Monte Carlo study on the self-assembly of nanoparticles into a nanorod structure.

Matin, Mohammad A,Kim, Hyojeong,Saha, Joyanta K,Zhang, Zhengqing,Kim, Jinkwon,Jang, Joonkyung American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.9

<P>It is well known that semiconductor nanoparticles (NPs) can assemble into a range of low dimensional structures, such as nanowires, nanorods and nanosheets. In this study, we investigate the self-assembly of CdTe NPs by using Monte Carlo simulation. Using a simple model for the anisotropic interaction of NPs, the present Monte Carlo simulation demonstrated that NPs with large dipole moments assemble spontaneously into a nanorod even if the short range interactions among NPs is isotropic. Interestingly, we found that the present nanorod grew by forming a transient structure which looks similar to a double ring. For NPs similar to CdTe, the dipole-dipole interaction had a dominant effect over van der Waals attractions and steric repulsion on the final structure of the NP aggregates. The simulated rods are similar to those observed in the experimental self-assembly of CdTe NPs. The NPs with relatively small electric dipole moments aggregated into more or less isotropic structures.</P>

Density Functional Theory Study on the Cross-Linking of Mussel Adhesive Proteins

Matin, Mohammad A.,Chitumalla, Ramesh Kumar,Lim, Manho,Gao, Xingfa,Jang, Joonkyung American Chemical Society 2015 The Journal of physical chemistry B Vol.119 No.17

<P>The water-resistant adhesion of mussel adhesive proteins (MAPs) to a wet surface requires a cross-linking step, where the catecholic ligands of MAPs coordinate to various transition-metal ions. Fe(III), among the range of metal ions, induces particularly strong cross-linking. The molecular details underlying this cross-linking mediated by transition-metal ions are largely unknown. Of particular interest is the metal–ligand binding energy, which is the molecular origin of the mechanical properties of cross-linked MAPs. Using density functional theory, this study examined the structures and binding energies of various trivalent metal ions (Ti–Ga) forming coordination complexes with a polymeric ligand similar to a MAP. These binding energies were 1 order of magnitude larger than the physisorption energy of a catechol molecule on a metallic surface. On the other hand, the coordination strength of Fe(III) with the ligand was not particularly strong compared to the other metal ions studied. Therefore, the strong cross-linking in the presence of Fe(III) is ascribed to its additional ability as an oxidant to induce covalent cross-linking of the catecholic groups of MAPs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2015/jpcbfk.2015.119.issue-17/acs.jpcb.5b01152/production/images/medium/jp-2015-011524_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5b01152'>ACS Electronic Supporting Info</A></P>

Monte Carlo Study on the Wetting Behavior of a Surface Texturized with Domed Pillars

Kim, Hyojeong,Lee, Su In,Matin, Mohammad A.,Zhang, Zhengqing,Jang, Jihye,Ha, Man Yeong,Jang, Joonkyung American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.45

<P>A lattice gas Monte Carlo simulation was performed to examine the wetting properties of a surface texturized with nanometer-sized, dome-shaped pillars. The vapor and liquid phases of the gap between the pillars were related to the Wenzel and Cassie–Baxter states of a macroscopic water droplet resting on top of the pillars. We studied the effects of the pillar size by systematically varying its height from 6 to 53 nm for a fixed ratio of the height to its width. With increasing interpillar spacing or pressure, the liquid on top of the domed pillars penetrated smoothly down into the gap between the pillars. This wetting transition contrasts with that observed for the gap between rectangular or cylindrical pillars, where a liquid abruptly fills in the interpillar gap at a critical interpillar spacing or pressure. The gap between the domed pillars was more susceptible to the intrusion of the bulk liquid on top of the pillars, due to the open geometry of the gap between the domed pillars. Also, the liquid penetrating into the gap between the domed pillars was locally more fluctuating in density and compressible than that penetrating into the gap between square or cylindrical pillars. This enhanced density fluctuation however was local and did not propagate into the bulk liquid sitting on top of the pillars. Simple analytic expressions of the critical spacing and pressure at which the wetting transition occurs for the domed pillars were derived using continuum theory. These continuum results agreed reasonably well with the present molecular simulations, even for pillars as small as a few nanometers in width.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-45/jp5076077/production/images/medium/jp-2014-076077_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5076077'>ACS Electronic Supporting Info</A></P>

