This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Polymer Nanocomposites”.
1. What happens to rubber composites reinforced with organophilic layered silicates in the absence of a coupling agent?
a) Retarded optical transparency
b) Reduction in Young’s modulus
c) Increased tensile strength
d) Reduced strain at break
View Answer
Explanation: Rubber nanocomposites using BR and SBR vulcanisates are often reinforced by organophilic layered silicates. These in the absence of coupling agents show increased tensile strength and enhanced mechanical properties. However, during reactive coupling tensile strength remains constant but strain at break decreases.
2. What is the mechanism behind the fire retardancy of graphite-polymer nanocomposites?
a) Hydrogen bonding upon annealing
b) Overlapping transition having two subrelaxations
c) Catalytic effect of the nucleation of char formation
d) Descend in viscosity of polymer
View Answer
Explanation: Graphite-polymer nanocomposite systems show good fire retardancy. The mechanism behind the fire retardancy is achieved by the formation of tortuous pathways and also by the catalytic effect of the nucleation of char formation by the aromatic sheets.
3. What is the purpose of using tungsten disulphide nanoparticles in forming polymer nanocomposites?
a) Enhances structural defects in polymers
b) Improves compressive and flexural mechanical properties
c) Enhances the electrical resistivity of nanocomposites
d) Increases the weight of bone implants
View Answer
Explanation: Tungsten disulphide nanoparticles are used as reinforcing agents to fabricate mechanically tough and strong biodegradable polymeric nanocomposites for bone tissues engineering. These nanocomposites show improved compressive and flexural mechanical properties. They can be used to form strong yet light weight bone implants.
4. Which of these properties is observed when polymer nanocomposites are created?
a) Increased density of base polymer
b) Degradation in optical properties
c) Less recyclable base polymers
d) Increased heat distortion temperature.
View Answer
Explanation: Polymer nanocomposites exhibit remarkable property enhancements such as increased modulus, gas barrier, heat distortion temperature, atomic oxygen resistance etc. compared to conventional composites. However, these improvements are achieved without raising the density of base polymer, without degrading its optical properties and without making it less recyclable.
5. Ultrasonic treatment of nanocomposites have retarded their mechanical properties.
a) True
b) False
View Answer
Explanation: Polymeric nanocomposites that are treated with ultrasonic irradiation exhibit improved yield strength and Young’s modulus with great increase of the elongation at break. Usually, polymer-clay nanocomposites show reduced ductility and fragile fracture upon higher clay loading. However, ultrasonic oscillations can overcome this drawback while enhancing other mechanical properties.
6. Why is carbon black added to rubber while manufacturing tires?
a) Increases octane number of fuel
b) Greater wet grip performance
c) Increased fuel consumption
d) Production of tires of smaller rolling resistance
View Answer
Explanation: Carbon black (Cb) has traditionally been utilized in the tire industry as fillers. It is easily produced by the incomplete combustion of coal tar and ethylene. It is added to rubber, forming nanocomposites that are used in making tires of reduced rolling resistance. This is anticipated to decrease the overall fuel consumption of cars since it requires less energy to thrust forward.
7. Which of the following methods is most suitable for the preparation of polymer clay mineral hybrids?
a) In-situ intercalative polymerization
b) Melt mixing
c) Sol-gel method
d) Nanoscale dispersion
View Answer
Explanation: In-situ intercalative polymerization is a great approach for preparing polymer clay mineral hybrids. Anisotropic layered silicates of montmorillonite type act as filters. These are subjected to modifications by ion exchange method with organic ammonium salts thus producing organophilic clays. They are often referred to as organoclays. The modifications afford compatibility between filler and polymer resulting in nanocomposites that possess superior stiffness, strength and heat distortion temperature.
8. Choose the correct statement from the following.
a) Molecular level of polymer filler interactions leads to lesser free volume
b) Platelet like morphology of nano filled latex membranes degrade gas barrier property
c) Layered silicates have lower aspect ratio and hence lesser contact surface between filler and matrix
d) Gas barrier properties of micro filled systems is enhanced by formation of micro-cavities
View Answer
Explanation: The molecular level of polymer filler interaction leads to reduced availability of free volume and decreased permeability of latex membranes. Platelet like morphology and high aspect ratio aid in the enhancement of gas barrier property of nano filled latex membranes. Poor gas barrier properties of micro filled system is owing to the poor physical and chemical interactions between organic and inorganic components that lead to aggregation of fillers that form microcavities at the interfacial region. Layered silicates possess high aspect ratio which leads to greater contact surface between the filler and the matrix.
9. Why is silica reinforced with rubber to form polymer nanocomposites that are often employed in automotive tire industry?
a) Shows heat resistance
b) Improves wet grip performance
c) Exhibits fluorescence
d) Increase overall fuel consumption
View Answer
Explanation: Carbon black is often replaced by silica in producing polymer nanocomposites that are employed in manufacturing green tires in the automotive tire industry. These tires have smaller rolling resistance as well as improved wet grip properties. Silica is hydrophilic in nature and to increase its compatibility with polymer matrix, silica is usually functionalized with coupling agents.
10. How can end tethered polymer layered silicate nanocomposites be produced?
a) Hydrolysis of metal alkoxides
b) In-situ polymerization of Ꜫ-caprolactone
c) Polycondensation of hydrolysed intermediates
d) Reinforcing SBR and BR vulcanisates
View Answer
Explanation: The end tethered polymer layered silicate nanocomposites can be synthesized by in-situ polymerization of Ꜫ-caprolactone. The technique involves conversion of a hydrophilic silicate surface to an organophilic surface using an ion exchange of the metal cations by 12-amino lauric acids. The polymerization of monomers is initiated by the carboxyl groups of the aminolauric acid while the propagation of the process is via a ring opening of Ꜫ-caprolactone.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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