bottom up manufacturing techniques and driving …...• bottom up manufacturing is self assembly...

Bottom Up Manufacturing

Bottom Up Manufacturing Techniques and Driving Forces

Terence Kuzma

Outline

• What is Bottom Up Manufacturing (Lecture 1)

– Examples in Bottom Up Manufacturing • SAMs• Functionalized Materials• Langmuir–Blodgett film

– Look at energy to drive self assembly • Surface energy• Bonds

• Bottom Up manufacturing is Self Assembly • Done by enabling a precursor on the

substrate and encouraging controlled growth.• For this lecture, we will concentrate on

particle to surface interactions• Let’s first look at the big picture of self

assembly, the later look at the energies driving the process

What is Bottom Up Manufacturing?

• SAMs are targeted to a specific precursor material.

• Early stages of adsorption on a target material is random and disordered.

• The final monolayer consists of close-packed molecules with a uniform orientation.

• The transition from early adsorption to a contiguous monolayer is a stepwise process

General Steps for SAMs Processing

• Initially a adsorbed molecules form a dilute 2D-vapor. This low-density of mobile molecules randomly adsorb to the target surface.

• An intermediate density of adsorbed molecules produces a variety of orientations of the molecules on the surface. Islands of solids will nucleate and grow on the target material.

• The final high-density phase consists of continuous closely packed highly ordered conformation of molecules on the target material.

• This process follows nucleation island growth and coalescence.



Annu. Rev. Phys. Chem. 2001. 52:107–37

Examples of SAMs

• Organosulfur compounds on gold are some of the most studies self assembled interactions. In particular alkanethiol SAMs are well understood.

Surface-active organosulfur compounds that form monolayers on gold.

Chemical Reviews, 1996, Vol. 96, No. 4

Examples of SAMs• The central mechanism for alkanethiol SAMs

involves a strong interfacial binding of sulfur to gold, and a comparably strong lateral interaction between hydrocarbon chains.

• Alkanethiols adsorb spontaneously on gold surfaces from solution and form alkanethiolates with loss of hydrogen.

• Support for the hydrocarbons is accomplished through of cumulative van der Waals forces between the fatty chains which can be functionalized to provide a desired material property such as wettability, and protection against corrosion.

J. Phys. Chem. B 1998, 102, 3456-3465

Examples of SAMs• Alkanethiols are physisorbed then chemisorbed

to a gold surface. Energy is the deciding factor as to which type of adsorption will dominate.

The amount of energy needed to physisorb an alkanethiol to a gold surface increases as the size of the hydrocarbon increases.

The amount of energy needed to chemisorb the alkanethiol to a gold surface stays relatively constant as the size of the hydrocarbon increases. This should be expected since S is responsible for chemisorption and not the hydrocarbon.

Adapted from J. Phys. Chem. B, Vol. 102, No. 18, 1998 3457

Examples of SAMs• Alkanethiols are chemisorbed and physisorbed

to a gold surface. Energy is the deciding factor as to which type of adsorption will dominate.

Adapted from J. Phys. Chem. B, Vol. 102, No. 18, 1998 3457

Examples of SAMs

A schematic description of fatty acid monolayers on AgO and Al2O3.

Chemical Reviews, 1996, Vol. 96, No. 4

•Many factors influence the tilt of carboxylic acid monolayers including:

•The cross sectional area of the molecular chains•The material to which the monolayer self assembled•Differences in materials are attributed to:

•Site specificity•Binging geometries•Binding strength and other factors.

Applications for SAMs

N.K. Chaki, K. Vijayamohanan / Biosensors & Bioelectronics 17 (2002) 1–12

SAMs can be used for communication between the redox-active enzymes and electrode surfaces. This table summarizes various glucose enzymes (EC 1.1.3.4) produced from a variety of bacteria, and the various functional groups that link the enzymes can metal electrodes.

Langmuir–Blodgett film• A Langmuir–Blodgett film contains one or more

monolayers of an organic material, deposited from the surface of a liquid onto a solid by immersing the solid substrate into (or from) the liquid.

