New Efficient methods to Characterize Effects of Framework - - PDF document

New Efficient methods to Characterize Effects of Framework Flexibility on CH4 Diffusion in 8MR Zeolites

Rohan Vivek Awati

rawati3@gatech.edu

• Prof. David Sholl

School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA Molecular dynamics and transition state theory predicts diffusion of molecules in nanoporous

• materials. To save computational time, the framework of the material is assumed rigid which may
• r may not be accurate. In our study, we systematically characterize the effect of framework

flexibility on diffusion in model zeolites that exhibit different patterns of window flexibility. We show that for molecules with kinetic diameters comparable (or larger) to the size of the window the rigid framework approximation can produce order(s) of magnitude difference in diffusivities as compared to the simulations performed with a fully flexible framework.. To account for framework flexibility effects efficiently and reliably, we introduce two new methods in which the flexible structure is approximated as a set of discrete rigid snapshots obtained from molecular dynamics simulations of an empty framework, using classical method. Both methods are orders of magnitude more efficient than the simulations with the fully flexible structure.

Enhancing Field-Effect Mobility of Conjugated Polymers through Rational Design of Branched Side Chains

Boyi Fu

Boyi.fu@chbe.gatech.edu

• Prof. Elsa Reichmanis

School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA The design of polymer semiconductors possessing effective π-π intermolecular interactions coupled with good solution processability remains a challenge. Here structure-property relationships associated side chain structure with resultant π-π intermolecular interactions, polymer solubility, and charge carrier transport is reported, based on a donor-acceptor(1)-donor- acceptor(2) polymer: 5-Decylheptadecyl (5-DH), 2-tetradecyl (2-DT) and linear n-octadecyl (OD) chains were substituted onto poly(bithiophene-benzothiazole-thiophene-diketopyrrolopyrrole- thiophene), pTBTD, to afford pTBTD-5DH, pTBTD-2DT, and pTBTD-OD, respectively. In 5- DH side chain the branching position is remote from the polymer backbone, whereas it is proximal in 2-DT. This study demonstrates that incorporation of branched side chains where the branching position is remote from the polymer backbone merges the advantages of improved solubility from branched units with effective π-π intermolecular interactions normally associated with linear

• chains. pTBTD-5DH exhibits superior qualities on the degree of polymerization, solution

processability, π-π interchain stacking, and 3 - 7 times of field-effect charge carrier mobility relative to the other analogs.

A Lattice Fluid Equation of State for Associating CO2 + Polymer/Ionic Liquid Systems

Mohammad Hossain

mhossain32@gatech.edu

• Prof. Amyn S. Teja

School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA The phase behavior of CO2 + polymer systems is of interest in polymer synthesis, flue and natural gas processing, and drug delivery. Theoretical and experimental evidence suggests that CO2 is able to interact with electron donating carbonyl groups in polymers to form weak Lewis acid-base (EDA) complexes. These interactions significantly affect phase behavior in CO2 + polymer

• systems. However, few thermodynamic models explicitly account for EDA complexes. The goal
• f the present work is to develop a new Equation of State (EOS) for associating systems that

contains two adjustable parameters that are temperature independent. This is achieved by incorporating complex formation in the Guggenheim-Huggins-Miller lattice fluid partition

• function. One parameter in the proposed EOS is obtained from independent in situ ATR FTIR

spectroscopy measurements. The significance of the new EOS is demonstrated by calculating the solubility of CO2 in associating polymers and the extent of swelling caused by CO2. In addition, the EOS is extended to other systems that involve complex formation, such as CO2 + Ionic Liquids.

Multi-scale Modeling of Novel Adsorbents for Gas Separations and Accelerated Materials Development

Ambarish R. Kulkarni

akulkarni34@gatech.edu

• Prof. David Sholl

School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA Owing to the significant improvements in available computational power, the role of molecular modeling has been increasing exponentially. One way of leveraging computational tools is by performing high throughput screening of materials to guide experimental synthesis. Grand Canonical Monte Carlo and Molecular Dynamics have been widely used to predict adsorption uptakes and diffusivities in nano-porous structures, but the accuracy of these methods is highly dependent on the quality of the force field used. Our approach involves the development of a transferable force field by performing high quality quantum chemical calculations to precisely describe the intermolecular interactions. Using this algorithm we are able to accurately predict CO2 adsorption in various siliceous and cationic zeolites. This methodology can be easily extended to other adsorbates (hydrocarbons, H2S) and materials such as Metal Organic Frameworks (MOFs). The final part of this talk will discuss high throughput screening of MOFs for alkane/ alkene separations using this approach.

High Sensitivity, Positive Tone, Low-k Polynorbornene Dielectric

Brennen K. Mueller

bkmueller@gatech.edu

• Prof. Paul A. Kohl

School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA In microelectronics packaging, low-k dielectrics are used to mechanically and electrically isolate conductive interconnects. Positive tone, aqueous developable, polymeric dielectrics are used for this purpose due to their high yield, environmentally friendly, and high throughput processing. Furthermore, these materials must have excellent mechanical and electrical properties, which typically require cross-linking of the polymeric film. Positive tone chemical amplification can provide high photospeed and contrast, but the photo-generated acid necessary for patterning also catalyzes cross-linking reactions. Presented in this work is the first chemically amplified, positive tone, cross-linkable dielectric. The base polymer is polynorbornene with pendent fluoroalcohol and tert-butyl ester moieties. This polymer is successfully patterned at photospeeds > 10x faster than existing materials. After photolithography, the dielectric is cross-linked via a Fischer esterification. The resulting film had a modulus of 2.99 GPa and a dielectric constant of 2.78, both very promising for its use in microelectronics.

