Extraction of Rotational Correlation Times from Noisy Single Molecule Fluorescence Trajectories

The Journal of Chemical Physics

Kaufman

2018

Self Cite

Using extrinsic probes to study a host system relies on the probes' ability to accurately report the host properties under study. Probes have long been used to characterize dynamic heterogeneity, the phenomenon in which a liquid near its glass transition exhibits distinct dynamics as a function of time and position, with molecules within nanometers of each other exhibiting dynamics that may vary by orders of magnitude. The spatial and temporal characteristics of dynamic heterogeneity demand the selection of probes using stringent criteria on their size and dynamics. In this report, we study the dynamic heterogeneity of the prototypical molecular glass former o-terphenyl by investigating single molecule rotation of two perylene dicarboximide probe molecules that differ in size and comparing this to results obtained previously with the probe BODIPY268. It is found that a probe's ability to accurately report dynamic heterogeneity in o-terphenyl depends on whether the reported distribution of dynamics overlaps with the intrinsic dynamics of the host, which is naturally related to the width of the intrinsic dynamics and the magnitude of dynamical shift in probe dynamics relative to the host. We show that a probe that rotates ≈15 times more slowly than the intrinsic dynamics of the host o-terphenyl senses the slowest ≈5% of the full dynamic heterogeneity whereas one that rotates ≈65 times more slowly than the host fails to report dynamic heterogeneity of the host. Published by AIP Publishing. https://doi.

Section: Discussionmentioning

confidence: 99%

Which probes can report intrinsic dynamic heterogeneity of a glass forming liquid?

The Journal of Chemical Physics

Kaufman

2018

Self Cite

“…For single frame rate data, median frame rate was chosen to be ∼ 15 frames per median τ fit and only molecules with (number of frames)/τ fit >2 and trajectory length >10 τ fit were analyzed. Data analysis was performed using IDL software (ITT Visual Information Solutions) as described previously (10,22).…”

Section: Methodsmentioning

confidence: 99%

Ideal probe single-molecule experiments reveal the intrinsic dynamic heterogeneity of a supercooled liquid

Proc. Natl. Acad. Sci. U.S.A.

Park

Hoang

et al. 2015

Self Cite

The concept of dynamic heterogeneity and the picture of the supercooled liquid as a mosaic of environments with distinct dynamics that interchange in time have been invoked to explain the nonexponential relaxations measured in these systems. The spatial extent and temporal persistence of these regions of distinct dynamics have remained challenging to identify. Here, singlemolecule fluorescence measurements using a probe similar in size and mobility to the host o-terphenyl unambiguously reveal exponential relaxations distributed in time and space and directly demonstrate ergodicity of the system down to the glass transition temperature. In the temperature range probed, at least 200 times the structural relaxation time of the host is required to recover ensemble-averaged relaxation at every spatial region in the system.espite decades of intensive study, a full theory of the glass transition is lacking; so too is a full understanding of the causal relationships between the unusual phenomena displayed by glass-forming liquids in the supercooled regime and the glass transition. One such phenomenon is the onset of nonexponential relaxations in the supercooled regime. Consistent with such relaxations, a variety of experiments have suggested the presence of dynamic heterogeneity, where-over a given time-molecular mobility in a given region may differ by orders of magnitude from that in another region, potentially just nanometers away (1, 2). While some experiments have sought to quantify the size of these regions, others have sought to quantify their persistence in time, as supercooled liquids are assumed to be ergodic, requiring that over long times, all dynamic environments are sampled (3-5). Precise description of dynamic heterogeneity in glass formers remains challenging due to the ensemble, subensemble, and/or time averaging inherent in most experimental techniques. However, such description remains of significant interest given the poorly understood causal relationship between dynamic heterogeneity and the glass transition as well as the need for experimental observations that may distinguish between various theories of the glass transition (6, 7).Typically, putative dynamic heterogeneity has been recognized in experiments through the shape of the ensemble relaxation, which is well described by a stretched exponential (exp[−(t/τ fit ) β ]) where the deviation of β below 1 describes the degree of stretching and has been interpreted as a barometer of dynamic heterogeneity. Multiple scenarios are consistent with an ensemble stretched exponential relaxation, and two limiting cases can be straightforwardly described: The ensemble stretched exponential emerges from (i) a superposition of exponentials with different relaxation times or (ii) identical stretched exponentials with the same relaxation time. The former limit describes a system with variation of time scales distributed in space but not time, while the latter represents the opposite extreme. The former case describes a system that is not ergodic over times acce...

“…Background intensity, signal-to-background ratio, and camera noise were applied as described previously. 36 A Gaussian fit was performed on the noisy PSF to determine centroid position before stochastic noise was renewed. This process was repeated 2700 times, and a MSD was constructed from the fitted positions, which will differ within localization accuracy.…”

Section: A Monitoring Dynamics During Polymer Film Swellingmentioning

confidence: 99%

In situ multi-modal monitoring of solvent vapor swelling in polymer thin films

Hoang

Yang

Review of Scientific Instruments

et al. 2016

Self Cite

Polymer processing techniques involving solvent vapor swelling are typically challenging to control and thus reproduce. Moreover, traditional descriptions of solvent swollen films lack microscopic detail. We describe the design and use of an apparatus that facilitates macroscopic and microscopic characterization of samples undergoing solvent vapor swelling in a controlled environment. The experimental design incorporates three critical characteristics: (1) a mass-flow controlled solvent vapor delivery system allows for precise control of the amount of solvent vapor delivered to the sample, (2) a sample prepared on a quartz crystal microbalance allows for real-time assessment of the extent of sample swelling, (3) a second sample prepared and assessed in parallel on a coverslip allows real-time fluorescence microscopy during swelling. We demonstrate that this apparatus allows for single-particle tracking, which in turn facilitates in situ monitoring of local environments within the solvent-swollen film.