Part 3 - Overview of nanomaterials Flashcards
What is the difference between a true solution, colloidal solution and a suspension?
Sizes of the particles. True solution, less than 1 nm. Colloidal solution, 1-100 nm. Suspension > 100 nm.
What kind of properties are attributed to the particle and what are attributed to the passivating ligand layer?
Particle: Optical properties, conductivity, magnetism, catalytic activity
Passivating ligand layer: Refractive index, polarity/solubility, charge and functionality.
What are the typical synthesis procedures for metallic nanoparticles?
- Reduction of metallic precursors in solution.
- Colloidal templating (reverse micelles)
- Seeded growth
- Sol-gel
- One-pot synthesis using globular proteins
- One-pot synthesis using stimuli-responsive polymers
- One-pot synthesis using viral templates
- Use of microorganisms for formation of metal NP
- Nucleotide-mediated synthesis of metal nanoparticles
- “Natural selection” of biomolecules capable of nanoparticle formation.
- Electrochemical deposition
- Dendrimer templated synthesis.
What are some typical synthesis route using reduction of metallic precursors?
Turkevich method - citrate reduction of chloride precursors. Ex: HAuCl4 + CitAc -> Au0 (citrate acts also as passivating ligand). Sizes 2-200 nm
Brust reaction - BH4- reduction of chloride precursors
Need surfactant as passivating ligand. Typically 1.5-8 nm particle sizes.
Goia reaction - reduction with iso-ascorbic acid of chloride precursor. Ascorbic acid acts as passivating ligand. 30-100 nm for stabilizer free synthesis. Can use gum arabic with high Au-conc to make larger particles (up to 5 µm).
Can also use hydrogen reduction through methods by Rampino and Henglein.
What is required for synthesis using reduction of metallic precursors?
- Metal precursor
- Passivating ligand
- Reducing agent
Draw a schematic of micellar templating.
See slides.
What are surface plasmon resonance?
The resonance of free electrons on the surface of a metal as a response to an oscillating electric field at a characteristic frequency.
What happens to the resonance peak of surface plasmons if the dimensions in one direction increases (such as in a nanorod?)
The peak is split, one corresponding to the transverse axis and one to the longitudinal axis. The longitudinal axis is split due to a difference in length in the two axes, and that there are more electrons available along the longitudinal axis, so that it requires less energy to oscillate them.
What is the difference in optical properties of nanorods with different aspect ratio?
Longer vs. shorter:
Larger extinction coeff. - Smaller ext. coeff.
Scatters more light at longitudinal plasmon - Scatters less light
Better performance in optical imaging - Improved efficiency in photothermal application.
Explain the zipping mechanism
Capping ligand is adsorbed onto specific surfaces, hindering growth in this direction. Growth in non-adsorbed direction, new capping agents adsorb to newly created facets.
Shortly explain the modified Goia reaction.
Multiple steps using three different reduction agents (citric acid, ascorbic acid and NaBH4). AR and morphology is heavily dependent on the relative concentrations of the different constituents.
Explain the sol-gel method for NP synthesis.
Formation of sol-gel network from two steps: hydrolysis of M(OEt)4 and polycondensation. Solvent removal by heating, air-drying, calcination.
Describe the use of stimuli-responsive polymers for particle synthesis.
Such polymers go from a collapsed state to an expanded state under a LCST. These can also be modified with pH-sensitive parts.
What is the difference between convergent and divergent strategy for making dendrimers?
Divergent: start from core and build outwards.
Convergent: start from outside and build in. Smaller dendrimers.
How are the dendrimers termed?
By generation. The generation refers to the number of repeating branching cycles.
