Polymer Chemistry and Material Properties Quiz
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Questions and Answers

What is required for the polymerization of a vinyl compound?

  • Free radicals (correct)
  • Catalysts without activators
  • Monomers with triple bonds
  • High temperatures

Which method is NOT used to activate benzoyl peroxide for polymerization?

  • Heat above 65°C
  • Contact with a tertiary amine
  • Mixing with silica (correct)
  • Exposure to light

How is the weight average molecular weight ($M_w$) calculated?

  • $M_w = rac{ ext{Sum of }(M_i)}{ ext{Total number of weights}}$
  • $M_w = rac{ ext{Sum of }(w_i imes M_i)}{ ext{Total number of weights}}$ (correct)
  • $M_w = rac{ ext{Sum of molecular weights}}{ ext{Number of polymer types}}$
  • $M_w = rac{ ext{Total number of chains}}{ ext{Total weight}}$

What happens during the termination phase of polymerization?

<p>Free radicals merge to form a stable molecule. (B)</p> Signup and view all the answers

What characterizes condensation polymerization compared to addition polymerization?

<p>Consists of combining different types of molecules. (C)</p> Signup and view all the answers

What characterizes the yield point of ductile materials during tensile testing?

<p>It marks the transition from elastic to plastic deformation. (D)</p> Signup and view all the answers

In stress-strain curves, how do brittle materials generally behave compared to ductile materials?

<p>They only show a linear elastic region without necking. (D)</p> Signup and view all the answers

What occurs during necking in the tensile deformation of ductile metals?

<p>Cross-sectional area decreases while length increases. (C)</p> Signup and view all the answers

Why is the compression test preferred over the tensile test for brittle materials?

<p>Compression tests provide results that are typically more consistent. (B)</p> Signup and view all the answers

Which surface indenter would be most suitable for testing the hardness of a ductile material?

<p>Vickers indenter (A), Brinell indenter (B)</p> Signup and view all the answers

What phenomenon describes the ability of silica to exist in different forms like quartz and glass?

<p>Polymorphism (A)</p> Signup and view all the answers

What is the glass transition temperature characterized by in amorphous solids?

<p>An increasing rate of change in specific volume (A)</p> Signup and view all the answers

Which factor increases the likelihood of larger, complex molecules forming glasses during solidification?

<p>Difficulty in achieving ordered arrangements (D)</p> Signup and view all the answers

What property of silica leads to a decrease in specific volume when crystallization occurs?

<p>Configurational contraction (B)</p> Signup and view all the answers

What is the primary reason for the formation of a glass when silica is rapidly cooled?

<p>Absence of crystal nuclei (B)</p> Signup and view all the answers

Which is NOT a component typically combined with aluminum oxide in ceramic formulations?

<p>Sodium chloride (C)</p> Signup and view all the answers

What characterizes the formation of covalent bonds compared to ionic bonds?

<p>Atoms share electrons. (A)</p> Signup and view all the answers

Which of the following correctly describes metallic bonds?

<p>Valence electrons form a free-moving cloud. (A)</p> Signup and view all the answers

What is the main difference between ionic and covalent bonds regarding their directionality?

<p>Covalent bonds are directional, ionic bonds are not. (C)</p> Signup and view all the answers

How does the bonding strength affect the properties of materials?

<p>Higher bonding strength usually results in higher melting points. (C)</p> Signup and view all the answers

Which of these elements is an example of a covalent solid?

<p>Carbon (C)</p> Signup and view all the answers

What is the consequence of mercury's weak bonding at room temperature?

<p>It does not maintain a solid structure. (D)</p> Signup and view all the answers

In terms of bond energies, which of the following bonds has the highest energy?

<p>C-C (B)</p> Signup and view all the answers

Which type of bond is characterized by the transfer of electrons leading to charged ions?

<p>Ionic bonds (C)</p> Signup and view all the answers

What primarily defines mechanical adhesion?

<p>Interlocking of adhesive components due to surface irregularities. (B)</p> Signup and view all the answers

Which factor is essential for successful chemical adhesion?

<p>Presence of reactive groups on both surfaces. (B)</p> Signup and view all the answers

Molecular entanglement in adhesion is characterized by which mechanism?

