Laser-Assisted Deposition of Polymer-Matrix Nanocomposites: A Combined Experimental and Computational Study

DMI # 0422632, Manufacturing Processes & Equipment Program: Nanomanufacturing

PI’s: J. M. Fitz-Gerald and L. V. Zhigilei

University of Virginia, Department of Materials Science and Engineering, Charlottesville, VA 22904

1. What is the dependence of the molecular ejection mechanisms on the concentration of polymer molecules and CNTs in the target?

2. What is the effect of mass and geometrical parameters of the ejected species on the efficiency of entrainment into the expanding plume and subsequent post-desorption acceleration?

3. What is mass/size limit for the molecules that can be ejected at a given laser fluence and absorption depth?

4. Is there any interaction among polymer molecules and CNTs in the ablation plume?

5. Do clusters of polymer molecules and CNTs form during the plume expansion and how does the cluster formation depend on the background gas pressure?

6. How sensitive is the quality of the deposited nanocomposite films to the initial distribution of polymer molecules and CNTs in the target material?

7. What are the conditions that would lead to the deleterious chemical modification of polymer molecules or damage of CNTs?

Broader Impact

Training graduate students with broad interdisciplinary background. Two Ph.D. students are currently supported by this program.

Providing research experience to minority undergraduate students through REU sponsored programs.

Development of a new core activity at the Materials Science Department in the area of laser-materials interactions and laser processing.

Development of a interdisciplinary experimental/computational course on Laser-Materials Interactions.

Integration of the research results into graduate courses on Materials Characterization and Modeling in Materials Science.

Knowledge of the fundamental mechanisms of entrainment via laser-matrix interactions will be obtained allowing exploration into large molecule transfer of both organic and inorganic classes of materials. Application Areas: polymer matrix nanocomposites, fragile material systems (organic tissue, DNA materials).

Overcoming rheology barriers in the development of thin films with controlled distributions of reinforcing elements in the matrix. Application Areas: polymer matrix and biocompatible composites with uniform structure at high loading fractions (>45%) of nanoscale constituents with negligible agglomeration effects.

Emergence of a novel mesoscopic computational model for polymer-CNT composites will provide an opportunity to investigate the effect of the CNTs on the matrix properties and the collective behavior of an ensemble of CNTs and polymer molecules. Application Area: computational investigation of nanocomposite materials at the mesoscale.

Research Objectives

Main Research Questions to be AddressedCombined Experimental – Computational Approach

Impact

References

Using polymer matrix carbon nanotube (CNT) nanocomposites as a model system, we are working on identification of the optimum conditions for an efficient fabrication of nanocomposite films with uniform dispersion of reinforcing nano-elements in a polymer matrix at concentrations that cannot be achieved by other methods. The conclusions obtained will be extended to other types of nanoelements of different masses, shapes and chemical / thermomechanical properties.

The objectives of the proposed research program are twofold:

1. to gain a better understanding of the fundamental mechanisms of laser-driven matrix-assisted entrainment of polymer molecules and nanoscale elements and

2. to apply this understanding for the development and optimization of a novel technique for deposition of polymer-matrix nanocomposite thin films and coatings.

laser pulse (193-1064 nm)

frozen “MAPLE” target

volatile solvent is pumped away

Substrate

volatile solvent

polymer

Nanoscale elements (CNT’s, nanopowders)Deposited system

(polymer or composite film)

30 nm 100 nm

200 nm

(a)

(c)

(b)

PEG matrix

Multiscale computational approach is used for investigation of the mechanisms of molecular transport in MAPLE: Molecular dynamics (MD) simulations of laser ablation of a multi-component target will provide input to Direct Simulation Monte Carlo (DSMC) modeling of the ablation plume expansion which, in turn, will provide the conditions for MD/MC simulations of the film deposition.

Snapshots from MD simulations of (a) laser ablation of molecular matrix and (b) matrix-assisted ejection of a polymer molecule (PMMA). In (b) matrix molecules are not shown to give a clear view of conformational changes of the polymer molecule during the ejection.

SWNT-PEG nanocomposite film deposited on Si [1]

The method for fabrication of nanocomposite films to be developed in this program is based on matrix-assisted pulsed laser evaporation (MAPLE) [1,2]. In MAPLE applied for deposition of nanocomposite films the initial target consists of three components: solvent, polymer, and nanoscale elements. The volatile solvent is heated by pulsed laser irradiation and is effectively ablated from the target surface entraining the polymer and nanoscale elements. The volatile solvent is pumped away from the ablation plume, whereas polymer and nanoscale elements are deposited on a substrate.

Characterization will be performed to elucidate the fundamental mechanisms of molecular transfer and the relations between the experimental parameters, materials systems, and the quality of the deposited nanocomposite films. Both in-situ and ex-situ characterization methods are utilized.

1. P. K. Wu, J.M. Fitz-Gerald, A. Piqué, D.B. Chrisey, and R.A. McGill, Deposition of nanotubes and nanotube composites using matrix-assisted pulsed laser deposition, Mat. Res. Soc. Proc. Spring 617, J2.3, 2000.

2. L. V. Zhigilei, Y. G. Yingling, T. E. Itina, T. A. Schoolcraft, and B. J. Garrison, Molecular Dynamics Simulations of Matrix Assisted Laser Desorption - Connections to Experiment, Int. J. Mass Spectrom. 226, 85-106, 2003.