Dissolution of percolation cluster on UV-cured polymeric films; a fluorescence study

UV-cured polimerik filmlerin çözünmesini çalışmak için kararlı durum floresans teknik (SSF)kullanıldı. Bu filmler piren(P) ile etiketli poli(metil metakrilat) (PMMA) zincirlerinden elde edildi. Burada P çözünme işlemini takip etmek için floresans madde olarak tanımlandı. Çeşitli oranlarda etilen-glikol dimetakrilat (EGDM) çapraz bağlayıcı içeren, 3 ve 25 saat UV radyasyonu ile ışınlanmış PMMA filmler %(80-20) klorofrom-heptan karışımında çözdürüldüler. 3 saat ışınlanmış filmler için bulunan perkolasyon eşiği (pc=0.35) nokta perkolasyon modeline uyarken, 25 saat ışınlanmış film için ölçülen perkolasyon eşiği (pc=0.25) bağ perkolasyon modeline uyar. Anahtar Kelimeler: Floresans, çapraz-bağlanma, perkolasyon, çözünme.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 for 3 and 25 hours, were dissolved in chloroform-heptane (80%-20%) mixtures. Dissolution of the films were monitored in real-time by the pyrene fluorescence intensity, IP change in the solvent mixture. It was observed that maximum P intensity, IP¥ increased and decreased  above a critical EGDM content for 3h and 25h irradiated films, respectively. It was atributed to the formation of a percolation cluster. The percolation treshold (pc=0.35) found for 3h irradiated films obeys site percolation model, however the measured percolation threshold (pc=0.25) for 25h irradiated films obeys the bond percolation model. Desorption rates, Dd were measured for films prepared with various EGDM content was observed that Dd values are much lower above pc than below pc for both films. These UV cured films dissolve much faster below the percolation threshold (pc) where dissolution coefficients were found to be around 10-9 cm2s-1. However above pc highly crosslinked films dissolve at least 4 times slower than low crosslinked films i. e. UV cured films hardly dissolve above critical EGDM content (pc) in the film.  Keywords: Fluorescence, cross-linking, percolation, dissolution

Reversible film formation from nano-sized PNIPAM particles below glass transition

Reversible film formation process from nano-sized Poly(N-isopropylacrylamide) (PNIPAM) microgel particles were studied during heating-cooling cycles at various rates. Photon transmission technique was used and transmitted photon intensity I (tr) was monitored during heating-cooling cycles. The increase and decrease in I (tr) during heating and cooling was explained with the void closure and void reconstruction processes, and the corresponding activation energies were measured. It was observed that PNIPAM microgels required less energy during reconstruction of voids than their closure.Publisher's Versio

Parental psychological distress associated with COVID-19 outbreak: A large-scale multicenter survey from Turkey

Aims: Pandemics can cause substantial psychological distress; however, we do not know the impact of the COVID-19 related lockdown and mental health burden on the parents of school age children. We aimed to comparatively examine the COVID-19 related the stress and psychological burden of the parents with different occupational, locational, and mental health status related backgrounds. Methods: A large-scale multicenter online survey was completed by the parents (n = 3,278) of children aged 6 to 18 years, parents with different occupational (health care workers—HCW [18.2%] vs. others), geographical (İstanbul [38.2%] vs. others), and psychiatric (child with a mental disorder [37.8%]) backgrounds. Results: Multivariable logistic regression analysis showed that being a HCW parent (odds ratio 1.79, p <.001), a mother (odds ratio 1.67, p <.001), and a younger parent (odds ratio 0.98, p =.012); living with an adult with a chronic physical illness (odds ratio 1.38, p <.001), having an acquaintance diagnosed with COVID-19 (odds ratio 1.22, p =.043), positive psychiatric history (odds ratio 1.29, p <.001), and living with a child with moderate or high emotional distress (odds ratio 1.29, p <.001; vs. odds ratio 2.61, p <.001) were independently associated with significant parental distress. Conclusions: Parents report significant psychological distress associated with COVID-19 pandemic and further research is needed to investigate its wider impact including on the whole family unit. © The Author(s) 2020

