Fra NanoWiki

Gå til: navigasjon, søk

Innhold

1 Pensum Del I (Jens-Petter Andreassen)
2 Pensum Del II (Sondre Volden)
3 Pensum Del III (Tor Grande)
4 Pensum Del IV (May-Britt Hägg)
- 4.1 Basics of membrane materials and separation
- 4.2 Selected nanostructured membranes
5 Pensum Del V (Magnus Rønning)
- 5.1 Catalysis

Pensum Del I (Jens-Petter Andreassen)

Crystallization fundamentals

Supersaturation

Concentration driving force: $Δ c = c - c *$ where c is the solution concentration and c* is the equilibrium saturation at a given temperature. Supersaturation ratio S is given as $S = \frac{c}{c^*}$ and the relative supersaturation ratio $\sigma = \frac{\Delta c}{c^*} = S-1$

Size dependant crystal growth

Homogeneous nucleation

The free energy associated with nucleation consists of two parts working against each other; the energetically favorable formation of solids and the unfavorable formation of new surfaces. $\Delta G = \Delta G_S + \Delta G_V = 4\pi r^2 \gamma + \frac{4}{3}\pi r^3 \Delta G_v$ Here $Δ G S$ is the surface excess free energy, $γ$ is the interfacial tension between the phases, $Δ G V$ is the volume excess free energy and $Δ G v$ is the same per unit volume. At the point where the $Δ G$ -curve is at its max, we find the critical nucleus size: above this radius the nucleus is stable. Finding this size is straightforward: $\frac{\delta \Delta G}{\delta r} = 0 \Rightarrow r_{crit} = \frac{-2\gamma}{\Delta G_v} \Rightarrow \Delta G_{crit} = \frac{16 \pi \gamma^3}{3(\Delta G_v)^2} = \frac{4}{3}\pi r^2_{crit} \gamma$
Inserting $-\Delta G_v = \frac{k_B T \ln{S}}{\nu}$ the critical energy for nucleation is $\Delta G_{crit} = \frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2}$
This energy originates from random fluctuations. Rate of nucleation can thus be expressed as an Arrhenius equation:
$J = A \exp(\frac{-\Delta G}{k_B T}) = A \exp(\frac{16 \pi \gamma^3 \nu^2}{3(k_B T \ln{S})^2})$

Heterogeneous nucleation

Critical energy changed due to availability of a solid surface. $\Delta G_{crit,hetr} = \phi\Delta G_{crit,hom}, \phi = \frac{1}{4}(2+\cos{\theta})(1-\cos{\theta})$

Growth rate limits

Diffusion controlled growth

Growth as change of particle radius per time is given as $\frac{dr}{dt} = D(C-C_S)\frac{V_m}{r}$ where r is the radius, D is the diffusion coefficient of the growth species, C is the bulk concentration, $C S$ is the solubility concentration and $V m$ is the molecular volume. Solving gives $r^2 = 2D(C-C_S)V_mt + r_0^2$

Diffusion controlled growth promotes unisized particles
Can be obtained by increasing viscosity or introducing a diffusion barrier

Radius difference between particles decreases with time: $\delta r = \frac{r_0\delta r_0}{\sqrt{k_Dt + r_0^2}}$

Surface integration controlled growth

Growth given by $G = \frac{dr}{dt}= k_g(S-1)^g$

Spiral growth (most common): g = 2 at very low supersaturation and g = 1 at large supersaturation
2D Nucleation: g > 2
Rough growth: g=1

Mononuclear growth (layer by layer): $\frac{dr}{dt} = k_mr^2 \Rightarrow \frac{1}{r}=\frac{1}{r_0} - k_mt$ and radius difference increases with time $\delta r = \frac{\delta r_0}{(1-k_mr_0t)^2}$
Polynuclear growth (multiple layers growing at once): $\frac{dr}{dt} = k_p \Rightarrow r=k_pt+r_0$ and radius difference remains unchanged $δ r = δ r 0$

Synthesis of metallic nanoparticles

Metal complexes in dilute solutions are reduced
Stronger reducing agent --> smaller particles
Polymers used as stabilizers and diffusion barriers

