Importance of Molecular Structure on the Thermophoresis of Binary Mixtures

Kumar, Pardeep; Goswami, Debabrata

doi:10.1021/jp5079604

Cited by 7 publications

(2 citation statements)

References 55 publications

(107 reference statements)

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“…Such molecular selective condensation could not be explained by simple thermal diffusion because these two isomers show almost the same thermophoresis behavior, especially under the present concentration conditions. 60,61 Even if thermophoresis effects contributed to trapping phenomena, the thermal force would be expected to be relatively small since the Solet coefficient depends on mainly molecular size. 62,63 Therefore, this SERS intensity increase would imply the changes in the number of molecules at the observation site induced by the light illumination.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Room-Temperature Molecular Manipulation via Plasmonic Trapping at Electrified Interfaces

2022

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For the motion control of individual molecules at room temperature, optical tweezers could be one of the best approaches to realize desirable selectivity with high resolution in time and space. Because of physical limitations due to the thermal fluctuation, optical manipulation of small molecules at room temperature is still a challenging subject. The difficulty of the manipulation also emerged from the variation of molecular polarizability depending on the choice of molecules as well as the molecular orientation to the optical field. In this article, we have demonstrated plasmonic optical trapping of small size molecules with less than 1 nm at the gap of a single metal nanodimer immersed in an electrolyte solution. In situ electrochemical surface-enhanced Raman scattering measurements prove that a plasmonic structure under electrochemical potential control realizes not only the selective molecular condensation but also the formation of unique mixed molecular phases which is distinct from those under a thermodynamic equilibrium. Through detailed analyses of optical trapping behavior, we established the methodology of plasmonic optical trapping to create the novel adsorption isotherm under applying an optical force at electrified interfaces.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Room-Temperature Molecular Manipulation via Plasmonic Trapping at Electrified Interfaces

2022

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“…We have shown that more generalizability can be achieved for the “active control” methodology with the help of programmable ultrafast pulse shaping approaches. However, under the abovementioned conditions, the requirement of having a single isolated system interacting with light remains important ( Kumar and Goswami, 2014 ).…”

Section: Introductionmentioning

confidence: 99%

Intense femtosecond optical pulse shaping approaches to spatiotemporal control

Goswami

2023

Front. Chem.

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For studying any event, measurement can never be enough; “control” is required. This means mere passive tracking of the event is insufficient and being able to manipulate it is necessary. To maximize this capability to exert control and manipulate, both spatial and temporal domains need to be jointly accounted for, which has remained an intractable problem at microscopic scales. Simultaneous control of dynamics and position of an observable event requires a holistic combination of spatial and temporal control principles, which gives rise to the field of spatiotemporal control. For this, we present a novel femtosecond pulse-shaping approach. We explain how to achieve spatiotemporal control by spatially manipulating the system through trapping and subsequently or simultaneously exerting temporal control using shaped femtosecond pulses. By leveraging ultrafast femtosecond lasers, the prospect of having temporal control of molecular dynamics increases, and it becomes possible to circumvent the relaxation processes at microscopic timescales. Optical trapping is an exemplary demonstration of spatial control that results in the immobilization of microscopic objects with radiation pressure from a tightly focused laser beam. Conventional single-beam optical tweezers use continuous-wave (CW) lasers for achieving spatial control through photon fluxes, but these lack temporal control knobs. We use a femtosecond high repetition rate (HRR) pulsed laser to bypass this lack of dynamical control in the time domain for optical trapping studies. From a technological viewpoint, the high photon flux requirement of stable optical tweezers necessitates femtosecond pulse shaping at HRR, which has been a barrier until the recent Megahertz pulse shaping developments. Finally, recognizing the theoretical distinction between tweezers with femtosecond pulses and CW lasers is of paramount interest. Non-linear optical (NLO) interactions must be included prima facie to understand pulsed laser tweezers in areas where they excel, like the two-photon-fluorescence-based detection. We show that our theoretical model can holistically address the common drawback of all tweezers. We are able to mitigate the effects of laser-induced heating by balancing this with femtosecond laser-induced NLO effects. An interesting side-product of HRR femtosecond-laser-induced thermal lens is the development of femtosecond thermal lens spectroscopy (FTLS) and its ability to provide sensitive molecular detection.

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