Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES
Article
Molecular understanding on the underwater oleophobicity of self-assembled monolayers: zwitterionic versus nonionic Gang Cheng, Mingrui Liao, Daohui Zhao, and Jian Zhou Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b03988 • Publication Date (Web): 25 Jan 2017 Downloaded from http://pubs.acs.org on January 30, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 41
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
Figure 1. Simulation cells for different grafting patterns and the structures of monomers. Only the first layer atoms of Si(111) are grafted with monomers. In simulation cells, the gray spheres represent the ungrafted Si atoms; the yellow, blue and red spheres denote grafting sites for neutral hydrophilic, positively charged and negatively charged monomers, respectively. The simulation cells (a), (b) and (c) explicate the grafting percentage of 50%, 37.5% and 25% of the neutral hydrophilic molecules, respectively; whereas the simulation cells (d), (e) and (f) stand for grafting percentage of 50%, 37.5% and 25% of mixed-charged molecules, respectively. As for monomers, gray spheres in the bottom layer mean the grafted Si atoms and C8 alkyl chains are used in all monomers except OEG and ETA systems. The main differences in these structures are the head groups.
ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Figure 2. The underwater OCAs and wetting configurations on SAMs.
ACS Paragon Plus Environment
Page 2 of 41
Page 3 of 41
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
Figure 3. Mean HB numbers of SAMs per chain under water. Green bars are for HBs between SAM-water (the left y-axis); while cyan bars are for HBs of SAM-SAM (the right y-axis). A dotted line separates each bar into two parts, which means HBs of different groups.
ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Figure 4. The underwater OCAs and wetting configurations on four mixed-charged SAMs
ACS Paragon Plus Environment
Page 4 of 41
Page 5 of 41
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
Figure 5. Structural and dynamic properties of water molecules in the first coordination shells of the head groups for charged monomers: coordination numbers Nco (a) and residence time τre (b) of the SO3- groups with different cations; coordination numbers Nco (c) and residence time τre (d) of NHx groups in alkyl ammonium ions (x=1, 2, 3). In (c) and (d), as no hydrogen atom is directly attached to the nitrogen atom in NC3+, thus no HBs are formed between NC3+ and water molecules.
ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Figure 6. Three grafting modes for NC3+-/SO3--SAMs. (a) C9 chain for SO3- monomer and C7 chain for NC3+ monomer; (b) C8 chains for SO3- and NC3+ monomers; (c) C7 chain for SO3- monomer and C9 chain for NC3+ monomer. The three grafting modes distinguish from each other only in the chain length of monomers.
ACS Paragon Plus Environment
Page 6 of 41
Page 7 of 41
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
Figure 7. The underwater OCAs and wetting configurations on NC3+-/SO3--SAMs for three different grafting modes. The three grafting modes are illustrated in Fig 6.
ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Figure 8. Snapshots of NC3+-/SO3--SAMs in water with three different grafting modes. The SAMs are shown with CPK, while the water near the SAM are shown in stick mode.
ACS Paragon Plus Environment
Page 8 of 41
Page 9 of 41
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
Figure 9. The underwater OCAs and wetting configurations on SAMs at different grafting percentages. Each row is for the same grafting percentage and each column is for the same SAM.
ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Figure 10. Density profiles of DCE molecules and key groups of SAMs along z axis at different grafting percentages of SAMs. The columns represent the SAMs of ETA-, OEG- and NC3+-/SO3--, respectively; while rows indicate the grafting percentage of 50%, 37.5% and 25%, respectively.
ACS Paragon Plus Environment
Page 10 of 41
Page 11 of 41
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
TOC graphic
ACS Paragon Plus Environment
Langmuir
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1 2 3
Molecular understanding on the underwater oleophobicity of
4
self-assembled monolayers: zwitterionic versus nonionic
5 6 7 8
Gang Cheng, Mingrui Liao, Daohui Zhao, Jian Zhou*
9 10 11 12 13
School of Chemistry and Chemical Engineering, Guangdong Provincial Key
14
Laboratory for Green Chemical Product Technology, South China University of
15
Technology, Guangzhou 510640, China
16 17 18
*
Address correspondence to J. Zhou.
E-mail:
[email protected] Fax: +86 20 87114069; Tel: +86 20 87114069. 1
ACS Paragon Plus Environment
Page 12 of 41
Page 13 of 41
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1
Langmuir
Abstract
2
Molecular dynamics simulations are conducted to investigate the underwater oleophobicity of
3
self-assembled monolayers (SAMs) with different head groups. Simulation results show that the
4
order of underwater oleophobicity of SAMs is methyl < amide < oligo (ethylene glycol) (OEG)