• A monolayer is adsorbed homogeneously with each immersion or emersion step, thus films with very accurate thickness can be formed.

Layered Biosensor ConstructionBy Joanna Cabaj and Jadwiga Sołoducho

• Langmuir–Blodgett films are named after Irving Langmuir and Katheryn Blodgett at General Electric Research and Development. Work was done in the late 1920’s.

• Similar to Atomic Layer Deposition (ALD), A monolayer is adsorbed homogeneously with each emersion dip step

• Total film thickness is predictable because the thickness of each monolayer is known and can therefore be added to find the total thickness

• These monolayers can be transferred to many different substrates

• Typical substrates include, silicon, silicon dioxide, glass, metals with oxidized surface.

• Surface must be contamination free• Substrates that have high surface energy such as gold, attract

contaminants and result in low quality LB films

Langmuir–Blodgett film

Langmuir–Blodgett film• Below is the vertical deposition method

https://www.uni-oldenburg.de/pc2/seiten/langmuir-blodgett/

Langmuir–Blodgett film• Surfactant molecules arranged on an air–water

interface

By Major measure - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5393833

Langmuir–Blodgett film• Surfactant, (surface-acting agents) are

compounds that lower the surface tension between two liquids, or a liquid and solid.

• Surfactants are usually referenced to an aqueous environment and are made from organic compounds that are amphiphilic that means the contain both a hydrophobic end known as a head, and a hydrophobic side termed a tail.

• Common amphiphilic substances are soaps, detergents, and lipoproteins, liposomes, micelles.

Langmuir–Blodgett film• Further an amphiphile is a molecule that is

insoluable in water. This stability may be based on pressure, heat, and other energies such as light. These may cause the amphiphile to degrade

• The solubility of an amphiphilic molecule in water dependson the balance between the alkyl chain length and the streangth of it’s hydrophilic head.

Langmuir–Blodgett film• Therefore, a surfactant contains both a water-insoluble (or oil-

soluble) component and a water-soluble component• Since the tails are hydrophobic, their exposure to air is

favored over that to water. Similarly, since the heads are hydrophilic, the head–water interaction is more favorable than air–water interaction. The overall effect is reduction in the surface energy (or equivalently, surface tension of water).

• An early experiment was done by Ben Franklin, and a teaspoon of oil was used to calm the water on a half acre pond. The oil formed a monolayer and “did not agglomerate”. This example was later used to prove Avogadro's number.

Langmuir–Blodgett film• A common form of surfactant is the lipid.

Fatty Acid

Phosphate

Choline Hydrophilic Head

Hydrophobic Tail


Water

Hydrophobic, Nonpolar tails

Hydrophilic, Polar head

Langmuir–Blodgett filmProperties of different head groups

Very Weak Weak Strong Very StrongHydrocarbon -CH2CH3 -CH2OH -SO4

-CH2I -C6H4OCH3 -COOH -OSO-CH2Be -COOCH3 -CN -C6HSO4

-CH2Cl -CN=NOH -NR-NO2 -C6H4OH

-CH2COCH3

-NHCONH2

-NHCOCH3

C. Guozhong. Nanostructures & Nanomaterials: Synthesis, Properties & Applications. Imperial College Press. London 2007

Langmuir–Blodgett filmSchaefer Method

• The Schafer method is used to transfer a mono layer from a water to air surface to a flat substrate.

Langmuir–Blodgett FilmIssues

• The critical micelle concentration is defined as the concentration of surfactants above which agglomeration of micelles form, and additional surfactants added to the system add to a micelles

• Generally for LB films, agglomeration of micelles is avoided, so concentration is carefully controlled. But the formation of micelles could be desirable for certain applications such as drug delivery.

Langmuir–Blodgett FilmIssues

• Aggregates can also be formed, such as spherical or cylindrical micelles or lipid bilayers.

