Molecular Dynamic simulation of heating of gold nanorod in water
Potential Model for Gold
Molecular dynamics (MD) simulations of the gold nano rods in presence of water were
performed using embedded atom method (EAM)
[7. Daw, M. & Baskes, M. Semiempirical, Quantum Mechanical Calculation of Hydrogen Embrittlement in Metals. Phys. Rev. Lett. 50, 1285–1288 (1983).
8. Daw, M. & Baskes, M. Embedded-atom method: Derivation and application to impurities, surfaces,and other defects in metals. Phys. Rev. B 29, 6443–6453 (1984). ] .
For the EAM, the total energy (Etot) for a system of N atoms can be written as equa S14.
To model the interactions of water molecules, we have employed flexible SPC/Fw water
model to conduct simulations at various temperatures9
. The potential interaction in the flexible
SPC/Fw, as shown in equation (S15), is a sum of pair-wise interactions for bonded and nonbonded
terms.
Potential model and parameters for gold-water interaction
We used the Lorentz-Berthelot rule to estimate the interaction between water and gold
that is modeled using standard 6-12 potential.
Melting temperatures as a function of nanorod aspect ratios:
We have further calculated the bulk melting point as well as the melting of nanorods with
different aspect ratios. The melting point of bulk gold predicted by the EAM potential used in this work is 1281 K. The experimental value is 1337 K and thus the prediction of our potential model is very good.
The melting points for nanorods with different aspect ratios (AR) are summarized below. It can be seen that nanorods with higher aspect ratios have lower melting points compared to bulk. This is not surprising since the surface area (Table S3) increases with increasing AR.
Ref: http://www.nature.com/srep/2015/150130/srep08146/extref/srep08146-s1.pdf
Online Services headline animator, feedBurner
Showing posts with label nanoparticles. Show all posts
Showing posts with label nanoparticles. Show all posts
Monday, May 18, 2015
Wednesday, April 22, 2015
gold nanoparticles. Surface stress
Among nanoparticles, gold nanoparticles (Au NPs) have been extensively studied;
this is partly because gold is the subject of one of the most ancient themes of
investigation in science. Au NPs are among the most stable metal nanoparticles [5]
since Au is relatively chemically inert. They present fascinating aspects such as
low-symmetry structures at some geometric magic numbers [9] and size-related
electronic, magnetic [5, 7] and optical properties (due to quantum size effect).
Moreover, their applications to catalysis, owing to the high surface-to-volume ratio,
and biology are also significant. For example, conjugates of Au NPs-oligonucleotides
are of great interest owing to the potential use of the programmability of DNA
base-pairing to organize nanocrystals in space. This gives multiple ways of providing
a signature for the detection of precise DNA sequences to develop biosensors, disease
diagnosis, and gene expression, etc [5]. Besides, research is expanding on Au NP
catalytic effects associated with CO oxidation, NO reduction, and the water-gas shift
reaction, i.e. the chemical reaction in which carbon monoxide reacts with water vapor
to form carbon dioxide and hydrogen; new Au NP based catalytic systems are now
being explored. [4][5]
Applications exploiting the optical properties of Au NPs utilize functionalization
of NPs with chromophores. Chromophore means the part of a molecule responsible for its color. These have diverse applications due to a range of options for the
chromophore. In 2003, K. Thomas et al. reported that gold nanoparticles associated
with fluorophores were utilized in photocurrent generation and fluorescent display
devices [10]. Furthermore, they also showed that gold nanoparticles can bind and
release amino acids when linked with appropriate chromophores. All in all, it appears
safe to assume that Au NPs will be a key building block for nano-science and
-technology in the 21st century.
Given the many applications of Au NPs, as well as the extensive literature on
them, this thesis will focus on Au NPs as a canonical metal NP system.
The structure of gold nanoparticles has been perhaps the most investigated aspect
about them.[4] It has been found, theoretically and experimentally that gold
nanoparticles have crystallographic structures different from the bulk material.[4,11]
In general, gold nanoparticles have icosahedral or decahedral motifs depending on
their size while bulk gold has face-centered cubic (fcc) crystal structure [4].
For Au NPs larger than 2 nm, the truncated-octahedral structure (fcc) is the dominant shape [4, 12].
