Polymers segment density profiles

COSGROVE ET Al.. Adsorbed Polymer Segment Density Profiles... 

In one example polymer segment density profiles of weak polyacid brushes consisting of polymethacrylic acid (PMAA) chains were investigated as a function of the pH of the environment by means of multiple-angle ellipsom-etry [68]. The polymer brushes were prepared by surface-initiated polymerization of methylacrylic acid as described above. 

FIG. 12 Segment density profile as function of the distance from the wall Z for flexible (empty symbols) and semi-rigid (full symbols) living polymer chains at T = 0.4 [28]. The fractional occupancy of lattice sites by polymer segments is shown for the layers in the left half of the box. Dashed lines are guides for the eyes. 

The theory of polymer adsorption is complicated for most situations, because in general the free energy of adsorption is determined by contributions from each layer i where the segment density is different from that in the bulk solution. However, at the critical point the situation is much simpler since the segment density profile is essentially flat. Only the layer immedia-... 

Several experimental parameters have been used to describe the conformation of a polymer adsorbed at the solid-solution interface these include the thickness of the adsorbed layer (photon correlation spectroscopy(J ) (p.c.s.), small angle neutron scattering (2) (s.a.n.s.), ellipsometry (3) and force-distance measurements between adsorbed layers (A), and the surface bound fraction (e.s.r. (5), n.m.r. ( 6), calorimetry (7) and i.r. (8)). However, it is very difficult to describe the adsorbed layer with a single parameter and ideally the segment density profile of the adsorbed chain is required. Recently s.a.n.s. (9) has been used to obtain segment density profiles for polyethylene oxide (PEO) and partially hydrolysed polyvinyl alcohol adsorbed on polystyrene latex. For PEO, two types of system were examined one where the chains were terminally-anchored and the other where the polymer was physically adsorbed from solution. The profiles for these two... 

Segment density profiles and hydrodynamic thickness measurements have been made for polyethylene oxides adsorbed on polystyrene latex. Comparison with theoretical models shows that the hydro-dynamic thickness is determined by polymer segments (tails) at the extremity of the distribution. It is also concluded that the sensitivity of the s.a.n.s. experiment precludes the measurement of segments in this region and that the experimental segment density profiles are essentially dominated by loops and trains. 

It is usually assumed that the micellar corona is a continuous phase extending from the micellar core to the micellar radius Rm. The internal structure of the micelle can be described by a density profile as shown in Fig. 8. The micellar core is a homogeneous melt or glass of insoluble polymer blocks. For hydrophobic blocks in aqueous solutions, the polymer volume fraction in the micellar core is 0C 1. The micellar shell is swollen with water or aqueous salt solution and has a polymer segment density that is expected to decrease in the radial direction as 0(r) r-a as typical for star polymers or... 

FIG. 6. The effect of bond correlations and bond backtracks on segment density profile for the polymer brush with 400 bonds. 

The effect of intermolecular interactions is characterized by the Floiy-Huggins interaction parameter. For the polymer brush with 400 bonds, three values of the interaction parameter were selected in the calculations and the segment density profiles are plotted in Fig. 9. x 0 corresponds to a good solvent and x 0.5 to a poor one. With increasing value of x, the height of the polymer bmsb decreases. For the poor solvent ( =0.5), the chant segments tend to be more uniformly distributed (curve 3). 

This review is intended to complement those of Cohen Stuart et al. (1986) and de Gennes (1987). The former details experimental techniques available for probing polymer-particle interactions and the lattice, i.e., mean field, theories that predict, via numerical solutions, segment-density profiles and interaction potentials. The latter constructs a simple and elegant picture of the same phenomena through scaling theories developed for semidilute solutions. 

Fig-i- Theoretical volume fraction vs. distance profile across an interface between PS and PVP polymers. A value of x = 0-12 appropriate to a temperature of 160 °C [ 105] has been used to predict an interface width a7 of 1.6 nm from Eq. (3). This profile is consistent with neutron reflectivity measurements of PS/PVP interface segment density profiles if the apparent broadening of the interface by capillary waves is taken into account [ 106]... 

---