Mechanisms for formation of spherical crystalline particles

Aggregation
Crystal Growth

Influences on the synthesis

From reducing agents
- Weak reduction agent: slow reaction rate, large particles. Slow reaction could lead to continuous formation of nuclei --> wide size distribution.
- Strong reduction agent: smaller particles.
- Affects morphology
From other factors (Very specific examples in the text)
- Chloride ion concentration affects syntehsis of Pt nanoparticles from $H 2 P t C l 6$
- Low concentration of reactant --> decreased reduction rate
From polymer stabilizers
- Introduced to form a monolayer on nanoparticle surface to prevent agglomeration (stabilizer)
- Adsorption of polymer occupies growth sites --> growth reduced
- Diffusion barrier
- May also react with solute, catalyst or solvent

1-D nanostructures

Techniques for growing

Spontaneous growth (Bottom-up): Driven by reduction of chemical potential (like nanoparticles) only now needs to be anisotropic
- Evaporation-condensation: Reduction in chemical potential by consumption of supersaturation
- Vapor-liquid-solid / Solution-liquid-solid (VLS/SLS)
- Stress-induced recrystallization
Template-based synthesis (Bottom-up)
- Electroplating and electrophoretic deposition
- Colloid dispersion, melt or solution filling
- Conversion with chemical reaction
Electrospinning (Bottom-up)
Lithography (Top-down)

2-D nanostructures

Techniques for growing

Vapor-phase deposition
- Performed under vacuum
Liquid based growth

Initial nucleation

Island growth / Volmer-Weber growth
Layer growth / Frank-van der Merwe growth
Island layer / Stranski-Krastonov growth

Pensum Del II (Sondre Volden)

Optical properties of metallic nanoparticles

LSPR

Localized surface plasmon resonance
Depends on size, morphology, metal, surroundings

Quasi-static approximation

Energy levels treated as a quasi-continuum of states
Assuming
- $D \le \frac{\lambda}{10}$ for the EM field to be treated as uniform within each spherical particle.
- Particles are small enough - the time of propagation in each sphere is small compared to the oscillation period of the EM field
- D larger than 2 nm (more than 100 atoms) for the separation of energy levels close to the particle surface to be comparable to that of the bulk metal
- Volume fraction small enough to treat particles as independent
- We can introduce an effective dielectric constant for the medium
Intensity through a medium of thickness L:
- $I t = I 0 exp( - α L)$ , where $α(ω)$ is the absorption coefficient
- For normal medium, $\alpha(\omega)=2\frac{\omega}{c}\Kappa(\omega)$
- For a matrix + nanosphere system, $\alpha(\omega) = \frac{9p \omega\epsilon^{3/2}_m}{c}\frac{\epsilon_2}{(\epsilon_1+2\epsilon_m)^2 + \epsilon_2^2} = \frac{\omega}{\epsilon^{1/2}_mc}p|f(\omega)|^2 \epsilon_2(\omega)$ , where p is the volume fraction of nanoparticles, and $ε 1$ is the complex dielectric constant of the matrix and $ε 2$ is the complex dielectric constant of the nanoparticles.
- $| f (ω) | 2$ represents enhancement of $E i$ . Enhancement occurs when $| f (ω) | 2 > 1$ , which happens if the contribution to the dielectric constant from conduction electrons is dominant.
- α(ω) expresses extinction by both absorption and scattering
  - $S_{scatt} = \frac{24\pi^3V^2_{np}\epsilon^2_m}{\lambda^4}|\frac{\epsilon - \epsilon_m}{\epsilon + 2\epsilon_m}|^2$ and $S_{ext} = \frac{18\pi V_{np}\epsilon^{3/2}_m}{\lambda}\frac{\epsilon}{|\epsilon + 2\epsilon_m |^2} = \frac{2\pi V_{np}}{\lambda\epsilon^{1/2}_m} |f(\omega)|\epsilon_2$
  - Ratio varies as volume of nanoparticles: $\frac{S_{scatt}}{S_{ext}} \propto (D/\lambda)^3$
If resonance condition $ε 1 (Ω R) + 2ε m = 0$ , SPR frequency is $\Omega_R = \frac{\omega_p}{\sqrt{\epsilon^{ib}_1(\Omega_R)+2\epsilon_m}}$
SPR shifted towards red with increasing ε_m
- Red shift = bathochromic shift = higher wavelength and lower energy
- Blue shift = hypsochromic shift = lower wavelength and higher energy

