In situ fast transient fluorescence technique (FTRF) to study swelling of gels made of various crosslinker contents

The fast transient fluorescence technique (FTRF), which uses the strobe master system (SMS), was employed to study the swelling of disc‐shaped PMMA [poly(methyl methacrylate] gels. Seven gels were prepared by free radical copolymerization (FCC) of methyl methacrylate (MMA) with various ethylene glycol dimethacrylate (EGDM) contents. Pyrene (P_y) was introduced as a fluorescence probe during polymerization. After drying these gels, swelling experiments were performed in chloroform at room temperature. P_y lifetimes were measured from fluorescence decay traces during the in situ swelling experiments. An equation was derived for low quenching efficiencies to interpret the behavior of lifetimes in the gel during swelling. It was observed that P_y lifetimes in the gel decreased as swelling proceeded. The Li–Tanaka equation was used to determine the cooperative diffusion coefficients, D_c, which were found to decrease as the crosslinker content was increased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 464–472, 2003     

Modeling of swelling by fluorescence technique in poly (methyl methacrylate) gels

A novel technique based on in-situ steady-state fluorescence (SSF) measurements is introduced for studying swelling processes in gels formed by free radical cross-linking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) in toluene. Gels were prepared at 75°C for various toluene contents with pyrene (Py) as a fluorescence probe. After drying these gels, swelling and desorption experiments were performed in toluene at 50°C by real-time monitoring of Py fluorescence intensity. A correction method was developed to obtain pure swelling curves, by using desorption curves of Py molecules. Li-Tanaka equation was employed to produce swelling parameters. Cooperative diffusion coefficients (D_c) were measured and found to be around 10⁻⁶ cm²/s for gels swollen in toluene. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1777–1784, 1997     

Fast transient fluorescence (FTRF) technique to study swelling of densely and loosely formed gels

A Strobe Master System (SMS) is introduced for studying the swelling of cylindrical densely (DG) and loosely (LG) formed gels. Gels were prepared by free radical copolymerization of methyl (methacrylate) (MMA) and ethylene glycol dimethacrylate (EGDM). Pyrene (P) was introduced as a fluorescence probe during polymerization, and the lifetimes of P were measured using (SMS) during in situ swelling processes. Chloroform was used as a swelling agent. A model is derived for low quenching efficiencies to measure mean lifetimes 〈τ〉 of P, and it was observed that 〈τ〉 values decreased as the swelling proceeded. The Li‐Tanaka equation was employed to determined the time constants, τ_c, and cooperative diffusion coefficients, D_c, which were found to be around 400 min and 10⁻⁵ cm²s⁻¹, respectively. No differences were detected in τ_c and D_c values of DG and LG gels. Quenching rate constants, κ, and the mutual diffusion coefficient, D_m, were measured and found to be around 10⁵ M⁻¹s⁻¹ and 10⁻¹⁰ cm²s⁻¹ for DG and LG gel samples. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1494–1502, 2000     

Fast transient fluorescence technique (FTRT) for studying dissolution of polymer glasses

The fast transient fluorescence technique (FTRT) was used for studying the swelling and dissolution of a glassy polymer formed by free‐radical polymerization of methyl methacrylate (MMA). Anthracene (An) was introduced during polymerization as a fluorescence probe to monitor swelling and dissolution. Swelling and dissolution processes of disc‐shaped poly(methyl methacrylate) (PMMA) glasses in a chloroform–heptane mixture were monitored by measuring the fluorescence lifetimes of An from its decay traces. A method is developed for low quenching efficiencies for measuring lifetimes, τ, of An, and it was observed that τ values decreased as the dissolution process proceeded. Desorption, D, and mutual diffusion, D_m, coefficients of An molecules were measured during dissolution of PMMA and found to be around 5.4 × 10⁻⁶ (cm²/s) and 2.2 × 10⁻⁵ (cm²/s), respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 948–957, 1999     

In situ fluorescence study of slow release and swelling processes in gels formed by solution free radical copolymerization

