Films formed from polystyrene latex/clay composites: A fluorescence study

This study reports a steady-state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene (PS) latex and Na-montmorillonite (SNaM) composites. The composite films were prepared from pyrene (P)-labeled PS particles and SNaM clay at room temperature and annealed at elevated temperatures in 10-min intervals above glass transition temperature (t₃) of polystyrene. During the annealing processes, the transparency of the film improved considerably. Scattered light (I_s) and fluorescence intensity (I_p) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of composite films was monitored by using photon transmission intensity, I_tr. Scanning electron microscopy (SEM) was used to detect the variation in physical structure of annealed composite films. Minimum film formation temperature, T_q, and healing temperatures, T_h, were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It was observed that both activation energies increased as the percent of SNaM was increased in composite films.     

Electrically controlled release of 5-fluorouracil from conductive gelatin methacryloyl-based hydrogels

Herein, electro-responsive hydrogels were obtained by incorporation of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) into the gelatin methacryloyl (GelMA) by using photopolymerization technique. Hydrogels were characterized by FTIR and scanning electron microscopy analyses. Cytotoxicity tests were performed by L929 cell lines to determine cell compatibility. Swelling tests were conducted to investigate the water uptake capacity of hydrogels. 5-fluorouracil (5-FU) was selected as a model drug as it is known as a topical drug for some skin cancer type treatment. The release of 5-FU from the hydrogel was provided in efficient and controlled manner at simulated skin cancer (pH = 5.5) and under 0 and 1.5 V. The simulated drug delivery experiments conducted in vitro revealed that the drug releasing amount was higher when voltage is applied to the hydrogels. All results visualized that the obtained GelMA-based PEDOT/PSS hydrogels with enhanced electrical properties could be a potential candidate as an electrically sensitive drug carrier for treatment of skin cancer in the future applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46914.     

Interaction between a tertiary amine methacrylate based polyelectrolyte and a sodium montmorillonite dispersion and its rheological and colloidal properties

The rheological and colloidal properties of sodium montmorillonite dispersions were investigated in the presence of a special type of cationic polymer [modified poly(ethylene glycol)]. 2‐(Dimethylamino) ethyl methacrylate was polymerized with monomethoxy‐capped oligo(ethylene glycol) via aqueous atom transfer radical polymerization. The tertiary amine residues of the resulting polymer were then quaternized with methyl iodide to obtain a cationic polyelectrolyte. The rheology and ζ‐potential experiments showed that the cationic polymer adsorbed onto the sodium montmorillonite surface strongly. The rheological parameters (plastic viscosity and yield value) were obtained with a rotational low‐shear rheometer. The results indicated a gradual increase in gelation with the addition of the cationic polymer, which reached a maximum at a cationic polymer concentration of 0.4–0.8 g/L. This gel‐like dispersion showed pronounced thixotropy. A further increase in the polymer concentration resulted in a reduction in this gelation. The adsorption of the cationic polymer onto the clay surface reduced the ζ potential to small values, but no isoelectric point was observed. The basal‐spacing measurements showed that the cationic polymer strongly adsorbed onto the sodium montmorillonite instead of entering the montmorillonite layers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 300–306, 2005     

Identification of spacewise and time dependent source terms in 1D heat conduction equation from temperature measurement at a final time

Inverse problems of identifying the unknown spacewise and time dependent heat sources F(x) and H(t) of the variable coefficient heat conduction equation u_t = (k(x)u_x)_x + F(x)H(t) from supplementary temperature measurement (u_T(x)?u(x, T_f)) at a given single instant of time T_f > 0, are investigated. For both inverse source problems, defined to be as ISPF and ISPH respectively, explicit formulas for the Fréchet gradients of corresponding cost functionals are derived. Fourier analysis of these problems shows that although ISPF has a unique solution, ISPH may not have a unique solution. The conjugate gradient method (CGM) with the explicit gradient formula for the cost functional J₁(F) is then applied for numerical solution of ISPF. New collocation algorithm, based on the piecewise linear approximation of the unknown source H(t), is proposed for the numerical solution of the integral equation corresponding to ISPH. The proposed two numerical algorithms are examined through numerical examples for reconstruction of continuous and discontinuous heat sources F(x) and H(t). Computational results, with noise free and noisy data, show efficiency and high accuracy of the proposed algorithms.     