Molecular Dynamics Study on the Self-Assembled Monolayer Grown from a Droplet of Alkanethiol

Kim, Hyojeong,Saha, Joyanta K.,Zhang, Zhengqing,Jang, Jihye,Matin, Mohammad A.,Jang, Joonkyung American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.20

<P>Direct-write lithography, where a nanoscale tip or a stamp serves as a molecular source, is used widely to fabricate self-assembled monolayers (SAMs), nanometers in size. The spatially narrow deposition of molecules creates a droplet, which then spreads to form an ordered SAM. Currently, the dynamics and mechanism for this spreading are largely unknown. Herein, the evolution of a droplet of 1-octadecanethiol into a circular island of SAM, where the sulfur atoms and alkyl chains are densely and orderly packed, was examined by using molecular dynamics simulations. The packing of sulfur atoms preceded the alignment and packing of alkyl chains. The SAM islands resembled the bulk SAM, but it contained defects where the molecules were standing upside down on the surface. We found two mechanisms pertaining to the growth of a SAM island in the direct-write lithography. In the first mechanism, the molecules penetrated into the SAM islands by pushing away the molecules below. In the other mechanism, the molecules diffused, reached the periphery of the SAM islands, and slid down to the surface. The chemisorption of sulfur atoms made the present droplet spread more slowly than a droplet interacting nonspecifically with a surface. A droplet laterally moving across the surface was also simulated to gain insight into the growth of a SAM line. The alkyl chains of the SAM line were directed preferentially toward the line direction.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-20/jp502707d/production/images/medium/jp-2014-02707d_0011.gif'></P>

Theoretical Calculations of Infrared Bands of CH3+ and CH5+

Mohammad A. Matin,장준경,박승민 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.7

Existing theoretical calculations predict that infrared spectra of the two most fundamental reactive carbo-ions, methyl cation CH3 + with D3h symmetry and protonated methyl cation CH5 + with Cs(I), Cs(II), and C2v symmetries, appear together in the 7-μm region corresponding to the C-H bending modes. Vibrational band profiles of CH3 + and CH5 + have been compared by ab initio calculation methods that use the basis sets of MP2/ aug-cc-pVTZ and CCSD(T)/cc-pVTZ. Our results indicate that the bands of rotation-vibration transitions of CH3 + and CH5 + should overlap not only in the 3-μm region corresponding to the C-H stretching modes but also in the 7-μm region corresponding to the C-H bending modes. Five band intensities of CH5 + among fifteen vibrational transitions between 6 and 8 μm region are stronger than those of the ν2 and ν4 bands in CH3 +. Ultimate near degeneracy of the two bending vibrations ν2 and ν4 of CH3 + along with the stronger intensities of CH5 + in the three hydrogen scrambling structures may cause extreme complications in the analysis of the highresolution carbo-ion spectra in the 7-μm region.

Theoretical Calculations of Infrared Bands of CH₃⁺ and CH₅⁺

Matin, Mohammad A.,Jang, Joonkyung,Park, Seung Min Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.7