<p>Penetration of the adhesive into the substrate and strong chemical attraction. (D)</p> Signup and view all the answers

What role does surface energy play in adhesion?

<p>Higher surface energy leads to better penetration by the adhesive. (B)</p> Signup and view all the answers

Debonding of adhesive joints typically involves which process?

<p>Fracture occurring in either the adhesive or the substrate material. (C)</p> Signup and view all the answers

What is a key requirement for mechanical adhesion to occur effectively?

<p>Perfect wetting of the adhesive on the substrate (C)</p> Signup and view all the answers

Which statement best describes chemical adhesion?

<p>It relies on the formation of covalent or ionic bonds between surfaces. (A)</p> Signup and view all the answers

What mechanism allows high bond strength in adhesion through molecular entanglement?

<p>Penetration of long-chain molecules into the substrate (C)</p> Signup and view all the answers

Which type of bonding is characterized by weak and reversible interactions?

<p>Physical adhesion (A)</p> Signup and view all the answers

What is the significance of air or vapor escaping from pits during mechanical adhesion?

<p>It ensures the adhesive can penetrate the surface irregularities. (D)</p> Signup and view all the answers

How does the bond strength in chemical adhesion compare to the tensile strength of the adhesive or substrate?

<p>It must not exceed the tensile strength to avoid failure. (C)</p> Signup and view all the answers

Which type of interaction is primarily responsible for physical adhesion?

<p>Secondary attractive forces (C)</p> Signup and view all the answers

What is a critical factor in achieving good chemical adhesion?

<p>Reactive groups on both surfaces (D)</p> Signup and view all the answers

What condition may inhibit metallic bonding during adhesion?

<p>Dirty or oxidized metal surfaces (A)</p> Signup and view all the answers

What does Young's modulus primarily measure in materials?

<p>Stiffness or modulus of elasticity (A)</p> Signup and view all the answers

Which of the following accurately describes proof stress?

<p>Stress required to induce 0.2% plastic strain (C)</p> Signup and view all the answers

How is resilience defined in the context of material mechanics?

<p>Energy absorbed before permanent deformation occurs (C)</p> Signup and view all the answers

What is the relationship between ultimate tensile strength (UTS) and fracture strength?

<p>UTS is distinct and usually different from fracture strength (C)</p> Signup and view all the answers

Which statement regarding ductility is correct?

<p>It indicates the amount of plastic strain until fracture occurs (A)</p> Signup and view all the answers

What does toughness measure in a material?

<p>Total energy absorbed before fracturing (A)</p> Signup and view all the answers

In a stress-strain curve, what does the area under the initial linear portion represent?

<p>Resilience of the material (B)</p> Signup and view all the answers

What is the significance of yield stress in material science?

<p>Marks the transition from elastic to plastic deformation (B)</p> Signup and view all the answers

Which of the following materials would you expect to have relatively high tensile strength?

<p>High-strength steels (D)</p> Signup and view all the answers

What is the correct unit for Young's modulus?

<p>N/m² or Pa (C)</p> Signup and view all the answers

Flashcards

Free radical

A chemical species with an odd number of electrons, highly reactive, and crucial for initiating polymerization.

Polymerization

A process where small molecules called monomers join together to form long chains called polymers.

Initiation

The step where free radicals interact with monomers, causing them to bond and initiate the formation of a polymer chain.

Propagation

The step where the growing polymer chain reacts with more monomers, adding to its length.

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Termination

The step where the growth of the polymer chain stops, usually due to the combination of free radicals.

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Necking

A localized reduction in cross-sectional area that occurs during tensile deformation of ductile materials and some plastics.

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Compression Test

A test where a material is compressed instead of pulled, often used for brittle materials, as it provides more consistent results.

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Ductile Material

A material like mild steel that shows a linear elastic region, a distinct yield point, and a large degree of ductility before breaking.

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Brittle Material

A material like plaster of Paris that only shows a linear elastic region and fractures without any plastic deformation.

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Stress-Strain Curve

A graph that shows how much a material stretches (strain) in response to the force applied (stress).

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Polymorphism

The ability of a substance to exist in different crystalline forms with distinct properties. For example, silica (SiO2) can exist as quartz, cristobalite, and tridymite, each with different structures and properties.

