Nanoparticle with endgrafted chains in polymeric solution

1
Nanoparticle with end-grafted chains in polymeric
solution

• Analee Miranda, Undergraduate
• Applied Math/Physics
• Department of Mathematics
• University of California, Riverside

2
Introduction

• Polymer brushes attached to a colloidal surface
  can be engineered through grafting techniques
  available in todays chemical engineering
  industries

3
Why investigate these structures?We need to
look at some facts about colloidal science first

• The introduction of nanoparticles into any system
  creates energy instability

4
The Facts

• Colloid-Colloid Interactions aid in the
  destabilization of the colloid-polymer mixture
  causing effects such as aggregation

5
The Facts

• Colloidal Dispersion is difficult to achieve

6
How the facts become problems to different
Industries

• Drug Development
• The biggest problem facing formulation
  development providers is solubility.
  www.researchediting.com
• Industrial Chemicals/Cosmetics
• Color infusion is dependent on dispersion of
  colloidal molecules into polymer solutions
• Petrochemicals
• The tendency of heavy organics from its oil phase
  into an aggregate causes arterial blockage
• Bio-Engineering
• Stable colloidal-polymer dispersion is necessary
  to produce biocompatible delivery methods

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Potential Solutions

• Introduction of Polymer Brushes to
• lyophobic colloidal surfaces. This may induce
  thermodynamic stabilization
• any colloidal surface interrupts aggregate
  formation by shielding colloids
• any colloidal surface increases solubility by
  engineering a connection between tails of polymer
  brushes and wet-polymers

8
Monte Carlo Method

• By using Density Functional Theory, the reduced
  Grand potential of a system based on different
  factors is calculated.
• We first investigated a system in which the
  nanoparticle does not carry the polymer brush in
  order to observe the instability.
• We then investigated the same system with the
  polymer brush in order to determine the
  improvements in system stability that the polymer
  brush provides.

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Potential Model

• Inter-segment interactions Cut and Shift
  Lennard Jones Potential

• Segment-Nanoparticle interactions Yukawa
  Potential. The energy parameter is negative to
  induce a very strong repulsion

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Effect of Size Ratio Between Colloid and Segment
Diameters
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Effect of Size Ratio Between Colloid and Segment
Diameters

• We can see that at very low surface coverage as
  the size ratio increases, the system becomes less
  stable.
• For the highest surface coverage, as the size
  ratio increases, the system becomes more stable.
• We can also see a sharp increase in stability as
  the size ratio increases, which suggests an
  optimum rate of stability with an increasing size
  ratio for the highest surface coverage

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Effect of Chain Length of Free Polymers
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Effect of Chain Length of Free Polymers

• We calculated two different densities. We can see
  that for the lower density, it is easier for the
  system to become more stable. The desired effect
  is not as great for the higher density.
• We can also see that the stability of the system
  reaches a maximum and does not undergo much
  transition as the chain length increases.

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Effect of the chain length of Polymer Brushes
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Effect of the chain length of Polymer Brushes

• Again, we see that the maximum stability can be
  attained by adding more polymer brushes to the
  nanoparticle surface.
• Increasing the chain length of the polymer
  brushes at this optimal condition can also yield
  a more stable system.
• The chain length of polymer brushes has a slight
  effect at lower surface coverage.

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Effect of Surface Coverage of Polymer Brush to
Colloid
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Effect of Surface Coverage of Polymer Brush to
Colloid

• We can now fully comprehend that as the surface
  coverage of polymer brushes on the colloid
  increases, the system becomes more stable.
• We can also see that at low densities, we see
  more stability in the system

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Conclusion

• Using density functional theory, we were able to
  prove the function of polymer brushes in the
  colloid systems, i.e., improve the stability of
  colloid dispersion or increase the solubility of
  colloid particles.
• The best results were achieved with low-density
  polymer solution with a high surface coverage of
  long polymer-brushes.

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Acknowledgements

• Dr. Jianzhong Wu, Department of Chemical
  Engineering, Bourns College of Engineering,
  University of California, Riverside
• Zhidong Li, Department of Chemical Engineering,
  Bourns College of Engineering, University of
  California, Riverside
• National Science Foundation

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Abstract

• Colloidal stability is critically important in a
  variety of biomedical and materials applications
  of nanoparticles. A conventional approach is to
  tether nanoparticles with a layer of highly
  soluble Polymer Chains, thereby introducing
  nanoparticle functionality and preventing
  nanoparticle aggregation by stearic repulsion.
  However, the microscopic structure and surface
  energy of Polymer Chains coated nanoparticles are
  not completely understood. This is particularly
  true if one considers the variation of
  interfacial properties with the particle size,
  the chemistry of Polymer Chains, their chain
  length and flexibility, and grafting density.

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• In this work, we have investigated the solvation
  energy and interfacial microscopic structure of
  isolated Polymer Chains -protected nanoparticles
  in polymer solutions through density functional
  theory. At low surface coverage of end-grafted
  Polymer Chains, the insertion of large
  nanoparticle is energetically unfavorable and the
  surface energy rises monotonically with the
  particle size. In this case, the increase of the
  Polymer Chains chain length alters the thickness
  of the protection layer but has only minor effect
  on the interfacial energy. At sufficiently high
  surface coverage, however, the surface energy of
  a large nanoparticle or longer Polymer Chains
  chains is much more negative than that of a small
  particle or short Polymer Chains chains,
  suggesting an increase in solubility with the
  particle size. In both cases, longer polymer
  chains and lower polymer concentration lead to
  improved stability of nanoparticles.

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References

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  science. London Royal Society of Chemistry.
• Yuri S. Lipatov. Translated from Russian by A.
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  Amsterdam New York Elsevier.
• J. Mahanty B. W. Ninham. (1976) Dispersion
  forces. London New York Academic Press.
• Ian D. Morrison Sydney Ross. (2002) Colloidal
  dispersions suspensions, emulsions, and foams.
  New York Wiley-Interscience.