-----------------
Because NPs in general - and Au NPs specifically - possess significant surface
area to volume ratio, their surface thermodynamic properties can be very important in
determining a NP‘s properties. An important surface thermodynamic quantity is the
surface stress. Surface stress, f, is a thermodynamic quantity that describes the amount
of energy or reversible work per unit area required to elastically deform a solid
surface. It differs from another fundamental thermodynamic parameter, i.e. surface
free energy γ, which represents the energy needed to form a new surface by a process
like cleavage.[24] In liquid, these two values are identical, as the configuration of
fluid surface remains constant owing to bulk atoms or molecules moving exteriorly to
the surface when a fluid surface is stretched. Put differently, a liquid cannot support a
shear stress so the only way to create/eliminate new surface is by adding/removing
atoms from the surface, rather than elastically deforming existing atoms at the surface.
In contrast, when a solid surface is put in tension (within an elastic limit), the total
number of surface atoms is conserved; therefore, the number of atoms per unit area
changes and consequently, f ≠ γ.
Ref: http://preserve.lehigh.edu/cgi/viewcontent.cgi?article=2257&context=etd
Molecular Dynamics Simulation of Gold Nanoparticles and Surface Stress Effect
Siming Zhang
Lehigh University
2011
this is partly because gold is the subject of one of the most ancient themes of
investigation in science. Au NPs are among the most stable metal nanoparticles [5]
since Au is relatively chemically inert. They present fascinating aspects such as
low-symmetry structures at some geometric magic numbers [9] and size-related
electronic, magnetic [5, 7] and optical properties (due to quantum size effect).
Moreover, their applications to catalysis, owing to the high surface-to-volume ratio,
and biology are also significant. For example, conjugates of Au NPs-oligonucleotides
are of great interest owing to the potential use of the programmability of DNA
base-pairing to organize nanocrystals in space. This gives multiple ways of providing
a signature for the detection of precise DNA sequences to develop biosensors, disease
diagnosis, and gene expression, etc [5]. Besides, research is expanding on Au NP
catalytic effects associated with CO oxidation, NO reduction, and the water-gas shift
reaction, i.e. the chemical reaction in which carbon monoxide reacts with water vapor
to form carbon dioxide and hydrogen; new Au NP based catalytic systems are now
being explored. [4][5]
Applications exploiting the optical properties of Au NPs utilize functionalization
of NPs with chromophores. Chromophore means the part of a molecule responsible for its color. These have diverse applications due to a range of options for the
chromophore. In 2003, K. Thomas et al. reported that gold nanoparticles associated
with fluorophores were utilized in photocurrent generation and fluorescent display
devices [10]. Furthermore, they also showed that gold nanoparticles can bind and
release amino acids when linked with appropriate chromophores. All in all, it appears
safe to assume that Au NPs will be a key building block for nano-science and
-technology in the 21st century.
Given the many applications of Au NPs, as well as the extensive literature on
them, this thesis will focus on Au NPs as a canonical metal NP system.
The structure of gold nanoparticles has been perhaps the most investigated aspect
about them.[4] It has been found, theoretically and experimentally that gold
nanoparticles have crystallographic structures different from the bulk material.[4,11]
In general, gold nanoparticles have icosahedral or decahedral motifs depending on
their size while bulk gold has face-centered cubic (fcc) crystal structure [4].
For Au NPs larger than 2 nm, the truncated-octahedral structure (fcc) is the dominant shape [4, 12].
-----------------
Because NPs in general - and Au NPs specifically - possess significant surface
area to volume ratio, their surface thermodynamic properties can be very important in
determining a NP‘s properties. An important surface thermodynamic quantity is the
surface stress. Surface stress, f, is a thermodynamic quantity that describes the amount
of energy or reversible work per unit area required to elastically deform a solid
surface. It differs from another fundamental thermodynamic parameter, i.e. surface
free energy γ, which represents the energy needed to form a new surface by a process
like cleavage.[24] In liquid, these two values are identical, as the configuration of
fluid surface remains constant owing to bulk atoms or molecules moving exteriorly to
the surface when a fluid surface is stretched. Put differently, a liquid cannot support a
shear stress so the only way to create/eliminate new surface is by adding/removing
atoms from the surface, rather than elastically deforming existing atoms at the surface.
In contrast, when a solid surface is put in tension (within an elastic limit), the total
number of surface atoms is conserved; therefore, the number of atoms per unit area
changes and consequently, f ≠ γ.
Ref: http://preserve.lehigh.edu/cgi/viewcontent.cgi?article=2257&context=etd
Molecular Dynamics Simulation of Gold Nanoparticles and Surface Stress Effect
Siming Zhang
Lehigh University
2011
Subscribe to:
Posts (Atom)