Gary Patterson

Light scattering characterization of polystyrene latex with and without adsorbed polymer

Dynamic light scattering (LS) is sometimes used to determine the thickness of adsorbed layers of polymers by comparing the hydrodynamic radii determined with and without the adsorbed layer. Here we point out a number of pitfalls with this method for one particular polystyrene latex. For example, even without an adsorbed layer, the hydrodynamic diameter determined by dynamic LS is 152 nm while that determined by TEM is 140 nm. Moreover, static LS also yields a larger diameter (150 nm) after subtracting a 3 nm correction for the difference between Mie and Rayleigh scattering. Both the angular dependence of dynamic LS and a cumulants analysis of the autocorrelation function at each angle suggest some polydispersity in size which explains the larger diameter from LS: TEM yields the number-average diameter whereas LS yields a z-average (heavily weighted toward larger particles). The greater polydispersity deduced from LS than reported with TEM might arise from doublet formation. The small difference between diameters determined by dynamic and static LS might be due to electroviscous effects or finite particle concentration. Non-sphericity of particles is not important. The polydispersity with adsorbed polymer (F108 Pluronic) was found to be larger than without. The layer thickness inferred from the difference in average hydrodynamic radius (11 nm) is overestimated owing to the increase in polydispersity with polymer adsorption.

Rayleigh–Brillouin spectroscopy of n-tetracosane. Are there transitions in the melt?

It has recently been suggested that a mesomorphic transition in the melt of n-tetracosane can be detected using Brillouin scattering. In the present paper we report measurements of both the longitudinal Rayleigh–Brillouin spectrum and the depolarized Rayleigh spectrum as a function of temperature from the melting point to 240 °C. The spectra are discussed in detail and it is shown conclusively that the light-scattering results are inconsistent with the existence of a mesomorphic transition above the melting point of n-tetracosane.

The effects of surface layers on third harmonic generation from solutions of a nematogenic polymer

Third harmonic generation (THG) is used to study the third-order nonlinear optical properties of nematic and isotropic solutions of poly(1,4-phenylene-2,6-benzobisthiazole) and related small-molecule model compounds. Maker fringe patterns (MFP) obtained using both plane slab and wedge-shaped cells for fundamental wavelengths of 1.542 and 1.907 μm are analyzed in terms of postulated surface layers in the isotropic preparations. The layers are postulated to comprise regions with concentration smaller than for the bulk sample, in which the rod-like chains tend to have their axes parallel to the plane of the surface, creating a negatively birefringent uniaxial nematic layer. The THG with the nematic solution exhibits intensity with polarization components unexpected for the uniaxial nematic symmetry attributed from linear optical properties, along with other unexpected features in the MFP. This behavior is attributed to the effects of surface layers, postulated to exhibit biaxial nematic symmetry, in which the uniaxial nematic symmetry is broken in regions on the scale of a wavelength. This provides for averaging that does not cause departure from the linear optical behavior expected for a uniaxial nematic, but does produce effects on nonlinear optical properties.

