Time-resolved light scattering

F re 5.5 Evaluation of LCST phase boundary by extrapolating to zero heating rate. 

The technique of static hght scattering can be applied to studies of the dynamic phenomena of polymer phase transitions by simultaneous acquisition of the angular dependence of the scattering pattern in one or two dimensions at relatively 

The correlation distance can be obtained from the slope and the intercept in the Debye-Bueche plot, versus q. Once the value of is known, the other 

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Lee, C. H., Saito, H. and Inoue, T., Time-resolved light scattering studies on the early stages of crystallization in poly(ethylene terephthalate), Macromolecules, 26, 6566-6569 (1993). 

H. Stolz, Time-Resolved Light Scattering from Excitons, Springer, Verlag, Berlin New York 1994. 

These results were confirmed by Sung and Han (1995). They observed that addition of a PS-PB diblock copolymer to a blend of the corresponding homopolymers (of lower molecular weight than the diblock) leads to a retardation of phase separation in both early and late stages. Using time-resolved light scattering they determined the spinodal peak position and intensity as a function of time. Addition of copolymer was found to reduce the critical temperature of the blend. 

Amino-l,2,4-benzotriazine 1,2-dioxide Thin layer chromatography Thymidine-5 -phosphate iV,iV,iV, iV -Telramclhylphcnylcncdiamine Tetranitromethane 3,5,4 -Trihydroxy-frans-stilbene 2-Amino-2-hydroxy-l, 3-propanediol Time-resolved light-scattering p-[meso-5-5,10,15,20-Tetra(pyridyl)porphyrin]tetra kis[ (ns-(bipyridine) chloride ruthenium(II)]... 

In basic solution, the observed rate of strand breakage after -OH-attack is low (0.4 s-1) and independent of pH, but increases by about three orders of magnitude in acid solution (Bothe and Schulte-Frohlinde 1982) (in neutral solution, a similar value, 3.7 s 1, has been obtained by time-resolved light-scattering Jones and O Neill 1991). Thus, there is a spontaneous and a H+-catalyzed reaction. 

A time-resolved light scattering set-up, schematically shown in Figure la, was utilized (18). It consists of a laser light source (He-Ne laser with a wavelength of 6328 A ), a set of polarizer and analyzer, a sample hot stage and a screen. 

The change of four-lobe to an intense isotropic scattering cannot be accounted for exclusively in terms of the spherulite melting, since there is a good chance that the phase separation may be involved (Figure 5). Since the phase behavior is extremely complex, only the time-resolved light scattering results at the 10 wt7. concentration will be presented here. 

It is of particular interest to know how fast long polymer chains change their conformation in response to a short laser pulse. The dynamics of this process can be studied in photoresponsive polymers which undergo photostimulated conformation changes [25]. The isomerization of photochromic chromophores can be induced in less than 10 s with a short laser pulse. The conformation change subsequent to it can be followed with a time resolved light scattering system combined with the short laser pulse source (Fig. 8). 

Fig. 8. Time-resolved light scattering measuring system combined with a short laser pulse...

Polyamide (6) was irradiated with a single 20 ns flash (530 nm) in A. iV-dimethyl-ac tamide. The kinetics of the cis to trans isomerization of backbone azobenzene residues was followed by time resolved optical absorption, and the subsequent conformation change of the total polymer chain by time resolved light scattering. Before each laser e eriment, the polymer was brought to a compact conformation by eontiimous ultraviolet irradiation, and then the unfolding proce was traced by the laser flash photolysis method. 

The photostimulated conformation change of polystyrene with pendant azobenzene groups in cyclohexane has also been studied by the time-resolved light scattering technique [26]. 

PEN (40) / PET (60) TSE at 280°C / NMR / time-resolved light scattering measurements during annealing Okamoto and Kotaka, 1997... 

PBT (50) /PC (50) TSE at 290°C / TEM / time-resolved light scattering / effect of transesterification on phase separation Okamoto and Inoue, 1994... 

W. Zhuang and E. Kiran, Kinetics of pressure-induced phase separation (PIPS) from polymer solutions by time-resolved light scattering. Polyethylene + n-pentane, Polymer, 39,2903-2915 (1998). 

Jones GDD, O NeiU P. Kinetics of radiation-induced strand break formation in single-stranded pyrimidine polynucleotides in the presence and absence of oxygen a time-resolved light-scattering study. Int J Radiat Biol. 1991 59 1127-1145. 

The time changes of Im(t) and qm(t) during pattern formation via SD were measured at various T by time-resolved light scattering experiments for SBR1/PB19 mixtures having near critical composition (58 wt/42 wt) (17). The results obtained were subjected to the reduced plot as shown in Fig.4 (17), in which... 

Time-resolved light scattering method, wha-ein the spinodal curve is measured based on vanishing mutual diffusivities. 

The polymer used in the thermal inversion process of making membranes was initially dissolved and maintained at a temperature above the critical point of the binary system under consideration. Solutions of 10wt% polystyrene in cyclohexanol were prepared at 90°C and then placed in an oven at a temperature of 115-120°C. Note that the upper critical solution temperature of polystyrene/cyclohexanol system is about 82°C (Shultz and Flory, 1953). Also, the critical composition is at a polymer volume fraction of about 0.03, while the polymer-rich binodal composition is at a volume fraction of about 0.20. Thus, the cast solutions are expected to coagulate inside the spinodal curve, as we have verified using a diode-array time-resolved light scattering system similar to that used by Hashimoto and his coworkers (Inaba et al., 1986). Solid membranes were then made within 24 h, after the solutions were prepared. These membranes were then sputter-coated with gold-palladium and observed under the microscope. 

Here we mention a fundamental remaining question. The bond-order parameter S should be coupled with density-order parameter p. Previously, we treated p as the conserved order parameter and assumed the diffusional dynamics. Then we considered the lowest order coupling between p and S. However, our recent time-resolved light scattering measurements of the process of LLT in triphenyl phosphite shows that the scattering intensity at = 0 grows upon LLT. This behavior is not consistent with the prediction. A more complete description, which takes into account the couplings of S to the density and velocity fields properly, will be reported elsewhere. 

Somwangthanaroj A, Lee EC, Solomon MJ (2003) Early stage quiescent and flow-induced crystallization of intercalated polypropylene nanocomposites by time-resolved light scattering. Macromolecules 36 2333-2342... 

SAS Sasaki, K. and Hashimoto, T., Time resolved light scattering studies on the kinetics of phase separation and phase dissolution of polymer blends. 3. Spinodal decomposition of ternary mixtures of polymer A, polymer B, and solvent. Macromolecules, 17, 2818, 1984. 

C-H Liu, BB Das, WL Sha Glassmann, GC Tang, KM Yoo, HR Zhu, L Akind, SS Lubicz, J Cleary, R Prudente, E Celmer, A Caron, RR Alfano. Raman, fluorescence and time-resolved light scattering as optical diagnostic techniques to separate diseased and normal biomedical media. J Photochem Photobiol B 16 187-209, 1992. 

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