The bulk dynamics of a compositionally asymmetric diblock copolymer studied using dynamic light scattering

Abstract

We have studied the bulk dynamics of a compositionally asymmetric poly(ethylene propylene)-poly(dimethylsiloxane) (PEP-PDMS) diblock copolymer in a large temperature range both in the ordered and in the disordered state. The volume fraction of the PEP block is 0.22. Apart from the disordered state, the sample shows three ordered morphologies. Using dynamic light scattering, we have investigated the dynamics in all four phases and combined these results with those obtained using pulsed field gradient NMR. In the disordered state, we find-apart from the slow cluster mode-the heterogeneity mode related to the self-diffusion of single chains. The relaxation time τ of this mode, reduced by temperature and the zero-shear viscosity η, log(τ T /η), increases with temperature. In the cubic phase right below the ODT temperature, we observe two diffusive processes, and we attribute the faster one to the mutual diffusion of micelles and block copolymers not bound to micelles ("free chains") through the PDMS matrix. The slower mode may either be due to the mutual diffusion of free chains and chains bound to PEP micelles or to the cooperative diffusion of micellar aggregates. In the non-cubic ordered state at intermediate temperatures, an additional weak diffusive mode is observed. The low-temperature ordered state is body-centered cubic, and here, only the mutual diffusion of micelles and free chains lies in our experimental time window.

Dynamics of amphiphilic diblock copolymers at the air–water interface

“…Whereas, in the q -range considered here they reflect the dynamics of the polymer close to the interface [33]. sembles a second order or a weak first order phase transition [24,25], in agreement with the change observed in surface pressure data (Fig. 3a); i.e.…”

“…In these different states the polymer changes both the conformation and the diffusion mechanism, which can be usually expressed by a different scaling law [2]. In a common solvent for the two blocks, a micro phase separation is encountered above a characteristic concentration which affects several diffusion and relaxation mechanisms [22,23,24,25,26,27]. In a selective solvent, on the other hand, polymer micelles are formed with a core built up by the insoluble block.…”

Dynamics and Viscoelasticity of Disordered Melts of Symmetric Diblock Copolymers

“…The dynamic structure factor S ( q , t ) in diblock copolymer melts and solutions has been measured by photon correlation spectroscopy (PCS) using both optical dynamic light scattering (DLS) − and, more recently, using small-angle X-ray PCS …”

“…Most optical DLS experiments on diblock copolymer melts and solutions have measured S ( q , t ) only at low values of wavenumber q , less than inverse polymer coil size. DLS experiments by several groups − showed evidence of both a nondiffusive mode, for which the decay rate Γ­( q ) remains nonzero as wavenumber q approaches zero, and a diffusive mode, for which Γ­( q ) ∝ q 2 . The nondiffusive mode was well anticipated by theories of idealized monodisperse block copolymers.…”

Dynamic Light Scattering Studies on Network Formation of Bridged Polysilsesquioxanes Catalyzed by Polyoxometalates

“…Dynamic light scattering (DLS) is a powerful tool to characterize the structure and dynamics for polymer solutions with micelles or aggeregates, 12,13 gels, [14][15][16][17][18] proteins, 19,20 and bulk copolymer. 21 Because of several advantages, such as short accession time and suitable length scale for polymer cluster investigation, DLS has been further developed for studying in situ the timedependent experiments of polymerization, protein aggregation, gelation, and vitrification. In our previous studies, we demonstrated that the acid-and basecatalyzed sol-gel process of tetramethoxysilane can be monitored by time-resolved dynamic light scattering (TRDLS).…”