A novel method based on steady state fluorescence (SSF) measurements is introduced for studying slow release and swelling processes in gels formed by free radical crosslinking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) in toluene. Gels were prepared at 75°C with various toluene contents with pyrene (P_y) as a fluorescence probe. After drying these gels, slow release and swelling experiments were performed in toluene at 50°C by real-time monitoring of the pyrene fluorescence intensity. Li-Tanaka and Fickian type equations were used to obtain swelling and slow release parameters. It was observed that slow release takes place after the gel is swollen. Cooperative and desorption (slow release) diffusion coefficients (D_c and D) were measured and found to be 10^-6cm²s^-1 in both cases. ©1997 SCI     

Effect of molar size and solubility parameter of solvent molecules on swelling of a gel: a fluorescence study

Gels were swollen in various solvents with different molar volume V and solubility parameter δ. In situ steady state fluorescence (SSF) measurements were performed for swelling experiments in gels formed by free radical crosslinking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM). Gels were prepared at 75 °C with pyrene (Py) as a fluorescence probe. After drying these gels, swelling and slow release experiments were performed in various solvents with different V and δ at room temperature by time monitoring of the Py fluorescence intensity. The Li–Tanaka equation was used to produce time constant τ₁ values. Cooperative diffusion coefficients (D_c) were measured and found to be strongly correlated to the molar volume of the solvents used. Solvent uptake and degree of swelling were found to be dependent on the solubility parameter of the solvent. © 2000 Society of Chemical Industry     

Swelling and drying kinetics of polytetrahydrofuran and polytetrahydrofuran–poly (methyl methacrylate) gels: A photon transmission study

A bifunctional polytetrahydrofuran (PTHF) macromonomer was synthesized by termination of the living polymerization of tetrahydrofuran (THF) initiated by triflic anhydride and the subsequent termination by sodium methacrylate. The PTHF macromonomer thus prepared was polymerized and copolymerized with methyl methacrylate (MMA) by free‐radical polymerization to yield a network and a segmented network of PTHF, both being homogeneous, respectively. These PTHF and PTHF–PMMA gels were used for swelling experiments in chloroform and chloroform vapor. Drying processes were monitored after removing the gels from the solvent and solvent vapor. Photon transmission from PTHF and PTHF–PMMA gels was monitored during swelling and drying processes using a UV‐visible (UVV) spectrophotometer. Transmitted light intensities, I_tr, from these gels increased when they were immersed in chloroform and/or subjected to its vapor. The increase in I_tr was attributed to the homogeneous lattice structure of PTHF and PTHF–PMMA gels which appeared during swelling. The increase in I_tr was modeled using the Li–Tanaka equation from which time constants, τ₁, and cooperative diffusion coefficients, D_C, were determined. A decrease in I_tr after removing choloform and/or its vapor from the cell was observed and attributed to the decrease in homogeneity of lattice structures during drying of the corresponding gels. Time constants, τ2, for the drying processes were also determined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 632–640, 2003     

Molecular weight effect on swelling of polymer gels in homopolymer solutions: a fluorescence study

A novel technique based on in situ steady state fluorescence measurements is introduced for studying swelling processes of gels formed by free radical crosslinking copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) in homopolymer solutions. Gels were prepared at 55±2 °C for various EGDM contents. After drying these gels, swelling experiments were performed in chloroform solution of anthracene labeled poly(methyl methacrylate) (An-PMMA) in various molecular weights at room temperature by real time monitoring of anthracene fluorescence intensity. Anthracene labeled PMMA chains having various molecular weights were prepared by atom transfer radical polymerization at 90 °C. During the swelling experiments, it was observed that anthracene emission intensities increased due to trapping of An-PMMA chains into the gel as the swelling time is increased. The trapping of An-PMMA chains in swollen gel, increase by obeying parabolic law in time. Penetration time constant, τ of PMMA chains were measured and found to be increased as the crosslinker density of gel is increased. It is observed that τ values are much higher for high molecular weight An-PMMA chains than low molecular weight chains in all gel samples.     

