Photochromic Activity Research Articles

Investigation of Marangoni and natural convection during protein crystal growth

The occurrence of Marangoni and natural convection has been experimentally investigated during lysozyme and cytochrome c′ protein crystal growth (PCG) using a vapor diffusion technique in a hanging droplet and a PCG apparatus. To detect the fluid motion, the photochromic dye activation and particle tracking velocimetry (PTV) techniques were used. In all the cases studied, the dye traces recorded by a CCD video camera did not show fluid movement with velocities greater than about 0.2 μm/s anywhere in the solution, even around the growing protein crystals. The PTV technique with a velocity resolution well below 0.2 μm/s also showed no detectable displacements of the tracer particles. These results indicate that an aqueous protein solution surface is highly resistant to Marangoni convection under typical PCG conditions.

Laser photochromic dye activation technique for the measurement of liquid free surface velocity on curved surfaces

An optical method is presented which permits the determination of the free surface velocity of liquid films flowing on curved surfaces. The feasibility of this technique, which involves the laser tomography and photochromic dye activation techniques, is demonstrated on an oil film flowing around a finned tube. Results for different tube geometries and flow conditions are presented. Advantages and limits of the laser photochromic velocimetry technique are discussed.

An experimental study of bubble behavior in a temperature gradient near a heated wall under low-gravity and microgravity conditions aboard NASA DC9 airplane

The behavior of a single bubble and a pair of bubbles under microgravity conditions has been investigated using the NASA-DC9 aircraft in order to understand the effects of various parameters and to control the bubble behavior in space. Silicone oil was used as the test liquid, and a nitrogen gas bubble was injected from the top wall under different experimental conditions. In an isothermal case, two different microgravity conditions were achieved by either fixing the experimental apparatus to the aircraft floor or freely floating the apparatus in the aircraft cabin. The bubble behavior was found to be clearly influenced by the quality of the microgravity environment, and variations of the bubble aspect ratio with the Bond number were presented. The results indicate that there is a critical Bond number of the order of 10−1 which determines the bubble shape deformation. In the free-floating experiments, a temperature gradient was imposed on the liquid around the bubble near the heated top wall. Marangoni convection was expected to occur around the bubble and the bubble behavior was studied under various temperature gradients. The bubble aspect ratio was found to decrease with an increase in the Marangoni number. A theoretical model for the relation between the Marangoni flow around the bubble and the aspect ratio is proposed based on simple assumptions. Visualization of Marangoni convection around the bubbles using the photochromic dye activation method was successfully performed. The aspect ratios predicted by the model agreed with the experimental results reasonably well. Direct measurements of surface velocity are, however, necessary to further evaluate the validity of the model.

Unusual UV (λexc = 303 nm) and visible (λexc = 574 nm) activated photochromism of an indeno-fused naphthopyran

In this work a completely novel photochromic mechanism exhibited by an indeno-fused naphthopyran (chromene) is presented. The studied molecule is the first case of a chromene-type compound exhibiting both photochromism and thermochromism. These phenomena were investigated in ethanol. Thermochromism was detected by monitoring absorption spectra in the 285–320 K temperature range: the enthalpy of the thermocoloration reaction was determined (ΔH = 25 kJ mol−1) and the equilibrium constant was estimated (Keq ≈ 10−3). For the photochemical investigation, carried out in the 200–270 K temperature range, continuous monochromatic light was used for excitation. The photocoloration was observed under two distinct stimulations: UV-irradiation (λexc = 303 nm), which is normally used for photochromic chromene activation, and visible-irradiation (λexc = 574 nm) of the thermally equilibrated solution. Two coloured species are involved in the photochemical and thermal processes. One of them, P, is photochemically produced by UV irradiation of the colourless form, while the other, T, is present in thermal equilibrium with the closed form. When the thermally equilibrated solution is irradiated with visible light, T is converted to P. This system not only results in a cyclic on–off chromogenic device, which can be switched-on by UV radiation, but it also exhibits on–off functionality using lower energy visible light. Such behaviour makes this photochromic system exceptionally efficient upon exposure to sunlight.

