Porogen Approach for the Fabrication of Plasma-Polymerized Nanoporous Polysiloxane Films

Abstract

Nanoporous polysiloxane films were fabricated by plasma polymerization of hexamethyldisiloxane mixed with cyclohexane under different conditions. The pores were generated through the elimination of carbonaceous aggregates (porogen) by annealing at 600 degrees C. Results of spectroscopic ellipsometry, Fourier transform infrared spectroscopy, and positron annihilation lifetime spectroscopy suggest that not only film porosity but also average pore size depends on the amount of the decomposable porogen. The pore size was controllable in a range between 0.6 and 1.0 nm in radius by proper selection of the substrate temperature and precursor composition.

Investigation on the variation in the fine structure of plasma-polymerized composite membrane by positron annihilation spectroscopy

“…2). However, at a deposition thickness greater than 0.9 m, a network of silica-like structure was produced in the bulk SiO x C y H z layer (region I), resulting in the further enhancement of O 2 /N 2 separation [3,7,8,26]. In accordance with other works [27][28][29], a film thickness of five times the pore diameter is needed to plug the pores on the surface of the substrate.…”

“…7) can be calculated from the measurement of the C 1s and Si 2p core-level peak areas. Here, the variation in the ratio of C/Si in the SiO x C y H z layer indirectly represents the structural differences because the existence of carbon groups, as many literatures have found [24][25][26], can introduce nano-pores in the SiO x C y H z layer. As a result, the C/Si ratio decreased with an increase in the applied power, indicating smaller free volume (fewer hydrocarbons) in the SiO x C y H z layer fabricated at a higher plasma power.…”

Application of positron beams to the study of positronium-forming solids

“…The discrepancy may partly arise from the different method to account for the very long lifetimes due to o-Ps annihilating in vacuum [25]. Applications of PALS to the evaluation of free volumes in thin films of functional materials include plasma polymerized films of hexamethyldisiloxane for sensors [43], photo-responsive polymers with azobenzene moieties [44], optical polymers [45], reverse osmosis membranes [46] etc.…”

Analytical Methods Using a Positron Microprobe

“…[3][4][5] Another stream of positron research is to clarify the fundamental characteristics of the positron as a "sub-atomic particle": e.g., the differences between positron and electron scattering processes in solid and gas phases, the formation of a positronium (the hydrogen-like bound state of a positron and an electron), and the interactions between a positronium and other atoms and molecules. [6][7][8][9] Since the 1980s, positron research has progressed due to improvements of experimental techniques (e.g., the generation of monoenergetic positron beams and microbeams).…”