1. nanotechnology and nanocomposites

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CHEG589: Polymer Nanocomposites

Chapter 1: Nanotechnology and Nanocomposites

Dr. Vikas Mittal, Summer 2015



The Beginning• In 1959, Physics Nobel Laureate Richard Feynman suggested: What I want

to talk about is the problem of manipulating and controlling things on a

small scale ... What are the limitations as to how small a thing has to be

before you can no longer mold it?

• The term nanotechnology was first used in 1974 by Norio Taniguchi to

refer to the precise and accurate tolerances required for machining and

finishing materials.

• In 1981, K. E. Drexler described a new "bottom‐up" approach, instead of

the top‐down approach discussed earlier by Feynman and Taniguchi. The

bottom‐up approach involved molecular manipulation and molecular

engineering to build molecular machines and molecular devices with

atomic precision.



What is Nanotechnology?• The term nano derives from the Greek word for dwarf. It is used as a prefix

for any unit such as a second or a meter, and it means a billionth of that unit.

Hence, a nanometer (nm) is a billionth of a meter, or 10‐9 meters.

• Nanotechnology means any technology on a nanoscale that has applications

in the real world. Nanotechnology encompasses the production and application of physical, chemical, and biological systems at scales ranging

from individual atoms or molecules to submicron dimensions, as well as the

integration of the resulting nanostructures into larger systems.



What is Nanotechnology?

• Despite the wide use of the word nanotechnology,

the term has been misleading in many instances. This is because some of the technology

deals with systems on the micrometer range and not on the nanometer

range (1‐100 nm).

• Nanomaterials are also not undiscovered materials. It is important to keep

in mind that some past technology such as, for example, nanoparticles of

carbon used to reinforce tires as well as nature's photosynthesis are

already a form of nanotechnology.



Approaches to Nanotechnologies

• top‐down approach: An operator first designs and controls a macroscale

entity to produce an exact copy of itself, but smaller in size. Subsequently, this downscaled entity, will make a replica of itself, but also a few times smaller in size. This process of reducing the scale continues until a nanosize entity is produced and is capable of manipulating nanostructures.

• One of the emerging fields based on this top‐down approach is the field of nano‐and micro‐electromechanical systems (NEMS and MEMS, respectively). MEMS research has already produced various micro

mechanical devices, smaller than 1 mm2, which are able to incorporate

microsensors, cantilevers, microvalves, and micropumps.

• An interesting example is the microcar fabricated by Nippondenso Co.



Approaches to Nanotechnologies

• The top‐down approach is not a friendly, inexpensive, and rapid way of producing nanostructures. Therefore, a bottom‐up approach needs to be

considered.

• The concept of the bottom‐up approach is that one starts with atoms or

molecules, which build up to form larger structures.

• In this context, there are three important enabling bottom‐up

technologies, namely (1) supramolecular and molecular chemistry, (2)

scanning probes, and (3) biotechnology.



Length Scale

Length scales ranging

from subatomic through

molecular, human, and

terrestrial to astronomic



Why is Nano Scale Important?• By creating nano‐scale structures, it is possible to control the

fundamental properties of materials, such as their melting

temperature, magnetic properties, charge capacity, and even their

color, without changing the materials’ chemical composition.

• Making use of this potential leads to new, high‐performance

products and technologies that were not possible before.

• Nanoscale structures such as nanoparticles and nanolayers have

very high surface to volume ratios, making them ideal for use in

polymeric materials.



Nanotechnology in NatureAbalone

• Abalone builds the shell from traditional

materials, namely calcium carbonate (CaCO3)and a protein, forming a layered

nanocomposite that is strong and resilient

• Looking at the shell under an electron

microscope at high magnifications, the shell

looks like a brick wall, with calcium carbonate "bricks" separated by the protein

"glue"

• The formation of the abalone shell starts with proteins, which self assemble into

"room walls" with a distribution of negatively charged sites. Inside each "room" there is seawater filled with calcium and carbonate ions, which are attracted to

the walls and eventually form crystals of CaCO3



Nanotechnology in NatureSpider Web

• The combined strength and flexibility of a spider web results from the

arrangement of nanocrystalline reinforcements embedded in a polymer matrix.

• A closer look at the spider web microstructure reveals the existence of strongly oriented nanocrystals, which adhere to the protein that composes their surrounding polymeric matrix. In other words, the spider web is a nanocomposite material composed of relatively stiff nanocrystals dispersed

within a stretchy matrix



Nanotechnology in NatureRhinoceros Horn

• The horn is a composite made of two types of keratin.

• One type is in the form of tubules that are densely packed. These tubules, which range from 300 to

500 μm, comprise around 40 layers of cells.

• Surrounding these tubules is another type of keratin that is continuous and acts as a matrix.

• Because the matrix and the tubules are the same material, the interfacial strength is very good, which

leads to a rigid material that is very tough to break.



Classes of Materials• Nanomaterials: The nanomaterial class of materials is extremely broad

because it can include all the previous classes of materials, provided they

are composed of a structural component at the nanoscale or they exhibit

one of the dimensions at the nanoscale.