고주파 삼각파 여자법을 사용한 실시간 슬러그 유동 측정용 전자기유량계

In order to investigate the characteristics of two-phase slug flow. an electromagnetic flowmeter with 240Hz triangular AC excitation was designed and manufactured. The signals and noise from the flowmeter were obtained. and analyzed in comparison with the observations with a high speed CCO camera. The uncertainty of the flowmeter under single-phase flow was:!: 2.24% in real-time. For two-phase slug flow. electromagnetic flowmeter provided real-time simultaneous measurements of the mean film velocity around Taylor bubble and thc relative location and the length of the bubble. Besides. it is an easier and cheaper method for measuring mean tilm velocity than others such as photochromic dye activation method or particle image velocimetry.br/

Instantaneous hydrodynamics of a laminar wavy liquid film

Experiments have been conducted to investigate instantaneous hydrodynamic characteristics of laminar falling films of 20 cS silicone oil on an inclined plate using a photochromic dye activation technique and high-speed video photography over a Reynolds number range of 11–220. Instantaneous velocity profiles across a wavy laminar film and axial profiles of film thickness have been measured simultaneously and statistically analyzed. Experimental data indicated that the time-averaged mean and maximum velocity data are significantly over-predicted by Nusselt's theory, while the time-averaged film thickness data are slightly under-predicted. The instantaneous velocity profiles examined in different regions of the wavy laminar film showed that in the smooth substrate film region, the velocity profiles matched Nusselt theory, however, under the large waves they were substantially smaller than Nusselt's predictions for films of the same thickness. Based on the measured velocity profiles, approximately 30–40% of liquid mass was estimated to be transported by the large waves. The instantaneous wall shear stress values were close to the gravity force per unit area in the substrate film, but much smaller under the large waves. The temporal variations of wall shear stress and film thickness showed that the peaks in wall shear stress more often preceded the film thickness peaks, suggesting that the liquid in the wave region experiences acceleration, while in the non-wavy region both acceleration and deceleration are experienced.

Photo- and Thermochromic Spirans. New Metal Chelates Based on Azomethines and Hydrazones Containing a Spiropyran Fragment

Imine- and hydrazone-based metal chelates containing a spiropyran fragment derived from 3-methyl-4-oxo[2H]-1,3-benzoxazinone were prepared. Attempts are made to monitor the photochromic activity of spiropyran using nontraditional π-acceptor substituents (products of condensation of the formyl group in 6"-dimethyl-8"-formylspiro-(4-oxo-3,4-dihydro-2H-1,3-benzoxazine-2,2"-[2H]chromene) with o- aminophenol and aromatic acid hydrazides) and using transition metal ions.

Turbulence Modification Due to Wave Action at Low Reynolds Numbers in Horizontal Open-Channel Flow

Wave-turbulence interaction was experimentally investigated in turbulent open-channel flows with a shear-free wavy surface using a photochromic dye activation technique. In the experiments conducted, two-dimensional waves of different amplitudes, wavelengths, and frequencies were superimposed on a liquid surface via a mechanical wave maker. The range of Reynolds numbers varied from 3900 to 5000 based on the hydraulic diameter, with the corresponding aspect ratio of the channel width to liquid depth varying from 7.5 to 5.Within the range of Reynolds numbers investigated, the results showed that the streamwise turbulence intensity increased in the bulk and interfacial regions in comparison to the undisturbed flow.Furthermore, video sequences of the flow visualization experiments clearly revealed that the spanwise motion of the liquid was significantly suppressed; the traces did not immediately deform in the spanwise direction but retained their shape with increasing wave amplitude and frequency as compared to smooth interface flows. This suggests that waves may have suppressed longitudinal vortices generated near the smooth interface. The suppression of the longitudinal vortices in wavy open-channel flows has been proposed as a mechanism responsible for the turbulence energy redistribution, different from that for smooth open-channel flows.

