NANOPARTICLE SYNTESIS ANS EMULSIONS Flashcards
Explain LaMer theory using the terms monomer accumulation, homogeneous nucleation, diffusion controlled growth, critical superstation (use e.g. figure 22 in Small 2011).
Explain the three different stages; stage 1 –production and accumulation of monomers; stage 2 –exceed solubility limit and reach the critical concentration needed to nucleate homogeneously (overcome energy barrier)–consume monomers and end of this phase consumed enough monomers to that homogeneous nucleation not can take place, stage 3 growth phase –remindingmonomers are used to growth. Here size focusing will take place (see below).
Explain the difference between thetwo main approaches(hot injection and heat-up)within colloidal synthesis that are used to obtain uniform nanoparticle size?Explain principles.
Hot-injection: One reagents is added quickly to boost the supersaturation
Heat-up: All reactants are added prior to heat-up. Supersaturation reacted during heating of all reactants3
What is mean by the term “diffusioncontrolled growth”? (Hint;Small 2011)
Transport of monomer to the surface is limiting the growth.
What is meant by “size focusing”, and in which part of the LaMer diagram will this process take place?(Hint: look into figures 2 and 3 in Small 2011)
Particles become more equal in size when monomer concentration sufficient and that we at the same time as diffusion controlled growth. The growth rate will the decline with increasing radii of particle. I.e., when particlesbecome larger the growth rate is slowed down. See figures 2 and3 in Small for a spherical particle.
xplain the concepts “Oswald ripening”, “coalescence” and “oriented attachment”. Are these phenomena described in the LaMer theory? Justify your answer.
Oswald ripening: at low monomer concentrations an equilibrium between deposition/bringing to solution is dominating. At such conditions, the smaller particles will have a larger driving force for going to solution and the monomer can easily deposit on the larger particle. We often say that the larger particles grow on the expense of the smaller ones.
Oriented attachment: particles are going together at specific orientations.
Coalesence: Coalescence is the process by which two or more droplets, bubbles or particles merge during contact to form a single daughter droplet, bubble or particle.
Explain in terms of thermodynamic at which conditions a nuclei become stable and continue to develop into a particle.
Important to highlight that surface energy become essential and hinder nuclei stabilization when particle is small. Should be able to explain equations if they are presented to you.
delta(G)=4pir^2surface energy + 4/3pir^3crystal energy
When the particle is small, surface energy can be an important factor, and the relation between crystal free energy and surface energy decides when the particle is stable and not.
Differentiate between homogeneous and heterogeneous nucleation, and explain which nucleation mechanism that is less energy demanding. Justify your answer.
Homogeneous nucleation: nuclei form spontaneously from the main matrix due to super saturation whereas the nuclei form on an already existing surface when we have heterogeneous nucleation. Heterogeneous nucleation is less energy demanding than homogeneous nucleation.
delta G (hetero) = delta G (homo) * f,
f is always smaller or equal than 1.
When contact angle is small (good wetting), cos(contact angle)1 implying less energy demanding (Gibbs energy less positive)
When solidifying a melt in a mold, normally where in the mold will you expect the nucleation to be initiated and in which part of the mold will solidify last?
Solidification starts at the walls. The walls are cooler than in the middle, so here it will begun to nucleate first.
Explain why it may beimportant to control particle size, particle morphology, chemical composition-element distribution as well as contamination levels in nanoparticlessynthesizedfor applications?
Nano behaviour is very dependant on size, morphology and chemical properties, therefore important to control them.
Explain the principles behind CdSe synthesis(include the term Ksp in you explanation). Explain how CdSe particle size control their optic properties. -Include definition of quantum dot and possible applications of quantum dots.
Hot injection
- Se dissolved in TOP (Se2-)
- Cold solution is injected into got CdMe2 in TOPO (300 degrees)
- Increase of temperature
Controlled synthesis: Time (size), Concentration, Temperature.
Quantum dot: discretization of the energy levels at the band edge. For semiconductors their size is smaller than the exciton Bohr radius (2-50 nm). Band gap is tuned with size, so different colour from size.
What is the plasmon effect? Which physical parameters of the nanoparticle is critical to controlin order to tune theplasmon effect?
Plasmon effect: Free electrons at the surface of metallic nanoparticle oscillate in one frequency (particle morphology –aspect ratio, type of metal). Resonance with incoming light -> bright color if energy is in visible light.
Explain the principlesbehind Co NP (nanoparticle) synthesis (use Zacharachi et al paper). -In your discussion, touch upon polymorphism for Co (which atomic arrangements are known) and possible size induced changes in magnetic properties when going down in size for a ccp Co particle).
Burst nucleation via hot injection
Formation of large numbers of nuclei in a short period of time, followed by growth without additional nucleation.
- Heat solvent + surfactant
- Cobold decompose when injected
- High concentration of monomer
- Triggers nucleation
hcp below 420 degrees, ccp NP’s, betha-Mn, bcc-
Magnetic properties are dependant on domains, so size will decide what kind of magnetic properties for the ccp NP’s.
Explain the phase diagram for Pt-Rh. In synthesis of Pt-Rh NPs suggest an explanation to that both core-shell and solid solution Pt-Rh nanoparticles can be obtained (hint: thermodynamics versus reaction kinetics of precursors). -Be ready to justify for various types of element distributions in bimetallic nanoparticles; synthesis parameters that can be modified to tune element distribution in the NPs.
Thermodynamics –solid solution despite de-mixing indicated by phase diagram. I.e., expect solid solution from phase diagram plus H-R rules. However, reaction kinetics on Pt-and Rh precursors is a key parameter. If one of the precursors is much faster, may promote core-shell.
Normally we use a heating element/block to heat up a solution during nanoparticle synthesis. Microwave assisted nanoparticle synthesis is also an approach frequently used to obtain nanoparticles. Explain the physical principles behind this approach.
Dielectric constant of solvent is an important parameter –Microwaves are electromagnetic waves, i.e. alternating polarization induced -> heat generated.
Basically a way of heating a solution. Solvent needs to be polar, like water.
Which three types of emulsion do we discuss in thiscourse? Define each of them.
Microemulsions:
- 4-200 nm
- Can form spontanously
- Thermodynamically stable
Nanoemulsions
- 10-200 nm
- Does NOT form spontanously
- Kinetically stable
