Session E56: Symposium Honoring Ryong-Joon Roe

Odyssey of Ryong-joon Roe: Through Polymer Physics over 1/2 Century.

In profound admiration and with deep respect, this is to chronicle and review the pioneering contributions of Ryong-Joon Roe to polymer physics and chemistry. They started from mid 1950s in UK till the onset of 21^st century at the University of Cincinnati.
His training began with Manfred Gordon in Glasgow, Scotland, in mid1950s, and blossomed into productive and fruitful collaborations at Manchester and Essex in England. The initial locales were the Royal Technical College in Glasgow, Scotland, College of Science & Technology in Manchester, England, subsequently at the University of Essex when Gordon joined its faculty. Upon coming to the US in 1962, he joined Bill Krigbaum’s Laboratory at Duke University as a postdoctoral associate. After a stint of 2 years, his odyssey in US began as an industrial polymer scientist, at Niagara Fall Laboratory and the Experimental Station in Wilmington of du Pont, then to the Bell Laboratories as a member of its technical staff. His final move was to the University of Cincinnati occurred in 1975.
The first series of 4 publications with Gordon appeared in 1956, where they demonstrated unambiguously by experiment that the classical theory of gelation by Flory and Stockmayer was well borne out, without interference by diffusion control of monomers and cross-linkers. By 1963, his first publication with Krigbaum was on the thermo-elasticity of Viton, a fluoroelastomer of major importance. His contributions blossomed therefrom in many significant areas of polymer physics. For brevity, only a few specific areas need to be noted, such as polymer surfaces and adsorption, orientation in semi-crystalline polymers, polymer blends and phase relations, block copolymers and physical aging of glassy polymers. The final coup de grace was the 2000 publication of a book entitled, “Methods of X-ray and Neutron Scattering in Polymer Science” by Oxford University Press. It has become a canonical reference for scatters of all shades and kinds.   

Phase Behavior of the Binary Mixtures of Pyrene and Polymers with and without Aromatic Side Groups.

The phase behaviors and thermodynamic properties of pyrene and polymers with and without aromatic side groups are studied using the differential scanning calorimetry technique. Polymers with aromatic side groups showed a relatively larger degree of depression of melting temperature, which suggests higher compatibility with pyrene. Using the enthalpy of melting of pyrene crystals, we could extract the compositions of polymer-rich phases. Surprisingly, the polymers with aromatic hydrocarbons showed much-pronounced miscibility with pyrene at symmetric compositions. In contrast, the polymers without aromatic side groups did not show the composition-dependent miscibility enhancements. These results suggest that the compatibility between polymers and polyaromatic hydrocarbons can be effectively tuned by judicious choice of chemical functional groups of polymers.   

Molecular Dynamics Simulation of Oligomer Liquid and Glass. Relation to Experiment.

Cooling an atomistic model system during molecular dynamics simulation leads to a specific volume profile resembling dilatometry experiments. The characteristic change in slope over a temperature region spanning a few degrees - the glass transition - also occurs in simulations although the width of the (higher) molecular dynamics transition extends over a few tens of degrees, due to the faster simulation cooling rate, ~100 deg per 10-100 ns of simulation time vs. ~100 deg per 24-48 hours using dilatometry.

In the present study we have chosen to study the molecular dynamics Tg using selected molecules for which:

1. PVT behavior of representative small molecules is reproduced accurately.
2. The range of experimental Tgs of high MW polymer spans a broad range.
3. Quality experimental data are available for a series of oligomers of each
polymer.

In this presentation we report simulation Tgs of the three polymers polystyrene, poly(α methyl styrene), and poly(dimethyl siloxane), with a range of oligomers examined for each case. We show that the chosen PCFF+ force field gives excellent agreement of liquid densities, and then discuss how the difference between experimental and simulation Tgs varies across the range of molecular weights. Relation to known cooling rate dependence is discussed.   

Structural Emergence in Nanoparticle Dispersions

The emergence of complex structures from simple building blocks is often seen in nature such as in the organization of starling flocks. Nanomaterials also display emergent structures such as the filler network and higher order structures in reinforced elastomers and complex hierarchical structures of pigments in printed inkjet ink. Small angle scattering of x-rays from semi-dilute dispersions of nanoparticles can be modeled using a pseudo-thermodynamic approach to describe structural emergence. Recent work will be discussed that has led to a new understanding of structural emergence in nanoparticle dispersions.

This presentation is in honor of Joon Roe.

A pseudo-thermodynamic description of dispersion for nanocomposites Y. Jin, et al. Polymer 129 (2017) 32-43.
Structural emergence in particle dispersions A. Mulderig, et al. Submitted Langmuir (2017).
Thermodynamic stability of worm-like micelle solutions K. Vogtt, et al. Soft Matter 13 (2017) 6068-6078.
  

On Cyclization in Advanced Polymeric Materials

This abstract not available.   

Microstructural investigation of butt-fusion joint of high density polyethylene pipes using X-ray scattering

Polyethylene pipes in gas and water applications have proven to be reliable over their 70 years of successful use. In designing a sound polyethylene piping system, the structural integrity of the joints between pipes is of importance. Among variety of pipe joining methods the butt-fusion method is the most widely used. During butt fusion, a melt fusion zone (MFZ) is formed, which contains various morphologies due to the difference in flow behavior within MFZ. In this study MFZ of polyethylene pipe joint was investigated employing synchrotron X-ray scattering at various locations of MFZ by changing the X-ray incidnet angles to probe the 3-dimensional structural features. Our results confirmed the combination of pressure and melt flow during joining process resulted in a complex structure. It was notable that the boundary of MFZ against the base material was found to be very different depending on the structures involved such as crystallographic unit orientation, lamellae orientation, crystallinity and spherulitic morphology.   

In situ SAXS investigations into growth of pyrolytic silica

Structural determination of disordered structures in ramified aggregates is challenging. The topological quantification of such nanomaterials is important in understanding their growth and properties. Small-angle scattering of x-rays from aggregates can provide unique quantitative information. Recently, a method has been developed for the quantification of topology in aggregated material using SAXS. It is applied to in situ measurements of a flame aerosol as a function of height above the burner. The details of the 3-step growth of primary and fractal aggregate structures will be presented.   

Quantifying branching: comparing small angle scattering and molecular simulations

Branching is pervasive in both natural and synthetic materials. The influence of branching on the physical properties has long been recognised. In spite of its fundamental interest and industrial relevance, characterising branching remains a challenge. In this context, one of us introduced a method to obtain quantitative structural information about branching using small angle scattering. The method has already been used to experimentally investigate branching in both organic and inorganic materials, and the results appear promising. To fully comprehend the power and the limitations of this approach, extensive testing against "well-characterised" samples would be worthwhile. Therefore, we used molecular simulations to generate well-defined branched architectures. Scattering functions of the generated architectures were calculated and analysed using the approach mentioned above. It was found that for branched structures that possess a certain symmetry, the quantitative measures obtained from the analysis of scattering data can be correlated to the branched structure in a straightforward manner. For branched structures that are not symmetrical in the aforementioned sense, care must be taken in interpreting the scattering data.