is Amorphous#

Introduction

Plan

Key Litterature:



Links

  • 1

  • 2

Amorphous Ices#

Litterature#

Study Title Year “Infrared spectra of amorphous solid water” by G.A. Baratta and J.A. Westley 1989 “Infrared spectra of amorphous solid water: Implications for interstellar and cometary ice” by L.D. Deshmukh et al. 2004 “H2O ice in the interstellar medium: a comparison between observed and simulated infrared spectra” by C.A. Boogert et al. 2015 “Ice grain morphology and infrared spectra in protoplanetary disks” by M. Min et al. 2016 “The Low-Temperature Infrared Spectrum of Amorphous Solid Water: A Spectroscopic and Theoretical Study” by J. P. Lewis et al. 2000 “Mid-infrared spectroscopy of interstellar ice analogs” by J.M. Brown et al. 2007 “A laboratory study of the mid-infrared spectra of amorphous solid water and water-rich ices” by A.G.G.M. Tielens et al. 2008 “Spectroscopic properties of amorphous solid water: a review” by P. Ehrenfreund et al. 2015

» Discovery and early history #

The first experimental description of amorphous water ice has been achieved in 1935 by [BURTON and OLIVER, 1935] that deposited water vapor on a copper rod maintained at -155 ℃. It has since been an intense subject of research

  • Why ?

  • …

Questions

  • difference between vitreous material and amorphous solid ?

  • Glassy vs vitreous ?

[Narten et al., 1976] showed that different deposition temperatures using the same vapor deposition setup and methodology would lead to two different forms of amorphous ice, where those differences are inferred from diffraction data (both Neutron and X-Ray):

Ice deposited at 77K is low density

  • Diffraction pattern consistent with a structure that has oxygen-oxygen nearest-neighbor tetrahedral symmetry on average, and a nearest neighbor 0-0 separation of 2.76 &#8491 with small dispersion; -> What is meant by this ?

  • Density estimated 0.94 g.cm-3

Ice deposited at 10K is high density

  • Diffraction pattern similar to, yet distinctively different from, that of the high temperature deposit. The 0-0 nearest neighbor distance is the same. 2.76 &#8491 but the dispersion in this separation is larger in the low temperature form.

  • Diffraction pattern shows an extra peak at 3.3 &#8491. corresponding to about 1.4 molecules. the existence of which is responsible for the estimated higher density, namely 1.1 g.cm-3

Question

How is the density determined from Diffraction data

» Polyamorphism #

[Loerting et al., 2011] 5 main categories of Amorphous ice

ASW

HGW

LDA

HDA

vHDA

When subject to increasing pressure, amorphous ice soften (what is meant by this ?) and then suddenly collapse to a denser but still amorphous phase. This result is verified by computer simulations where density and structure of the high density amorphous form depends on the potential function chosen to represent the water.

  • to verify (ref 5 - 7) simulation 8-9

Despite the non-crytalline nature of the molecular arrangements in LDA, both the thermodynamic state and the vibrational characteristics are those of a highly ordered substance. The heat carrying phonons of low temperature amorphous water behave like those in a crystal.

  • What does this mean, where does it come from ? Similar (but less dramatic) behaviour have been observed in other tetrahedrally coordinated solid (SiO2, GeO2, ZNCl2 etc).

ASW#

Vapor deposition methods were employed to prepare ASW for the following studies:

  • Calorimetry

  • Spectroscopy

  • vapor pressure and free energy

  • Crystalisation 33,35,34,36

  • Dielectric relaxation

  • Neutron and X-ray diffraction structure studies

  • diffusion studies

  • electron microscope

  • vibrational dynamics studies (by neutron scattering)

  • Thermal conductivity studies

The sharp crystallization exotherm commencing in the range of 150–160 K during reheating is the one universal feature of all previous studies of ASW or vitreous water.

Other preparation techniques#

  • cold microtoming method (68)

  • decompression amorphization (73)

  • electron bombardment vitrification (67, 76, 76a) - could be compatible with accoustic levitation

  • radiation damage–induced vitrification (77)

  • phase-separation vitrification (12)

  • plunge freeze (67)

Note

strong upswing in heat capacity seen in bulk laboratory supercooling water (81)

Heat capacity increase is also a main varying parameter obeserved during glass transition (Tg)

Narten et al. (39)

  • random structure of ASW.

