Positron annihilation and N2 adsorption for nanopore determination in silica-polymer composites

Abstract

Silica has two different, fragmented and smooth, visual appearances when deposited onto porous Amberlite polymer substrate from TEOS at acidic and basic pH, respectively. The low temperature N 2 adsorption isotherms on both materials seem to be a combination of Type 1 and Type 4 isotherms with H2 hysteresis, indicating the presence of both micro (D , 2 nm diameter) and meso (2 nm , D , 50 nm) pores. Their mesopore distributions, computed by both BJH and DFT methods, show maxima near Dy5 nm with a narrower pore size distribution range than the organic support alone. For comparison, pores were also tested by positron annihilation lifetime spectroscopy (PALS) which can scan the full micro to mezo size range in one measurement without cooling and using any adsorbate molecules. These PALS results indicated the presence of Dy0.5, 0.8 and 1.5 nm diameter micropores and an average Dy5 nm diameter mesopores in both the base and the acid set materials. When the organic substrate is burned out from the two differently made composites, the new adsorption isotherms, BET surface areas, and differently measured pore sizes became distinctly different both from each other and from those of the parent materials.

What can positronium tell us about adsorption?

“…The silica gel preparation, used in this experiment was in detail described earlier in references (Halasz et al 2011;Zaleski et al 2012a). The commercially available Amberlite XAD7HP supplied by ROHM and HAAS (now Dow Chemical Co.) was used as a polymer porous template.…”

“…This silica material shows non-typical pore structure which results from the applied preparation procedure (Halasz et al 2011;Zaleski et al 2012a). The state of the adsorbate phase during successive stages of pore filling and pore evacuation is deduced from PALS results.…”

Effect of condensing tetraethoxysilane on desorption of organic compound from porous polymer

“…The swelling ratio determined by the volume change before and after adding TEOS for the polymer with naproxen (PNH) equals S% ¼ 80% and differs significantly from those obtained for the pure polymer. The much lower swelling ratio for the composites is the result of the presence of the drug in the sample and the stiffening of the polymer skeleton (Halasz et al, 2011;Kierys et al, 2010;Zaleski et al, 2012).…”

“…Next, a part of PNH sample was loaded with the silica precursor by wetting the beads with TEOS (1.46 g TEOS/ 1 g of PNH), until all beads were swollen and glassy but did not stick to each other. TEOS is a very effective agent causing the swelling of polymers (Halasz et al, 2011;Kierys et al, 2010;Krasucka et al, 2015;Zaleski et al, 2012). Therefore, it is important for the described preparation procedure to add only so much TEOS, which can be totally entrapped within the pores of the polymer beads.…”

Incorporation of inorganic components into organic matrices on the basis of polymer swelling in inorganic precursors as a way of composite materials synthesis without modifier application

“…Appropriate investigations with composite material characterisation obtained by the polymer swelling strategy on the basis of different polymer matrices (Amberlite XAD7HP and poly(trimethylopropane trimethacrylate)) and precursors of different inorganic phases (tetraethoxysilane and titanium(IV) ethoxide) were made first by Kierys et al [19,20] and Zaleski et al [21,22]. Kierys et al and Zaleski et al demonstrated that composite materials synthesised on the basis of the polymer swelling strategy exhibit interesting porosity which is under the influence of the preparation conditions (especially pH).…”