  Highly regular polyampholytic structures adsorbed directly from solution; ; et al in Journal of Colloid and Interface Science (2001), 242(1), 36-43 This article concerns the adsorption of the diblock polyampholyte poly(methacrylic acid)-block-poly((dimethylamino)ethyl methary-late) (PMAA-b-PDMAEMA) from aqueous solution on silicon substrates. The ... [more ▼] This article concerns the adsorption of the diblock polyampholyte poly(methacrylic acid)-block-poly((dimethylamino)ethyl methary-late) (PMAA-b-PDMAEMA) from aqueous solution on silicon substrates. The investigated polyampholyte is characterized by a small molecular weight around 15,000 g/mol and a big positively charged PDMAEMA block. The adsorbed amount determined by ellipsom-etry was str ongly influenced by the pH of the adsorption solution. Using dynamic light scattering polyampholytic structures with diameters around 50 nm were found in aqueous solution. The hy-drodynamic diameter was hardly affected by changing the pH of the polymer solution. Analogous regular structures were also found by scanning force microscopy (SFM) and grazing incidence, small angle X-ray scattering (GISAXS) at the silicon surface after the adsorption process. While SFM provides a topographical image of a small part of the adsorbed polyampholytic layer; GISAXS was used to get a statistical description of the lateral surface structures. The adsorbed structures were highly regular and their sizes were nearly pH independent over a lar ge pH region. Only directly at the isoelectric point of the polyampholyte larger adsorbed structures were observed. Compared with earlier investigated PMAA-b-PDMAEMA systems we are now able to prepare highly regular polyampholytic structures at silicon surfaces. There are two kinds of interactions for the adsorbed micelles. First, the charged block of the chains is directly attracted to the substrate via electrostatic interactions, while the uncharged part of the chains is only hydrophobically attracted via the hydrophobic core of the adsorbed micelle. [less ▲] Detailed reference viewed: 13 (1 ULg) Lateral structures of thin films of ampholytic diblock copolymers adsorbed from dilute aqueous solution at the solid/liquid Interface; ; et al in Langmuir (1999), 15(20), 6984-6990 The lateral structures of dried thin films of the ampholytic diblock copolymer poly((methacrylic acid)-block-((dimethylamino)ethyl methacrylate)) adsorbed from dilute aqueous solution onto silicon ... [more ▼] The lateral structures of dried thin films of the ampholytic diblock copolymer poly((methacrylic acid)-block-((dimethylamino)ethyl methacrylate)) adsorbed from dilute aqueous solution onto silicon substrates were investigated by scanning force microscopy (SFM) and diffuse X-ray scattering. The adsorbed amount of polymer, as a function of pH, reveals a maximum near the isoelectric point (IEP) of the polyampholyte. Different lateral structures are determined for samples adsorbed at pH values above the maximum of the adsorbed amount, as compared to the ones adsorbed at pH values below this maximum. At a pH around the IEP, the polyampholyte precipitates and the layers are formed by adsorption of flocks with sizes in the micrometer range. Lateral structures measured by SFM are similarly detected by diffuse X-ray scattering. The later technique delivers a statistical description of the lateral surface structures averaged over a larger area. The structures investigated are related to the polyampholyte structure in solution and can be explained by the interplay of the electrostatic interactions of the two oppositely charged blocks of the polyampholyte and the charged surface, as well as by the dependencies of charge densities on pH. [less ▲] Detailed reference viewed: 10 (1 ULg)Adsorption of polyampholyte copolymers at the solid/liquid interface: the influence of pH and salt on the adsorption behaviour; ; et al in Physical Chemistry Chemical Physics [=PCCP] (1999), 1(17), 3853-3856 Polyampholytes are macromolecules that contain oppositely charged groups. We have studied the adsorption of the polyampholyte diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl ... [more ▼] Polyampholytes are macromolecules that contain oppositely charged groups. We have studied the adsorption of the polyampholyte diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), PMAA-b-PDMAEMA, on oxidized silicon surfaces. The amount of polymer adsorbed from aqueous solution of different pH and salt concentration was measured by ellipsometry. The influence of the added salts NaCl, Na2SO4 and CaCl2 was determined. In every case adsorption took place, although the polyampholyte and the substrate exhibit the same sign of net charge. For all types of salt, the adsorbed amount shows two maxima close to the isoelectric point (IEP) of the polymer as a function of pH. Directly at the IEP of the polyampholyte, no adsorption was found. The measured dependences can be explained by the adsorption of one or the other of the two blocks depending on acidity and ionic strength. Furthermore, the lateral structure of the dried films was investigated by scanning force microscopy (SFM). [less ▲] Detailed reference viewed: 22 (1 ULg)Adsorption of ampholytic diblock copolymers from dilute aqueous solution at the solid/liquid interface; ; et al in Langmuir (1999), 15(4), 1260-1267 The adsorption of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate) (PMAA-b-PDMAEMA) and the corresponding homopolyelectrolytes of the two blocks, PMAA ... [more ▼] The adsorption of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate) (PMAA-b-PDMAEMA) and the corresponding homopolyelectrolytes of the two blocks, PMAA and PDMAEMA, was investigated from dilute aqueous solution on silicon substrates. The adsorbed amount of polymer as a function of pH, polyampholyte concentration, and salt concentration in solution has been determined by ellipsometry at room temperature. As a function of pH the adsorbed amount reaches its maximum at the isoelectric point of the polyampholyte. Some adsorption takes place even in pH ranges where the surface charge has the same sign as the net charge of the polyampholyte. By variation of the polyampholyte concentration, typical adsorption isotherms were determined at several pH values. With increasing salt concentration the adsorbed amount increases, and above a critical concentration it diverges to very large values. The measured dependencies can be explained by the adsorption of one or the other of the two blocks depending on acidity and ionic strength and are in good agreement with theoretical predictions. Adsorption kinetics has also been studied in detail, and the diffusion coefficient of the polyampholyte toward the surface has been obtained in the early state of adsorption as a function of pH, polyampholyte concentration, and salt concentration. [less ▲] Detailed reference viewed: 11 (1 ULg) |
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