Theory of dynamic depolarized light scattering from nonrigid polymer chains. II. Freely rotating chains

Moro, Keiji; Pecora, R.

doi:10.1063/1.439782

Cited by 6 publications

(4 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The value of the mean square radius of gyration for a flexible wormlike coil may be substituted to clarify the large differences, RG2 = L2/6a. The theories of Moro and Pécora5,16 give very similar forms where the off-diagonal terms contain the sum of y¡ + y* and the values of these numbers depend on the flexibility parameter. The differences arise from the fact that the eigenvalue problem in our case is strictly that of a fourth-order operator and that the angular variables for overall rotation have been taken into account, giving a time constant that is the sum of three processes: one rotation plus two flexing modes.…”

Section: Discussionmentioning

confidence: 98%

“…Moro and Pécora5, 16 have presented two attempts to understand the experiments by the introduction of polymer rigidity into the calculation. The models successfully showed an increase in the weights of the first few modes as the rigidity is increased, yet at the same time, the models are incapable of yielding the correct rigid rod limit.…”

Section: T H I S C O N T E N T Imentioning

confidence: 99%

See 1 more Smart Citation

Forward depolarized dynamic light scattering from wormlike chains

Aragón¹

1987

Macromolecules

View full text Add to dashboard Cite

The forward depolarized light scattering correlation function is calculated for a dilute solution of polymers modeled as elastic wormlike chains in the free-draining limit. The polymer is represented hydrodynamically by an effective cylindrically symmetric body and characterized by a single end-over-end rotational diffusion coefficient, 8. The correlation function for N polymer molecules is an infinite series of decaying exponentials of the form C(t) = (Np2/15)e~tClkajkbjk(U) exp[-l)(xp + Xk4)t/(2d2)], where p is the segment optical anisotropy, D is the translational diffusion coefficient, L is the contour length, and a = XL is the number of Kuhn lengths. The quantities xi N (2j + 1)7r/2 are eigenvalues of the elastic bending problem.An important feature of the above result is the combination of rotational and flexural contributions to the time constants of the relaxation terms. The relative contribution of each of these processes is a function of flexibility. Comparison with Brownian dynamics simulations indicates that the weights are greatly affected by the neglect of hydrodynamic interactions in the theory. Nevertheless, this equation is the first calculation of the depolarized scattering from a semiflexible molecule that has the correct rigid rod limit. It should also be applicable for the description of the field-free decay of the birefringence from molecules without a permanent dipole moment. The theory is in good agreement with experimental data from DNA restriction fragments.

show abstract

Section: Discussionmentioning

confidence: 98%

Section: T H I S C O N T E N T Imentioning

confidence: 99%

Forward depolarized dynamic light scattering from wormlike chains

Aragón¹

1987

Macromolecules

View full text Add to dashboard Cite

show abstract

“…It is, however, possible to use this formalism and study the effect of chain stiffness on the relaxation time spectrum. 25 We will return to this point later.…”

Section: = (Idmentioning

confidence: 98%

Effect of the disorder-to-order transition in diblock copolymers on the segmental dynamics: a study using depolarized photon correlation spectroscopy

Hoffmann¹,

Koch²,

Stuehn³

1993

Macromolecules

View full text Add to dashboard Cite

Depolarized light scattering has been applied to study the anisotropy fluctuations in a series of polystyrenelpolyisoprene diblock copolymers. This method is selective for the dynamica of the polystyrene block. The molecular weights of the block copolymers (10500-20800) were chosen such that the microphase separation transition (MST) occurs at temperatures which are experimentally acceeeible with photon correlation spectroscopy. Small-angle X-ray scattering (SAXS) was used to identify the disordered regime, the fluctuationcontrolled transition regime, and the ordered state. The relaxation time spectrum in the disordered state is similar to that of bulk polystyrene. Concentration fluctuations increasingly broaden the spectrum and lead to a bimodal shape. Close to the MST the spectrum becomes dominated by a slow, nearly single exponential contribution. Comparison with the SAXS results suggests that this splitting of the relaxation time spectrum can be related to chain stretching.

show abstract

“…This diffusion coefficient is given by D = f ( c ) k B T /6πη s R g , with η s being the solvent viscosity, R g the radius of gyration, and f ( c ) a function of polymer concentration that accounts for the interactions between the polymer chains; f [ c ) ≈ (1 + [ − 1] c − c 2 ), where is the dynamic virial coefficient (for c → 0, f ( c ) → 1). A second mode of relaxation also exists that can give a depolarized contribution and which arises from orientation fluctuations of Kuhn segments due to conformation fluctuations of the polymer chains , (Kuhn segments are rodlike objects, optically anisotropic). For qR g ≪ 1, this latter mode is independent of the magnitude of the wave vector and its characteristic relaxation time is given by the terminal Rouse time for dilute solutions, τ Rouse .…”

Section: Discussionmentioning

confidence: 99%

Relaxation Processes in Semidilute Solutions of Polymers in Liquid Crystal Solvents

2005

View full text Add to dashboard Cite

We investigate the relaxation phenomena in a polymer (polystyrene)/liquid crystal (4-cyano-4'-n-octyl-biphenyl) system, in its homogeneous isotropic phase near the isotropic-isotropic, isotropic-nematic, and isotropic-smectic coexistence curve, using both polarized and depolarized photon correlation spectroscopy (PCS). We study this system for different polystyrene molecular weights (4750, 12 500, and 65 000 g/mol), different compositions (50, 40, 30, and 10% polystyrene (PS) by weight), and different temperatures close to phase boundaries. First of all, we determine the phase diagrams of this system for the different molecular weights. The shape of the phase diagrams strongly depends on the molecular weight. However, in all cases, at low temperatures, these systems separate into an almost pure liquid crystalline (LC) phase and polystyrene-rich phase. PCS measurements show that the relaxation processes in the homogeneous phase are not affected by the proximity of the nematic, or smectic, boundaries (even at a temperature of 0.1 degrees C above the phase separation in two phases). In polarized PCS experiments, we always see three relaxation processes well separated in time: one, very fast, with a relaxation time of the order of 10(-5) s; a second one with a relaxation time within the range 10(-2)-10(-3) s; and a last one, very slow, with a relaxation time of the order of 1 s. Both the fast and slow modes are independent of the wave vector magnitude, while the intermediate relaxation process is diffusive. In depolarized PCS experiments, the intermediate mode disappears and only the fast and slow relaxation processes remain, and they are independent of the magnitude of the wave vector. The diffusive mode is the classical diffusive mode, which is associated with the diffusion of polymer chains in all polymer solutions. The fast mode is due to the rotational diffusion of 4-cyano-4'-n-octyl-biphenyl (8CB) molecules close to polystyrene chains (transient network). Finally, we assign the slowest mode to reorientational processes of small aggregates of PS chains that are not dissolved in 8CB.

show abstract

Theory of dynamic depolarized light scattering from nonrigid polymer chains. II. Freely rotating chains

Cited by 6 publications

References 14 publications

Forward depolarized dynamic light scattering from wormlike chains

Forward depolarized dynamic light scattering from wormlike chains

Effect of the disorder-to-order transition in diblock copolymers on the segmental dynamics: a study using depolarized photon correlation spectroscopy

Relaxation Processes in Semidilute Solutions of Polymers in Liquid Crystal Solvents

Contact Info

Product

Resources

About