Fast transient fluorescence method for measuring swelling and drying activation energies of a polystyrene gel

The time-resolved, fast transient fluorescence (TRF) technique which uses a strobe master system (SMS), was employed for studying swelling and drying of disc-shaped polystyrene gels. Disc-shaped gels were prepared by free-radical crosslinking copolymerization of styrene and ethylene glycol dimethacrylate. Pyrene was introduced as a fluorescence probe during polymerization and lifetimes, τ of pyrene were measured during in situ swelling and drying processes. Chloroform was used as an organic vapor agent to induce gel swelling at various temperatures. It was observed that τ values decreased as swelling is proceeded. Li-Tanaka equation was used to determine the swelling time constant, τ_c and cooperative diffusion coefficients, D_c for the swelling processes. It is observed that lifetimes, τ of pyrene increased during drying process and an empirical equation was introduced to determine the desorption coefficient, D for drying at various temperatures. The activation energies, ΔE were measured for the swelling and drying processes and found to be 80.0 and 33.5 kJ mol⁻¹, respectively.     

A fluorescence study on dissolution of polymeric glasses prepared in various molecular weights

Poly(methyl methacrylate) (PMMA) discs in various molecular weights, M_w, were prepared by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the gelation and dissolution processes in chloroform vapor and solvent, respectively. In-situ steady state fluorescence (SSF) experiments were performed to monitor vapor uptake and chain desorption processes. Direct illumination of PMMA discs were performed to excite the P molecules embedded inside the PMMA glass. Variation in P intensity, I, was monitored during the swelling of the PMMA material exposed to chloroform vapor. It was observed that PMMA film swells like a crosslinked polymeric gel at early times by obeying the Li-Tanaka equation. Swelling time constants, τ_c, of PMMA discs were measured and found to have a strong correlation with the molecular weight, of PMMA. In a separate experiment, when the PMMA discs were in chloroform, desorption of PMMA chains from glass discs was monitored by observing the change of pyrene fluorescence intensity. A diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It was observed that desorption coefficient, D, decreased by increasing M_w by obeying the D≈M_w ⁻¹ law. Presented at the 80th Annual Meeting of the Federation of Societies for Coatings Technology, October 30–November 1, 2002, New Orleans, LA. Department of Physics, 80626 Maslak, Istanbul. Turkey.     

Small molecule desorption prior to dissolution of a polymeric glass

Poly(methyl methacrylate) (PMMA) discs in various molecular weights (M_w) were prepared by free‐radical polymerization. Pyrene (Py) was introduced during polymerization as a fluorescence probe. In situ steady state fluorescence experiments were performed to monitor desorption processes in chloroform solvent. When the PMMA discs were in chloroform, desorption of Py molecules were monitored by observing the change of Py fluorescence intensity I_P. To understand the mechanism of desorption, two different experiments were carried out in the meantime. In the first experiment, the weight of swelling and dissolving PMMA discs against dissolution time was monitored. The parallel experiment was conducted by measuring fluorescence intensity I_P from the desorbing Py molecules. Then, a set of desorption experiments were performed by monitoring I_P for various discs with different molecular weight of PMMA. A Fickian diffusion model was employed to quantify the fluorescence data produced from the swelling PMMA discs to measure desorption coefficients D_d. The measured D_d values decrease as the molecular weight of PMMA is increased in the swelling glass. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 908–912, 2006     

Studies on drying and swelling of PAAm‐NIPA composites in various compositions

The steady‐state fluorescence technique was introduced for studying the drying and swelling of disc‐shaped PAAm‐NIPA composites. Disc‐shaped gels were formed with various acrylamides (AAm) and N‐isopropylacrylamides (NIPA) by free radical crosslinking copolymerization in water. Composites were prepared with pyranine (Py) doped as a fluorescence probe. Scattered light, I_sc, and fluorescence intensities, I, were monitored during drying of these gels. The fluorescence intensity of pyranine increased and decreased as drying and swelling time increased respectively for all samples. The Stern‐Volmer equation combined with moving boundary and Li‐Tanaka models were used to explain the behavior of I during drying and swelling, respectively. It was found that the desorption coefficient, D, increased as NIPA contents were increased for a given temperature during drying. However, the cooperative diffusion coefficient, D₀, increased as NIPA contents were decreased during swelling at a given temperature. Supporting gravimetrical and volumetric experiments were also carried out during drying and swelling of PAAm‐NIPA composites. It was observed that NIPA contents affect the drying and swelling process. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Photon transmission technique for monitoring formation and swelling of polyacrylamide gels