Photochromic activity of dihydropyridine derivatives: energetics and kinetics of photochemically driven reactions in polycrystalline 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropydridine

Kinetics of thermally driven reactions in a crystalline photochromic solid 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine (DHP) has been studied. The processes have been monitored by measuring the isothermal bleaching of coloured species produced upon UV irradiation of DHP, and by measuring the heat flow in non-isothermal differential scanning calorimetry experiments. Signatures of two processes were detected; a combination of quantum-chemical calculations and spectroscopic measurements allowed us to attribute them to reactions occurring in the photochromic system. The model put forward in the paper assumes that the primary photochemically driven reaction (intramolecular phenyl shift) is irreversible; the photochromic cycle consists of two parallel processes: 2,4-ring closing and intramolecular hydrogen shift.

Two-phase flow measurements using a photochromic dye activation technique

A novel flow visualization method called photochromic dye activation (PDA) technique has been used to investigate flow structures and mechanisms in various two-phase flow regimes. This non-intrusive flow visualization technique utilizes light activation of a photochromic dye material dissolved in a clear liquid and is a molecular tagging technique, requiring no seed particles. It has been used to yield both quantitative and qualitative flow data in the liquid phase in annular flow, slug flow and stratified-wavy flows.

Photochemical properties of a photochromic naphthoxazine upon UV irradiation in the presence of transition metal ions

1,3,3-Trimethylspiro[indoline-2,3′-[3H]-naphth-[2,1-b][1,4]oxazine] was synthesized in order to study its photochromic activity in the presence of transition metal ions. Its photochemistry and irreversible phototransformation were studied on UV-irradiation in the presence of 10 −5-10 −6 M concentrations of transition metal ions in methanol, ethanol and acetonitrile. A new, stable strongly luminescent product appeared, giving rise to broad and unstructured luminescence. The obtained absorption and emission spectra were used to calculate the fluorescence quantum yields.

Falling film hydrodynamics in slug flow

Non-intrusive flow visualization using photochromic dye activation is applied to study the near-wall region around individual and coalescing pairs of Taylor bubbles rising in stagnant kerosene in a vertical 25.6 mm ID tube. Instantaneous velocity profile measurements have been performed in the liquid film flowing past the rising Taylor bubble. A simple predictive procedure for estimating film velocity is successfully implemented. New and interesting phenomena are observed primarily in the wake region that are of significance to slug flow modeling.

Investigation of flow structures in vertical slug flow

The flow structure of gas–liquid slug flow in a vertical tube has been investigated experimentally and numerically. A photochromic dye activation method was used to obtain two-dimensional liquid velocity profiles around a Taylor Bubble rising in stagnant kerosene in a vertical 25.6 mm I.D. pipe. A numerical simulation of the flow was conducted using a Volume-of-Fluid approach to predict both the shape of the Taylor Bubble and the velocity profiles in the liquid phase. In order to test the hypothesis that a trailing bubble can accelerate, catch up and coalesce with a leading bubble because of lateral motion and reduced drag force, a second experiment was performed using a solid Taylor Bubble placed in a steady downward flow of liquid. The measured drag force showed significant reduction as the bubble was moved from the tube axis towards the wall, giving support to the hypothesis.

Turbulence structure and prediction of interfacial heat and mass transfer in wavy‐stratified flow

AbstractThe turbulence structure of the liquid phase near a wavy gas‐liquid interface in stratified flow was experimentally investigated in a 50 mm (H) × 100 mm (W) rectangular duct. The characteristic parameters of the organized motion under the liquid waves such as the frequency of appearance and length scale were estimated by using the variable‐interval time‐averaging and the photochromic dye activation techniques. These characteristics were used in a hybrid surface renewal‐eddy cell model to predict the interfacial heat‐ and mass‐transfer coefficients in stratified two‐phase flow. The predictions for cocurrent and countercurrent flows agreed reasonably well with experimental data available in the literature.

