Removal of siloxanes from biogas using acetylated silica gel as adsorbent

Biogas can be used as an alternative energy source for producing heat and electricity; however, volatile methylsiloxanes(VOSiC) present in biogas can severely damage heat exchangers, turbines and gas engines. Consequently, e cient removal of VOSiC from biogas that is used as a biofuel is required. In this work, acetylated silica gel(Ac@SG) was synthesized,via treatment of microporous silica gel(SG) with acetic anhydride as an adsorbent, for removal of VOSiC from biogas,and characterized with XRD, SEM–EDS, N_2-BET and FT-IR. This Ac@SG adsorbent exhibited a meso-/microporous structure and hydrophobic surface, indicating it was a more e cient adsorbent for removing hexamethyldisiloxane(L2) and octamethylcyclotetrasiloxane(D4) from biogas samples than conventional SG. It was found that the adsorption capacities of Ac@SG reached 304 mg L2/g for hexamethyldisiloxane and 916 mg D4/g for octamethylcyclotetrasiloxane at lower temperatures in the experimental range, and water had no significant e ect on its absorption e ciency. The used Ac@SG could be easily regenerated by heating it at 110 °C, and the adsorption capacity of recycled Ac@SG for hexamethyldisiloxane and octamethylcyclotetrasiloxane was kept constant in four recycle adsorption experiments.     

Adhesion and friction behaviours of polydimethylsiloxane - A fresh perspective on JKR measurements

The self-adhesion of a variety of polydimethylsiloxanes (PDMS) has been investigated using a newly developed JKR apparatus that can also determine the associated friction behaviour of the same sample. The results have been interpreted using the complete JKR model by incorporating the indentation data also in the analysis. By varying the molecular mass M_c of PDMS from 6 to 28 kg/mol the elastic modulus E decreases from 1.16 to 0.71 MPa while the work of adhesion remains about constant. In contrast measurements of the friction of the same systems indicate an increase of the friction force. Introduction of dangling chains leads to a strong decrease of E from 1.16 to 0.56 MPa for low M_c and from 0.71 to 0.09 MPa for high M_c and again only to minor changes in W. The latter results can be understood from an inward distribution of the dangling ends.     

The Preparation and Characterization of Small Mesopores in Siloxane‐Based Materials That Use Cyclodextrins as Templates

Porous thin films containing very small closed pores (～ 20 Å) with a low dielectric constant (～ 2.0) and excellent mechanical properties have been prepared using the mixture of cyclic silsesquioxane (CSSQ) and a new porogen, heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (tCD). The pore sizes vary from 16.3 Å to 22.2 Å when the content of tCD in the coating mixture increases to 45 wt.‐% according to positronium annihilation lifetime spectroscopy (PALS) analysis. It has also been found that the pore percolation threshold (the onset of pore interconnectivity) occurs as the ～ 50 % tCD porogen load. The dielectric constants (k = 2.4 ～ 1.9) and refractive indices of these porous thin films decreased systematically as the amount of porogen loading increased in the coating mixture. The electrical properties and mechanical properties of such porous thin films were fairly good as interlayer dielectrics.     

Relaxation nuclear magnetic resonance imaging (R-NMRI) of PDMS/PDPS siloxane copolymer desiccation

Relaxation nuclear magnetic resonance imaging (R-NMRI) was employed to study the effects of desiccation on SiO₂-filled and unfilled polydimethylsiloxane-polydiphenylsiloxane (PDMS/PDPS) copolymers. Uniform NMR spin-spin relaxation time (T₂) profiles were observed across the sample thickness indicating that the drying process is approximately uniform, and that the desiccation of the silicone copolymer is not a H₂O diffusion limited process. In a P₂O₅ desiccation environment, significant reduction of T₂ was observed for the SiO₂-filled and unfilled copolymer material for desiccation up to 225 days. A very small reduction in T₂ was observed for the unfilled copolymer between 225 and 487 days. The increase in relative stiffness with desiccation was found to be higher for the unfilled copolymer.     

Siloxane Copolymers for Nanoimprint Lithography

Presented here is the novel use of thermoplastic siloxane copolymers as nanoimprint lithography (NIL) resists for 60 nm features. Two of the most critical steps of NIL are mold release and pattern transfer through dry etching. These require that the NIL resist have low surface energy and excellent dry‐etching resistance. Homopolymers traditionally used in NIL, such as polystyrene (PS) or poly(methyl methacrylate) (PMMA), generally cannot satisfy all these requirements as they exhibit polymer fracture and delamination during mold release and have poor etch resistance. A number of siloxane copolymers have been investigated for use as NIL resists, including poly(dimethylsiloxane)‐block‐polystyrene (PDMS‐b‐PS), poly(dimethylsiloxane)‐graft‐poly(methyl acrylate)‐co‐poly(isobornyl acrylate) (PDMS‐g‐PMA‐co‐PIA), and PDMS‐g‐PMMA. The presence of PDMS imparts the materials with many properties that are favorable for NIL, including low surface energy for easy mold release and high silicon content for chemical‐etch resistance—in particular, extremely low etch rates (comparable to PDMS) in oxygen plasma, to which organic polymers are quite susceptible. These properties give improved NIL results.