Institute of Robotics and Intelligent Systems Department of Mechanical and Process Engineering (DMAVT) ETH Zurich

Exercise Session 4 NANOROBOTICS 2015 Assistants: Marcus Hoop (mhoop@student.ethz.ch)

Berna Özkale (oezkaleb@ethz.ch) Dr. Salvador Pané Prof. Dr. Bradley J. Nelson

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Paper 1

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Paper 1

Nature Materials 6, 429 – 433, 2007

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Question 1

•  Additionally a graph showing the influence of solvent polarity on swelling ratio is reported in the same paper (Figure 1). If the reported hydrogel were meant to be used for cleaning VOCs, discuss how effective it would be if the spillage mainly contains THF (ε = 7.6) or acetonitrile (ε = 36). Would you use type 1 or type 2? Explain your answer.

Type I

Type II

Q ≈ 5

Q ≈ 25

Q ≈ 125 §  Type I §  THF collection

would be more effectively achieved since the hydrogel can absorb 25x more THF compared to acetonitrile.

Swelling ratio: Q = (Wwet −Wdry )Wdry Nature Materials 6, 429 – 433, 2007

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Question 1

•  Nanorobots made of type I hydrogel are used to clean up a small scale spillage involving tetrahydrofuran (THF) as a proof of concept. The nanorobots have the shape of a perfect solid sphere. Assuming that the swelling ratio stays the same, determine the number of hydrogel nanorobots necessary to clean 1 l of THF. The diameter of the sphere is 2 µm.

v2,s =VpVg

=Q−1

VpVg

=125−1

Vp =43πr3

Vp = 4.2µm3

Vg = 525µm3

Vg,t =1015 µm3

525µm3=1.9×1012nanorobots

1 l = 1000 ml = 1000 cm3 = 1015 µm3

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Question 2

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Question 2

•  Write the oxidation and reduction reactions involved. •  Explain the working principle of the described hydrogel. How does the hydrogel change

its shape, on which component is this mechanism dependent on?

Cu+ Cu2+ + 1e-

reduction

oxidation

ACS Macro Letters 2, 1095 – 1099, 2013

§  Chemical stimulus: oxidation in air and recovery by sodium metabisulfite

§  Electrochemical stimulus: negative potential