Session L18: Invited Session: Industry Day: Dynamics and Non-Equilibrium Processes of Colloids and Filled Polymer Blends

Structure-Property Relationships of Architectural Coatings by Neutron Methods

Architectural coatings formulations are multi-component mixtures containing latex polymer binder, pigment, rheology modifiers, surfactants, and colorants. In order to achieve the desired flow properties for these formulations, measures of the underlying structure of the components as a function of shear rate and the impact of formulation variables on the structure is necessary. We have conducted detailed measurements to understand the evolution under shear of local microstructure and larger scale mesostructure in model architectural coatings formulations by small angle neutron scattering (SANS) and ultra small angle neutron scattering (USANS), respectively. The SANS results show an adsorbed layer of rheology modifier molecules exist on the surface of the latex particles. However, the additional hydrodynamic volume occupied by the adsorbed surface layer is insufficient to account for the observed viscosity by standard hard sphere suspension models (Krieger-Dougherty). The USANS results show the presence of latex aggregates, which are fractal in nature. These fractal aggregates are the primary structures responsible for coatings formulation viscosity. Based on these results, a new model for the viscosity of coatings formulations has been developed, which is capable of reproducing the observed viscosity behavior.   

Thermal Imaging Processes of Polymer Nanocomposite Coatings

Laser induced thermal imaging (LITI) is a process whereby infrared radiation impinging on a coating on a donor film transfers that coating to a receiving film to produce a pattern. This talk describes how LITI patterning can print color filters for liquid crystal displays, and details the physical processes that are responsible for transferring the nanocomposite coating in a coherent manner that does not degrade its optical properties. Unique features of this process involve heating rates of 10$^7$ K/s, and cooling rates of 10$^4$ K/s, which implies that not all of the relaxation modes of the polymer are accessed during the imaging process. On the microsecond time scale, the polymer flow is forced by devolatilization of solvents, followed by deformation akin to the constrained blister test, and then fracture caused by differential thermal expansion. The unique combination of disparate physical processes demonstrates the gamut of physics that contribute to advanced material processing in an industrial setting.   

Dynamics of Polyelectrolyte Chains within Layer-by-Layer Assemblies

Layer-by-layer (LbL) assembly of charged polymers/nanoparticles finds diverse industrial applications ranging from NIR reflective heat-reduction to multi-stage drug delivery. Internal layering of film components lies at the heart of their performance. I will discuss experiments aimed to unravel relationships between center-of-mass diffusion of polyelectrolyte (PE) chains within LbL films, PE molecular characteristics, environmental conditions (salt concentration), and film structure. Upon film annealing in salt solutions, chain diffusion is highly anisotropic (as probed by fluorescence recovery after photobleaching and neutron reflectometry), and is strongly coupled with film structure. For layered LbL films, PE diffusion in the direction parallel to the substrate reveals quasi-Rouse scaling with molecular weight (\textit{D $\sim$ M}$^{-1})$, even for long chains, suggesting that chains disentangle upon adsorption. Finally, I will discuss quantitative aspects of salt-induced PE chain diffusion in directions parallel and perpendicular to the substrate, and their consequences for persistent layering within LbL films.   

Field responsive shear thickening fluids for personal protective equipment and MMOD shielding for spacecraft and astronauts

Shear thickening fluids (STFs) are novel, field responsive materials and have been shown to provide enhanced ballistic and puncture resistance when integrated into nanocomposites. In this talk, I will review the basic principles of shear thickening in colloidal dispersions by introducing new, recent results describing the unique material functions of the shear thickened state and how these material functions relate to those observed in simulation and experiments, as well as models for these material functions and their dependence on particle concentration. Next, performance data for STF-Armor(TM) nanocomposites (STF intercalated with aramid and other textiles) in puncture, ballistic and hypervelocity impact experiments, as well as energy absorbing impact experiments, will be shown and related back to the material properties of the STF fluids. Finally, advances in product development to achieve suitable puncture resistance for novel applications such as puncture resistant surgical gloves (STF Technologies LLC) will be presented along with challenges for the future product development.   

Nanostructured Block Copolymer Solutions and Composites: Mechanical and Structural Properties

Self-assembled block copolymer templates are used to control the nanoscale structure of materials that would not otherwise order in solution. In this work, we have developed a technique to use close-packed cubic and cylindrical mesophases of a thermoreversible block copolymer (PEO-PPO-PEO) to impart spatial order on dispersed nanoparticles. The thermoreversible nature of the template allows for the dispersion of particles synthesized outside the template. This feature extends the applicability of this templating method to many particle-polymer systems, including proteins, and also permits a systematic evaluation of the impact of design parameters on the structure and mechanical properties of the nanocomposites. The criteria for forming co-crystals have been characterized using small-angle scatting and the mechanical properties of these soft crystals determined. Numerous crystal structures have been reported for the block copolymer system and we have taken advantage of several to generate soft co-crystals. The result of this templating is spatially ordered nanoparticle arrays embedded within the block copolymer nanostructure. These soft materials can be shear aligned into crystals with long range order and this shear alignment is discussed. Finally, the dynamics of nanoparticles within the nanostructured material are characterized with fluorescence recovery after photobleaching (FRAP). The applications and general behavior of these nanostructured hydrogels are outlined.