• This aggregation occurs when the critical micelle concentration is exceeded

• Naturally this destroys the L/B process and should be avoided

Bottom Up Manufacturing

Bottom Up Manufacturing Techniques and Driving Forces

Part 2

Terence Kuzma

Outline

• What is Bottom Up Manufacturing (Lecture 1)

– Examples in Bottom Up Manufacturing • SAMs• Functionalized Materials• Langmuir–Blodgett film

– Look at energy to drive self assembly • Surface energy• Bonds

Size Dynamic

• Generally accepted material properties are derived from bulk materials.

• As the material surface to volume ratio changes, the properties of mechanics, optics, electricity, magnetism, and chemistry change.

• The ability to craft products that take advantage of these unique nanoscale properties will continue to create jobs.

Size Dynamic• Nanoparticles exhibit unique properties due to

their high surface area to volume ratio. Naturally as this surface area to volume changes, the properties of the particles change. The properties are not only dependent upon size, but are impacted by the net contribution of the outer valence electrons in the packet.

• The properties of materials change as their size approaches the nanoscale and as the percentage of atoms at the surface of a material becomes significant. The interesting and sometimes unexpected properties of nanoparticles are not partly due to the aspects of the surface of the material dominating the properties in lieu of the bulk properties.

Surface energy

• Where• γ = Surface Energy• Nb = Number of broken bonds• ℰ = the bond strength • ρa = the number of atoms per unit area on the

new surface (surface atomic density)

C. Guozhong. Nanostructures & Nanomaterials: Synthesis, Properties & Applications. Imperial College Press. London 2007

Surface bond “uniqueness”• W W W W W W W = Math model derived from

“bulk” view inside a materials such as a crystal lattice. Basically the entire material has near neighbors that share bonds. The surface lacks this bonding, and these bonds are called dangling bonds

• W WW WW W WW = lowered energy by sharing near neighbor bonds. Difficult to calculate, and is often measured.

A Table of surface energies and bulk material energies can be found in:Jiang, et al., Journal of Physics C (Condensed matter), 16, 521 (2004)

Cu(111) 1.83Au(111) 1.52Ag(111) 1.20Pt(111) 2.54Fe(111) 3.62Mo(111) 4.62

Surface Energy, J/m2

Al2O3 1.7 – 2.6SiO2 ~1.5

Forces in Bottom Up Manufacturing


• Intermolecular Bonds: short-range attractive forces operating between particles and medium that suspends the particle.

-Weak in nature-Most common in self assembly-Stable molecular structure in self assembly is formed by many non-covalent bonds

Brown, LeMay, Bursten. Chemistry: The Central Science 8th ed. Prentice Hall. Upper Saddle River, NJ. 2000


• Van der Waal Forces: forces of attraction within the volume of a molecule.• Also called dispersion forces• Occurs due to an atom’s electron cloud

fluctuates causing a temporary electric dipole • Electrostatic attraction based upon closeness

of atom• Electron cloud size determines the correct

distance (Van der Waal radius) for the reaction

• Energy 1-2 KJ/MolBrown, LeMay, Bursten. Chemistry: The Central Science 8th ed. Prentice Hall. Upper Saddle River, NJ. 2000.


• Hydrogen Bond: intermolecular attractions between molecules containing hydrogen bonded to an electronegative element.• Forms as a result of Coulombic forces • Electrostatic attraction occurs between H of

an atom and a pair of non-bonded electrons in O-H & N-H with O & N- groups

• Among the strongest of dipole-dipole attractions

• Energy 1 - 2 KJ/mol

Brown, LeMay, Bursten. Chemistry: The Central Science 8th ed. Prentice Hall. Upper Saddle River, NJ. 2000.


• Ionic Bonds: formed between oppositely charged ions.

• Atoms either transfer or share their outer electrons

• Goal is to get lower energy state by filling outer valance shell

• Energy 1-5 KJ/mol



• Covalent bonds: formed between two or more atoms by a sharing of electrons.

-Strong bonds that share electrons-For most self-assembly covalent bonds are not required

-Are not found in natural self assembly processes. (requires thermodynamic control of the structure to form the bonds)

-Common bond in Nanotube and buckyballstructures


Forces Used to Direct Bottom Up Manufacturing

• Capillary forces– Particle – particle Interactions

• Small objects on an aqueous surface attract each other.

