Steady film casting

Figure 4.14 Steady-state fluorescence emission speara of crystalline iPS obtained from gel and atactic PS film cast from chloroform at room temperature, excitation wavelength 257 nm Reprinted from Polymer, Volume 32, B. Wandelt, Correlation of photophysical parameters with conformational structure of crystalline iPS and comparison with data of atactic PS, 2708, copyright 1991, with permission from Elsevier Science)...

Piz-Lopez, M.E. and Co, A. (1996) Multilayer film casting of modified giesekus fluids. Part 1. Steady-state analysis. J. Non-Newtonian Fluid Meek, 66, 71-93. 

The objective of the analysis is to calculate the thickness and temperature at the chill-roll as a function of the take-up speed, rheology, distance L, and conditions at the die lips. In the case of vco > T ho, changes in the y direction can be considered insignificant for the rest of the analysis. Then, we postulate the following surface velocity field for the steady-state film-casting problem ... 

A paper by Ozturk, Palsson, and Dressman (OPD), reporting a refinement of the MMSH model, did create some controversy. OPD developed a film model with reaction in spherical coordinates and applied quasi-steady-state assumptions to the boundary conditions at the solid surface [11], They theorized that the flux of all species at the solid surface must be zero, except for HA, or the other species (A-, H+, OH ) would penetrate the solid surface. A debate by correspondence in the Letters to the Editor columns of Pharmaceutical Research ensued [12,13], The reader is invited to evaluate which author s arguments are more convincing. What is difficult to evaluate is whether the OPD model produces dissolution results which are different from those which would be predicted using the MMSH model cast in comparable spherical geometry. Simply, these authors never graphically demonstrate how their model predictions compare to the MMSH model. Algebraically, the solutions to both models appear comparable. 

To illustrate the capabilities of the system shown in Fig. 16.12, we present new, previously unpublished results from our laboratory. In Fig. 16.13, we illustrate results for three fluorescent probe molecules (pyrene, DCM [4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran], and PRODAN [6-propionyl-2-(/V,/V-dimethylamino)naphthalene]) that were doped within a series of PFFA/Pluronic P104 BP blends. In the initial experiments, 16 BP formulations were prepared manually using micropipettes, while subsequent experiments utilized the ALHS to prepare 21 BP formulations. These formulations were spun cast into thin films employing quartz microscope slides as substrates. To characterize the local microenvironment surrounding each probe within a given formulation, steady-state fluorescence measurements using a conventional spectrofluorometer were performed. 

The polymer donor participation in the CT interactionjirith TCNQ in the composite films is evident from Fig. 3 TCNQ concentrations produced in the cast films are all different among the polymers, and some of, the typical donor polymerg show a steady increase of [TCNQ ] with an increase of TCNQ concentration, whereas the DMF contribution to the [TCNQ ] shonld show a reverse trend (8). If there ig no or negligible CT interaction between polymers and TCNQ in the cast films, TCNQ produced in the films should be the sole result of DMF participation in the interaction and thus the total TCNQ concentrations in the films should be all the same at a given concentration of TCNQ, since the volume of DMF and the amount of polymers are kept constant in the casting solution. 

In order to remove the cast elastomer film from the Teflon support, a strip of Kapton based adhesive tape is fixed at one end of the swollen gel. Kapton is used as it can withstand high temperatures and is stable towards organic solvents. The film is now removed from the support by slowly pulUng the tape. In some cases it is useful to rinse the space between the elastomer film and the Teflon foil with toluene. The elastomer film is fixed at a metal holder and hung vertically. At the lower end of the film a small load, e.g., a paper chp, is attached and held steady with Kapton tape from both sides (Fig. 10). 

Mb can be taken up from pH 5.5-7 buffers into cast liquid crystal films of didodecyldimethylammonium bromide (DDAB) on electrodes [17]. We observed chemically reversible voltammetry for the heme Fe /Fe redox couple of Mb taken up from solution into 0.5-20 [tm DDAB films (Figure 3) [17-19]. No vol-tammetric peaks were observed for bare pyrolytic graphite (PG) electrodes in Mb solutions, so the surfactant film turns on the protein electrochemistry. Mb-DDAB films retain more than 80% of the original steady state voltammetric peak current after a month s storage in buffer. DDAB and Mb are both positive at pH 5.5, so hydrophobic interactions are probably important for film stability. 

In contrast to RCs from R. viridis where charge separation is blocked by double reduction of and Q, the membrane bound RC of the Dll mutant could be cast into a PVA film, thus allowing the application of electric fields at low temperatures. Measurements of the steady state fluorescence yield show that the lifetime of P increases by 1.5% in an external electric field of c 710 V/cm. This effect is by a factor of 2 4 larger than the Stark effect measured in the peak of the Qy absorption band of the dimer P. In principle, this field induced decrease of the fluorescence may arise from two sources (i) the increase of the internal conversion rate by mixing in charge transfer states and (ii) a field induced transfer to the inactive B-branch. 

Two copolymers, a poly(styrene-6-isoprene-7>-styrene) (SIS) triblock (60 wt% S Mn=100,000, Mw/Mn=1.04) and a poly(styrene-Wsoprene) (SI) diblock (70 wt% S Mn=50,000, Mw/Mn=1.05), were synthesized by anionic polymerization. The selective solvent used here was an aliphatic white mineral oil (MO) produced by Witco (380PO). Specific masses of each copolymer and MO weae dissolved in cyclohexane and cast into molds. Upon solvent evaporation, the resultant films were vacuum-dried for up to 7 h at 120 C. Steady-shear tests were performed on a Rheometrics dynamic stress rheometer (DSR) as a function of shear stress (x) to measure the solution viscosity (q), while dynamic tests were performed here to discern G and G" as functions of x, oo and temperature. 

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