The in situ, real-time photon transmission technique was used to monitor the free radical crosslinking copolymerization of acrylamide and N,N′-methylenebisacrylamide (Bis). Gelation experiments were performed with various Bis contents at various wavelengths. It was observed that the transmitted photon intensity, I _tr, decreased dramatically at a certain reaction time, which is attributed to the increase in scattered light intensity, I _sc, during the formation of microgels in the system. The increase in I _scwas modeled using Rayleigh's equation where the reaction time was found to be proportional to the volume of the microgels. The disc-shaped polyacrylamide (PAAm) gels were dried before use during swelling experiments. Transmitted light intensity, I _tr, from the gel increased at initial stages when PAAm gels were immersed in water and then decreased exponentially as the swelling time increased. Decrease in I _trwas attributed to the lattice heterogeneities, which might have originated between microgels and holes in the swelling gel. Decrease in I _trwas modeled using the Li–Tanaka equation from which cooperative diffusion coefficients, D _c, were determined for gels of various Bis contents. It is observed that the D _cvalues increased with the Bis content.     

Comparison of dissolution and mutual diffusion coefficients during dissolution of poly(methyl methacrylate) films

Steady state fluorescence measurements have been used for studying the dissolution of polymer films. These films are formed by free radical polymerization of methyl methacrylate (MMA) in which pyrene ( P_y ) was introduced as a fluorescence probe. Dissolution of poly(methyl methacrylate) (PMMA) films in chloroform–heptane mixtures were monitored in real-time by the P_y fluorescence intensity change. Dissolution coefficients D_d of P_y molecules were measured during dissolution of PMMA films, and found to be about 10⁻⁶ cm² s⁻¹. After dissolution, fluorescence quenching measurements were performed and the Stern–Volmer equation was employed to measure the mutual diffusion coefficients of heptane (D_h) and P_y (D_Py) molecules; these were found to be about 10⁻⁵ cm² s⁻¹. © 1999 Society of Chemical Industry     

Molecular weight effect on polymer dissolution: a steady state fluorescence study

In situ steady state fluorescence (SSF) technique was used to study the dissolution of disc-shaped polymer glasses in various molecular weights, M_W. The glass discs were formed by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the dissolution process in chloroform. Desorption of poly(methyl methacrylate) (PMMA) chains from discs were monitored simultaneously by observing the change of P fluorescence intensity, I. Diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It is observed that desorption coefficient, D decreased by increasing molecular weight, M_W by obeying D≈M⁻¹ law.     

Percolation cluster on partially dissolving polymer film

Steady state fluorescence (SSF) technique was used for studying dissolution of UV-induced polymer films. These films are formed from poly(methyl methacrylate) (PMMA) chains labeled with pyrene (P) which was introduced as a fluorescence probe to monitor the dissolution processes. PMMA films in various ethylene glycol dimethacrylate (EGDM) content, cured by UV radiation, were dissolved in chlorofrom-heptane (20-80%) mixtures. Dissolution of the films were monitored in real-time by the P fluorescence intensity change in the solvent reservoir. It is observed that P intensity decreased dramatically above a critical EGDM content, which was atributed to the formation of a percolation cluster. The measured percolation threshold, (p_c=0.25) was found to be in accord with the bond percolation model. Desorption coefficients, D_d were measured for films prepared with various EGDM content and it was observed that D_d values are much lower above p_c than below p_c.     

