Functional Materials and Polymers Overview

Functional Materials

• Classification is based on heat response and conducting electricity.
• Polymers (ABS and Bakelite) are categorized for synthesis and application.
• Conducting polymers include polyacetylene and doping effects.
• Nano materials are introduced with classification and properties (surface area and quantum effects).
• Top-down and bottom-up approaches for synthesis (ball mill and sol-gel) are discussed in terms of bulk vs. nano (gold).

Introduction to Polymers

• Polymers are used in everyday life for various purposes.
• Common examples include grocery bags, soda/water bottles, textile fibers, phones, computers, food packaging, auto parts, and toys.

Definition of Polymer

• Polymers are macromolecules with high molecular weight, formed through the repeated linking of small molecules.
• These small molecules are called monomers.
• An example of a polymer is polyethylene (formed by linking monomer ethylene).

Polymer - Classification

• Polymers are classified based on their occurrence (natural, synthetic, semi-synthetic).
• They can also be classified by the type of polymerization (addition or condensation).
• Polymers are categorized by their monomeric units (homopolymers, copolymers), and their thermal effects (plastics, rubbers).

Classification – Thermal Effect

• Polymers are classified into plastics and rubbers.
• Plastics are further classified into thermoplastics and thermosetting plastics (thermosets).
• Thermoplastics do not undergo chemical change upon heating, and can be remoulded.
• Thermosets are hardened upon heating and cannot be remoulded.

Plastics

• Plastics are high molecular weight organic polymer materials that can be molded into any shape using heat and pressure.
• Types of plastics include thermoplastics and thermosets.

Types of Plastics

• Thermoplastics do not undergo significant chemical changes when heated and can be remolded multiple times.
• Examples of thermoplastics include polyethylene and polyvinyl chloride.
• Thermosetting plastics undergo chemical changes and harden permanently upon heating, and cannot be remolded.
• Bakelite and polyester are examples of thermosets.

Difference between Thermoplastic and Thermosetting Polymers

• Thermoplastics soften on heating, while thermosets do not.
• Thermoplastics can be remelted and reshaped, while thermosets cannot.
• Thermoplastics are often soluble in some organic solvents, whereas thermosets are largely insoluble.
• Thermoplastics are usually recyclable, while thermosets are generally not.

Properties and engineering applications

• Specific types of thermoplastic and thermosetting polymers are discussed.
• Examples include PVC, Teflon (PTFE), ABS, Novolac, and Bakelite.

TEFLON (PTFE) - Preparation & Properties

• Teflon (PTFE) is a polymer made by polymerizing tetrafluoroethene.
• Teflon is a hard, strong, chemically resistant compound with a high melting point and very low surface friction.

TEFLON (PTFE) - Uses

• Teflon is used in motors, transformers, capacitors, pipes, tanks, and for storage of chemicals.
• It is also found in non-stick appliances and as a lubricant to reduce friction and wear in machinery.

Acrylonitrile-Butadiene-Styrene (ABS)

• ABS is a widely used thermoplastic and amorphous polymer.
• ABS is known for its strong resistance to corrosive chemicals and physical impacts.
• It can be easily molded and has a low melting temperature, making it easy for processing methods like injection molding and 3D printing.

Thermosetting Plastics - Bakelite/Phenolic resins

• Phenolic resins, like Bakelite, are condensation polymerization products of phenol derivatives and aldehydes.
• The products (Bakelite) are hard, scratch-resistant, infusible, water-resistant, and insoluble in many organic solvents, although they can be affected by alkali.
• They have excellent electrical insulating properties.

Conducting Polymers

• Polymers with conjugated p-bond structures exhibit improved conductivity when doped with conductive materials.

Nobel Prize in Chemistry (2000)

• Alan MacDiarmid, Alan Heeger, and Hideki Shirakawa received the Nobel Prize for their work on conductive polymers.
• Specific examples of conductive polymers are discussed alongside classifications regarding doping methods.

Different Types of Conducting Polymers

• Intrinsically conducting polymers.
• Doped conducting polymers.
• Externally conducting polymers.

