Study Notes on Material Choice and Properties

Chapter 4: Material Choice (10/02/2026)

Fundamental Concepts of Polymers

  • Polymer: A large molecule composed of repeating structural units (monomers) connected by covalent chemical bonds.

  • Monomer: Basic building block of polymers.

  • Covalent bonds: Strong bonds formed by the sharing of electrons between atoms.

  • Natural Polymers: Polymers that occur naturally, such as proteins and DNA.

  • Synthetic Polymers: Man-made polymers, e.g., plastics.

  • Alkene: A hydrocarbon with at least one carbon-carbon double bond, which acts as a monomer for many polymers.

  • Intermolecular forces: Forces of attraction or repulsion between neighboring molecules.

Properties and Characteristics of Polymers

1. Types of Polyethylene

  • High Density Polythene (HDPE):

    • Properties: Stronger, stiffer, and has higher crystallinity.

  • Low Density Polythene (LDPE):

    • Properties: Weaker, more flexible, and has less crystallinity.

Ceramics

  • Common Glass Types:

    • Soda-lime glass is primarily made from:

    • Silica (SiO₂)

    • Sodium carbonate (Na₂CO₃)

    • Borosilicate Glass:

    • Made from boron trioxide (B₂O₃)

    • Higher melting point than soda-lime glass.

  • Clay Ceramics:

    • Made by shaping wet clay and heating it in a furnace.

Composites

  • Definition: A composite material is made from two or more materials (reinforcement and binder or matrix) to achieve certain desirable properties.

  • Examples of Composite Materials:

    • Concrete:

    • Binder: Cement and Water

    • Reinforcement: Sand and crushed rock

    • Uses: Construction of buildings.

    • Composite Wood (Plywood):

    • Binder: Adhesives

    • Reinforcement: Wood fibers

    • Uses: Furniture and buildings.

Alloys

  • Definition of Alloy: A mixture of two or more metals.

  • Examples of Alloys:

    • Steel: Mixture of iron and other elements.

    • Gold Alloys:

    • Gold mixed with copper, silver, or zinc to alter properties.

    • Aluminium Alloys:

    • Mixture with magnesium and copper resulting in a strong but low density material.

    • Bronze: Copper and tin mixture.

    • Brass: Copper and zinc mixture.

Gold Alloys

  • 24-Carat Gold: 99.99% gold; pure, highly malleable but soft.

  • 9-Carat Gold: Approximately 37.5% gold; tougher than pure gold but less malleable.

Impurities in Iron and Steel Making

  • Impurities: Enhance strength in iron by making it harder through controlling amounts added.

  • Making Steel:

    • Low carbon content (0.5%): Can be easily shaped.

    • Medium carbon content (1%): Stronger but less workable.

    • High carbon content (1.5%): Very strong but brittle.

    • Stainless Steel: Alloyed with chromium and nickel to enhance corrosion resistance.

Monomers and Polymers

  • Ethene as a Monomer:

    • Structure: C=C

    • Process:

    • Step 1: Break double bond.

    • Step 2: Addition of ethene molecules results in polyethene through Addition Polymerisation.

Additional Drawing of Ethene and Its Polymer

  • Polyethene:

    • General formula for addition polymerisation:
      nextC<em>2extH</em>4<br>ightarrowext(C<em>2extH</em>4)nn ext{C}<em>2 ext{H}</em>4 <br>ightarrow ext{(C}<em>2 ext{H}</em>4)_n

Properties of Common Polymers

  • Polythene: Used for bags and crates. Available in LD and HD forms.

  • Polyvinyl Chloride (PVC): Commonly used in water pipes and window frame coatings.

  • PTFE (Teflon): Non-stick coating in cookware.

Condensation Polymerisation (Higher Tier only)

  • Description: Involves monomers with two functional groups, which when reacted, lose small molecules like water.

  • Example: Reaction of carboxylic acids with alcohols forming polyesters or polyamides.

  • General Formula for Condensation Polymerisation:
    nextRCOOH+nextR′OH<br>ightarrowextPolymer+nextH2extOn ext{RCOOH} + n ext{R'OH} <br>ightarrow ext{Polymer} + n ext{H}_2 ext{O}

Structure of DNA and its Importance

  • DNA: A polymer essential for life, stores genetic instructions, composed of two polymer chains of nucleotides in a double helix shape.

  • Monomer: Nucleotides comprise a sugar, phosphate group, and a nitrogenous base.

  • Other Natural Polymers: Include starch, proteins, and cellulose.

Amino Acids and Protein Formation

  • Amino Acids: Contain two functional groups, can create polypeptides through condensation polymerisation.

    • Example: Glycine polymerized results in chains of amino acids leading to proteins.

Structure of Carbon and Its Bonding

  • Covalent Bonds: Carbon's four outer shell electrons allow for four covalent bonds, contributing to diverse compounds.