Performance and Mechanisms of Hindered Amine Light Stabilizer in Spirooxazine Photostabilization

One of the key requirements for optical switching apertures for ophtalmic, building and automobile glazing is long lived product. However, oxidation of a spirooxazine yields photoproducts such as oxindoie derivatives, naphthoxazole, dihydro-2,6-quinolone and 1-N-formylimino-2-naphthoquinone devoid of photochromic activity, and limits the commercialisation of these useful systems. Achieving this long lived product can be provide by use of hindered amine light stabilizers (HALS). This paper describs the comportment of a spirooxazine irradiated in the presence of a HALS and the main stabilization mechanisms are discussed.

Liquid turbulence structure at a sheared and wavy gas-liquid interface

Interfacial momentum transfer was studied in cocurrent and countercurrent wavy-stratified flows in a rectangular channel using both the hot-wire anemometry (HWA) and the non-intrusive photochromic dye activation (PDA) techniques. In cocurrent and countercurrent stratified flows with a wavy interface, the interfacial shear and waves were found to change the kinematic and turbulence structures of the liquid phase significantly. In particular, the mean streamwise velocity profile became nearly constant in the upper half of the liquid phase, and the magnitude of the turbulent streamwise and vertical fluctuations correlated with the interfacial shear and the wave amplitude, respectively. Numerical predictions of the experimental data were obtained with the k- ϵ model of turbulence. New interface conditions were proposed for wavy flows which yielded predictions in good agreement with the experimental data for both cocurrent and countercurrent flows.

Photochromic Polysulfones. 2. Photochromic Properties of Polymeric Polysulfone Carrying Pendant Spiropyran and Spirooxazine Groups

Photochromes, bound to polysulfone via carboxyamide bonds and physically blended in a polymeric matrix, were prepared and their physical and photochromic properties investigated. In order to express the photochromic activity, plasticization is required; this is readily achieved by using the swelling solvent, N-methylpyrrolidone (NMP). The photochromic activity is repressed in the presence of carboxylic groups, and this requires complex blocking of any acidity, e.g., by esterification or amidation. The photochromic activity was expressed in membranes made from functional and blended polysulfones, yet the photoresponsive membranes did not produce a significant electroresponse or, if they did, this decayed rapidly. Obviously, membranes with a much higher degree of covalent binding are needed.

Photochromic compounds: Chemistry and application in ophthalmic lenses

Abstract

Visualization of Free Surface Phenomena Using Photochromic Dye.

Surface tension variation along a gas-liquid interface has a considerable effect on flow near the interface. In order to clarify this, the so-called Marangoni effect, we observed the prevention of natural convection by the surface tension change due to a contaminant in a cavity. The velocity profiles near the interface were measured by the photochromic dye activation method, and the surface tension gradient and the contaminant concentration distribution along the interface were determined. Development of a stagnant surface region induced by contaminant accumulation was theoretically investigated. The theory agreed well with the experimental results. A surface spreading motion due to the Marangoni effect was also investigated using an ultraviolet laser beam, and all the experimental results were correlated with dimensional analysis considering the surface tension variation due to the ionization.

Photochromic 8-Ethoxy-2-methylspiro(syn-5,6-benzo-2-azabicyclo[2.2.2]oct-5-ene-3,3'-[3H]naphth[2,1-b][1,4]oxazine)

In the photochromic title compound, C 25 H 24 N 2 O 2 , the C spiro -O bond can be broken on photoexcitation. Conformational parameters and oxazine-ring puckering have been investigated by considering similar photochromic compounds. It is shown that when the C spiro -O bond is elongated, and therefore weakened, the ring-puckering coefficient is smaller and photochromic activity increases.