Small molecule desorption from a swelling polymeric glass in polymer solution: Energy transfer method

Direct energy transfer (DET) method conjunction with fast transient fluorescence (FTRF) technique were used to study small molecule desorption from a swelling poly(methyl methacrylate) (PMMA) glass in polymer solution, which is consist of naphthalene (N)-labeled PMMA chains in chlorofrom-heptane mixture. Desorption coefficients, D-d of pyrene (P) desorbing from the swelling PMMA glass prior to dissolution were measured and found to be 8.3 x 10(-8) and 1.3 x 10(-5) cm(2) s(-1) in short and long time regions, respectively.Publisher's Versio

Time evolution of film formation from polystyrene particles: a percolation approach

This work reports the film formation process from surfactant-free polystyrene (PS) latex particles. Steady state fluorescence and photon transmission techniques were used to study the evolution of film formation. The films were prepared from fluorescein (F)-labeled PS latex particles at room temperature and annealed in 2.5-min-time intervals above the glass transition temperature (T-g) of PS. Fluorescence intensity (I-F) from F was measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films was monitored by using the photon transmission intensity, I-tr. Drastic increase in I-tr and I-F above the critical annealing times t(r) and t(c) respectively, were attributed to the percolation behavior of the PS material. Critical exponents, beta, of percolation clusters were measured and found to be around 0.31 and 0.37 for Itr and IF measurement, respectively, which were attributed to the site percolation model.Publisher's Versio

Film formation from pure and mixed latices; transient fluorescence study

PubMed ID: 16009372A fast transient fluorescence technique was used to study latex film formation induced by organic solvent vapor. Mixtures of pyrene (P)- and naphthalene (N)-labeled and/or pure naphthalene-labeled latex films were prepared separately from poly(methyl methacrylate) (PMMA) particles. Then these pure and mixed latex films were exposed to vapor of various chloroform-heptane mixtures in seven different experiments. In both films, fluorescence lifetimes from N were monitored during vapor-induced film formation. It was observed that N lifetimes decreased as the vapor exposure time is increased. A Stern-Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in N lifetimes. A Prager-Tirrell model was employed to obtain back-and-forth frequencies, v, of reptating PMMA chains during latex film formation induced by solvent vapor. In both pure and mixed latex films, v values were found to be correlated with the chloroform content in the vapor mixture. It was observed that polymer interdiffusion obeyed a t(1/2) law during film formation.Publisher's Versio

Percolation approach to film formation from surfactant-free polystyrene particles

In this study, a film formation process from surfactant-free polystyrene (PS) latex particles is reported. Steady state fluorescence (SSF) and photon transmission (UVV) techniques were used to study the evolution of film formation. The latex films were prepared from pyrene (P)-labeled PS particles at room temperature and annealed at time intervals of 2.5 min above the glass transition temperature (T-g) of PS. During the annealing processes, the transparency of the film changed considerably. Fluorescence intensity (I-0P) from P was measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films were monitored by using photon transmission intensity, I-tr. A drastic increase in I-tr and I-0P above the critical annealing times, t(r) and t(c) were attributed, respectively to percolation behavior of PS material from one side to the other side of the latex film. Critical exponents, beta of percolation clusters were measured and found to be around 0.35 and 0.25 for I-tr and I-0P measurements, respectively.Publisher's Versio

Film formation from nano-sized polystyrene latex particles

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

This study reports a steady-state fluorescence (SSF) technique for studying film formation from surractant-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 (T-g) of polystyrene. During the annealing processes, the transparency of the fllm improved considerably. Scattered light (I-s) and fluorescence intensity (I-s) 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 flIm formation temperature, T-o, and healing temperatures, T-h, were determined. Void closure and interdiff-usion 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.Publisher's Versio