• Nanomaterials are typically categorized according to the number of

dimensions that are not at the nanoscale

0‐D (nanoparticles),

1‐D (nanowires, nanotubes, and nanorods),

2‐D (nanofilms and nanocoatings),

3‐D (bulk)



Classification of Nanomaterials• The most typical way of classifying

nanomaterials is to identify them

according to their dimensions.

• Nanomaterials can be classified as (1)

zero‐dimensional (0‐D), (2) one‐

dimensional (1‐D), (3) two‐

dimensional (2‐D), and (4) three‐

dimensional (3‐D).

• This classification is based on the

number of dimensions, which are not

confined to the nanoscale range (<100

nm).



Classification of Nanomaterials0‐D

The most common representation of zero‐dimensional

nanomaterials are nanoparticles. These nanoparticles

can:

• Be amorphous or crystalline

• Be single crystalline or polycrystalline

• Be composed of single or multichemical elements

• Exhibit various shapes and forms • Exist individually or incorporated in a matrix

• Be metallic, ceramic, or polymeric




1‐D nanomaterials differ from 0‐D nanomaterials in that

the former have one dimension that is outside the

nanoscale. This difference in material dimensions leads to

needle‐shaped nanomaterials. One‐dimensional

nanomaterials include nanotubes, nanorods, and

nanowires. 1‐D nanomaterials can be:

• Amorphous or crystalline

• Single crystalline or polycrystalline

• Chemically pure or impure

• Standalone materials or embedded in within another

medium

• Metallic, ceramic, or polymeric




2‐D nanomaterials are materials in which two of the

dimensions are not confined to the nanoscale. As a result,

2‐D nanomaterials exhibit platelike shapes. Two‐

dimensional materials can be:


• Made up of various chemical compositions

• Used as a single layer or as multilayer structures

• Deposited on a substrate

• Integrated in a surrounding matrix material





These materials have three dimensions above 100 nm.

Despite their bulk dimensions, these materials possess a

nanocrystalline structure or involve the presence of features

at the nanoscale. With respect to the presence of features at

the nanoscale, 3‐D nanomaterials can contain dispersions of

nanoparticles, bundles of nanowires, and nanotubes as well as multinanolayers. Three‐dimensional nanomaterials can be:


• Chemically pure or impure

• Composite materials

• Composed of multinanolayers




Classification of Nanomaterials• The 2‐D nanomaterial may be called a

nanocrystalline film because of two features:

(1) the material exhibits an overall exterior

thickness with nanoscale dimensions, and (2)

its internal structure is also at the nanoscale.

• Though this example helps illustrate two

possible ways of categorizing of 2‐D

nanomaterials, both these restrictions do not

need to be in place for the material to be

considered a nanomaterial.

• In fact, if the exterior thickness remains at the nanoscale, it is possible for the same film to

have a larger (above 100 nm) internal grain

structure and still qualify the entire material

as a nanoscale material.



Classification of Nanomaterials• Generally, 2‐D nanomaterials, are deposited on

a substrate or support with typical dimensions

above the nanoscale. In these cases, the overall

sample thickness dimensions become a

summation of the film's and substrate's

thickness. When this occurs, the 2‐D

nanomaterial can be considered a nanocoating.

• When the substrate thickness does have

nanoscale dimensions or when multiple layers,

with thicknesses at the nanoscale are deposited sequentially, the 2‐D nanomaterial can be

classified as a multilayer 2‐D nanomaterial.

Within each layer, the internal structure can be

at the nanoscale or above it.



Classification of Nanomaterials• For 3‐D nanomaterials: from our previous

definition, bulk nanomaterials are

materials that do not have any dimension

at the nanoscale. However, bulk

nanomaterials still exhibit features at the

nanoscale. Bulk nanomaterials with

dimensions larger than the nanoscale can be composed of crystallites or grains at the

nano scale. These materials are then called

nanocrystalline materials.



Classification of NanomaterialsAnother group of 3‐D nanomaterials are called nanocomposites. These

materials are formed of two or more materials with very distinctive

properties that act synergistically to create properties that cannot be

achieved by each single material alone. The matrix of the nanocomposite,

which can be polymeric, metallic, or ceramic, has dimensions larger than the

nanoscale, whereas the reinforcing phase is commonly at the nanoscale.



Classification of Nanomaterials



What is

a Polymer?

• A GIANT molecule

• Made up of units

called monomers

• If a carbon atom was the size of a tennis

ball:

PE = 30km

DNA = 70,000km



Uses of Polymers



Petrochemical Value Chain based on Cracker

Source: Linde



Definitions

• Monomer ‐ simple molecular unit which when reacted

together forms a polymer.

• Oligomer ‐ low molecular weight compound with

several repeat units joined together.

• Polymer ‐ substance composed of molecules with a

large molecular weight formed from repeating units

covalently bonded together.



