The properties of positronium annihilating in the micellar template in MCM-41 materials were investigated. For alkyltrimethylammonium bromide surfactants (C-n = 14,16,18) the template interior is liquid-like; the bubble model of positronium, elaborated for bulk liquids, can be applied. The equivalent surface tension is linearly dependent on temperature, like in classic liquids. A very long-lived component in o-Ps lifetime spectrum (approximate to 20 ns) can be ascribed to o-Ps in cracks in the elongated template structure. (C) 2003 Elsevier Science B.V. All rights reserved.