Dynamic Structure of Interacting Spherical Polymer Brushes

Abstract

Multiarm star polymers represent a valuable model system for investigating the dynamics of tethered chains, spherical brushes, or grafted colloidal spheres. Because of their topology, the multiarm stars exhibit a nonuniform monomer density distribution leading to a core−shell morphology, which is responsible for their rich dynamic structure. When the stars interpenetrate, they exhibit liquidlike (macrocrystalline) order due to the enhanced osmotic pressure which balances the entropic stretching of the near-core segments and the excluded volume effects. Using dynamic light scattering, we probe three relaxation modes in the semidilute regime: (i) the fast cooperative diffusion, which is characteristic of their polymeric nature (entangled shell arms); (ii) the self-diffusion of the stars (essentially cores), probed because of finite functionality polydispersity, as confirmed by independent pulsed-field gradient NMR measurements; and (iii) the structural mode, which corresponds to rearrangements of the ordered stars. We develop a mean-field scaling theory, which captures all features observed experimentally with good quantitative agreement. The two slow modes, ii and iii, are reminiscent of the behavior of interacting hard colloidal spheres and are governed essentially by the same physics. We propose these model soft spheres as appropriate vehicles for unifying the descriptions of the dynamics of polymers and soft colloidal dispersions.

Unusual dynamical arrest in polymer grafted nanoparticles

“…However, for polymer grafted nanoparticles, the interaction potential is likely to contain an additional term due to attractive interaction between the cores, which is obviously known to be present since capping is required to overcome this attraction induced aggregation. The effect of this attraction is expected to become more pronounced at low f. Is it possible to observe the predicted dynamical arrest in our polymer-grafted nanoparticle systems at low temperatures and high volume fractions ͑melts͒ as predicted earlier 16,17 for star polymers in good solvents? If such an effect can indeed be observed it would allow for creation of new type of soft material which could show gelation or glasslike behavior for a much larger set of parameters.…”

“…For concentrated star polymer solutions and melts, existence of multiple relaxation modes have been predicted 16 and observed. 7,16 In melts the faster mode is associated with a cooperative diffusion or arm relaxation related to the polymeric arm ͑independent of f͒, corresponding to the relaxation time R , whereas the slow mode is associated with entire star motion or structural rearrangement 7 with relaxation time C . This slow mode seems to be absent in sample B, at least within the measured temperature range.…”

Polystyrene–Poly(sodium methacrylate) Amphiphilic Block Copolymers by ATRP: Effect of Structure, pH, and Ionic Strength on Rheology of Aqueous Solutions

“…26 The first part of the curve can be interpreted in terms of scaling concepts valid for solutions of linear polymers, 41 later verified also for star polymers and micelles. 42,43 According to the theory, the viscosity starts to increase sharply at the overlapping concentration c*. Above c*, in the semidiluted regime, the micelles start to interpenetrate and shrink, with subsequent increase of volume fraction until the percolation threshold for gelation is reached.…”

Star Polymers: From Conformations to Interactions to Phase Diagrams

“…It is essentially in the limit f ≫ 1 where a description of star polymers as sterically stabilized colloidal particles holds. This polymer-colloid hybrid character of star polymers has been explored in a number of publications dealing with the structural [4,6,11,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and dynamical [4,27,28,[39][40][41][42][43][44][45][46][47][48] properties of the same.…”