Mechanisms for optical properties

Intraband

Optical transitions without change of band
Due to quasi-free electrons in conduction band
Described by Drude model: $\epsilon_{Drude} = 1-\frac{\omega_p^2}{\omega(\omega+i\gamma_0)}$ where $\omega_p^2 = \frac{n_ee^2}{\epsilon_0m_e}$
Absorption must be assisted by a third particle - another electron or a phonon, to conserve energy and momentum
Dominates in red and infrared

Interband

Optical transitions between electronic bands
From filled bands to conduction band or from conduction band to empty bands of higher energy
Dominates in visible and ultraviolet

The Mie Model

For larger sizes, variations across the size of object must be considered

Synthesis procedures

Turkevich reaction

Citrate reduction of chloride precursor $(H A u C l 4)$ , aqueous phase
Citrate acts as reducing agent and passivating ligand
Most common commercially available method
Typically at 100 degrees C
Sizes 2-200nm
Wide array of surface functionalities through ligand exchange

Brust reaction

$BH_4^-$ reduction of chloride precursor
1.5-8nm size
Very stable particles
Wide array of surface functionalities through ligand exchange

Goia reaction

Reduction of auric acid with iso-ascorbic acid
Stabilizer-free, like with citrate
Room temperature, aqueous phase, rapid nucleation and growth
Tunable particle size through pH, reaction ratios, concentration
30-100 nm, or 80-5000 nm if in presence of gum arabic and high Au concentration

One-pot synthesis

Using stimuli-responsive polymers
Using tiopronin or co-enzyme A
Using globular proteins
Using starch-glucose
Using viral templates

Functionalization of metallic nanoparticles

Ag or Au nanoparticles need a surface layer of a passivating ligand to be stable
Direct functionalization: Reducing agent is passivating ligand
Post-synthesis functionalization: Passivating ligand added after synthesis
- Can displace or bind to existing ligand

Adsorption

Chemisorption
- Covalent / ionic bonds, high binding energy
- "Irreversible**
- Monolayer
Physisorption
- van-der-Waals interactions, low binding energy
- Reversible
- Mono or multilayer
Driven by reduction of free energy
Surfactant adsorption on hydrophobic surfaces
- Monolayer
- Hemi-micelles
Surfactant adsorption on hydrophilic surfaces
- At high concentrations: double layer
- Alternatively, close packed micelles
Fractional surface coverage $\theta = \frac{number\;of\;molecules\;adsorbed\;onto\;surface}{number\;of\;molecules\;adsorbed\;at\;monolayer\;coverage} = \frac{N}{N_{mono}}$

Self-assembled monolayers (SAMs)

One head group interacts with substrate, the other determines properties.

Macromolecular adsorption

Entropy of mixing: $S = k lnΩ$ , where $\Omega = \frac{(n_A + n_B)!}{n_A!n_B!}$ . Given that $x j$ is the mole fraction of j, we have $- Δ S m i x = k [n a ln x A + n B ln x B]$ . Assume nearest neighbour interactions only. We get the Flory-Huggins free energy of mixing: $\frac{\Delta G_{mix}}{RT} = n_A\phi_Bx+n_A\ln\phi_A+n_B\ln\phi_B$ . Theory is a bit limited by approximations, shapes of monomers and solvents, and application areas.

Formation of an adsorbed layer happens in three steps: Diffusion towards surface, attachment, and spreading.

Adsorption rate: $\frac{\delta\Gamma}{\delta t} = k(c^b-c^s)$ where $Γ$ is the surface coverage, k is the diffusion and hydrodynamic rate coefficient, $c s$ is the subsurface concentration and $c b$ is the bulk concentration.

New drug delivery vectors

Desirable size: 10-30 nm for access to nucleus
Active vs passive

Approaches

Viral: proteines, peptides
- Very efficient
- Not easy to tune, size restricted
- Elicits strong immune responses
- Can mutilate, can be cytotoxic
- Incapable of delivering chemotherapy agents or short oligonucleotides
Non-viral: Often passive, liposomes, polymers, dendrimers, microspheres
- Inefficient
- Challenging to add functions
- Possibly to control immune reactions
- Not infectious, often cytotoxic
- Capable of delivering chemotherapy agents or short oligonucleotides
Combination vectors: metallic nanoparticle vectors
- Tunable efficiency
- Easy to incorporate different functions
- Size tunable
- Not infectious, controllable cytotoxicity
- Capable of delivering chemotherapy agents or short oligonucleotides

Gold nanoparticles

Can be seen in differential interference contrast microscopy (DIC). Even though the particles are 5-30nm, they appear as reflections of 200-400nm, while cellular structures appear actual size.