Block Copolymer Directed Self-Assembly: Understanding Defect Free Energies for Computer-Aided Material and Process Design

Andrew Peters

andrew.peters@chbe.gatech.edu Clifford Henderson School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technique for producing sub-20 nm pitch patterns that will be required for future semiconductor device generations. Development of DSA methods and materials is difficult and time consuming experimentally due to many factors including the difficulty of metrology on nanoscale patterns. DSA advancement could greatly benefit from use of computer simulations to rapidly guide material and process development efforts. In this work, molecular dynamics (MD) simulations using realistic polymer potentials are used to create DSA process simulations. In particular, defect level control is critical to semiconductor processing and an understanding of factors controlling this behavior is critical to DSA development. Using thermodynamic integration, the free energy behavior of DSA processes and the impact of material and process parameters on defect free energies has been studied. The translation of these results into material and process design recommendations will be presented.

Stability in fiber spinning: the role of rheology and phase separation kinetics

Kyung Hee Oh

koh33@gatech.edu

• Dr. Victor Breedveld

School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA Instabilities are often encountered during fiber spinning from polymer melts and solutions. In particular, draw resonance is commonly observed, a periodic perturbation in diameter of the liquid fiber without breakage at high draw ratios. In melt spinning, reasonably good understanding and theoretical predictions exist for the onset of draw resonance, but such knowledge does not exist for solution spinning. In this study, we demonstrated that the melt spinning predictions have limited predictive power for solution spinning, where phase separation kinetics complicate the fiber formation process. We quantified the rheology of membrane dopes and their solidification

• kinetics. Then, we created spinnability diagrams that describe the spinning regimes as a function
• f key process parameters (i.e. spinneret velocity, draw ratio and air gap length). Our experiments

quantify how rheology and phase separation kinetics affect the spinnability of dopes. Increasing dope viscosity and enhancing phase separation both resulted in expansion of the stable spinning regime.

Surface Chemistry Stabilized Semiconductor Nanowire Growth

Saujan V. Sivaram

saujan@gatech.edu

• Prof. Michael A. Filler

School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA Semiconducting nanowires are poised to serve as quintessential building blocks for next- generation energy conversion and storage, electronic, and photonic applications. The vapor-liquid- solid mechanism remains the signature method for fabricating these nanomaterials; however, the exploration of complex and even simple nanostructures has been hindered by the scarcity of fundamental chemical information that dictates this bottom-up synthesis. To that end, we used in situ infrared spectroscopy to investigate the impact of surface chemistry, specifically chemisorbed hydrogen, on the growth of germanium nanowires. We show that covalently bonded hydrogen atoms, which are a byproduct of precursor (Ge2H6) decomposition, are essential for stable nanowire synthesis. We determine the surface hydrogen coverage via a novel semi-quantitative approach and find that below a critical threshold coverage, the catalyst droplet destabilizes and nanowire growth subsequently terminates. Finally, we leverage our knowledge of surface chemistry to enable stable nanowire growth beyond the traditional hydride process window.

Markov Decision Process based Dynamic Programming for Colloidal Self-Assembly Process Optimal Control Xun Tang

xtang38@gatech.edu Martha A. Grover School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA Self-assembly broadly refers to the process of a disordered system converging to a well-arranged state without human intervention. We propose to apply a Markov decision process (MDP) based dynamic programming optimal control algorithm to manipulate a SiO2 colloidal self-assembly process for two-dimensional defect-free crystals. The movement of the particles is manipulated by the dipole-dipole and dipole-field interactions, which are controlled by changing the magnitude of the voltage on the electrodes surrounding the system. A two-dimensional Langevin equation is developed to simulate the dynamics of this SiO2 colloidal system. Markov chain models are developed based on simulations from the low dimensional Langevin equation. With the predictions

• n the system state evolution, an infinite-horizon MDP optimization problem is formulated and

the optimal control policy is solved by dynamic programming with policy iteration. Our MDP- based dynamic programming control policy is able to accelerate the SiO2 colloidal self-assembly process for two-dimensional defect-free crystals.

DFT Modeling of Physisorbed R-3-Methylcyclohexanone on Complex Cu Surfaces

Daniel S. Wei

dsawei@gmail.com

• Prof. David S. Sholl

School of Chemical and Biomolecular Engineering Georgia Institute of Technology, Atlanta, GA The physisorption of R-3-Methycyclohexanone (R3MCHO) on low and high Miller index Cu surfaces was studied with temperature programmed desorption (TPD) and density functional theory (DFT). Earlier calculations with nonhybrid functional were shown to qualitatively capture adsorption energy changes in physisorbed R3MCHO on surfaces vicinal to Cu(111). However, the failure to account for van der Waals forces in the nonhybrid functional caused a significant underestimation of total adsorption energy. The development of dispersion corrected methods attempted to address this gap between simulation and experiment. This study utilized three of the dispersion corrected methods – D2, vdW-optB86b, and vdW-optB88. The adsorption energies calculated by the dispersion corrected methods were show to be more comparable to the TPD results than those calculated without dispersion corrections, although, the corrected methods had a tendency to overbind the surface adsorbates. The implementation of dispersion corrected methods also indicated a possible adsorbate induced surface reconstruction on Cu(110).