Observation of Pore Scale Liquid Behavior with NIR-Microscopy and

Advanced Laser Techniques

Markus Tuller and Dani Or

Dept. of Plants, Soils and Biometeorology, Utah State University

Microscopic Observation of Capillary Condensation in Glass Micromodels

Dew Point Generator

Temperature Controller

Video Microscope

MicroscopeControl Units

HeatExchangerSealed

Chamber

A high resolution video microscope (1000x) with black&white CCD camera was used to detect liquid configurations using IR light (880 nm) emitted from a LED light source (capitalizing on water adsorption properties at this wavelength).

A narrow bandpass interference filter with a central wavelength of 880 nm was installed on the CCD camera to increase image contrast for water.

The observations were performed in a temperature and vapor pressure controlled chamber.

Environmentally Controlled Observation Chamber

VideoMicroscope

IR Backlight880 nm

Thermistor

Glass Model

SampleManipulator

Chamberwith

Water Jacket

X-Y Positioning Stage

A temperature controller connected to a thermistor and two thermoelectric Peltier cooling elements are used to maintain a constant temperature within the chamber.

Two heat exchangers connected to two closed water loops are attached to the “hot” and “cool” sides of the Peltier plates.

One loop is guided through the water jacket surrounding the observation chamber, and the second loop is connected to a larger water reservoir.

A LI-COR dew point generator with an accuracy of 0.02 oC was used to control the vapor pressure within the observation chamber.

Observation of Capillary Menisci in Micro Glass Beads

The experimental setup was tested with micro glass beads having an average diameter of 325 m.

Observed capillary menisci for various chemical potentials were compared with calculated menisci obtained from solutions of the Young-Laplace equation for pendular water.

- 3500 J/kg - 4500 J/kg - 7000 J/kg - 12000 J/kg - 25000 J/kg

0

400

800

400 8000

[m]

[m

]

- 4500 J/kg

a Glass bead radius [m] Liquid-vapor surface tension [N/m] Liquid density [kg/m3] Chemical potential [J/kg]

Observation of Capillary Menisci and Liquid Redistribution in Micro Glass Cells

0

0.4

0.8

1.2

1.6

0 0.5 1 1.5 2 2.5[mm]

[mm

]

- 0.25 J/kg

- 0.16 J/kg- 0.16 J/kg

- 0.15 J/kg

- 0.18 J/kg

- 0.28 J/kg - 0.18 J/kg - 0.16 J/kg- 0.17 J/kg - 0.21 J/kg

Quasi equilibriumNon equilibrium

- 0.19 J/kg

Advanced Techniques to Measure Thickness and Configuration of Adsorbed Liquid Films

Several micro-scale techniques will be applied to measure the thickness of adsorbed liquid films.

Currently we are testing the following methods to measure the structure of surface water on channeled silica substrates:

Laser Interferometer

EllipsometryFor layers from 0.5 nm to 10 nm

InterferometryFor layers from 10 nm to 1 m

Phase-Contrast MicroscopyResolution down to 2 m

Diffraction Analysis

Conceptual Sketch of the Experimental Setup

Reflectometry for Measurement of Film Thickness

IlluminationFibers

ReadFiber

ReflectionProbe

Probe Holder

Quartz Sample

Pulsed XenonLight Source

ReflectanceSpectrum

EXPERIMENTAL SETUP

A miniature fiber optic spectrometer (Ocean Optics PC2000) with high-performance CCD-array detector and high-speed A/D converter is used to measure the reflectance spectrum of thin films coating solid substrates.

All measurements are conducted with an incidence angle perpendicular to the sample surface and relative to a standard sample with known absolute reflectance.

Reflectometry – Preliminary Results

Air Between Quartz Slides (38 mm Spacers)

Air Between Quartz Slides (No Spacers)

h=12.4 m

h=41.6 m

Diffraction Analysis to Determine LiquidConfigurations within Periodic Structures

Analysis of the diffraction pattern is used to determine the average interfacial curvature of liquid, filling the periodic structure.

Model Prototype

45 m

Diffraction Order

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Re

lati

ve

Op

tic

al

Po

we

r

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

Diffraction Order

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Re

lati

ve

Op

tic

al

Po

we

r

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

DRY WET

Theoretically Derived Diffraction Patterns for Dry and Liquid-Filled Periodical Structures

Diffraction Order

0 1 2 3 4 5

Rel

ativ

e O

pti

cal P

ow

er

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

DryWet

Measured Diffraction Patterns for Dry and Liquid-Filled Periodical Structures