Relaxational mode structure for optical probe diffusion in high molecular weight hydroxypropylcellulose

Abstract

We studied translational diffusion of dilute monodisperse spheres (diameters 14 < d < 455 nm) in aqueous 1 MDa hydroxypropylcellulose (0 ≤ c ≤ 7 g/L) at 25°C using quasielastic light scattering. Spectra are highly bimodal. The two spectral modes (“slow,” “fast”) have different physical properties. Probe behavior differs between small (d < Rh) and large (d ≥ Rg) probes; Rh and Rg are the matrix polymer hydrodynamic radius and the radius of gyration, respectively. We examined the dependences of spectral lineshape parameters on d, c, scattering vector q, and viscosity η for all four probe‐size and mode‐type combinations. We find three time scale‐separated modes: (1) a large‐probe slow mode has properties characteristic of particle motion in a viscous medium; (2) a large‐probe fast mode and small‐probe slow modes share the same time scale, and have properties characteristic of probe motion coupled to internal chain dynamics; and (3) a small‐probe fast mode has properties that can be attributed to the probe sampling local chain relaxations. In the analysis, we also attempted to apply the coupling/scaling (CS) model of Ngai and Phillies [Ngai, K. L., Phillies, G. D. J. J. Chem. Phys., 105, 8385 (1996)] to analyze our data. We find that the second mode is described by the coupling/scaling model for probe diffusion; the first and third modes do not follow the predictions of this model. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3087–3100, 1998

Spectral time moment analysis of microgel structure and dynamics

“…The stretched exponential form used in the line shape analysis provides an accurate while not necessarily unique representation for the field correlation function. To understand the physical properties of the scatterers one can carefully study the behavior of A i , θ i , and β i for each mode as function of scattering angle and temperature as was previously reported for HPC polymer chains20–23 However, the unattractive feature of this approach is that θ i , the pseudorate of relaxation, has the dimensions of time to a noninteger power β i which is not the same in different spectra and different modes.…”

“…HPC is readily available, FDA‐approved nontoxic food additive used in soups and ice creams as an emulsifier9 and encapsulator 10. Because of its electrical neutrality, semiflexible nature, and solubility in a wide range of solvents, HPC has been widely used for studies of polymer dynamics 11–24…”

Diffusion on a molecular scale as observed using PGSE NMR

“…However, experiments on multiple systems (26)(27)(28)(29) find that logðg ð1sÞ ðq; DÞÞ depends non-linearly on q 2 . The convention in most light scattering papers is that q is in units radians/cm, to be contrasted with the cycles/ m of the PGSE NMR q.…”

Neutral polymer slow mode and its rheological correlate

“…Optical‐probe methods were applied to HPC/water systems by Brown and Rymden,7 Yang and Jamieson,8 Russo and coworkers,9, 10 and Streletzky and Phillies 11, 12, 16–18. Brown and Rymden7 found that 720‐Å spheres diffuse through solutions of 800 kDa HPC more rapidly than expected from η p .…”

“…For 907‐Å‐radius probes, the slow‐mode relaxation rate corresponds to the Stokes–Einstein diffusion coefficient. Streletzky and Phillies11, 12, 16–18 studied probe diffusion in aqueous 1 MDa HPC with optical probes with radii of 70–2270 Å and at HPC concentrations ranging from dilute to nearly 4 c + . Their QELSS field correlation functions were bimodal: where subscripts s and b refer to the sharp and broad modes, A s and A b are mode amplitudes, θ s and θ b are relaxation pseudorates, and β s and β b are stretching exponents.…”