Types

of

Polymers

natural polymers

- cellulose

- proteins

- DNA

- natural rubber

- shellac

- amber

synthetic polymers

- polyethylene

- polypropylene

- poly(vinylchloride)

- synthetic rubber

- polyamides- polyurethanes

- melamine resins



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• The dimer of ethylene is a gas, but

oligomers with a DP of 3 or more are

liquids, with the liquid viscosity increasing

with the chain length.

• Polyethylenes with DPs of

about 30 are grease like, and those with

DPs around 50 are waxes.

• As the DP value exceeds 400 or the

molecular weight exceeds about 10,000,

polyethylenes become hard resins with

softening points about 100°C. The increase

in softening point with chain length in thehigher-molecular-weight range is small.

Importance of DP



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• Tensile strength properties

increase rapidly first as the chain length

increases and then level off

• The melt viscosity continues to increase

rapidly with molecular weight

• Polymers with very high molecular

weights have superior mechanicalproperties but are difficult to process and

fabricate due to their high melt viscosities.

• The range of molecular weights chosen

for commercial polymers represents acompromise between maximum properties

and processability.

Importance of Molecular Weight



Uniqueness of Nanostructured Materials

• What is unique to nanofillers compared to micrometer‐scale

traditional fillers, and how do the composites compare to

their macroscopic counterparts?

Small size of filler particles (optical clarity)No stress concentration

Exceptionally large interfacial area



Nanocomposites• Nanocomposites are a class of materials in which one or more phases with

nanoscale dimensions (0‐D, 1‐D, and 2‐D) are embedded in a metal,

ceramic, or polymer matrix.

• The general idea behind the addition of the nanoscale second phase is to

create a synergy between the various constituents, such that novel

properties capable of meeting or exceeding design expectations can be

achieved.

• The properties of nanocomposites rely on a range of variables, particularly

the matrix material, loading, degree of dispersion, size, shape, and

orientation of the nanoscale second phase and interactions between the

matrix and the second phase.



NanocompositesPolymer‐matrix nanocomposites

• Polymer type: thermoset, thermoplastic, elastomer• Reinforcement: nanoparticles (0‐D), nanotubes (1‐D) and nanoplates (2‐D)

Polymer‐matrix nanocomposites with 0‐D materials

• Depending on the type of nanoparticles added, the mechanical, electrical,

optical, and thermal properties can be altered

• In the case of mechanical properties, modulus and strength depend on the

degree of interaction between the particle and the polymer. For example, in poly(methyl methacrylate) (PMMA) nanocomposites reinforced with

alumina, the modulus decreases due to the weak interaction, whereas in

polystyrene nanocomposites reinforced with silica nanoparticles, the

modulus increases due to a strong bonding.



NanocompositesPolymer‐matrix nanocomposites with 1‐D materials

• Carbon nanotubes (CNTs) are widely used as reinforcement.

• Several critical factors need to be addressed:

(1) uniform dispersion of carbon nanotubes within the polymer matrix,

(2) alignment of CNTs in the nanocomposite,

(3) good interfacial bonding between the CNTs and the polymer matrix.

• With respect to the dispersion of CNTs, they

exhibit smooth surfaces and intrinsic Van der Waals

interactions, which tend to promote clustering when

dispersed in a polymer matrix



NanocompositesPolymer‐matrix nanocomposites with 2‐D materials

• Plate like layered materials (layered silicates)

with a thickness on the order of 1 nm but with

an aspect ratio of 25 or above.

• Significant improvements in different properties

• For these layered silicates to be useful in

nanocomposites, the layers must be separated

and dispersed within the polymer matrix.

However, these layers are highly hydrophilic, and

thus individual layers do not easily disperse in

relatively hydrophobic species, such as an

organic polymer.



Nanocomposites• The resulting nanocomposites can exhibit

various microstructures.

• Intercalated nanocomposites, when the

polymer diffuses into the clay layers, thereby

expanding the distance between the clay layers,

but the order (or periodicity) is still maintained

• Exfoliated nanocomposites when individual

delaminated silicate layers are dispersed in a

polymer matrix, thus completely disturbing the

order of the clay layers.



Mechanical Properties



Role of Aspect Ratio on Properties



Other Properties

• Apart from mechanical and permeation properties, other properties attributed to polymer nanocomposites are:

improved thermal resistance

improved flame resistance

improved moisture resistance

improved charge dissipation

improved chemical resistance

ff f l



Size Effects: Surface‐to‐Volume

Ratio Versus Shape

• Properties of large‐scale traditional materials are determined by the

properties of their bulk, due to the relatively small contribution of a small

surface area, however, for nanomaterials this surface‐to‐volume ratio is

inverted.

• a nanomaterial's shape is of great interest because various shapes will produce

distinct surface‐to‐volume ratios and

therefore different properties.

Sphere A/V = 3/r

Cylinder A/V = 2/r

Cube A/V = 6/L

Si Eff S f V l



Size Effects: Surface‐to‐Volume

Ratio Versus Shape

How much of an increase in surface area will result from a spherical particle

of 10 μm diameter to be reduced to a group of particles with diameter of 10

nanometer, assuming that the volume remains constant?

1. nanotechnology and nanocomposites

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