Effect of LCST on the swelling of PAAm-NIPA copolymers: a fluorescence study

Temperature sensitive copolymers were prepared by free radical crosslinking copolymerization in aqueous solution with different molar percentage of N-isopropylacrylamide (NIPA) and acrylamide (AAm) monomers. N,N′-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as a crosslinker and an initiator, respectively. The steady-state fluorescence (SSF) technique was used to determine the low critical phase transition temperature (LCST) for PAAm-NIPA copolymers. Swelling experiments were performed in water at various temperatures by real time monitoring of pyranine (Py) fluorescence intensity, I which decreased as swelling proceeded. The Stern–Volmer equation is modified for low quenching efficiencies to interpret the behavior of pyranine intensity during the swelling of PAAm-NIPA copolymers. The Li–Tanaka equation was used to determine the swelling time constants, τ ₁ and the cooperative diffusion coefficients, D ₀ from fluorescence intensity, weight and volume variations of the copolymers at various temperatures. It was observed that τ ₁ first increased up to LCST, and then decreased; naturally D ₀ decreased up to LCST and then increased upon increasing temperature. It was understood that (LCST) increases as PAAm contents increase in the PAAm-NIPA copolymers.     

Preparation and properties of silicone‐containing poly(methyl methacrylate) gels

Poly(methyl methacrylate) (PMMA) gels with varying amounts of silicone and solvent and constant amounts of crosslinker were prepared by solution free radical crosslinking copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) comonomer systems. They were then studied in benzene at a total monomer concentration of 3.5 mol L^?1 and 70 °C. The conversion of monomer, volume swelling ratio, weight fraction and gel point were measured as a function of the reaction time, silicone concentration and benzene content up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in benzene, gel fraction and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by SEM. Based on the obtained results, it was concluded that the FTIR data did not have the capacity to show the presence of the VTES or TEOS moiety in these kinds of copolymers. On the other hand, the variation of weight fraction of gel, W_g, and its equilibrium volume swelling ratio in benzene, q_v, exhibited the same behaviour as that of MMA/EGDM copolymers. Also, the dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percent of conversion and gel fraction. Finally, TEOS is not an ideal silicone compound for reaction in the MMA/EGDM copolymerization system, whereas VTES is a suitable silicone comonomer for this system and it has been proved useful. Copyright © 2005 Society of Chemical Industry     

Temperature effect on the swelling of PAAm‐κ‐carrageenan composites

The steady‐state fluorescence (SSF) technique was used for studying swelling of disc‐shaped polyacrylamide (PAAm)‐κ‐carrageenan (κC) composites which were prepared by free‐radical crosslinking copolymerization at 80°C. Pyranine was introduced as a fluorescence probe during polymerization. Swelling experiments were performed in water at various temperatures by real‐time monitoring of the pyranine (Py) fluorescence intensity, I which decreased as swelling proceeded. Stern–Volmer equation is modified for low quenching efficiencies to interpret the behavior of Py intensity during the swelling of PAAm‐κC composites. The Li‐Tanaka equation was used to determine the swelling time constants, τ₁, and cooperative diffusion coefficients, D₀, from fluorescence intensity, weight, and volume variations of the composites at various temperatures. It was observed that τ₁ first decreased up to 40°C and then increased; naturally, D₀ increased up to 40°C and then decrease for all κC content gels. Swelling activation energies, ΔE, were measured for the swelling composites, which are found to be exothermic and endothermic in between 30–40 and 40–60°C, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Determination of reaction activation energy during gelation in free radical crosslinking copolymerization using the steady-state fluorescence method

The steady-state fluorescence technique was used to study the sol-gel transition in free radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate (EGDM). Pyrene methyl pivalate was used as a fluorescence probe for the in situ polymerization experiments. The times required for the onset of gelation t_c and the critical exponent β were recorded for various EGDM contents and at different polymerization temperatures. A simple kinetic model was used to interpret the experimental gel point data. The results show that the fluorescence technique can be used to measure the critical exponent β, the gel point t_c, and the activation energy during sol-gel phase transition processes. © 1996 John Wiley & Sons, Inc.