Coil Dimensions of Polystyrene Chains in Colloid−Polymer Mixtures at the Protein Limit:  A SANS Study

Abstract

A new combination of polymer chains and small colloids is presented in order to investigate the behavior of colloid-polymer mixtures in solution (CP) in the protein limit. To this end, hydroxyfunctionalized silica particles (OHSil) were prepared according to a procedure [J. Am. Chem. Soc. 2003, 125, 3712], which led to colloid radii as small as 1.2 nm. Compared to this small size, the coil dimensions of the polystyrene (PS) chains used as the polymer component were larger by more than an order of magnitude. Investigation of the CP focused on the dimension of the PS chains in the presence of a varying amount of OHSil colloids. Chain size and shape were characterized by means of light scattering, viscosity experiments, and small-angle neutron scattering (SANS). Two solvents have been used. A mixture of dimethylformamide (DMF) with toluene was isorefractive to the OHSil particles, giving access to single chain behavior of PS. Pure DMF, on the other hand, allowed an efficient contrast matching of OHSil suitable for SANS experiments on fully deuterated PS. All characterization techniques provided clear evidence for a shrinking of the coil dimensions with increasing OHSil content in the solution. Particle scattering factors from SANS yielded a detailed picture of this chain compaction. The smallest coil dimensions were recorded close to the liquid-liquid phase boundary, occurring at an OHSil volume fraction of ∼0.17. This is considered to be a first experimental evidence for a shift of the liquid-liquid phase boundary toward lower colloid volume fractions if the colloid size increases. Altogether, present data extend earlier measurements on two chemically different CP in the protein limit, thus establishing the observed shrinking to be a universally valid feature of these systems. The results are in qualitative agreement with theoretical predictions.

Computer simulation study of a single polymer chain in an attractive solvent

“…4͑b͒ at ps =0͔. There are numerous theoretical, [28][29][30] experimental, 31,32 and computational [33][34][35][36] studies of this effect in literature. Within a mean-field approach, the addition of hard particles is equivalent to worsening the solvent properties and can be described in terms of the classic Flory-Huggins theory with parameter adjusted appropriately according to the particle size and concentration.…”

Polymer fullerene solution phase behaviour and film formation pathways

“…Experimentally, phase separation and crystallisation have been observed in a number of systems. 5,[18][19][20][21] In all cases, the polymer was a linear polystyrene chain and the small colloid was either octa-n-propylsilsesquioxane (R C ¼ 0.7 nm), crosslinked poly (ethyl methacrylate) (R C ¼ 8-42 nm), hydroxyl functionalized silica nanoparticles (R C ¼ 11 nm) or C 60 fullerene (R C ¼ 0.35 nm). For some systems, signicant coil contraction (z50%) was found in the presence of high enough (T8 wt%) colloid concentration.…”

Polymer crowding and shape distributions in polymer-nanoparticle mixtures

“…Direct measurements [20] show, for example, that rodlike and spherical depletants induce significantly different interactions between colloids. Confinement and crowding effects are thus of practical concern for their impact on the properties of polymernanoparticle composite materials [12,[21][22][23][24][25][26][27] and for their role in diseases associated with protein aggregation [28].…”