Acrylic acid pore size

The preparation of monodisperse hydrogel microspheres, such as poly-acrylam-ide-co-acrylic acid, poly(N-isopropylacrylamide-co-acrylic acid), has been performed for drug devices thanks to their biocompatibility [77, 79]. The average diameters of the microspheres were dependent on the pore sizes (from 0.33 to 1.70pm) of SPG membranes used in the preparation procedure. 

In addition to the assessment of pore sizes and quality control, AFM provides direct access to the dynamic changes of smart pores, for instance pores that are equipped with a stimulus-responsive coating. Iwata et al. reported on the pH control of pore opening and closing of poly (acrylic acid) (PAA) -functionalized pores, as shown in Fig. 3.83. [174] The pores of two different membranes are closed, as seen by CM-AFM, at high pH due to the deprotonation of the PAA coating and concomitant expansion of the polymeric layer into the opening of the pore. 

Comparisons of commonly used XAD resins have been published for the isolation of both fulvic acid (Aiken et al., 1979) and humic acid (Cheng, 1977) from water. These resins differ in pore size, surface area, polymer composition, and polarity (Table 5) (Kunin, 1977). As with anion-exchange resins, hydrophobic styrene-divinylbenzene resins (XAD-1, XAD-2, XAD-4) were found more difficult to elute than hydrophilic acrylic-ester resins (Table 6). This is due to hydrophobic interactions, and possible tt-tt interactions with the aromatic resin matrix of styrene-divinylbenzene resins. In addition, ki-... 

D. Freilich and G.B. Tanny, Hydrodynamic and microporous support pore size effects on the properties and structure of dynamically formed hydrous Zr(IV)-polyacrylate membranes, Desalination, 1978, 27, 233-251 A.J. van Reenen and R.D. Sanderson, Dynamically formed hydrous zirconium(IV) oxide-polyelectrolyte membranes, VI. Effect of copolymer composition on the stability of poly(acrylic acid - covinyl acetate) and poly(acrylic acid - covinyl alcohol) membranes, Desalination, 1989, 72, 329-338. 

PET membranes (Poretics, polyester, pore size 0.2 pm, membrane thickness 10 pm) were purchased from Osmonics, Inc. Diethylether (99%), 2,2 -azobisisobutyronitrile (AIBN), copper (1) bromide (CuBr) (98%), acetone (min. 99.5%), methanol (99%), ethanol (99%), methyl ethyl ketone (MEK) (99%) and polyethylenimine (hygroscopic) were purchased fiom VWR International and used as received. 4,4-Dinonyl-2,2-dipyridine (DNBP) (97%) and ethyl-2-bromoisobutyrate (98%) were purchased from Sigma-Aldrich. Tetrahydrofiiran (THF) was supplied by the Eh Co. Poly(acrylic acid) (PAA) (25% aqueous solution) and 2,3,4,5,6-pentafluorostyrene (PFS) were obtained from Polyscience Inc. and Oakwood Products Inc., respectively. Glycidyl methacrylate (min 95%) was purchased from TCI, America. 

The present study is concerned with the modification of functional polymers onto porous silica particle surfaces. Our primary interest is to improve particle surface characteristics. Poly(acrylic acid) was chosen as the functional polymer to provide pH-intelligent, surface-responsive particles. The PAA chains under acid conditions are usually coiled, while under basic conditions the chains are extended due to electrostatic repulsion of the carboxylate ions. By controlling the pH, the surface characteristics can be tailored to respond to specific pH environments. Pore size distribution and specific surface area of modified silica are calculated from the amount of nitrogen adsorbed on the surface. The water penetration rate and porosity for different pH were measured for estimation of the surface properties ... 

However, the magnitude of the decrease of permeability at pH 4 to pH 7 was somewhat lower than that of the PVDF membrane. This may be caused by two possible factors the large pore size of the PA membrane and the lower acrylic acid content in the feed solution. 

Ito Y, Kotera S, Ibana M, Kono K and Imanishi Y, Control of pore size of polycarbonate membrane with straight pores by poly(acrylic acid) . Polymer, 1990, 31, 2157. 

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