This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Characteristics of Nanocomposites”.
1. Why is tungsten disulphide NTs reinforced with PPF nanocomposites?
a) Uniform dispersion of inorganic NTs
b) Poor mechanical properties
c) Increased resistivity of NCs
d) Reduced cross linking density
View Answer
Explanation: Tungsten disulphide nanotubes reinforced PPF nanocomposites possess high mechanical properties. This is attributed to a uniform dispersion of inorganic nanotubes in the polymer matrix. The increased crosslinking density of the polymer in the presence of tungsten disulphide nanotubes also aids in the increase of mechanical properties.
2. There is a consistent rise in microhardness of the ceramic – CNT nanocomposites with increase in CNT.
a) True
b) False
View Answer
Explanation: The microhardness of the ceramic – CNT nanocomposites increase with the increase in the CNT content upto 4% (by weight). This is due to the grain size effects and the reinforcement role of CNTs. But the effect is not consistent since with the increase in the CNT content above 4% (by weight), the microhardness decreases. This may be due to the poor cohesion between the CNTs and the matrix.
3. Why do exfoliated Nylon-6 and intercalated PMMA nanocomposites exhibit increase in stress at break?
a) Loss in ultimate elongation
b) Intercalation of the PP chains
c) Lack of interfacial adhesion between non polar PP and polar – layered silicates
d) Polar PMMA and ionic interactions between the matrix and the silicate layer
View Answer
Explanation: Exfoliated Nylon-6 and intercalated PMMA nanocomposites exhibit a large increase in the stress at break. This is because of the ionic (Nylon-6 grafted onto the layers) and polar (PMMA) interactions between the matrix and the silicate layers. The increase in stress is observed to be layer in Nylon-6 nanocomposites.
4. What is the size limit of nanocomposites for exhibiting catalytic activity?
a) < 20nm
b) < 500nm
c) < 5nm
d) < 100nm
View Answer
Explanation: Nanocomposites having sizes less than 5nm show catalytic activity. Those with sizes less than 20nm are used for making a hard magnetic material soft. While nanocomposites with sizes less than 50nm show refractive index changes. Particles with sizes less than 100nm are employed for achieving super paramagnetism and mechanical strengthening.
5. How are heat resistant nanocomposites able to withstand high temperatures?
a) By interacting between phase interfaces
b) By producing aggregates that act as structural defects
c) By the addition of carbon dots
d) By responding to external stimulus
View Answer
Explanation: In the recent years extensive research has led to the development of nanocomposites that have the ability to withstand high temperatures. This has been brought by adding carbon dots in the polymer matrix. These kinds of nanocomposites find their applications in high temperature environment.
6. Match the metal nanocomposites with their respective properties.
I. Ag/Au (i) Improved microhardness II. Al/SiC (ii) Improved Li+ intercalation properties III. Cu/Al2O3 (iii) Improvement in catalytic activity IV. CNT/Sb (iv) Improved elastic moduli
a) I – (i); II – (iii); III – (iv); IV – (ii)
b) I – (iv); II – (ii); III – (iii); IV – (i)
c) I – (ii); II – (iii); III – (iv); IV – (i)
d) I – (iii); II – (iv); III – (i); IV – (ii)
View Answer
Explanation: Ag/Au nanocomposites have improved catalytic activity. Al/SiC nanocomposites have enhanced hardness and elastic moduli. Cu/Al2O3 nanocomposites exhibit increased microhardness. CNT/Sb nanocomposites display improvements in Li+ intercalation properties.
7. What makes conventional composite materials different from nanocomposites?
a) Structure
b) Aspect ratio
c) Morphology
d) Density
View Answer
Explanation: The main differentiating factor between nanocomposites and conventional composite materials is the high surface to volume ratio of nanocomposites in their reinforcing phase along with the exceptionally high aspect ratio. The materials can be made up of particles, sheets or fibres.
8. Why is there a decrease in the bending strength at high loading of CNT in ceramic – CNT nanocomposites?
a) Low probability for aggregation
b) Hindrance caused by CNTs
c) Increased bonding
d) Reduced pull out from the matrix
View Answer
Explanation: In case of ceramic – CNT nanocomposites there is a decrease in the bending strength at high loading due to the hindrance produced by CNTs during densification while they show higher probability for agglomeration. This leads to the loss of bonding. The higher the loading of CNTs, the higher is the pullout from the matrix during stress transfer.
9. Why do polymer layered silicate nanocomposites have remarkable improvements?
a) Stronger interfacial interactions
b) Poor hydrogen bonds
c) Ion – exchanged
d) Low aspect ratio
View Answer
Explanation: Polymer layered silicate nanocomposites exhibit remarkable improvements compared to the conventional filter reinforced systems. This is due to the stronger interfacial interactions between the matrix and the silicate.
10. Which of the given factors does not affect thermal conductivity of nanocomposites?
a) Polydensity of nanoparticles
b) Thermal property mismatch
c) Orientation of nanoparticles
d) Percolation threshold
View Answer
Explanation: There are certain factors that significantly affect the effective thermal conductivity of nanocomposites. These include orientation and arrangement of asymmetric nanoparticles, thermal property mismatch at the interface, polydensity of nanoparticles and interface density per unit volume of nanocomposites.
Sanfoundry Global Education & Learning Series – Nanotechnology.
To practice all areas of Nanotechnology, here is complete set of 1000+ Multiple Choice Questions and Answers.
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