Method for inducing a volumetric change in a nanoporous material

Abstract

The invention is directed to a method for inducing a surface stress-induced volumetric change in a nanoporous material and to a device for carrying out the method. The method of the invention comprises—accumulating polar molecules onto the surface of the nanoporous material by physical adsorption of the polar molecules from the vapour phase thereby inducing surface stress to said surface; or—dissipating accumulated polar molecules from the surface of the nanoporous material by physical desorption of the polar molecules into the vapour phase thereby inducing surface stress to said surface, wherein the nanoporous material comprises a nanoporous metal or alloy. The device comprises a) a nanoporous metal material which, upon physical adsorption from the vapour phase or physical desorption into the vapour phase of polar molecules onto or from the surface of the nanoporous metal material, exhibits a volumetric change; and b) a mechanism for detecting and/or transferring the volumetric change.

1 . Method for creating a surface stress-induced volumetric change in a nanoporous material, comprising
 accumulating polar molecules onto the surface of the nanoporous material by physical adsorption of the polar molecules from the vapour phase thereby inducing surface stress to said surface; or   dissipating accumulated polar molecules from the surface of the nanoporous material by physical desorption of the polar molecules into the vapour phase thereby inducing surface stress to said surface,   
       wherein the nanoporous material comprises a nanoporous metal or alloy. 
     
     
         2 . Method according to  claim 1 , wherein said nanoporous material is a nanoporous metal or nanoporous alloy. 
     
     
         3 . Method according to  claim 1 , wherein
 said accumulating comprises the physical adsorption of at least a monolayer of the polar molecules onto the surface of the nanoporous material and wherein the accumulation preferably leads to the nanoporous material being filled with polar molecules to less than 10 vol. % of the total pore volume of the nanoporous material; or   said dissipating comprises the physical desorption of at least a monolayer of accumulated polar molecules from the surface of the nanoporous material and wherein the dissipation preferably leads to the nanoporous material being depleted in polar molecules by less than 10 vol. % of the total pore volume of the nanoporous material.   
     
     
         4 . Method according to  claim 2 , wherein said nanoporous metal or alloy comprises a noble metal, preferably selected from the group consisting of Au, Pt, Pd and Ag, preferably the nanoporous material is nanoporous gold. 
     
     
         5 . Method according to  claim 1 , wherein said polar molecules comprise one or more selected from the group consisting of water, methanol and ethanol, more preferably said polar molecules comprise water molecules. 
     
     
         6 . Method according to  claim 1 , wherein the nanoporous material has a surface-to-volume ratio of 10 m 2 /cm 3  or more, preferably 25 m 2 /cm 3  or more, more preferably in the range of 25-500 m 2 /cm 3 . 
     
     
         7 . Method according to  claim 1 , wherein the nanoporous material has a porosity of 0.3 or more, preferably in the range of 0.3-0.95. 
     
     
         8 . Method according to  claim 1 , wherein the nanoporous material is a material wherein the pores have an average cross-sectional diameter of 500 nm or less, preferably 100 nm or less, more preferably in the range of 2-60 nm. 
     
     
         9 . Method according to  claim 1 , wherein the physical adsorption or desorption is the result of a change in vapour pressure of the polar molecules in the environment, preferably the physical adsorption or desorption is the result of a change in relative humidity of the environment. 
     
     
         10 . Method according to  claim 1 , wherein said volumetric change is at least partially reversible. 
     
     
         11 . Method according to  claim 1 , wherein the volumetric change has a size and/or a sign that is/are dependent on
 the nature, such as the polarity sign, of the polar molecules; and/or   the state, such as the cleanness, of the surface of the nanoporous material.   
     
     
         12 . Method according to  claim 1 , wherein said volumetric change is characterised by a strain amplitude of 0.005% or more, preferably 0.01% or more in response to a change in vapour pressure of the polar molecules in the environment of 15%. 
     
     
         13 . Device for carrying out the method of  claim 1 , comprising
 a) a nanoporous metal material which, upon physical adsorption from the vapour phase or physical desorption into the vapour phase of polar molecules onto or from the surface of the nanoporous metal material, exhibits a volumetric change; and   b) a mechanism for detecting and/or transferring the volumetric change.   
     
     
         14 . Device according to  claim 13 , wherein the nanoporous metal or alloy material has a layered structure wherein each layer comprises a multitude of scales, and wherein at least a part of the scales in each layer are locally attached to one or more scales of an adjacent layer. 
     
     
         15 . Device according to  claim 13  in the form of a sensing device or actuating device. 
     
     
         16 . Device according to  claim 13 , which device is operative in the absence of electricity, heat, and chemical reaction energy external stimuli.