Adsorption of organic molecules on silica surface.

Experimental aspects of polymer adsorption at solid/solution interfaces

Polymer adsorption at solid-liquid interfaces

The synthesis of two types of polystyrene with dendritic branching was achieved through the development of a novel method that combines living anionic polymerization with a convergent process in a one-pot reaction. The method is based on the slow addition of a reactant such as 4-(chlorodimethylsilyl)styrene (CDMSS), which contains a polymerizable vinyl group and a moiety capable of undergoing quantitative SN2 reaction, to a solution of living polystyryl anions. The sequence of reactions results in star-shaped polymers with the initial chains forming the arms and the residue from the CDMSS forming a hyperbranched core. Different amounts of styrene monomer were added along with the CDMSS in order to increase the molecular weight between branch points. The molecular weights and polydispersities of the dendritic polystyrenes were characterized by GPC coupled with MALLS. The molecular weights of dendritic polystyrenes without added comonomer corresponded to dendritic growth of the core of 3.1−3.4 average gener...

Polystyrene with Dendritic Branching by Convergent Living Anionic Polymerization

High molecular weight polymer solutions have a powerful tendency to deposit adsorbed layers when exposed to even mildly attractive surfaces. The equilibrium properties of these dense interfacial layers have been extensively studied theoretically. A large body of experimental evidence, however, indicates that non-equilibrium effects are dominant whenever monomer–surface sticking energies are somewhat larger than kT, a common case. Polymer relaxation kinetics within the layer are then severely retarded, leading to non-equilibrium layers whose structure and dynamics depend on adsorption kinetics and layer ageing. Here we review experimental and theoretical work exploring these non-equilibrium effects, with emphasis on recent developments. The discussion addresses the structure and dynamics in non-equilibrium polymer layers adsorbed from dilute polymer solutions and from polymer melts and more concentrated solutions. Two distinct classes of behaviour arise, depending on whether physisorption or chemisorption is involved. A given adsorbed chain belonging to the layer has a certain fraction of its monomers bound to the surface, f, and the remainder belonging to loops making bulk excursions. A natural classification scheme for layers adsorbed from solution is the distribution of single-chain f values, P(f), which may hold the key to quantifying the degree of irreversibility in adsorbed polymer layers. Here we calculate P(f) for equilibrium layers; we find its form is very different to the theoretical P(f) for non-equilibrium layers which are predicted to have infinitely many statistical classes of chain. Experimental measurements of P(f) are compared to these theoretical predictions.

Non-equilibrium in adsorbed polymer layers

Adsorption of polystyrene having a molecular weight ranging from 600 to 2,000,000 onto Aerosil 130 from cyclohexane solutions at the theta temperature was studied by UV and IR spectroscopy. Adsorbance, (A) was determined using UV spectroscopy while both the fraction of the surface sites occupied, (Σ) and the fraction of the segments adsorbed per polymer chain, (p) were measured by IR spectroscopy. Adsorbance increases with increasing molecular weight up to Mw=50×104 and then levels off. The value of Σ increases while the p value decreases with increasing molecular weight. The close correlation between the adsorbed amount Γ per site determined UV spectroscopy and the ratio Σ/p measured by IR spectroscopy can be observed except for cases involving high molecular weight samples. The data were compared with the theories of Scheutjens and Fleer and Silberberg based on a lattice model. There was excellent agreement between the data and these theories.

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Kazuhisa Hayakawa

Papers

Adsorption of polystyrene onto silica at the theta temperature.

Adsorption of polystyrene onto a metal surface in good solvent conditions