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Does shining light on gold colloids influence aggregation?

Bhattacharya S, Narasimha S, Roy A, Banerjee S - Sci Rep (2014)

Bottom Line: In the literature, the electrostatic interactions, van der Waals interactions, and the change in free energy due to ligand-ligand or ligand-solvent interactions are mainly considered to be the dominating factors in determining the characteristics of the gold aggregates.However, our light scattering and imaging experiments clearly indicate a distinct effect of light in the growth structure of the gold colloidal particles.We attribute this to the effect of a non-uniform distribution of the electric field in aggregated gold colloids under the influence of light.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Indian Institute of Technology Kharagpur, India.

ABSTRACT
In this article we revisit the much-studied behavior of self-assembled aggregates of gold colloidal particles. In the literature, the electrostatic interactions, van der Waals interactions, and the change in free energy due to ligand-ligand or ligand-solvent interactions are mainly considered to be the dominating factors in determining the characteristics of the gold aggregates. However, our light scattering and imaging experiments clearly indicate a distinct effect of light in the growth structure of the gold colloidal particles. We attribute this to the effect of a non-uniform distribution of the electric field in aggregated gold colloids under the influence of light.

No MeSH data available.


I(q) versus q plots for gold colloid recorded for different excitation wavelengths.Inset exhibits background subtracted plasmon resonance band of the gold colloid. The arrows indicate the excitation wavelengths used in scattering measurements.
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f3: I(q) versus q plots for gold colloid recorded for different excitation wavelengths.Inset exhibits background subtracted plasmon resonance band of the gold colloid. The arrows indicate the excitation wavelengths used in scattering measurements.

Mentions: To investigate whether light indeed has any effect on colloidal aggregation, we studied the characteristics of the fractal structures of the gold aggregates using light scattering measurements with different excitation wavelengths. Light scattering measurements are commonly used to study colloidal aggregation. It measures the scattering intensity I(q) from a sample, as a function of the scattering wavevector, q = (4πn/λ)sin(θ/2). Here λ is the incident wavelength, n is the refractive index of the solvent (water) and θ is the scattering angle. The scattering intensity I(q) is proportional to the scattering factor3S(q), where S(q) ~ (qRg)−Df for qRg ≫ 1. Fig 3 presents the I(q) versus q plot in a logarithmic scale for the sol of 1:8 dilution, recorded for different wavelengths (488, 532, 633 and 785 nm) using static light scattering measurements. All plots in Fig. 3 corresponding to different excitation wavelengths exhibit a power-law behavior at high q, and nearly q-independent isotropic behavior for low q. The range of q over which the cross-over between these two regimes occurs, is sensitive to the values of Rg and Df (since I(q)∞S(q)). However, it is not expected to differ appreciably with excitation wavelength30. Interestingly, we observe the cross-over at much high q regime for 532 nm excitation wavelength, in comparison with the cross-over q values found with λ = 488 nm. To check the possibility of any photo-induced effect on ligand molecules, we have measured the UV-vis absorption of the ligand (sodium citrate) in solution over the spectral range between 200 and 900 nm. We do not find any absorption of radiation over the given range. This excludes any photo-induced effect on the ligand in the sol.


Does shining light on gold colloids influence aggregation?

Bhattacharya S, Narasimha S, Roy A, Banerjee S - Sci Rep (2014)

I(q) versus q plots for gold colloid recorded for different excitation wavelengths.Inset exhibits background subtracted plasmon resonance band of the gold colloid. The arrows indicate the excitation wavelengths used in scattering measurements.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4048914&req=5

f3: I(q) versus q plots for gold colloid recorded for different excitation wavelengths.Inset exhibits background subtracted plasmon resonance band of the gold colloid. The arrows indicate the excitation wavelengths used in scattering measurements.
Mentions: To investigate whether light indeed has any effect on colloidal aggregation, we studied the characteristics of the fractal structures of the gold aggregates using light scattering measurements with different excitation wavelengths. Light scattering measurements are commonly used to study colloidal aggregation. It measures the scattering intensity I(q) from a sample, as a function of the scattering wavevector, q = (4πn/λ)sin(θ/2). Here λ is the incident wavelength, n is the refractive index of the solvent (water) and θ is the scattering angle. The scattering intensity I(q) is proportional to the scattering factor3S(q), where S(q) ~ (qRg)−Df for qRg ≫ 1. Fig 3 presents the I(q) versus q plot in a logarithmic scale for the sol of 1:8 dilution, recorded for different wavelengths (488, 532, 633 and 785 nm) using static light scattering measurements. All plots in Fig. 3 corresponding to different excitation wavelengths exhibit a power-law behavior at high q, and nearly q-independent isotropic behavior for low q. The range of q over which the cross-over between these two regimes occurs, is sensitive to the values of Rg and Df (since I(q)∞S(q)). However, it is not expected to differ appreciably with excitation wavelength30. Interestingly, we observe the cross-over at much high q regime for 532 nm excitation wavelength, in comparison with the cross-over q values found with λ = 488 nm. To check the possibility of any photo-induced effect on ligand molecules, we have measured the UV-vis absorption of the ligand (sodium citrate) in solution over the spectral range between 200 and 900 nm. We do not find any absorption of radiation over the given range. This excludes any photo-induced effect on the ligand in the sol.

Bottom Line: In the literature, the electrostatic interactions, van der Waals interactions, and the change in free energy due to ligand-ligand or ligand-solvent interactions are mainly considered to be the dominating factors in determining the characteristics of the gold aggregates.However, our light scattering and imaging experiments clearly indicate a distinct effect of light in the growth structure of the gold colloidal particles.We attribute this to the effect of a non-uniform distribution of the electric field in aggregated gold colloids under the influence of light.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Indian Institute of Technology Kharagpur, India.

ABSTRACT
In this article we revisit the much-studied behavior of self-assembled aggregates of gold colloidal particles. In the literature, the electrostatic interactions, van der Waals interactions, and the change in free energy due to ligand-ligand or ligand-solvent interactions are mainly considered to be the dominating factors in determining the characteristics of the gold aggregates. However, our light scattering and imaging experiments clearly indicate a distinct effect of light in the growth structure of the gold colloidal particles. We attribute this to the effect of a non-uniform distribution of the electric field in aggregated gold colloids under the influence of light.

No MeSH data available.