Existing theoretical calculations predict that infrared spectra of the two most fundamental reactive carbo-ions, methyl cation $CH{_3}^+$ with $D_{3h}$ symmetry and protonated methyl cation $CH{_5}^+$ with $C_s(I)$, $C_s(II)$, and $C_{2v}$ symmetries, appear together in the 7-${\mu}m$ region corresponding to the C-H bending modes. Vibrational band profiles of $CH{_3}^+$ and $CH{_5}^+$ have been compared by ab initio calculation methods that use the basis sets of MP2/aug-cc-pVTZ and CCSD(T)/cc-pVTZ. Our results indicate that the bands of rotation-vibration transitions of $CH{_3}^+$ and $CH{_5}^+$ should overlap not only in the 3-${\mu}m$ region corresponding to the C-H stretching modes but also in the 7-${\mu}m$ region corresponding to the C-H bending modes. Five band intensities of $CH{_5}^+$ among fifteen vibrational transitions between 6 and 8 ${\mu}m$ region are stronger than those of the ${\nu}_2$ and ${\nu}_4$ bands in $CH{_3}^+$. Ultimate near degeneracy of the two bending vibrations ${\nu}_2$ and ${\nu}_4$ of $CH{_3}^+$along with the stronger intensities of $CH{_5}^+$ in the three hydrogen scrambling structures may cause extreme complications in the analysis of the high-resolution carbo-ion spectra in the 7-${\mu}m$ region.

Molecular Dynamics Study of the Hydrophilic-to-Hydrophobic Switching in the Wettability of a Gold Surface Corrugated with Spherical Cavities

Zhang, Zhengqing,Matin, Mohammad A.,Ha, Man Yeong,Jang, Joonkyung American Chemical Society 2016 Langmuir Vol.32 No.37

<P>This paper reports a large scale molecular dynamics (MD) simulation study of the wettability of a gold surface engraved with (hemi)spherical cavities. By increasing the depth of cavities, the contact angle (CA) of a water droplet on the surface was varied from a hydrophilic (69 degrees) to a hydrophobic value (>109 degrees). The nonmonotonic behavior of the CA vs the depth of the cavities was consistent with the Cassie-Baxter theory, as found in the experiment by Abdelsalam et al. (Abdelsalam, M. E.; Bartlett, P. N.; Kelf, T.; Baumberg, J. Wetting of Regularly Structured Gold Surfaces. Langmuir 2005, 21, 1753-1757). Depending on the depth of cavities, however, the droplet existed not only in the Cassie-Baxter state, but also in the Wenzel or an intermediate state, where the cavities were penetrated partially by the droplet.</P>

Molecular Dynamics Simulation Study on the Wetting Behavior of a Graphite Surface Textured with Nanopillars

Joyanta K. Saha,Mohammad A. Matin,장지혜,장준경 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.4

Molecular dynamic simulations were performed to examine the wetting behavior of a graphite surface textured with nanoscale pillars. The contact angle of a water droplet on parallelepiped or dome-shaped pillars was investigated by systematically varying the height and width of the pillar and the spacing between pillars. An optimal inter-pillar spacing that gives the highest contact angle was found. The droplet on the dome-covered surface was determined to be more mobile than that on the surface covered with parallelepiped pillars.

Molecular Dynamics of Carbon Nanotubes Deposited on a Silicon Surface via Collision: Temperature Dependence

Leton C. Saha,Shabeer A. Mian,김효정,Mohammad A. Matin,Joyanta K. Saha,장준경 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.2

We investigated how temperature influences the structural and energetic dynamics of carbon nanotubes (CNTs) undergoing a high-speed impact with a Si (110) surface. By performing molecular dynamics simulations in the temperature range of 100 - 300 K, we found that a low temperature CNT ends up with a higher vibrational energy after collision than a high temperature CNT. The vibrational temperature of CNT increases by increasing the surface temperature. Overall, the structural and energy relaxation of low temperature CNTs are faster than those of high temperature CNTs.

Molecular Dynamics Simulation Study on the Wetting Behavior of a Graphite Surface Textured with Nanopillars

Saha, Joyanta K.,Matin, Mohammad A.,Jang, Jihye,Jang, Joonkyung Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.4

Molecular dynamic simulations were performed to examine the wetting behavior of a graphite surface textured with nanoscale pillars. The contact angle of a water droplet on parallelepiped or dome-shaped pillars was investigated by systematically varying the height and width of the pillar and the spacing between pillars. An optimal inter-pillar spacing that gives the highest contact angle was found. The droplet on the dome-covered surface was determined to be more mobile than that on the surface covered with parallelepiped pillars.