Controlling the dynamics of soft spheres: From polymeric to colloidal behavior

Abstract

We probe the dynamic structure factor of multiarm star polymer solutions in good solvent above the overlap concentration with photon correlation spectroscopy and NMR. With the aid of a mean-field theoretical approach, which accounts for the interplay between the topologically enhanced osmotic pressure and the arm entropic stretching, we identify three mechanisms for relaxing the concentration and density fluctuations: cooperative diffusion, self-diffusion and structural relaxation. These model spherical brushes exhibit a behavior intermediate between polymers and colloids.

Colloids with polymer stars: the interaction

“…The factor 5/18 is found by matching the cone approximation for Θ (2) f f to the known values of the contact exponents for f = 1, 2 [1]. This matching in turn proposes an approximate value for the η f exponents, The prefactor Θ f 1 f 2 of the force between two star polymers at short distance calculated in non-resummed 1-loop and resummed 3-loop RG analysis in comparison to the result of the cone approximation.…”

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.…”

Structure and Dynamics of Irregular Multiarm Star Polymers

“…Star polymers with a high number of arms (functionality) and a spherical core, thereafter called "regular" multiarm stars (see figure 1) are a class of architecturally complex soft materials with properties that can be regarded as intermediate between those characteristic for polymers (the individual arms) and those characteristic for colloids (with a compact spherical shape) [1][2][3][4]. This can be rationalized by considering, that, on the one hand the polymers (a contiguous sequence of N covalently bonded monomers) are characterized by weak interactions at monomeric scales, of O(k B T ) or less, and by a relevant correlation length ξ c of O(nm) independent of N. Consequently, very high concentrations are needed in order to reach short range ordering, if attainable at all.…”

“…This type of weak order persists in the melt state as well [9,10], however, as a consequence of excluded volume effects on the macromolecular scale because of the intramolecular monomer density reaching the values of the bulk material [11]. The dynamics in non-dilute solutions revealed the presence of cooperative diffusion (poly- ) LS2 267 4460 -93 LS3 278 9300 -92 LS4 267 18300 -91 LS5 269 29300 -92 LS6 263 42300 -92 meric) and self diffusion and structural relaxation (colloidal) modes [4,12], whereas unusual thermal gelation behaviour was detected as a result of the strong excluded volume interactions [13]. In the melt state, the dynamics was characterized by a two-step terminal viscoelastic relaxation, consisting of a fast mode related to arm relaxation (independent of functionality f , but strongly dependent on arm molecular weight, M a ) and of a slow mode attributed to structural relaxation (cooperative rearrangements of stars, strongly dependent on both f and M a ) [9,10,14].…”