The effects of free surfaces and molecular confinement on relaxation processes in thin polymer films

Glass transition, physical aging and dielectric relaxation in ultra-thin polymer films (< 100 nm) were investigated using complementary techniques (ellipsometry and dielectric spectroscopy). PtBMA films of different thicknesses were prepared and the thickness dependence of the glass transition temperature (Tg(h)) was investigated with ellipsometry. The uncapped films thinner than 40nm showed signicant depression of Tg and this was explained using the enhanced molecular mobility near the free surfaces. Several sets of PtBMA film samples were then prepared and capped by Al layers; the coating procedure is different for each set. The Tg(h) in PtBMA films with evaporated Al capping layers was essentially the same as that of the uncapped PtBMA films, and this suggests evaporated Al capping layers can not remove the free surface effect. Another set of samples was capped with Al layers using a novel '2(h=2)' sample preparation procedure, and was expected to have no free surface effect. These samples exhibit no apparent thickness dependence. These results suggest that the effect of free surfaces are responsible for the altered dynamics in thin polymer films. However great care has to be taken in attempt to remove the free surface effects caused by solid capping layers. The frequency dependence of the thickness dependence of α relaxation temperature (Tα(h)) in ultra-thin PVAc films was measured using dielectric spectroscopy. Films thinner than 80nm exhibit smaller Tα's than the bulk values at a measurement frequency lower than 10Hz, but there is no signicant thickness dependence of Tα at measurement frequencies higher than 10Hz. The results demonstrated that the Tα(h) has an intrinsic dependence on measurement frequency. We also measured the cooling rate dependence of the Tg(h) using the same samples, and compared Tg(h) with Tα(h) for different cooling rates/measurement frequencies. The results help to address the existing controversial reports about the apparent discrepancies observed between measurements that are performed using different techniques. Dielectric spectroscopy in the temperature domain ε"(T) was measured on thin(1Hz) this thickness dependence doesn't exist. This was explained using the existence of the liquid-like surface layer with enhanced molecular mobility, and using the measurement frequency effects. PS films of different thickness were prepared and physical aging process in these samples was investigated using ellipsometry. On each sample the measurements were performed at different aging temperatures, and a trend of a decreasing aging rate with decreasing aging temperature is found for all samples. In ultra-thin PS films (<100nm thick) a maximum aging rate at ~17K below Tg film is observed, and these observations were explained using the competition of the two factors that affect the aging, that is, the distance to the equilibrium and the fraction of the free volume. A comparison between the thickness dependence of aging rate and the thickness dependence of Tg suggests that the aging rate serves as a more sensitive probe in the study of polymer molecular dynamics than Tg does

The effects of free surfaces and molecular confinement on relaxation processes in thin polymer films

Glass transition, physical aging and dielectric relaxation in ultra-thin polymer films (< 100 nm) were investigated using complementary techniques (ellipsometry and dielectric spectroscopy). PtBMA films of different thicknesses were prepared and the thickness dependence of the glass transition temperature (Tg(h)) was investigated with ellipsometry. The uncapped films thinner than 40nm showed signicant depression of Tg and this was explained using the enhanced molecular mobility near the free surfaces. Several sets of PtBMA film samples were then prepared and capped by Al layers; the coating procedure is different for each set. The Tg(h) in PtBMA films with evaporated Al capping layers was essentially the same as that of the uncapped PtBMA films, and this suggests evaporated Al capping layers can not remove the free surface effect. Another set of samples was capped with Al layers using a novel '2(h=2)' sample preparation procedure, and was expected to have no free surface effect. These samples exhibit no apparent thickness dependence. These results suggest that the effect of free surfaces are responsible for the altered dynamics in thin polymer films. However great care has to be taken in attempt to remove the free surface effects caused by solid capping layers. The frequency dependence of the thickness dependence of α relaxation temperature (Tα(h)) in ultra-thin PVAc films was measured using dielectric spectroscopy. Films thinner than 80nm exhibit smaller Tα's than the bulk values at a measurement frequency lower than 10Hz, but there is no signicant thickness dependence of Tα at measurement frequencies higher than 10Hz. The results demonstrated that the Tα(h) has an intrinsic dependence on measurement frequency. We also measured the cooling rate dependence of the Tg(h) using the same samples, and compared Tg(h) with Tα(h) for different cooling rates/measurement frequencies. The results help to address the existing controversial reports about the apparent discrepancies observed between measurements that are performed using different techniques. Dielectric spectroscopy in the temperature domain ε"(T) was measured on thin(1Hz) this thickness dependence doesn't exist. This was explained using the existence of the liquid-like surface layer with enhanced molecular mobility, and using the measurement frequency effects. PS films of different thickness were prepared and physical aging process in these samples was investigated using ellipsometry. On each sample the measurements were performed at different aging temperatures, and a trend of a decreasing aging rate with decreasing aging temperature is found for all samples. In ultra-thin PS films (<100nm thick) a maximum aging rate at ~17K below Tg film is observed, and these observations were explained using the competition of the two factors that affect the aging, that is, the distance to the equilibrium and the fraction of the free volume. A comparison between the thickness dependence of aging rate and the thickness dependence of Tg suggests that the aging rate serves as a more sensitive probe in the study of polymer molecular dynamics than Tg does