  • second form of ASW - additional peak at 3.3 ̊Angstrom (interstitial water molecule) - Higher density (observed at 10K)

  • First indication of the existence of polyamorphism

do they coexist in metastable equilibrium Mishima 5-7

Influence of the Substrate#

  • [Smith et al., 1996]

    • desorption kinetics are substrate dependent and suggest strongly that the film morphology is governed by the hydrophilicity of the substrate.

    • crystallization kinetics are independent of substrate but depend strongly on both temperature and film thickness and are consistent with a spatially random nucleation and isotropic growth model.

  • [Dohnálek et al., 2000]

    • dramatic acceleration of the crystallization rate is observed for amorphous films on crystalline ice substrates

    • crystallization-induced cracking of the films

To check

  • Katrina …

Amorphous vs Crystaline Ice#

How does amorphous ices differs from its crystaline conterpart ? Well it depends on the formation route of the amorphous ice.

Crystaline

  • Polymorph: 18 ?

  • Ice rules

Amorphous

  • Polymorph: 5

  • Structure dependant on deposition conditions

Note

  • Show 2 samples deposited at different T conditions

  • Same T but different thickness

Amorphous ice - supercooled liquid water

ASW Properties#

Note

Debye frequency spectrum

Vibrational dynamics#

  • 2, 28, 30, 31, 61, 82, 91, 105, 107

  • Rice and coworkers (29 - 30b) review 2

Note

  • Dangling bonds in crystaline solids (106)

Bulk Organisation#

Definition#
Experiments#

  • Variation of the deposition angle

Controlling the Morphology of Amorphous Solid Water

  • Deposition temperature variations

  • Annealing processes

Porosity#

[Carmack et al., 2023]

Definition#

  • Controlling the

Experiments#

  • Different types

Insert here table of different groups:

  • NASA Ames: Mastrapa, Sandford

    • Is data available, yes

Infrared Spectroscopy#

Key Papers:

  • Mastrapa (2008, 2009)

  • Jenny

What did we leran#

  • ASW is porous

  • 3 µm band is changing when the T is increased

  • Water ice IR Band assignement taken from [Mastrapa et al., 2009]

Crystaline (cm -1)
[Bertie and Whalley, 1964]

Amorphous (cm -1)
[Hardin and rvey, 1973]

Assignment

A values (cm/molecule)
[Hudgins et al., 1993]

840

802

𝜈R [Ockman, 1958]

2.8 × 10-17

1650

1660

𝜈2 [Ockman, 1958]

1.0 × 10-17

2266

2220

𝜈2 + 𝜈R [Whalley, 1977]

3.3 × 10-18

3150

3191

𝜈1 in phase [Whalley, 1977]

3220

3253

𝜈3 TO [Whalley, 1977]

1.7 × 10-16

3380

3367

𝜈3 LO, 𝜈1 out of phase [Whalley, 1977]

to cite:

Note

  • TO, LO, what does this mean ?

Insert own crystaline and amorphous spectra with different asssignments vertical bar

Link with Optical Constants

  • Real and imaginary part (how do they relate to what we observe in space)

Differential Scanning Calorimetry#

tg at 136K (ramp 30K.min-1) –> Increase in heat capacity (lower than other amorphous solid: similar to SiO2 - GeO2) –> Imply limited number of entropically different configurational states in the fluid state following tg

Dielectric relaxation behaviour expected to be determined by two processes both involving a thermaly activated dipolar reorientation:

  • translational-rotational diffusion of water molecules if the whole H-Bonded network relaxed within limitation of entropically different configurations

  • rotational diffusion of water molecules within a fixed H-Bonded structure as breaches of the Bernal-Fowler rules. –> 2 kinds of Bjerrum defects

    • Scattering

ASW at 140K - true glass or very viscous liquid ? What is the difference

Crystalisation#

At molecular scales (few molecules up to 100 ?) - Matrix isolation techniques

Water_moleucule

Desorption#

[Rosu-Finsen et al., 2022]

Porosity#

[Cazaux et al., 2014]

Is it Amorphous ?#

../../_images/Ice-process-PPD1.PNG

Fig. 10 Source#