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Marjorie Ladd ParadaPostdoc

About me

I am a postdoc at the XSoLaS group, focusing mainly on amorphous ice and its transitions, including to crystalline ice. Working mainly with XRD, and XPCS techniques.I did my PhD on Food Science at Leeds University, studying cacao butter and how its crystallisation kinetics are affected by pressure and different thermal treatments, using techniques such as DSC, XRD and NMR. 

I am interested in phase transitions of different materials and the application of X-ray methods to further our understanding of their structure and dynamics.

I am also keen on Science Communication, I have participated in a few Pint of Science events, and during my PhD was also part of Research Nights and PubhD. You can follow me on Twitter @M_LaddParada.

Publications

A selection from Stockholm University publication database

  • Experimental observation of the liquid-liquid transition in bulk supercooled water under pressure

    2020. Kyung Hwan Kim (et al.). Science 370 (6519), 978-982

    Article

    We prepared bulk samples of supercooled liquid water under pressure by isochoric heating of high-density amorphous ice to temperatures of 205 ± 10 kelvin, using an infrared femtosecond laser. Because the sample density is preserved during the ultrafast heating, we could estimate an initial internal pressure of 2.5 to 3.5 kilobar in the high-density liquid phase. After heating, the sample expanded rapidly, and we captured the resulting decompression process with femtosecond x-ray laser pulses at different pump-probe delay times. A discontinuous structural change occurred in which low-density liquid domains appeared and grew on time scales between 20 nanoseconds to 3 microseconds, whereas crystallization occurs on time scales of 3 to 50 microseconds. The dynamics of the two processes being separated by more than one order of magnitude provides support for a liquid-liquid transition in bulk supercooled water.

    Read more about Experimental observation of the liquid-liquid transition in bulk supercooled water under pressure
  • Enhancement and maximum in the isobaric specific-heat capacity measurements of deeply supercooled water using ultrafast calorimetry

    2021. Harshad Pathak (et al.). Proceedings of the National Academy of Sciences of the United States of America 118 (6)

    Article

    Knowledge of the temperature dependence of the isobaric specific heat (Cp) upon deep supercooling can give insights regarding the anomalous properties of water. If a maximum in Cp exists at a specific temperature, as in the isothermal compressibility, it would further validate the liquid–liquid critical point model that can explain the anomalous increase in thermodynamic response functions. The challenge is that the relevant temperature range falls in the region where ice crystallization becomes rapid, which has previously excluded experiments. Here, we have utilized a methodology of ultrafast calorimetry by determining the temperature jump from femtosecond X-ray pulses after heating with an infrared laser pulse and with a sufficiently long time delay between the pulses to allow measurements at constant pressure. Evaporative cooling of ∼15-µm diameter droplets in vacuum enabled us to reach a temperature down to ∼228 K with a small fraction of the droplets remaining unfrozen. We observed a sharp increase in Cp, from 88 J/mol/K at 244 K to about 218 J/mol/K at 229 K where a maximum is seen. The Cp maximum is at a similar temperature as the maxima of the isothermal compressibility and correlation length. From the Cp measurement, we estimated the excess entropy and self-diffusion coefficient of water and these properties decrease rapidly below 235 K.

    Read more about Enhancement and maximum in the isobaric specific-heat capacity measurements of deeply supercooled water using ultrafast calorimetry
  • Crystal Memory near Discontinuous Triacylglycerol Phase Transitions

    2020. David A. Pink (et al.). Molecules 25 (23)

    Article

    It is proposed that crystal memory, observed in a discontinuous solid-liquid phase transition of saturated triacylglycerol (TAG) molecules, is due to the coexistence of solid TAG crystalline phases and a liquid TAG phase, in a superheated metastable regime. Such a coexistence has been detected. Solid crystals can act as heterogeneous nuclei onto which molecules can condense as the temperature is lowered. We outlined a mathematical model, with a single phase transition, that shows how the time-temperature observations can be explained, makes predictions, and relates them to recent experimental data. A modified Vogel-Fulcher-Tammann (VFT) equation is used to predict time-temperature relations for the observation of crystal memory and to show boundaries beyond which crystal memory is not observed. A plot of the lifetime of a metastable state versus temperature, using the modified VFT equation, agrees with recent time-temperature data. The model can be falsified through its predictions: the model possesses a critical point and we outline a procedure describing how it could be observed by changing the hydrocarbon chain length. We make predictions about how thermodynamic functions will change as the critical point is reached and as the system enters a crossover regime. The model predicts that the phenomenon of crystal memory will not be observed unless the system is cooled from a superheated metastable regime associated with a discontinuous phase transition.

    Read more about Crystal Memory near Discontinuous Triacylglycerol Phase Transitions

Show all publications by Marjorie Ladd Parada at Stockholm University