Photon Transmission Technique Research Articles

In situ real-time photon transmission technique for monitoring formation of polyacrylamide gels at various crosslinker contents

The in situ, real-time, photon transmission technique was used to monitor the free-radical crosslinking copolymerization (FCC) of acrylamide (AAm) and N,N′-methylenebisacrylamide (Bis). Gelation experiments were performed with various Bis contents at various wavelengths. It was observed that the transmitted photon intensity, Itr, decreased dramatically at a certain reaction time, which is attributed to the increase in scattered light intensity, Isc, during the formation of microgels in the system. The increase in Isc was modeled using Rayleigh's equation where the reaction time was found to be proportional to the volume of the microgels. In most cases, the change in Isc was found to be inversely proportional to the 2.5 power of the wavelength, λ, from which the size of the microgel particles were estimated during the FCC. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 823–830, 2001

Film Formation from Nanosized Copolymeric Latex Particles: A Photon Transmission Study

The photon transmission technique was used to monitor the evolution of transparency during film formation from nanosized copolymeric latex particles. The latex films were prepared from poly(methyl methacrylate-co-butyl methacrylate) (P(MMA-co-BMA)) particles which were produced by microemulsion polymerization. These films were annealed at elevated temperatures in various time intervals above the glass transition temperature (Tg) of P(MMA-co-BMA). It is observed that the transmitted photon intensity (Itr) from these films increased as the annealing temperature increased. There are three different film formation stages. These stages are explained by the void closure, healing, and interdiffusion processes, respectively. The activation energies for viscous flow (ΔH≈16 kcal/mol), minor chains (ΔEH≈27 kcal/mol), and backbone motion (Δ Eb≈132 kcal/mol) were obtained using various models. Void closure (τv, Tv) and healing points (τH, TH) were determined. Using the time–temperature pairs, void closure and healing activation energies were measured and found to be 21 and 30 kcal/mol, respectively.

Photon transmission technique for monitoring drying processes in acrylamide gels formed with various crosslinker contents

In situ photon transmission experiments were performed using UV-visible (UVV) spectrometer during the drying of polyacrylamide (PAAm) gels. These gels are formed from acrylamide (AAm) with various N,N′-methylenebis(acrylamide) (Bis) contents by free radical crosslinking copolymerization (FCC) in water. The transmitted light intensity, Itr increased continuously as PAAm gels are dried. Increase in Itr was attributed to the decrease in the scattered light intensity, Isc, which might be originated from the contrast between “frozen blob clusters” and holes in the drying gel. Decrease in Isc was modeled using Rayleigh's equation, where drying times with various exponents were found to be proportional to the volume of frozen blob clusters. It was observed that the radius of frozen blob cluster (correlation length), ξc increased in various power of time, depending on Bis contents during drying of gels. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1898–1906, 2001

In situ photon transmission technique for monitoring phase separation in real time during gelation

In situ, real time photon transmission technique was used to monitor the formation of heterogeneities during the free-radical crosslinking polymerization of acrylamide in the presence of N,N'-methylenebis(acrylamide) (BAAm) as a crosslinker. Two different gelation experiments were performed with various BAAm and water contents separately at room temperature. It was observed that the transmitted photon intensity, I tr decreases dramatically at a certain time, in both type of experiments during the gel formation process from interconnected microgels. Decrease in I tr was interpreted in terms of phase separation during gelation. The extent of phase separation was measured depending on the crosslinker content and on the degree of monomer dilution during the gel formation process.

Synchrotron X-ray study of bulk lattice strains in externally loaded Cu-Mo composites

A synchrotron X-ray transmission technique was applied to study the internal load transfer and micromechanical damage in molybdenum particle-reinforced copper matrix composites during plastic deformation. Mechanically loaded, 1.5-mm-thick specimens were irradiated with a monochromatic beam of 65 keV X-rays. Low-index diffraction rings of both phases were recorded with a high-resolution two-dimensional detector. By means of newly developed data processing routines, we could quantify as a function of applied stress both the ring distortion (from which the volume-averaged elastic strains in the two phases were calculated), and the ring graininess (which is related to the Bragg peak broadening). Based on this information, the deformation and damage processes in these alloys were studied in detail. As compared to conventional neutron diffraction methods, the photon transmission technique yielded similar precision but at much reduced measurement times. The main sources of experimental errors were identified and strategies to minimize these errors were developed.

Comment on "Photon transmission technique for studying multiple phase transitions in a liquid crystal".

Contrary to the recently published results by Ozbek et al. [Phys. Rev. E 59, 6798 (1999)], we argue that the transmitted light intensity through an unoriented sample is by no means a good measure of the order parameters of the different phase transitions of a liquid crystal.

