Mitchell Anthamatten

Condensation and Polymerization of Supersaturated Monomer Vapor

Initiated chemical vapor deposition (iCVD) of poly(glycidyl methacrylate) from supersaturated monomer vapor is reported. Rapid film growth rates, up to 600 nm/min, were observed. Films grown from supersaturated monomer exhibited distinct surface undulations. The temporal evolution of surface features during film growth was studied and is explained by monomer condensation followed by droplet coalescence and film growth. High droplet densities were observed at the early times and are attributed to rapid polymerization of monomer within condensed liquid nuclei. Droplet nucleation resulting in surface undulations can be avoided by first depositing a thin, cross-linked film from ethylene glycol diacrylate monomer followed by deposition of supersaturated monomer vapors.

Deformation behavior of ion-irradiated polyimide

This work was performed under the auspices of the U. S. Department of Energy by the University of California, LLNL under Contract No. W-7405-ENG-48. The project (03-FS- 027) was funded by the Laboratory Directed Research and Development Program at LLNL.

Porous polymers by controlling phase separation during vapor deposition polymerization.

A template-free method is described to fabricate continuous-phase, porous polymer films by simultaneous phase separation during vapor deposition polymerization. The technique involves concurrent polymerization, crosslinking, and phase separation of condensed species and reaction products. Deposited films form open-cell, macroporous structures consisting of crosslinked and glassy poly(glycidyl methacrylate). By limiting phase separation during vapor phase deposition, spatially dependent morphologies, such as layered morphologies, can be grown. Results show that combining vapor deposition polymerization with phase separation establishes morphological control, which may be applied to applications including cellular scaffolds, thin cushions and vibration dampers, and membranes for separations.

Synthesis, swelling behavior, and viscoelastic properties of functional poly(hydroxyethyl methacrylate) with ureidopyrimidinone side-groups

In this report the swelling and linear viscoelastic behavior of a hydrophilic polymer containing reversibly associating hydrogen bonding side-groups will be examined. Ureidopyrimidinone (UPy) moieties self-associate to form hydrogen-bonded dimers (DDAA) in non-polar media; however, UPy behavior in water-swollen hydrogel environments is unclear. A series of technologically important, poly(hydroxyethyl methacrylate) (poly(HEMA)) polymers, with varying UPy side-group content, were prepared using a reversible addition–fragmentation chain transfer (RAFT) polymerization. Water swelling experiments revealed that UPy side-groups retard early time (<24 h) Fickian-like swelling and lead to two-stage, temperature-dependent, water sorption. At longer times UPy side-groups promote water swelling. Rheological studies show that the materials viscosity and viscous relaxation time both increase with increasing UPy-content. The activation energy of the shear-induced flow scales linearly with UPy-content, suggesting cooperative dynamics. These results are similar to observations made for hydrophobic polymers bearing hydrogen-bonding side-groups and suggest some UPy hydrogen-bonding occurs in hydrated poly(HEMA), despite competitive H-bonding with water. Experimental observations can be explained by reversible association of UPy side-groups within water-excluded domains of poly(HEMA)s secondary structure.

IR absorptive properties of plastic materials used in ICF capsules

Abstract One approach to improving the quality of the DT ice layer on the inside of a NIF capsule target is to enhance the natural β-layering process by heating the ice with infrared light (IR) tuned to a D2 or DT excitation band. However to do this the IR must pass through the capsule wall, and absorption by the capsule material results in heat generation that is deleterious both in terms of reducing the energy input to the ice as well as increasing the difficulty of symmetrically cooling the capsule. In order to optimize the choice of wavelength we have measured the wavelength dependent transmission properties of IR through the plastic materials we are considering for capsule fabrication. We will present wavelength dependent extinction coefficient data for normal and fully deuterated plasma polymer and vapor deposited polyimide.

Thermally activated diffusion in reversibly associating polymers

Mass transport of a small molecule dye through dynamic polymer networks containing reversibly associating side-groups was directly compared to steady-shear viscosity measurements suggesting that viscous relaxation is limited more by the frequency of dissociation events while mass transport is determined primarily by the degree of association.

Synthesis and thermotropic behaviour of imidazole-terminated liquid crystals

Two novel liquid crystals containing terminal imidazole groups (Imi-COOH and Imi-DAH) were designed and synthesised. Imi-COOH exhibits a high-temperature monotropic smectic mesophase that is substantially stabilised by hydrogen bonding between acid and imidazole end-groups. Despite its rigid diacylhydrazine core, which offers the capability of forming lateral hydrogen bonds, Imi-DAH exhibits a nematic mesophase. Fourier transform infrared analysis suggested that the terminal imidazole group interferes with lateral hydrogen bonding between diacylhydrazine cores and destabilises the smectic mesophase. Future studies will examine how proton transport is affected by anisotropic mesophases.

Progress Toward Meeting NIF Specifications for Vapor Deposited Polyimide Ablator Coatings

Abstract We are developing an evaporative coating technique for deposition of thick polyimide (PI) ablator layers on ICF targets. The PI coating technique utilizes stoichiometrically controlled fluxes from two Knudsen cell evaporators containing a dianhydride and a diamine to deposit a polyamic acid (PAA) coating. Heating the PAA coating to 300°C converts the PAA coating to a polyimide. Coated shells are rough due to particles on the substrate mandrels and from damage to the coating caused by the agitation used to achieve a uniform coating. We have developed a smoothing process that exposes an initially rough PAA coated shell to solvent vapor using gas levitation. We found that after smoothing the coatings developed a number of wide (low-mode) defects. We have identified two major contributors to low-mode roughness: surface hydrolysis, and deformation during drying/curing. By minimizing air exposure prior to vapor smoothing, avoiding excess solvent sorption during vapor smoothing, and using slow drying we are able to deposit and vapor smooth coatings 160 μm thick with a surface roughness less than 20 nm RMS.

Hydrogen Bonding in Supramolecular Polymer Networks: Glasses, Melts, and Elastomers

Nature utilizes hydrogen bonding to guide the supramolecular assembly of lipids, proteins, and DNA, thereby imparting remarkable stimuli-responsiveness, structure-forming ability, and elasticity. Supramolecular polymers and networks containing reversibly associating groups are now synthetically accessible and offer diverse properties that are highly sensitive to temperature and other stimuli. This review examines how dynamic hydrogen bonding between functional macromers influences supramolecular network formation and physical properties. The emphasis is on condensed phases, including concentrated solutions, melts, and glasses. We discuss how microscopic factors such as the polymer architecture, backbone mobility, mesoscopic ordering, and aggregation or phase segregation of binding groups influence the supramolecular structure, phase behavior, and dynamics of these materials. This understanding is crucial to advance emerging technologies such as thermoplastic elastomers, shape-memory elastomers, and self-healing materials.

Photoinduced Diffusion Through Polymer Networks

Photomediated addition-fragmentation chemistry is applied to demonstrate the precisely controlled diffusion of chemical species through polymer networks. Fluorescent groups connected to polymer networks by allyl sulfide moieties become mobile upon irradiation with UV light due to radical-mediated addition-fragmentation bond exchange. Photoinduced transport through the bulk, into solution, and across film interfaces is demonstrated.