Adsorption kinetics of block copolymers from a good solvent: a two-stage process

Abstract

The adsorption kinetics and adsorption isotherm of a polystyrene (PS)-poly(ethy1ene oxide) (PEO) diblock copolymer onto a silicon wafer from toluene solution was measured in situ by ellipsometry. Both blocks are in good solvent conditions but the small PEO block is adsorbed while the much larger PS block dangles in solution. Thus, PS-PEO behaves like an end-adsorbed chain. The adsorption kinetics shows two processes on a clearly seperated time scale. In the beginning, the time behavior of the adsorbed amount can be described as a diffusion-controlled process leading to a surface coverage with small interaction between molecules. A still denser surface coverage is achieved by the penetration of chains through the existing monolayer combined with the conformational rearrangement to a more brushy conformation. Experiments with different molecular weights indicate that the repulsion between the nonadsorbing PS blocks determines the maximal adsorbed amount. The adsorbed monolayer can be rapidly and completely displaced by PEO oligomer with a length comparable to the PEO block in the block copolymer. Models of the adsorption process are discussed in detail.

Looped Polymer Brushes Formed by Self-Assembly of Poly(2-vinylpyridine)−Polystyrene−Poly(2-vinylpyridine) Triblock Copolymers at the Solid−Fluid Interface. Kinetics of Preferential Adsorption

“…Figure 1 shows that the kinetics of assembly, based on the adsorbed amount, of PVPb-PS-b-PVP triblock copolymers follows the traditional twostep process observed for the self-assembly of A-B diblock copolymers. 9,14 A fast initial adsorption occurs at early times when there is sufficient free surface area and therefore little interaction among tethered chains. While this regime is often labeled as a "diffusion-limited" regime, at this stage we refer to this regime more generally as the fast initial regime.…”

“…These two differences can be explained if we consider that each selfassembled triblock contributes two tethering points (i.e., two equivalent diblocks) to the brush structure. For diblock copolymers, it has been shown that the assembly of the layer, once an overlapped brush is established on the surface, follows an exponential time decay dependence: 14 In eq 8, A deq is the plateau value of the adsorbed amount, A d * and t* are the values of the adsorbed amount and corresponding time after which the exponential model is valid, respectively, and k is the rate constant for this regime. Values of A d * and t* are reported in Table 1 for all copolymers studied.…”

Ellipsometry in Interface Science

“…A linear relationship between and the prevailing concentration c of amphiphile within the adsorption layer is well established [11] …”

Assembling of xyloglucans and lectin onto si wafers and onto amino-terminated surfaces

“…19,20 Each layer is usually characterized sequentially regarding independent ellipsometric determinations of thickness and refractive index. 19,20 One should also notice that ellipsometry enables the independent determination of n and d, only if the optical contrast in the system is large enough or if the layer thickness is thick enough. When λ is 633 nm and d >> 30 nm, it is possible to obtain n and d for the uppermost layer independently.…”