Confinement effects on the chain conformation in thin polymer films

Abstract

The chain conformation of thin polymer films was investigated via diffuse neutron scattering. The samples consist of blend films of protonated and deuterated polystyrene spin coated onto glass substrates. A variation of the thickness of the blend films in a range of about 41 down to 0.66 times the radius of gyration R g of the chains in the bulk enables the determination of film thickness and confinement effects. With diffuse neutron scattering in a reflection geometry the chain conformation in thin polymer films with film thicknesses less than 20 nanometers could be investigated. With decreasing film thickness d below approximately 6 R g the in-plane dimension of the chains starts to increase which is caused by distortion of the chain conformation along the direction parallel and perpendicular to the surface of the film. This increase is quite significant below d < Rg and can be compared to theoretical predictions and simulations.

Effects of carbon nanotubes on polymer physics

“…In such studies, the results have been mixed; some studies have found no change in the radius of gyration in the plane of the surface for polymethyl methacrylate on glass, 25 and polystyrene on hydrogen-passivated silicon, 26 while others have found a significant lengthening for polystyrene on glass. 27,28 A very detailed and precise study on nanoscale silica with no agglomeration exhibited no changes in chain dimensions upon the addition of filler. 29 This latter paper critically examined the literature and concludes that with proper conditions, in particular monodisperse chains, then no chain extension should occur.…”

Confinement enhances dispersion in nanoparticle–polymer blend films

“…The bond orientational order parameter was calculated as S B,i ¼ 0.5 [3/cos 2 y j,z S i À 1], where y is the angle made by the bond between beads j and j À 1 with z axis and /yS represents the ensemble average taken over all segments of a single chain i. As expected [31][32][33][34]37,38 , S B becomes B0 in the bulk for the thicker films, but retains a small but noticeable value even in the bulk for the thinnest film simulated.…”

Evaluation of Morphological Effect on Thermal and Mechanical Performance of PS/PMMA/CdS Nanocomposite Systems

“…According to their reported work, change in the T g is attributed to the change in the viscosity of the PS phase. The enrichment of nanoparticles at interfaces between the polymeric blend phases has also been found in numerical simulations [1,2,7,8] that indicate that there may be an accumulation of the nanoparticles at the phase interfaces with similar energetic interaction of nanoparticles for both polymer phases. In the present study it appears that this energetic interaction between respective polymer phases and nanoparticles is of van der waal type interaction that restricts the mobility of polymer chains and thus more energy is required by the system to achieve the glass transition state and therefore an increase in glass transition temperature of that particular polymeric phase in respective nanocomposite series, is observed.…”

“…Since PS/PMMA blend systems are immiscible, the incorporation of the CdS nanoparticles with different composition dependent morphological blend structures present tailored tensile properties. Bonding between nanoparticles and polymer matrix leads good adhesion between matrix and filler [8] leading to higher density of nanocomposite structure. In this way compactness of composite is directly related to their respective prominent elastic properties.…”

“…These studies suggest that under certain conditions the polymer molecules and the nanoparticles should not be regarded as individual entities within the blend, but instead as complex aggregates. Numerical simulations of polymer nanocomposites have shown that the introduction of hard spheres into a polymer blend has similar effects to the introduction of new polymer/hardwall interfaces [7,8]. Vacatello [9] performed simulations of polymer systems filled with particles of a size comparable to the polymer chains and found that even in the absence of specific interactions with the polymer, the filler particles behaved as highly functional physical crosslinks, reducing the overall mobility of the polymer chains compared to the unfilled polymer matrix.…”