In situ photon transmission technique for monitoring formation of hydrogels in real-time at various water contents

In situ photon transmission technique was used to monitor the free radical crosslinking copolymerization (FCC) of acrylamide (AAm) and N,N′-methylenebis (acrylamide) (Bis) in real-time. Gelation experiments were performed in various water contents at various wavelengths. It was observed that transmitted photon intensity, Itr, decreased dramatically at a certain gelation time, which is attributed to the increase in scattered light intensity, Isc, during FCC. Increase in Isc was modeled using Rayleigh's equation where gelation time was found to be proportional to the volume of the microgels. The change in Isc is found to be inversely proportional to the thirth power of the wavelength, λ, for high water content samples at early times. However, low water content samples produce smaller and constant power of λ during FCC at all times. The sizes of microgel particles and phase-separated domains were estimated.

Photon transmission technique for monitoring free radical crosslinking copolymerization in various crosslinker contents

Photon transmission technique was used to monitor the free radical crosslinking copolymerization (FCC) of acrylamide (AAm) and N, N′-methylenebis (acrylamide) (Bis) in time. FCC experiments were performed with various Bis contents. It was observed that transmitted photon intensity, I tr decreased dramatically at a certain gelation time, which is attributed to the increase in scattered light intensity, I sc during macrogel formation from interconnected microgels. Increase in I sc was modeled using Rayleigh's equation where gelation time was found to be proportional to the volume of the microgels.

Photon transmission technique for studying multiple phase transitions in a liquid crystal.

A photon transmission technique was used to monitor the multiple phase transitions in a 4-butoxyphenyl4(')-declyoxybenzoate (BOPDOB) liquid crystal. Drastic decreases in the transmitted photon intensity (I) were attributed to the sequential phase transitions in BOPDOB upon cooling. In this paper, it is assumed that the order parameter rho is proportional to the transmitted photon intensity. The isotropic-nematic and nematic-smectic-A transitions were observed and found to be of first order. It was observed that the smectic-A-smectic-C and smectic-C-smectic-G transitions are second order. It was found that for the smectic-A-smectic-C transition, critical exponent crosses over from beta=0.513+/-0.006, which is consistent with mean-field theory, to beta=0.35+/-0.009, which is consistent with heliumlike behavior, as the Ginzburg criterion predicts. The critical exponent for the smectic-C-smectic-G transition was found to be beta=0.703+/-0.001. Transition temperatures were established at each phase transitions and found to be 84.92 degrees C, 74.85 degrees C, 52.96 degrees C, and 33.03 degrees C for isotropic-nematic, nematic-smectic-A, smectic-A-smectic-C and, smectic-C-smectic-G transitions, respectively.

Photon transmission technique for studying film formation from polystyrene latexes prepared by dispersion polymerization using various steric stabilizers

A photon-transmission method was used to monitor the evolution of transparency during film formation from various polystyrene (PS) particles which were produced using different steric stabilizers, that is, poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), and polyvinylpyrrolidone (PVP). The latex films were prepared from PS particles at room temperature and annealed at elevated temperatures in various time intervals above the glass transition (Tg). To simulate the latex film-formation process, a Monte Carlo technique was performed for photon transmission through a rectangular lattice. The number of transmitted (Ntr) photons were calculated as a function of particle–particle interfaces that disappeared. The increase in the transmitted photon intensity (Itr) was attributed to the increase in the number of interfaces that disappeared. The Prager–Tirrell (PT) model was employed to interpret the increase in crossing density at the junction surface. The backbone activation energy (ΔE) was measured and found to be around 120 kcal mol−1 for a diffusing polymer chain across the junction surface for all PS latex films. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1257–1267, 1998

In situ photon transmission technique for studying ageing in acrylamide gels due to multiple swelling

In situ photon transmission experiments were performed using an ultra-violet-visible (u.v.-vis) spectrometer during the multiple swelling of polyacrylamide (PAAm) gel in water. The transmitted light intensity, I tr decreased continuously as the PAAm gel swelled. The decrease in I tr was attributed to the increase in scattered light intensity which might have orginated from the contrast between ‘frozen blob clusters’ and holes in the swollen gel. It was observed that the correlation length, ξ c, increased by 1 4 power of the swelling time. The sudden increase in the gel relaxation time, τ, was attributed to the rupture of the network structure after the eight swelling step during multiple swelling of the PAAm gel.

Fluorescence method of studying void closure kinetics during film formation from high-T latex particles

Void closure process due to viscous flow was studied during film formation from high-T latex particles. Steady-state fluorescence and photon transmission techniques were used to probe the evolution of optical clarity during film formation. The latex films were prepared from pyrene (P)-labeled poly(methyl methacrylate) particles and annealed in 10-min time intervals above glass transition temperature. Fluorescence intensity from P was measured after each annealing step. A relation for void closure time versus fluorescence intensity was derived, using the Vogel—Fulcher equation. Viscosity constant B was measured from the above relation and found to be as 11 × 103 K. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 655–661, 1997

Photographic film dosimetry by low energy photon transmission

Studies were carried out on the use of low energy photon transmission technique for the evaluation of gamma exposures recorded by film dosimeters. A GM counter with a compact counting equipment was used for recording Ti X-rays ( 3H/Ti source) transmitted through the processed film. The results of the studies carried out on Kodak type 2 and Agfa-Gevaert PM films are reported. By this technique, exposures from 25 mR to as high as 900 R could be estimated with reasonable accuracy.