Towards in situ fluorescence spectroscopy and microscopy investigations of asphaltene precipitation kinetics

Abstract

We perform a spectroscopic analysis of asphaltene in solution and in crude oil with the goal of designing an optical probe of asphaltene precipitation inside high-pressure cells. Quantitative analysis of steady-state spectroscopic data is employed to identify fluorescence and Raman contributions to the observed signals. Time-resolved fluorescence spectroscopy indicates that fluorescence lifetime can be used as a spectroscopic probe of asphaltene in crude oil. Quantitative confocal laser-scanning microscopy studies of asphaltene in n-heptane are used to calculate particle-size distributions as a function of time, both at the sample surface and asphaltene interior. The resulting precipitation kinetics is well described by stochastic numerical simulations of diffusion-limited aggregation. Based on these results, we present the design and construction of an apparatus to optically probe the in situ precipitation of asphaltene suitable for studies inside high pressure cells. Design considerations include the use of a spatial light modulator for aberration correction in microscopy measurements, together with the design of epi-fluorescence spectrometer, both fiber-based and for remote sensing fluorescence spectroscopy.

Combined experimental and molecular dynamics investigation of 1D rod-like asphaltene aggregation in toluene-hexane mixture

“…We have calculated the total area of the aggregates and the average length and thickness of the particles using ImageJ analysis [38]. The approximate total number of particles is calculated using the following Eq.…”

Hydrogen peroxide disproportionation: time-resolved optical measurements of spectra, scattering and imaging combined with correlation analysis and simulations

“…Data analysis algorithms were developed in-house and are based in our previous published works. Further details of the experimental setup and data analysis are described in references [10][11][12][13].…”

“…[6][7][8][9] Previously, we have studied different ways in which time-resolved laser spectroscopy can be used to learn more about physical chemical processes and reaction mechanisms. [10][11][12] In ref 12, using as examples stochastic dynamics simulations of Brownian motion in a bistable asymmetric well, photochemical kinetics of conjugated polymer photo-degradation from experimental solution-filled optical fiber time-resolved fluorescence spectra, and ultrafast spectroscopy for the same system, we discussed how more information about the reaction can be obtained as a function of sampling rate, number of molecules being probed, and spectral range to be studied, respectively. More recently, we have reported mechanistic studies of photocatalytic degradation of organic molecules with in situ micro-spectroscopy and optical tweezers: we monitored images and time-dependent spectra, and quantitative optical microscopy was used to characterize spatially-dependent reaction rates and correlate with stochastic dynamics of individual catalytic nanoparticles.…”

On the Fly” Characterization of YbIII:ErIII Co-Doped Upconversion Nanoparticle Nonlinear Optical Response from Single-Particle Trajectories

“…Prior to the measurements, the samples were taken to a tip sonicator to ensure particle dispersion and colloidal stability, which was checked by dynamic light scattering (DLS) particle size measurement. Upconversion microscopy and optical tweezers measurements were performed as described previously [26,27]. Briefly, a 975 nm laser beam is sent to a nonlinear microscope set up in a vertical, epifluorescence geometry.…”