X-ray photoelectron spectroscopy and scanning electron microscopy are used to study the surface composition and morphology of poly(vinyl chloride) -polydimethylsiloxane (PVC-PDMS) and polystyrene-poly(propylene oxide) (PS-PPO) solvent-cast blends as a function of the blend composition and constituent molecular weights. The PVC-PDMS blends show a pronounced surface enrichment of PDMS, which is higher the lower the molecular weight of PDMS. The surface behavior of the PPO-PS blends is strongly dependent on the solvent used. Despite the much lower surface tension of PPO compared to that of PS, no surface segregation of PPO is observed in the PPO-PS blends cast from tetrahydrofuran, while the blends cast from chloroform exhibit a high surface enrichment of PPO.
The effect of addition of poly (propylene oxide) (PPO) and polystyrene with low molecular weight (LPS) to polystyrene (PS) was investigated blending these polymers in a Haake internal mixer. The PPO and LPS range was established up to 10% by weight. The blends were analysed by differential scanning calorimetry (DSC) and carbon-1 3 nuclear magnetic resonance spectroscopy at solid state (NMR), using conventional NMR techniques as cross-polarisation/magic angle spinning (CP/MAS) and proton spin-lattice relaxation time in the rotating frame (TIHp). The addition of 1 and 5% of PPO and 5% of LPS to PS made the blends of PSjPPO and PS/LPS more rigid.
Sol-gel derived silica particles are candidates for injectable controlled drug-delivery vehicles. In this study, Proteinase K was the model biomolecule encapsulated in the silica xerogel, ambigel, and aerogel particles. The surface area and average pore diameter of these particles are reported. Both the amount of Proteinase K released from the particles and the activity of the released Proteinase K were measured as a function of time. Aerogels showed a significantly lower specific activity compared to xerogels and ambigels. A variety of factors such as surface chemistry, processing parameters, solvent interaction, and pore structures were investigated as possible causes. The primary finding of this study is the effect of pore diameter on the specific activity of Proteinase K released from these particles. Mater. Res. Soc. Symp. Proc. Vol. 915
Resumo: Misturas poliméricas de poliestireno (PS1) com poli(óxido de propileno) (PPO) e de poliestireno (PS1) com poliestireno de baixíssima massa molecular (PS2), foram preparadas, em diversas composições, para avaliação das propriedades térmicas, mecânicas e de escoamento. As propriedades térmicas foram avaliadas por calorimetria diferencial de varredura (DSC) e as propriedades mecânicas e de escoamento foram determinadas através de ensaios de tração e monitoração do valor do torque durante o processamento das misturas, respectivamente. Foi observado que o PPO atua como plastificante do poliestireno enquanto que o PS2 não apresenta este comportamento. Entretanto, a adição de ambos os componentes produz mudança no empacotamento molecular, originando o aparecimento de fissuras na superfície dos materiais.
Palavras-chave:Misturas poliméricas, poliestireno, poli(óxido de propileno), fissuras, oligômeros.
X-ray photoelectron spectroscopy and scanning electron microscopy are used to study the surface composition and morphology of poly(vinyl chloride) -polydimethylsiloxane (PVC-PDMS) and polystyrene-poly(propylene oxide) (PS-PPO) solvent-cast blends as a function of the blend composition and constituent molecular weights. The PVC-PDMS blends show a pronounced surface enrichment of PDMS, which is higher the lower the molecular weight of PDMS. The surface behavior of the PPO-PS blends is strongly dependent on the solvent used. Despite the much lower surface tension of PPO compared to that of PS, no surface segregation of PPO is observed in the PPO-PS blends cast from tetrahydrofuran, while the blends cast from chloroform exhibit a high surface enrichment of PPO.
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