Extraction optimization of Eucommia ulmoides Oliver and its effect on bone quality in OVX rats

Purpose: To maximize the yield of extract from Eucommia ulmoides Oliver and its effect on bone quality. Methods: Different extraction indices were optimized with response surface methodology (RSM) for maximization of extract yield from Eucommia ulmoides Oliver. Box–Behnken design (BBD) was used to identify the effects of temperature, time, and liquid to solid ratio on extract yield from Eucommia ulmoides Oliver. After 4-week acclimatization, thiry-two rats were randomly assigned to 4 groups (n = 8): group 1 (sham) given vehicle only; group 2 (OVX rats given Eucommia ulmoides Oliver extract at a dose of 4 g/kg; group 3 (OVX + vehicle); group 4 (OVX + EUOE), i.e., OVX rats given Eucommia ulmoides Oliver extract (4 g/kg). Sham rats had intact ovaries. After surgery, the rats received gentamicin intramuscularly for 3 successive days. Two months after surgery, blood and trabecular bones was taken for analysis. Results: Temperature and liquid-to-solid ratio had marked impact on extract yield from Eucommia ulmoides Oliver, with the best conditions being temperature of 88 °C, time of 137 min, and liquid to solid ratio 16:1. Using these optimized conditions, the maximum yield of extract obtained experimentally (2.53%) was very close to the predicted value of 2.49 %. There was a good fit between the mathematical model evolved and the data on extract yield. The extract significantly (p &lt; 0.01) increased the Ca and P and Cr levels in OVX + EUOE group compared to those in OVX control. Moreover, the extract significantly (p &lt; 0.01) increased macro-mechanical indices of trabecular bone in OVX+EUOE group, relative to those in OVX control. Conclusion: The yield of Eucommia ulmoides Oliver extract has been successfully optimized using RSM. The extract exhibited strong effects on bone quality. Keywords: Optimization, Eucommia ulmoides, Box–Behnken design, Response surface methodology, Bone loss, Gen

Effect of total flavonoids from Drynaria rhizome on bone loss in ovariectomized rats

Purpose: To determine the potential effect of total flavonoids from Drynaria rhizome on bone loss in ovariectomized (OVX) rats. Methods: The rats were divided into four groups: normal control, ovariectomized (OVX) control, and two Drynaria rhizome (DR) flavonoids treatments. Post-operation, osteoporotic OVX rats were given Drynaria rhizome total flavonoids for 3 months. Thereafter, the expressions of bone-related genes and biochemical indices were investigated in samples taken from the serum and bone of the rats. Results: Treatment with total flavonoids from Drynaria rhizome prevented bone mineral loss and improved some related biochemical indices associated with osteoporosis: alkaline phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP), bone gla protein (BGP) and estradiol (E2). Reverse transcription-polymerase chain reaction (RT-PCR) data showed that treatment with the total flavonoids significantly downregulated mRNA expression of Wnt10b, β-catenin, recombinant human bone morphogenetic protein-2 (BMP2) and BMP4 in OVX rats, but significantly reversed OVX-induced downregulation of dickkopf1 (Dkk1) mRNA expression. Conclusion: These results indicate that total flavonoids from Drynaria rhizome exert anti-osteoporotic effects in rats via WNT signaling and BMP-2 signaling pathways

AcrFinder: genome mining anti-CRISPR operons in prokaryotes and their viruses

Anti-CRISPR (Acr) proteins encoded by (pro)phages/(pro)viruses have a great potential to enable a more controllable genome editing. However, genome mining new Acr proteins is challenging due to the lack of a conserved functional domain and the low sequence similarity among experimentally char- acterized Acr proteins. We introduce here AcrFinder, a web server (http://bcb.unl.edu/AcrFinder) that combines three well-accepted ideas used by pre- vious experimental studies to pre-screen genomic data for Acr candidates. These ideas include ho- mology search, guilt-by-association (GBA), and CRISPR-Cas self-targeting spacers. Compared to existing bioinformatics tools, AcrFinder has the following unique functions: (i) it is the first online server specifically mining genomes for Acr-Aca operons; (ii) it provides a most comprehensive Acr and Aca (Acr-associated regulator) database (populated by GBA-based Acr and Aca datasets); (iii) it combines homology-based, GBA-based, and self-targeting approaches in one software package; and (iv) it provides a user-friendly web interface to take both nucleotide and protein sequence files as inputs, and output a result page with graphic representation of the genomic contexts of Acr-Aca operons. The leave-one-out cross-validation on ex- perimentally characterized Acr-Aca operons showed that AcrFinder had a 100% recall. AcrFinder will be a valuable web resource to help experimental microbiologists discover new Anti-CRISPRs