NOVELTY - A wicking apparatus (1) comprises a composite condenser membrane containing a substrate layer, vapor inlet end, liquid discharge end, cavities disposed in substrate layer, and nanoporous filler material; a liquid conduit (4) having first and second end; and composite evaporator membrane containing substrate layer, liquid inlet end, vapor discharge end, cavities disposed in the substrate layer and nanoporous filler material.    USE - As wicking apparatus (claimed), which is used in lab-on-a-chip systems for synthesis and analysis, electrodes for low temperature fuel cells, and water recovery in arid environments.    ADVANTAGE - The wicking apparatus is capable of pumping liquids at large negative pressures. The wicking apparatus overcomes external influences such as force of gravity, inertial forces, and resistance to viscous flow by operating at a large negative pressure. The apparatus operates in an undercharged regime, thus the under-charged regime provides yield faster transients due to the reduced thermal mass of the working fluid, improved heat transfer in the condenser due to the absence of a bulk fluid layer, and reduced resistance to vapor flow due to the absence of condensate in the vapor path. The heat pipe operates passively with no moving parts such as pumps-the temperature gradient itself drives the phase change and mass transfer; allows operation down to very large negative pressures.    DETAILED DESCRIPTION - A wicking apparatus (1) comprises a composite condenser membrane containing a substrate layer, vapor inlet end, liquid discharge end, several of cavities disposed in the substrate layer fluidly coupling the vapor inlet end to the liquid discharge end, and a nanoporous filler material disposed within the cavities, where the nanoporous filler material having a first open pores having a maximum diameter of 0.2-200 nanometers; a liquid conduit (4) having first end and second end, where first end of the liquid conduit is fluidly coupled to the liquid discharge end of the composite condenser membrane; and a composite evaporator membrane containing substrate layer, liquid inlet end, vapor discharge end, several of cavities disposed in the substrate layer fluidly coupling the liquid inlet end to second end of the liquid conduit, and nanoporous filler material disposed within the cavities, the nanoporous filler material having a second open pores having a maximum diameter of 0.2-200 nanometers. The substrate layer of the condenser membrane and the substrate layer of the evaporator membrane are porous. The respective substrate layer comprises silicon. The nanoporous filler material disposed within the cavities of at least the composite evaporator membrane comprises a molecular gel. The molecular gel is a sol-gel or hydrogel. INDEPENDENT CLAIMS are included for following:    (1) a composite membrane for use in capillary wick comprising a substrate layer having a liquid end, vapor end, and cavities fluidly coupling the liquid end to the vapor end; and filler material disposed within the cavities, the filler material having open pores having a maximum diameter of 0.2-100 nanometers; and    (2) operating the heat pipe containing a condenser, a composite evaporator membrane, a liquid conduit fluidly coupling the condenser to the composite evaporator membrane, and a vapor conduit fluidly coupling the composite evaporator membrane to the condenser, involving providing a heat source proximate to the composite evaporator membrane; providing a heat sink proximate to the condenser; providing a first open pores in the composite evaporator membrane; providing a working fluid within the liquid conduit; and maintaining a pressure of the working fluid in the liquid conduit at less than -0.01 megapascals.    DESCRIPTION OF DRAWING(S) - The figure shows simplified cross-sectional view of a heat pipe.    Wicking apparatus (1)    Microporous membranes (2, 3)    Conduit (4)    Working fluid (5)    Heat source (6)