Limits...
Radical re-appraisal of water structure in hydrophilic confinement.

Soper AK - Chem Phys Lett (2013)

Bottom Line: The water in the pore is divided into three regions: core, interfacial and overlap.The average local densities of water in these simulations are found to be about 20% lower than bulk water density, while the density in the core region is below, but closer to, the bulk density.There is a decrease in both local and core densities when the temperature is lowered from 298 K to 210 K.

View Article: PubMed Central - PubMed

Affiliation: ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, UK.

ABSTRACT

The structure of water confined in MCM41 silica cylindrical pores is studied to determine whether confined water is simply a version of the bulk liquid which can be substantially supercooled without crystallisation. A combination of total neutron scattering from the porous silica, both wet and dry, and computer simulation using a realistic model of the scattering substrate is used. The water in the pore is divided into three regions: core, interfacial and overlap. The average local densities of water in these simulations are found to be about 20% lower than bulk water density, while the density in the core region is below, but closer to, the bulk density. There is a decrease in both local and core densities when the temperature is lowered from 298 K to 210 K. The radical proposal is made here that water in hydrophilic confinement is under significant tension, around -100 MPa, inside the pore.

No MeSH data available.


Related in: MedlinePlus

(a) Density profile of Si (solid), O (dashed) and OS (dashed, crosses) of the simulated dry MCM41 substrate. Also shown is the expected bulk density of Si atoms (dotted). (b) Si–O (solid) and Si–OS (dashed) radial distribution functions, together with the corresponding running coordination numbers,  (solid, circles) and  (dashed, crosses).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4376068&req=5

f0025: (a) Density profile of Si (solid), O (dashed) and OS (dashed, crosses) of the simulated dry MCM41 substrate. Also shown is the expected bulk density of Si atoms (dotted). (b) Si–O (solid) and Si–OS (dashed) radial distribution functions, together with the corresponding running coordination numbers, (solid, circles) and (dashed, crosses).

Mentions: In the present case the final pore diameter after structure refinement was set by the choice of minimum distances between q atoms and the Si and O atoms of the substrate as given in Table 1. To determine the radius that finally emerged using these values, Figure 5a shows the density profile of the Si, O and OS atoms as a function of distance from the pore centre. It can be seen that the pore radius achieved after structure refinement is ∼12.0 Å, based on the oxygen atom density distribution. However the silica substrate is highly structured near the surface, with a pronounced shell of silicon just below the surface, and surface oxygen (O) and silanol oxygen (OS) atoms attached to this. Figure 5b shows a detail of the Si–O and Si–OS radial distribution functions together with the corresponding Si–O and Si–OS running coordination numbers , where(3)Nαβ(r)=4πρβ∫0rr′2gαβ(r′)dr′.These indicate that the total oxygen coordination number in the first shell of silicon is close to 4, as happens in bulk amorphous silica.


Radical re-appraisal of water structure in hydrophilic confinement.

Soper AK - Chem Phys Lett (2013)

(a) Density profile of Si (solid), O (dashed) and OS (dashed, crosses) of the simulated dry MCM41 substrate. Also shown is the expected bulk density of Si atoms (dotted). (b) Si–O (solid) and Si–OS (dashed) radial distribution functions, together with the corresponding running coordination numbers,  (solid, circles) and  (dashed, crosses).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4376068&req=5

f0025: (a) Density profile of Si (solid), O (dashed) and OS (dashed, crosses) of the simulated dry MCM41 substrate. Also shown is the expected bulk density of Si atoms (dotted). (b) Si–O (solid) and Si–OS (dashed) radial distribution functions, together with the corresponding running coordination numbers, (solid, circles) and (dashed, crosses).
Mentions: In the present case the final pore diameter after structure refinement was set by the choice of minimum distances between q atoms and the Si and O atoms of the substrate as given in Table 1. To determine the radius that finally emerged using these values, Figure 5a shows the density profile of the Si, O and OS atoms as a function of distance from the pore centre. It can be seen that the pore radius achieved after structure refinement is ∼12.0 Å, based on the oxygen atom density distribution. However the silica substrate is highly structured near the surface, with a pronounced shell of silicon just below the surface, and surface oxygen (O) and silanol oxygen (OS) atoms attached to this. Figure 5b shows a detail of the Si–O and Si–OS radial distribution functions together with the corresponding Si–O and Si–OS running coordination numbers , where(3)Nαβ(r)=4πρβ∫0rr′2gαβ(r′)dr′.These indicate that the total oxygen coordination number in the first shell of silicon is close to 4, as happens in bulk amorphous silica.

Bottom Line: The water in the pore is divided into three regions: core, interfacial and overlap.The average local densities of water in these simulations are found to be about 20% lower than bulk water density, while the density in the core region is below, but closer to, the bulk density.There is a decrease in both local and core densities when the temperature is lowered from 298 K to 210 K.

View Article: PubMed Central - PubMed

Affiliation: ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, UK.

ABSTRACT

The structure of water confined in MCM41 silica cylindrical pores is studied to determine whether confined water is simply a version of the bulk liquid which can be substantially supercooled without crystallisation. A combination of total neutron scattering from the porous silica, both wet and dry, and computer simulation using a realistic model of the scattering substrate is used. The water in the pore is divided into three regions: core, interfacial and overlap. The average local densities of water in these simulations are found to be about 20% lower than bulk water density, while the density in the core region is below, but closer to, the bulk density. There is a decrease in both local and core densities when the temperature is lowered from 298 K to 210 K. The radical proposal is made here that water in hydrophilic confinement is under significant tension, around -100 MPa, inside the pore.

No MeSH data available.


Related in: MedlinePlus