Functionalization methodologies:
- Attachment of payload through protein intermediate (Bovine Serum Albumin, BSA): Peptide-BSA-MBS-Au
- Direct attachment of payload to substrate through thiol chemistry
Plasmonically heated Au nanoparticles
- LSPR excited nanomaterials are heated by adsorbed light
- Localized increase in temperatures --> hyperthermal therapy
- LSPR should be in near-infrared because body is more transparent there

Dealing with Cancer

Cancer cells overexpress certain receptors, but receptor targetting still targets healthy cells
Due to lactic acid buildups, cancer cells have lower pH than healthy tissue
Core-shell hydrogel swelling can be tuned to within 0.1 pH
- Nanoparticles suspended within gel, and released upon pH changes

Plant virus nanotechnology

Don't inherently target human cells
Can be used to carry chemotherapeutic agents with little risk
Biologically degradable

Dendrimers

Superbranched polymers
- Core: chemical species in specific nanoenvironment
- Interior monomer layers: encapsulation of molecular species
- Multifunctional surface: determines macroscopic properties
Synthesis
- Divergent (bottom-up): large structures available, lengthy separation procedures, limited by exponentially growing number of end groups
- Convergent (top-down): max 4G, more economically viable, limited by steric constraints
Properties
- Monodispersity
- Biocompatibility
- Size and shape
- Polyvalency
- Interior compartment
Advantages
- Uniform tunable size
- Hydrophilic exterior, hydrophobic interior
- More stable than micelles
- Tunable surface functionalization

Dendriers with cationic surface groups are cytotoxic, and more so with increasing generations. Anionic less so. Hydroxy- and methoxyterminated dendrimers non-toxic. Cytotoxicity can be reduced by cloaking, but some cationic functionality is desired to interact with negatively charged cell membranes.

Release from the "dendritic box" can be done by hydrolysis. Partial hydrolysis releases small molecules, total hydrolysis will release all molecules. Otherwise, the spatial configuration of the dendrimer alters with pH and iconic strength, which can be used for release - especially remembering the pH difference between healthy tissue and tumor tissue.

Targeting mechanisms

Enhanced permeability and retention (EPR)
- There are increased amounts of biofluids around tumors
- High weight polymers accumulate in solid tumor tissue
- Passive targeting
Tumor receptor / antigen targeting
- Tumors often have unique receptors / antigens

Dendrimers as drugs

Antiviral: Competes with cells for viruses. Can inhibit influenza, herpex simplex, HIV.
Antibacterial: Adheres to and damages bacterial cell membranes
Photodynamic therapy: Photoactivated, generates reactive oxygen species

Pensum Del III (Tor Grande)

Micro- meso- and macroporous materials

Adsorption isotherms: Amount of adsorbed gas as a function of pressure.
Macropores: d>50nm
Mesopore: 2nm<d<50nm
Micropores: d<2nm

Types of porous solids

Zeolites (crystalline aluminosilicates)
- Hydrothermal synthesis: Solvent, precursors and a mineralizing agent. A structure-directing agents (cations or organic molecules) fill up pores and balance the charge of the framework. Needs to be removed later.
- Applications: Molecular sieves, chromatography, heterogeneous catalysis, ion exchange, sensing
Metal organic frameworks (MOF)
- Low density
- May have permanent porosity if solvent can be removed
- Synthesis: Hydrothermal or solvothermal
- Applications: Gas adsorption and storage
Ordered mesoporous oxides (Amorphous materials with ordered pores)
- Synthesis: Like zeolite, milder conditions. Needs a source for framework element oxide, a surfactant, a solvent, and a pH modifier
- Size of pores controlled by surfactant size
- Applications: Gas separation, catalysis, gas adsorption. Also, sensing, biosensing, drug delivery, optics, batteries, fuel cells.
Sol-gel derived oxides (random mesoporous solids)
Nano-crystalline Titanium Oxide
- Photocatalycic applications (pollutant degradation, water splitting)
Porous silicon technology
- Preparation: etching
- Applications: sensing technology, support for CNT growth

Core-shell structures

Heteroepitaxial semiconductor core-shell structures

One semiconductor grown epitaxially on particles of another semiconductor. (Formation of shell material on the particle core is a continuation of particle growth, but with different chemical composition.)

