Adsorption of Graft Copolymers onto Silica and Titania

Abstract

The adsorption of graft copolymers of poly(acrylamide) (PAAm, backbone) and poly(ethylene oxide) (PEO, side chains) from aqueous solution onto silica and titania was studied with reflectometry. Two high-molar-mass copolymers were used with different PEO graft densities (10 and 18% w/w PEO in copolymers G10 and G18, respectively). On titania only the PAAm backbone adsorbs and the PEO does not. This results in adsorbed amounts of 0.83 and 0.85 mg m-2, respectively, which is about the same as that for a PAAm homopolymer. On silica the situation is reversed: now the PEO side chains adsorb and the PAAm backbone does not. The adsorption as a function of time shows a maximum, before the stable plateau is reached. The adsorbed amount on silica is much higher than that on titania: in the final plateau it is 1.35 and 1.2 mg m-2 for G18 and G10, respectively. On silica the polymers form longer loops and tails so that more molecules can be accommodated at the surface. The overshoot on silica depends on the polymer concentration, suggesting that it is not caused by a conformational change of the adsorbed layer but by exchange with polymer molecules from solution. Differences in graft distribution and graft density in the polymer sample are probably responsible for the displacement. The average number of grafts per polymer is rather low. On statistical grounds there should be an appreciable polydispersity in graft distribution and in graft density. Molecules in which the grafts are clustered in a few groups can displace molecules with more regularly separated grafts, and molecules with a high graft density can displace those with a lower number of side chains. The newly arriving molecules can then adsorb in a flatter conformation with a lower adsorbed amount as the extra loss in conformational entropy is compensated by the gain in adsorption energy.

Effect of Block and Graft Copolymers on the Stability of Colloidal Silica

“…The polymers used were described in more detail in previous papers on the adsorption onto silica and titania (3)(4)(5). Molar masses per block and the adsorbed amount on silica are given in Table 1, where for the graft copolymers the total molar mass is given.…”

“…In previous papers we reported on the adsorption of different types of block and graft copolymers onto silica and titania (3)(4)(5). In this paper we study the effect of these polymers on the stability of an aqueous silica dispersion in the presence of salt.…”

Stuffed brushes: theory and experiment

“…PEO is usually end-tethered to the surface through irreversible adsorption of block or triblock copolymers from solution. When a hydrophilic block like PEO is chemically bound to a hydrophobic block, such as poly-propyleneoxide (PPO) or an alkyl chain, the polymer density at the surface is enhanced as the hydrophobic block is prone to adsorb strongly on a hydrophobic surface [8]. Moreover, as desorption of the hydrophobic block from the hydrophobic surface is unfavourable, the surface density remains constant under varying conditions, in contrast to hydrophilic homopolymer that can desorb.…”

Structure and Molecular Motion of Poly(ethylene oxide) Chains Tethered on Silica by Solid-State 13C NMR Method

“…[1][2][3][4][5][6] A few papers have been also presented about the adsorption behavior of polymer on the silica surface modified by different polymer chains. 7,8 The development of hybrid materials comprised of organic and inorganic compounds can be expected.…”