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Glass Transition Temperature

A temperature at which an amorphous solid, like glass, undergoes a significant change in its specific volume with temperature, transitioning from a rigid to a more fluid state.

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Vitrification

The process of quickly cooling a molten liquid, preventing proper crystal formation and resulting in a solid with a disordered, glassy structure.

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Crystallization

The process of forming a solid from a liquid, where the molecules arrange themselves in a highly ordered, repeating pattern. Think of salt, sugar, or ice.

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Amorphous Solid

A solid with a disordered, non-repeating arrangement of molecules, lacking a defined crystal structure. Think of glass.

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Silica Glass

A solid material made of silica (SiO2), usually formed through rapid cooling of a molten liquid, resulting in a disordered, glassy structure.

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Covalent Bond

Atoms share electrons, creating a stronger bond compared to ionic.

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Metallic Bond

Atoms lose valence electrons, forming a "sea" of electrons around positive ions.

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Ionic Bond

An atom gains an electron, becoming a negative ion (anion) and another atom loses an electron, becoming a positive ion (cation). These oppositely charged ions attract each other.

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Bond Energy

The energy required to break a chemical bond between two atoms.

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Electrical Conductivity

The ability of a substance to conduct electricity due to free-moving electrons, typical of metals.

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Electronegativity

The tendency of an atom to attract electrons in a chemical bond.

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Cation

A positively charged ion formed when an atom loses one or more electrons.

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Anion

A negatively charged ion formed when an atom gains one or more electrons.

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Mechanical Adhesion

Interlocking of material components, like fitting puzzle pieces. Surface roughness (pits and fissures) helps create microscopic undercuts for the adhesive to grab onto.

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Chemical Adhesion

Chemical bonding occurs when molecules attach to a surface by forming covalent (shared electrons) or ionic bonds. Like the bond between atoms in a molecule.

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Adhesion through Molecular Entanglement

Long chain-like adhesive molecules intertwine with the surface, creating a tangled network for a strong bond. Think of a fishing line that gets stuck on a hook.

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Physical Adhesion

When surfaces are close, weak electrical forces (dipole interactions) attract them. These forces are generally weak and reversible.

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Wettability

The ability of a liquid to spread over a solid surface; a good adhesive will wet the surface completely.

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Penetration

The process where a liquid penetrates microscopic holes and fissures on a surface.

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Tensile Strength

The force required to break a material, indicating its resistance to being pulled apart. A weak adhesive will have low tensile strength.

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Cohesive Failure

The type of failure where the adhesive itself breaks.

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Adhesive Failure

The type of failure where the bond between the adhesive and the surface breaks.

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Application Pressure

The process of applying pressure to remove air or vapor from microscopic areas. This helps the adhesive better contact the surface.

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Surface Energy

The amount of energy a surface has that attracts other molecules to it. It's like how much the surface wants to hold onto the adhesive.

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Young's Modulus

The ratio of stress to strain in the elastic region of a material, representing its stiffness.

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Yield Stress

The stress at which a material begins to deform permanently.

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Ultimate Tensile Strength (UTS)

The maximum stress a material can withstand before breaking.

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Ductility

The amount of plastic deformation a material undergoes before fracturing.

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Resilience

The ability of a material to absorb energy before permanent deformation.

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Toughness

The total amount of energy a material can absorb before fracturing.

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Tensile Test

A test that stretches a material to measure its properties, like strength and ductility.

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Fracture Strength

The stress required to break a material.

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Proof Stress

A measure of the onset of yielding, defined as the stress needed for a specific amount of plastic strain.

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Study Notes

Free Radical Polymerization

  • Free radicals are reactive chemical species with an odd number of electrons
  • Initiators are compounds that create free radicals
  • Activation: A vinyl compound needs free radicals
  • Propagation: Free radical reacts with a monomer. The process repeats
  • Termination: Free radicals react to form a stable molecule

Condensation Polymerization

  • Two molecules react with the elimination of a small molecule (often water)
  • Not necessary to have a carbon-carbon double bond
  • Example: formation of silicones (from silanols)

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Description

Test your knowledge on polymerization processes and material properties with this comprehensive quiz. Questions cover topics like activation methods for benzoyl peroxide, molecular weight calculation, and the behavior of materials under tensile testing. Ideal for students studying polymer chemistry and material science.

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