Physical chemistry of macromolecules

INTRODUCTION TO MACROMOLECULES What is a Macromolecule? The Discovery of Macromolecules The Structure of Macromolecules in Solution The Remarkable Properties of Pure Bulk Polymers Building New Materials Using Macromolecules Suggestions for Further Reading DESCRIBING POLYMER STRUCTURE Geometric Structure of Macromolecules Bond Probability Distributions Rotational Isomeric State Approximation Mean-Squared End-to-End Distance Statistics of the Random Coil Chain Flexibility and the Persistence Length MEASURING POLYMER STRUCTURE Polymer Composition and Sequence Distribution NMR Spectroscopy of Polymers Measuring Local Conformations of Polymers Vibrational Spectroscopy Conformational Statistics of N-Hexane Global Measures of the Chain Structure Light Scattering From Dilute Polymer Solutions THE MACROMOLECULAR BASIS OF RUBBER ELASTICITY The Thermodynamics of Ideal-Rubber Elasticity The Statistical Theory of Rubber Elasticity Thermoelastic Inversion Point The Force of Extension of Real Rubber STRUCTURE AND PROPERTIES OF POLYMERS IN DILUTE SOLUTION The Structure of Macromolecules in Dilute Solution Flory Theory of Chain Expansion Thermodynamics of Two Component Solutions Osmotic Pressure Flory Theory of the Second Virial Coefficient Light Scattering From Two-Component Solutions Flory Theory of Light Scattering in Dilute Solution Diffusion of Particles in Solution Kirkwood Theory of Macromolecular Friction Concentration Fluctuations and Mutual Diffusion The Viscosity of Dilute Polymer Solutions The Effect of Molecular-Weight Polydispersity STRUCTURE AND PROPERTIES OF POLYMERS IN SEMIDILUTE SOLUTION The Remarkable Behavior of Semidilute Solutions Microscopic Theory of Semidilute Solutions Viscosity in Semidilute Solutions Structure Near Overlap STRUCTURE AND PROPERTIES OF POLYMERS IN CONCENTRATED SOLUTION Flory-Huggins Theory of Concentrated Solutions The Thermodynamics of Swollen Rubber: Gels Light Scattering From Concentrated Solutions Real Solutions and the Flory-Orwoll Theory Diffusion in Concentrated Solutions Viscoelasticity in Concentrated Polymer Solutions STRUCTURE AND PROPERTIES OF POLYMERS IN THE PURE AMORPHOUS LIQUID STATE Free Volume and Viscosity Viscosity of Low-Molecular-Weight Chain Liquids Phenomenology of the Glass Transition Temperature and Pressure Dependence of Relaxation Near the Glass Transition STRUCTURE AND PROPERTIES OF RODLIKE POLYMERS IN SOLUTION Characterization of Rodlike Polymers in Solution Second Osmotic Virial Coefficient Thermodynamics of Rodlike Polymer Solutions STRUCTURE AND PROPERTIES OF POLYELECTROLYTE CHAINS IN SOLUTION Structure of Linear Polyelectrolyte Chains in Dilute Solution Thermodynamics of Polyelectrolyte Solutions Viscosity of Polyelectrolyte Solutions References Index * Each contains an Introduction section

Depolarized Rayleigh scattering from simple molecular liquids: Investigation of transitions in the melt

Depolarized Rayleigh scattering photometry has been employed to study the temperature dependence of the optical anisotropy for benzene, hexafluorobenzene, and carbon tetrachloride. The depolarized Rayleigh intensity from carbon tetrachloride is entirely due to scattering by pairs of density fluctuations and increases monotonically with temperature. The total depolarized Rayleigh ratio RVH for benzene and hexafluorobenzene decreases smoothly and monotonically with temperature, in contradiction to a recent report [J. Chem. Phys. 95, 1223 (1991)]. The temperature dependence of the total depolarized Rayleigh ratio can be analyzed in terms of an increasing contribution due to scattering by pairs of density fluctuations and a decreasing contribution due to orientational fluctuations of optically anisotropic molecules. No anomalous behavior is observed anywhere in the liquid range for these three fluids.

Polymer Science from 1935-1953

1935 was a very good year for polymer science. More than 200 scientists, engineers and technologists had gathered in Manchester to present and discuss the field of polymerization and the discipline of polymer science.

Concluding Reflections and Further Thoughts

The period from 1935-1953 was a very profitable and dynamic era in the history of polymer science. The worldwide community that coalesced in 1935 was very active in identifying the key phenomena and forging satisfying qualitative and quantitative theories. The state of the community in 1953 will be surveyed from several perspectives.

Other Emerging Leaders

Many other scientists committed a major part of their work to the study and understanding of macromolecules. In this chapter, brief surveys of these emerging leaders are given.

Speed Marvel and Friends

Carl Shipp Marvel (1894-1988) took the mantle left by Wallace Carothers . It is not surprising that he also came from the University of Illinois. The towering figure at Illinois in this period was Roger Adams (1889-1971). He was Department Head from 1916-1954. Adams was from a famous New England family and attended Harvard University.

Flory and Friends

Although Wallace Carothers (1896-1937) was not alive to personally interact with the ongoing polymer science community, he left a legacy of publication that was quickly collected and edited by Herman Mark (1895-1992) and G. Stafford Whitby (1887-1972).