Dynamic Light Scattering of Rigid Rods - A Universal Relationship on the Apparent Diffusion Coefficient as Revealed by Numerical Studies and Its Use for Rod Length Determination

2012 ◽  
Vol 213 (16) ◽  
pp. 1697-1705 ◽  
Author(s):  
Tao Liu ◽  
Zhiwei Xiao
Keyword(s):  
Diffusion Coefficient ◽  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Apparent Diffusion Coefficient ◽  
Numerical Studies ◽  
Rigid Rods ◽  
Apparent Diffusion ◽  
Universal Relationship ◽  
Length Determination

Dynamics of Polystyrene in Confining Geometry: Transition from Dilute to Semidilute

1992 ◽  
Vol 290 ◽  
Author(s):  
Iwao Teraoka ◽  
Kenneth H. Langley ◽  
Frank E. Karasz
Keyword(s):  
Diffusion Coefficient ◽  
Light Scattering ◽  
Apparent Diffusion Coefficient ◽  
Chemical Potential ◽  
Polymer Concentration ◽  
Polymer Chains ◽  
Molecular Weights ◽  
Highly Nonlinear ◽  
Wide Range ◽  
Apparent Diffusion

AbstractDynamics of polystyrene molecules inside controlled pore glasses, a typical confining geometry, was studied by dynamic light scattering over a wide range of concentrations of polystyrene in solutions in equilibrium with the porous glasses. Index-matching of the solvent to the silica glasses effectively facilitates the acquisition of information on the dynamics of polymer chains inside the pore without compromising that information by multiple light scattering. When the concentration outside the pore is much smaller than the overlap concentration v*, the apparent diffusion coefficient Dporc of polymers within the pore shows little dependence on concentration. As the outside concentration increases and approaches v*, Dporc rapidly increases. This tendency is more pronounced for polystyrene samples that have higher molecular weights and are predicted to have a lower concentration inside the pore. With further increases of concentration beyond v*, Dporc approaches the apparent diffusion coefficient outside the pore. Moreover, Dporc becomes almost the same for the three different molecular weights of polystyrene fractions studied and depends primarily on the weight concentration of the solute outside the pore. These features are typical of a semidilute solution regime for flexible polymers. The rapid increase in Dporc, is ascribed to a drastic increase of the polymer concentration inside the pore, which results from an equilibration of the chemical potential of the polymer molecule between the interior of the pore and the exterior. Thus, a rapid increase in the osmotic pressure outside the pore drives the polymers into pore channels even at the expense of reduced entropy. We present a quantitative analysis of this highly nonlinear partitioning of polymer molecules.

Diffusion tensor imaging reveals microstructural differences between subtypes of trigeminal neuralgia

2020 ◽  
Vol 133 (2) ◽  
pp. 573-579 ◽  
Author(s):  
Matthew S. Willsey ◽  
Kelly L. Collins ◽  
Erin C. Conrad ◽  
Heather A. Chubb ◽  
Parag G. Patil
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Tensor Imaging ◽  
Trigeminal Neuralgia ◽  
Apparent Diffusion Coefficient ◽  
Diffusion Tensor ◽  
Statistical Significance ◽  
Region Of Interest ◽  
Pain Syndrome ◽  
Radial Diffusivity ◽  
Apparent Diffusion

OBJECTIVETrigeminal neuralgia (TN) is an uncommon idiopathic facial pain syndrome. To assist in diagnosis, treatment, and research, TN is often classified as type 1 (TN1) when pain is primarily paroxysmal and episodic or type 2 (TN2) when pain is primarily constant in character. Recently, diffusion tensor imaging (DTI) has revealed microstructural changes in the symptomatic trigeminal root and root entry zone of patients with unilateral TN. In this study, the authors explored the differences in DTI parameters between subcategories of TN, specifically TN1 and TN2, in the pontine segment of the trigeminal tract.METHODSThe authors enrolled 8 patients with unilateral TN1, 7 patients with unilateral TN2, and 23 asymptomatic controls. Patients underwent DTI with parameter measurements in a region of interest within the pontine segment of the trigeminal tract. DTI parameters were compared between groups.RESULTSIn the pontine segment, the radial diffusivity (p = 0.0049) and apparent diffusion coefficient (p = 0.023) values in TN1 patients were increased compared to the values in TN2 patients and controls. The DTI measures in TN2 were not statistically significant from those in controls. When comparing the symptomatic to asymptomatic sides in TN1 patients, radial diffusivity was increased (p = 0.025) and fractional anisotropy was decreased (p = 0.044) in the symptomatic sides. The apparent diffusion coefficient was increased, with a trend toward statistical significance (p = 0.066).CONCLUSIONSNoninvasive DTI analysis of patients with TN may lead to improved diagnosis of TN subtypes (e.g., TN1 and TN2) and improve patient selection for surgical intervention. DTI measurements may also provide insights into prognosis after intervention, as TN1 patients are known to have better surgical outcomes than TN2 patients.

Sign in / Sign up

Export Citation Format

Share Document