– Interaction between a particle and the environment.

• When two hydrophobic surfaces come in contact with each other they remain in contact.

– O3 treatment of PDMS

Forces Used to Direct Bottom Up Manufacturing

• Magnetic forces– It forms high ordered structures with rational

orientation.– It involves attraction force to create self assembly

systems

• Electrostatic forces – This force controls the way particles move in a

solution by applying a voltage.– For the most part the particles assemble into a

chain like structure

Functionalization• Reaction products with acceptable stability can

also be formed from physical forces alone such as the attachment or clustering of the hydrophilic ends of a surfactant.

• Some chemical reactions go instantaneously while others require an input of energy.

• Invariably, reactions involve the use of chemically reactive materials.

• These functional groups act as “selective velcro” to localize a reaction.

Functionalization

• Functionalization– Functionalization is crafting a surface, or a

molecule to meet specific needs.• In most cases, modification of the surfaces

via self assembly is brought about by chemical reactions.

Functionalized Metal Surface

From: www.waterlink.com

Surface Types ReactantsGold Thiols, Silanes, Carboxylic Acid

Silicon Alkanes

Silver Carboxylic Acids

Metallic Oxides Siloxanes

Surface modification of bulk materials may require the use of ultra high vacuum, electron or ion beams, and intense ultra violet light.

Chemical Functional Groups

Wade, L.G. Jr, Organic Chemistry 4th Ed. Prentice Hall. Upper Saddle River, NJ. 1999

Strategies to Functionalize Gold Nanoparticles

• Gold nanoparticles can be used for many applications ranging from pigments in pottery to targeted drugs, to active materials for sensors.

• We will narrow the scope of applications and look at nanoscale gold for biological interaction such as smart drugs


• These drugs are defined as smart because the functionalization make the gold selective to specific biological interface.

• Gold nanoparticles currently look like a viable option that poses little harm biologically.


• These metal particles are also useful because gold nanoparticles exhibit plasmon resonance (light emission though stimulation). These particles can also be used to capture energy to ablate surrounding tissue.


• Gold nanoparticles are useful for biological applications because they can be made from 20-200nm, and this size scale is conducive to cells.

• Cells can intake particles by two main pathways. – Through junction ports in the cell– Through endocytosis, where the cell wall

engulfs the particle.


• Both receptor mediated modes prefer spherical particles, and generally shun rods, squares and triangles.

https://www.boundless.com/biology/textbooks/boundless-biology-textbook/structure-and-function-of-plasma-membranes-5/bulk-transport-67/endocytosis-339-11476/


• Gold nanoparticles are commonly functionalized in three modes.– Nude gold with little to no capping agent.

Materials like citrate are often displaced by the functionalizing material. The material in this case is a linking thiol.

– Nude gold with little to no capping agent. Materials like antibodies are commonly applied directly to the gold.

– Coated gold with a purposeful capping agent that interfaced the gold and antibody


• Nude gold with little capping agent can use thiols as a linker molecule to attach a functional group

Innova Biosciences


• Di-thiols offer stronger attachment to the gold, but may reduce the amount of functional groups.

Innova Biosciences


• Nude gold with little capping agent such as residual citrate from manufacturing can be accept antigens. This is known as passive incorporation of antigens to the gold.

• The specific mechanism is not well understood but empirical methods produce good results.


Innova Biosciences


• A third option for functionalization is to coat the gold particle with a shell to provide binding to the next interface layer.

• This method tends to be robust


• Specially treated gold with specific coatings

Innova Biosciences

Summary• Self assembly can be driven by the surface

energy of a nanoparticles.• Langmuir–Blodgett film contains one or more

monolayers of an organic material, deposited from the surface of a liquid onto a solid by immersing the solid substrate into (or from) the liquid.

• Nanoparticles can be functionalized to promote specific self assembly

bottom up manufacturing techniques and driving …...• bottom up manufacturing is self assembly...

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