites Flashcards
What is a nanocomposite?
at least one dimension is l < 100nm (1-100nm)
What forces connect the atoms in a polymer and what connect the polymer chains with each other?
Covalent bondings and van der Waals forces
Explain 0D, 1D, 2D and 3D. [Classification of their dimension]
0D: All dimensions at nanoscale [Nanoparticles]
1D: Two dimensions at nanoscale, other dimension is not [Nanowires, nanorods]
2D: One dimension at nanoscale, other two dimensions are not [Nanocoatings and nanofilms]
3D: No bulk dimension at nanoscale. [Nanocrystalline and nanocomposite materials.]
What are the main nano particle material types?
- clay,
- carbon,
- metal and metal oxide
- cellulose
- silica
Why do we want to use nanofillers in PMCs?
Because we want new and/or improved functional properties/ multifunctional properties.
What kind of properties can you get by using nanofillers?
Mechanical reinforcement Thermal resistance Thermal conductivity Flame resistance Moisture resistance Gas permaebility Reaction kinetics Chemical resistance Antibacterial properties Lubricating properties Electrical properties Charge dissipation Damping properties
Where can the nanofillers be located=
In the fibers, in the core material, in the matrix
What is the route towards nanocomposites?
Nanofiller preparation - Incorporation into matrix - Processing
What is the “Motto” about manufacturing of nanocomposites?
The history of the process will influence the final properties
Which are the three main types that we study?
- Layered-silicate nanoplatelets (commonly referred to as nanoclay)
- Carbon nanotubes (CNTs)
- Graphene
What can Layered-silicate nanoplatelets be called?
Nanoclay
What is a tactoid?
Layered clay
What does it take to make nanoclays?
Main processes:
(a) diffusion
(b) shear + diffusion
What does it take to make carbon nanotubes?
Are mostly lab-grown, require:
• heat
• carbon source
• catalyst (growth seeds) -> will require purification
But there is also natural CNTs available! tex in Precambrian rock and -> • by arc discharge • by laser ablation • by HiPCo process • by chemical vapour deposition (CVD)
explain arc discharge
direct-current arc voltage is applied across two graphite electrodes immersed in an inert gas
• scalable
• superior dispersibility in
polymers, mechanical and electrical properties
Describe HiPCo process
high-pressure carbon
monoxide process: the
gas-phase reaction of iron carbonyl with high-pressure carbon monoxide gas.
Describe CVD
“When the cavemen lit a lamp and soot was deposited on the wall of a cave,”
=
CVD or material -> vacuum chamber -> coating material is heated, or the pressure around it is reduced - > vaporization -> deposition on substrate
What three atomic structures does CNTs have?
- Zig-zag
- Chiral
- armchair
What decides the structure of CNTs?
chiral vector, C
chiral angle, Θ
translational vector, T
What conducting properties does the atomic structures of CNTs have?
- zigzag - semiconducting
- armchair - electrically conducting (like metallic)
- chiral - semiconducting
what does FLG and MLG mean?
Few-layers graphene and multilayer graphene
What Characterization techniques are used for nanotubes and composites containing nanotubes?
• Optical microscopy (OM)
• transmission electron microscopy (TEM),
• scanning electron microscopy (SEM) and
• atomic force microscopy (AFM);
• Raman spectroscopy,
• X-ray photoelectron spectroscopy (XPS)(also
called ESCA),
• thermogravimetric analysis (TGA),
• Fourier Transform Infrared spectroscopy (FTIR)
What can you characterize with the different techniques?
size of nanofillers, agglomeration, purity, functionalization, filler damage, state of dispersion in matrix, orientation
How does SEM work?
Electrons are produced with an electron gun. (For the study of nanomaterials, the gun is normally an FEG.) The electrons are then accelerated, usually with a voltage between 1 kV and 30 kV, and demagnified by a set of two condenser lenses.
How does TEM work?
The electron beam generated by the gun is demagnified through the first con- denser lens; the second condenser lens converges the probe at the specimen and controls the spot size. Just below the second con- denser lens is a condenser aperture that can be used to change the electron current and therefore the intensity of the beam as well as change the angle of beam convergence, which modifies the coher- ence of the beam. The specimen sits below the condenser lens and above the objective lens.
Describe Atomic force microscopy
It measures the atomic force between the atoms at the surface of the sample and the tip of a needle at the end of a cantilever, when scanned over the sample surface
Describe Raman spectroscopy
in Raman spectroscopy, the vibrational frequency and thus the wavelength of groups of atoms are measured as a shift from the incident beam frequency
Describe FTIR
Differences in the chemical and atomic structure of materials give rise to specific vibrational characteristics and yield unique IR spectra for each material.
Differences in the chemical and atomic structure of materials give rise to specific vibrational characteristics and yield unique IR spectra for each material.
Describe TGA
Uses a scale in a furnace in a controlled atmosphere to see how the material acts in temperatures.
What four techniques are used for Incorporation into polymers?
In-situ polymerization
Solution Blending
Melt Blending
Dry-coating
How does In-situ polymerization work and what can be critical issues?
Ideally, monomers intercalated between layers! \+ covalent bonding between the functionalized sheets and polymer matrix via various chemical reactions Critical issues: • high viscosities at high conversions • may require the presence of solvents -> removal necessary!
How does solution blending work and what can be critical issues?
Dispersion of filler in a suitable solvent
incorporation of the polymer
removal of the solvent by distillation or evaporation
Critical issues: solvent removal, toxic solvents
How does melt blending work and what can be critical issues?
Compounding (e.g. twin screw extruder) It’s free from toxic solvents! Critical issues: • less effective mixing especially at high filling ratios due to increase in viscosity • defects in fillers sometimes observed
How does dry-coating work and what can be critical issues?
(method taken from graphene)
Liquid exfoliation in water/ solvent OR
Freeze- grinding of the polymer matrix
–>
Dry coating of the nano filler on the surface of the grinder polymer
Critical issues:
• what are suitable solvents?
