In-Situ AFM of the Crystallization Kinetics of POSS-Based Nanocomposite Thin Films

1. Polymer Surface Modification and Characterization of Metal Adhesion and In-Situ Crystallization KineticsBrian H. Augustine, James Madison University, DMR 1005641 Halogenated Solvent Pre-Treatment of PMMA To Significantly Improve Au or Pt Thin Film Adhesion In-Situ AFM of the Crystallization Kinetics of POSS-Based Nanocomposite Thin Films FIGURE 1: (top) Au dot array remaining on PMMA surface with a variety of surface pretreatments. (Bottom) DFT modeling of model PMMA surface. (a.) Lewis acid-base adduct formed between chloroform and ester O (red atom) (b.) Au insertion (yellow atom) into bond (c.) halogen atom extraction (d.) O—Au—Cl bond remaining on PMMA surface. Figure 2 (above): 30 x 30 µm AFM image (left) of 30 wt% POSS-MA film 50 hr. after deposition with dendritic features shown. (center) IDL image after morph gradient applied. (right) Final IDL image after reduced to 25 levels from which area is calculated.Figure 3 (left): Avrami curve of in-situ AFM of a similar sample as above. Eight distinct dendritic features were measured individually and averaged. The dimensionality of growth constant was calculated to be 2.54 consistent with a 2D crystallization model. We have discovered that exposing the surface of PMMA with halogenated solvents can change the adhesion of Au or Pt thin films from nearly 0% to over 90%. Non-complexing solvents with a high Gutmann acceptor number such as CHCl3 improve adhesion on PMMA substrates over a factor of 4. ATR-FTIR, XPS and EGA-FTIR evidence shows that there is residual solvent which remains after several days. A Lewis acid-base adduct with a binding energy of ~35 kJ/mol is formed with the ester groups in PMMA which does not happen in complexing solvents such as THF and hexanes. DFT calculations and high resolution XPS show that the solvent molecule is able to interact with the metal atoms to form an O—M—Cl bond at the surface. We have used in-situ and real-time AFM to study the crystallization kinetics of 30 wt% POSS-MA thin films over the course of several hours to days. Recently, we have developed a software protocol for batch analyzing AFM data to obtain quantitative information using Avrami kinetics. We are currently studying the Avrami growth constant at a variety of in-situ temperature conditions to determine the activation energy of the crystallization process. We are also attempting to deposit a free standing 20 nm thick POSS-MA film on a TEM grid to measure the chemical composition of the dendritic features.

2. Polymer Surface Modification and Characterization of Metal Adhesion and In-Situ Crystallization KineticsBrian H. Augustine, James Madison University, DMR 1005641 • Four undergraduate students were directly funded through this project this past summer. Two of these students are undergraduate chemistry majors and two are undergraduate physics majors at JMU. All are rising seniors: Courtney Wardwell, Skylar White (JMU Chemistry), Thomas Hoke and Ethan Cummings (JMU Physics).Wardwell worked on the metal adhesion project along with technician Alan Mo (JMU Biology May 2011). White and Cummings worked on AFM studies of the phase kinetics of POSS-MA thin films along with Sebenzile Shabalala (Chemistry at U. KwaZulu-Natal, South Africa). Hoke worked on novel fabrication of microfluidic devices using in-situ photopolymerization. • In addition, Stuart Hall High School (Va) chemistry and physics teacher, Mr. Kevin Carini, worked on fabricating polymer microfluidic structures which could be used in the teaching of Virginia Standards of Learning topics in high school chemistry and physics classes. Carini successfully fabricated 100 microfluidic devices and presented at a high school science teacher workshop in July 2012 at JMU. Thomas Hoke (L) and Ethan Cummings (R) looking at polymer film sample deposited onto a TEM grid in optical microscope. Courtney Wardwell and Alan Mo testing Au metal adhesion on a PMMA substrate after chloroform vapor exposure. Sebenzile Shalala (School of Chemistry, University of KwaZulu-Natal, South Africa) looking at POSS-MA polymer thin films using in-stiu atomic force microscopy.