Styrenated sunflower oil polymers from raft process for coating application

Oil-based macroinitiator (MI) obtained from sunflower oil was styrenated using reversible addition–fragmentation chain transfer polymerization (RAFT) in the presence of phenacyl morpholine dithiocarbamate (PMDC) as chain transfer agent. The solvent effect and effect of the molar ratio of the transfer agent, PMDC, on polydispersity and molecular weight of the polymers were investigated. The obtained results showed that, 1,4-dioxane is a better solvent and 1/4 molar ratio of [MI]/[PMDC] provides relatively low polydispersities. No homopolystyrene was detected under these conditions, indicating the efficiency of PMDC in the chain transfer process. Livingness of the polymerization process was confirmed by chain extension with styrene using the preformed polymer as macrotransfer agent. The film properties of styrenated oil samples were determined according to the related standards. To improve film properties, the polymer obtained by RAFT technique was modified by reaction with MI. The resulting material gave transparent films with good film properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical and rheological behavior of highly filled polystyrene with lignin

The mechanical, rheological, and morphological properties of polystyrene (PS)/lignin blends over a wide range of lignin content (0–80 wt%) have been studied in this work. PS/lignin blends were compounded in an internal batch mixer with and without the addition of a linear triblock copolymer based on styrene, ethylene, and butylene (SEBS). A morphological analysis was carried out by scanning electron microscopy to determine the state of dispersion and the interfacial adhesion between the lignin particles and the PS matrix. It was found that the flexural and torsion moduli both increased, while the tensile properties decreased with increasing lignin content. Nevertheless, compatibilizer addition was found to improve the tensile properties of the lignin/PS blend. The shear rheological behavior of the lignin/PS blends was also studied in this work where viscosity, dynamic moduli, and activation energy were found to be very sensitive to both lignin and compatibilizer contents. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Ambient Vibration Tests of a Steel Footbridge

The paper presents analytical and experimental modal analysis of a steel footbridge for modal parameter identification. 3D finite element model is established for the steel footbridge based on the design drawing and modal parameters are obtained from deformed configurations. The field test is carried out by ambient vibration test under human walking excitation. Both Peak Picking method in the frequency domain and the Stochastic Subspace Identification method in the time domain are used for the output-only modal identification. From the study, good agreement is found between mode shapes, but some differences in the natural frequencies and analytical frequencies are bigger.     

Reservoir water effects on earthquake performance evaluation of Torul Concrete-Faced Rockfill Dam

This study presents earthquake performance analysis of the Torul Concrete-Faced Rockfill (CFR) Dam with two-dimensional dam-soil and dam-soil-reservoir finite element models. The Lagrangian approach was used with fluid elements to model impounded water. The interface elements were used to simulate the slippage between the concrete face slab and the rockfill. The horizontal component of the 1992 Erzincan earthquake, with a peak ground acceleration of 0.515g, was considered in time-history analysis. The Drucker-Prager model was preferred in nonlinear analysis of the concrete slab, rockfill and foundation soil. The maximum principal stresses and the maximum displacements in two opposite directions were compared by the height of the concrete slab according to linear time-history analysis to reveal the effect of reservoir water. The changes of critical displacements and principal stresses with time are also shown in this paper. According to linear and nonlinear time-history analysis, the effect of the reservoir water on the earthquake performance of the Torul CFR Dam was investigated and the possible damage situation was examined. The results show that the hydrodynamic pressure of reservoir water leads to an increase in the maximum displacements and principal stresses of the dam and reduces the earthquake performance of the dam. Although the linear time-history analysis demonstrates that the earthquake causes a momentous damage to the concrete slab of the Torul CFR Dam, the nonlinear time-history analysis shows that no evident damage occurs in either reservoir case.     

Electroconductive hyaluronic acid/gelatin/poly(ethylene oxide) polymeric film reinforced by reduced graphene oxide

Novel electroconductive polymeric films with enhanced mechanical performance were fabricated by encapsulating reduced graphene oxide (RGO) at different concentrations (0–50 vol %) into a hyaluronic acid/gelatin/poly(ethylene oxide) (HyA/Gel/PEO) polymeric structure. The obtained RGO-reinforced polymeric films were characterized by Fourier transform infrared and scanning electron microscopy analyses. Mechanical performances were measured with a universal mechanical testing machine. The results verified that the RGO reinforcement significantly enhanced the mechanical performances of the films. To determine the biocompatibility of the polymeric films, L929 (murine fibroblast) cell lines were used. The water uptake capacities were measured using swelling tests. A four-probe method was used to measure conductivity characteristics. The conductivity results indicated that HyA/Gel/PEO film containing 20 vol % RGO has the highest average electrical conductivity (1.832 × 10⁻⁶ S/cm). All of the results demonstrated that the obtained electroconductive films could be used in biomedical fields in the future, especially in controlled drug release systems and tissue engineering. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46905.