Factors that affect polymer conductivity

• Density of charge carriers
• Charge carrier mobility
• Direction of movement of charge carriers
• Presence of doping materials.
• Temperature

Intrinsically Conducting Polymers (ICPs)

• ICPs consist of alternating single and double bonds (conjugated double bonds).
• Conjugation leads to a stronger sigma bond, but weaker localized pi bonds.
• This conjugation pattern allows for the delocalization of π-electrons through the backbone.

Dopant Considerations in Conducting Polymers

• Both p-doping(oxidation) and n-doping (reduction) methods can improve conductivity.
• The doping process introduces new charge carriers.

p-Doping

• Achieved through oxidation (removal of electrons). Oxidative doping is commonly utilized.
• p-dopants include halogen molecules and lewis acids.
• Results in positive charge carriers formation, like polarons and solitons.

n-Doping

• Achieved through reduction (addition of electrons). Reductive doping is an alternative method.
• n-dopants typically include lewis bases.
• Results in negative charge carriers formation, like polarons and solitons.

Doping in ICPs

• Doping process in intrinsically conducting polymers has a detailed mechanism.
• Positive and negative charge carriers formation are observed following the doping process.

Introduction to Nanomaterials

• Nanomaterials are substances with at least one dimension between 1 and 100 nanometers.
• Examples include individual chemical bonds, small molecules, proteins, and living cells.

Categories of Nanomaterials

• Nanomaterials are categorized into carbon based materials (organic), inorganic materials, and polymeric materials.

Why do nanoparticles behave differently?

• Two main factors lead to differences in properties compared to bulk materials: Surface area effect (surface to volume ratio) Quantum effect (quantum confinement)

Surface Area Effect

• The surface area to volume ratio greatly increases as the size decreases in nanoparticles.
• This heightened ratio significantly influences reactivity.

Quantum Effect

• Quantum effects become apparent in materials at the nanoscale. Quantum confinement is pivotal.

Quantum Confinement

• Quantum confinement significantly alters the optical, electrical, and magnetic properties in nanomaterials.

Quantum Dots

• These are semiconductor particles with dimensions in the nanometer range.
• They exhibit unique optical and electronic properties compared to larger particles.

Quantum Dots - Applications

• Quantum dots are utilized in various applications:
• Cancer cell imaging
• Metal ion sensing
• Light-emitting diodes

Emission Properties of Quantum Dots

• Quantum dots exhibit distinct emission properties influenced by their size.
• With increasing size, the band gap decreases, and emission wavelengths shift redwards.

Top-down Approach

• Top-down methods involve starting with a larger piece of material and reducing it down to the desired nanoscale.
• Common methods include mechanical milling/machining, etching, and laser ablation.

Bottom-up Approach

• Bottom-up methods involve building up nanostructures from atoms or molecules.
• Examples methods include surface deposition, sol-gel synthesis, chemical vapor deposition, and precipitation.

Synthesis and Characterization of Nanoparticles

• A variety of synthesis methods are discussed, both physical(ball milling, sputtering etc.) and chemical (sol-gel process etc.);.

Advantages and Disadvantages of Sol-Gel Processing

• Advantages include:
  • Low temperature processing.
  • Monodispersed nanoparticles.
• Disadvantages include:
  • Formation control of particles, preventing agglomeration.
  • Complete reactant removal
  • Slow processing rate

Top down vs Bottom up Synthesis

• Top down methods are more expensive and time-consuming, but allow more control over nanostructured design.
• Bottom up methods are cheaper, but allow less control over nanostructure features

What makes nanoparticles different?

• Size and dimensionality changes
• Numerous interfaces and grain boundaries
• Heterogeneous structure at the nanoscale

Gold: Bulk vs. Nano

• Differences in properties between bulk and nano gold are clarified.

Milling Process

• Mechanical milling is a method of nano-sized material production
• Methods like ball milling, shaker milling etc.are discussed
• Advantages and disadvantages of this process are detailed.

Overall Sol-Gel Steps

• The overall steps involved in the sol-gel process are outlined, highlighting the formation of the sol, gelation, aging, drying, and calcination stages.

Sol-Gel Processing

• Sol-gel processing is a method to synthesize nanomaterials by chemically transforming a liquid sol into a solid gel. The method is used to create thin films etc.