Metal-oxide structures

For gold nanoparticles coated with silica, a polymer layer functionalized to bind to gold on one end and silica on the other needs to be in between.

Metal-polymer structures

Prepared by emulsion polymerization or membrane based synthesis.

Oxide-polymer structures

Prepared by polymerization at surface or adsorption.

Fuel cells, batteries

Pensum Del IV (May-Britt Hägg)

Basics of membrane materials and separation

Microporous membrane: Separation according to selective surface flow - largets molecule permeates
Dense polymers: Permeability P equal to diffusion times solution, P=DS
- Influenced by state of polymer, type of gas, pressure, temperature
- Other polymeric membranes: SFTM (selective facilitated transport membrane).
Molecular sieving: Separation according to molecular size (smallest molecule goes through.)
- P=DS but diffusion factor most important
Basic equations for membrane separation
- $P = D S$ where $D [c m 2 / s]$ is diffusivity and $S [c m 3 (S T P) / c m 3 b a r]$ is solubility
- Selectivity $α = P i / P$
- Production rate (flux) $\frac{q}{A_m} = J_i = \frac{P_i}{l}(p_hx_0 - p_ly_p)$ where $A m$ is the membrane area, $l$ is the membrane thickness, $p h, p l$ are feed and permeate pressures and $x 0, y p$ are mole fractions of component i.

Total feed flow given by material balance, $L f = L 0 + V p$ , where $L f$ is the feed in, $L 0$ is the reject feed out and $V p$ is the permeate out.

Selected nanostructured membranes

Mixed Matrix Membranes

Polymeric matrix with dispersed porous inorganic particles

Carbon Molecular Sieve Membranes

Improved flux and selectivity
Tailoring pore size by adjusting pyrolysis parameteres and post treatment (oxidation to increase pore size or organic vapor deposition to decrease pore size)

Glass Membrane

Surface of glass pore can be functionalized to improve flux and selectivity

Pensum Del V (Magnus Rønning)

TKP4190 - Fabrikasjon og anvendelse av nanomaterialer

Fra NanoWiki

Innhold

Pensum Del I (Jens-Petter Andreassen)

Crystallization fundamentals

Supersaturation

Homogeneous nucleation

Heterogeneous nucleation

Growth rate limits

Diffusion controlled growth

Surface integration controlled growth

Synthesis of metallic nanoparticles

Mechanisms for formation of spherical crystalline particles

Influences on the synthesis

1-D nanostructures

Techniques for growing

2-D nanostructures

Techniques for growing

Initial nucleation

Pensum Del II (Sondre Volden)

Optical properties of metallic nanoparticles

LSPR

Quasi-static approximation

Mechanisms for optical properties

Intraband

Interband

The Mie Model

Synthesis procedures

Turkevich reaction

Brust reaction

Goia reaction

One-pot synthesis

Functionalization of metallic nanoparticles

Adsorption

Self-assembled monolayers (SAMs)

Macromolecular adsorption

New drug delivery vectors

Approaches

Gold nanoparticles

Dealing with Cancer

Plant virus nanotechnology

Dendrimers

Targeting mechanisms

Dendrimers as drugs

Pensum Del III (Tor Grande)

Micro- meso- and macroporous materials

Types of porous solids

Core-shell structures

Heteroepitaxial semiconductor core-shell structures

Metal-oxide structures

Metal-polymer structures

Oxide-polymer structures

Fuel cells, batteries

Pensum Del IV (May-Britt Hägg)

Basics of membrane materials and separation

Selected nanostructured membranes

Mixed Matrix Membranes

Carbon Molecular Sieve Membranes

Glass Membrane

Pensum Del V (Magnus Rønning)

Catalysis

Personlige verktøy

Navnerom

Varianter

Visninger

Handlinger

Søk

Navigasjon

Verktøy