  • Examples of carbon structures: Include polymers, diamonds, and fullerenes, forming homologous series with distinct properties.

Different Forms of Elements and Compounds

  • Ionic Structures: Example: Sodium chloride, forming cubic lattices held together by ionic bonds.

  • Giant Covalent Structures: Example: Diamond and graphite, demonstrating contrasting properties due to their bonding configurations.

    • Diamond: Strong bonds make it hard; high melting point.

    • Graphite: Layered structure with weak interlayer bonds; conducts electricity due to free electrons.

Metallic Structures and Bonding

  • Description: Metals consist of structures with delocalised electrons creating metallic bonds, allowing for conductivity and malleability.

Simple Covalent Molecules

  • Characteristics: Very low melting and boiling points due to weak intermolecular forces which are easily overcome.

Revisiting Polymer Types

  • Reinforcement of previously covered information about thermosoftening and thermosetting polymers based on intermolecular forces and their properties.

Forces between Molecules

  • Longer polymer chains generally exhibit stronger intermolecular forces, leading to materials that are stronger and harder to melt.

Nanotechnology

Definition and Applications

  • Nanotechnology: Field focusing on structures 1-100 nm in size, presenting unique properties compared to bulk materials; significant due to large surface area to volume ratio.

  • Applications: Include advancements in building materials and medical technology.

Surface Area to Volume Ratio Calculations

  • Example Calculation: Surface area and volume ratios for cubes of 1 cm and 10 cm sides highlight how size affects ratios:

    • Cube 1 (1 cm): Surface Area = 6 cm², Volume = 1 cm³, Ratio = 6:1

    • Cube 2 (10 cm): Surface Area = 600 cm², Volume = 1000 cm³, Ratio = 0.6:1

Graphene and Fullerenes

  • Graphene: A single layer of carbon atoms, offering potential for various advanced applications.

  • Fullerenes: Structures of carbon atoms forming cages, utilized in drug delivery and as lubricants; include carbon nanotubes which are strong and conductive.

Examples of Nanotechnology in Products

  • Tennis Racket: Utilizes nanoparticles for improved strength.

  • Silver Nanoparticles: Exhibit antibacterial properties significantly affecting E. coli bacteria.

Use of Nanoparticles in Sunscreen

  • Small nanoparticles improve skin coverage and enhance protection against UV light and skin cancer.

Rusting and Redox Reactions

  • Rust Formation:

    • Ingredients: Iron + Oxygen + Water leads to hydrated iron(III) oxide (rust).

  • Redox Reactions Overview: Involves loss (oxidation) and gain (reduction) of electrons.

    • Oxidation example: extFe<br>ightarrowextFe2++2exte−ext{Fe} <br>ightarrow ext{Fe}^{2+} + 2 ext{e}^-

    • Reduction example: 2extCl−<br>ightarrowextCl2+2exte−2 ext{Cl}^- <br>ightarrow ext{Cl}_2 + 2 ext{e}^-

Investigating Rust Causes

  • Experimental Design: Use four tubes with varying conditions to observe rust formation:

    • Tube 1: Drying agent (no rust)

    • Tube 2: Boiled water (no rust)

    • Tube 3: Water + air (rust)

    • Tube 4: Water + air + salt (lots of rust)

Prevention of Rusting

  1. Electroplating: Coating iron with a more reactive metal.

  2. Sacrificial Protection: Uses a more reactive metal to protect against oxidation.

  3. Physical Barriers: Oil, grease, or paint applied to iron surfaces.

  4. Galvanization: Coating iron with a layer of zinc to prevent oxygen access.

Life Cycle Assessments (LCAs)

Steps in LCA

  1. Raw Materials and Manufacture: Assess resource use and environmental impacts.

  2. Use Phase: Identify energy consumption and its environmental effects.

  3. Disposal Phase: Examine how products are disposed of and the resultant footprint.

Case Study: Carrier Bags

  • Lifecycle:

    1. Crude oil drilling.

    2. Fractional distillation to achieve ethene.

    3. Polymerisation of ethene.

    4. Transport to stores and landfills.

  • Pollution Reduction:

    1. Use recycled materials.

    2. Minimize consumption.

    3. Local manufacturing.

    4. Facilitate recycling post-use.

Recycling Benefits and Considerations

Reasons to Recycle Metals

  1. Decreases landfill space requirements.

  2. Reduces energy demand (only 1/10 of energy in recycling compared to new production).

  3. Conserves raw materials.

  4. Lowers excavation costs.

Recycling of Materials

  • Melt and Recast Metals: Change shapes or create new products from recycled metals.

  • Glass Recycling: Crushing and melting glass for new applications.

Viability of Recycling

  • Important considerations include:

    • Availability of raw materials.

    • Material's recyclability.

    • Economic feasibility of recycling processes.

    • Energy costs associated with transportation and demand for recycled products.

    • Evaluate environmental impact versus raw material extraction.