Synergistic Effects of Gamma Irradiation,Tensile Stress and Moisture on the Radiolysis of Silicone Foam

The present work involves the investigation of the synergistic effects of gamma irradiation,tensile stress and absorbed moisture on the radiolysis behaviors of silicone foams by experiments and theoretical simulations.For both the pristine and dehydrated samples,the permanent tensile set increases with the initial tensile strain.Further analysis uncovers that the dehydrated samples exhibit greater permanent tensile sets,lower further elongation and higher Young’s modulus than the counterparts of the pristine samples with the same initial tensile strain and gamma dose,verifying the vital synergistic effects on crosslinking network and aggregation structures caused by moisture and gamma radiation.The synergistic effects unveiled by reactive molecular dynamics at the atomic scale are due to the moisture-induced neutralization and stabilization of the macromolecular radicals.The steric hindrance of moisture located at the interface of silica and polymer chains also conduces to the observed synergistic effects due to the inhibited crosslinking reactions.

Incorporation of liquid fillers into silicone foams to enhance the electro-mechanical properties

Silicone foams with and without liquid fillers(silicone oils of various types and glycerol,respectively)are synthesized and analyzed to be used as dielectric layers in capacitive sensors.A simple fabrication technique involving only four components i.e.Sylgard 184,glycerol,sodium hydroxide and ethanol is used to make these silicone foams after which they are filled with silicone oil or glycerol by soaking the foam in respective liquid.Mechanical and dielectric properties of the foams are examined.The oil reinforces the foam’s dielectric properties,softens the foam and improves its capacitive response,making it a very good dielectric material for fabricating capacitive pressure sensors.Compared to dry silicone foams,foams filled with-and swollen by-chloropropyl-functional silicone oil,show a low Young’smodulus(31 kPa),a high and stable relative dielectric permittivity of around 5,and a high capacitive response of 132%for an appliedpressureof 12 kPa.Thepresence of oil stabilizes the soft foam and ensures that it does not buckle under high pressure.

Study on properties of tetrapod-like zinc oxide whisker/silicone rubber foam composites

In this paper, the microcellular silicone rubber foams, strengthened with tetrapod-like Zinc Oxide whisker（T-ZnOw） are prepared. Through further characterization, it can be seen that the average cell diameter size of the filled with T-ZnOw is reduced. The distribution uniformity of microcellulars is improved obviously with increasing T-ZnOw filler. The reason that introduction of T-ZnOw can greatly enhance mechanical properties of the microcellular silicone rubber foams is its good interfacial adhesion with the matrix contributes. It is also found that the reducing effects of T-ZnOw on the compressive stress relaxation ratio of microcellular silicone rubber foams, and the improvement is obvious with increasing T-ZnOw filler.

High Strength Silicon Carbide Foams and Their Deformation Behavior

Silicon carbide （SIC） foams with a continuously connected open-cell structure were prepared and characterized for their mechanical performance. The apparent densities of SiC foams were controlled between about 0.4 and 2.3 g/cm^3, with corresponding compressive strengths ranging from about 23 to 60 MPa and flexural strengths from about 8 to 30 MPa. Compressive testing of the SiC foams yielded stress-strain curves with only one linear-elastic region, which is different from those reported on ceramic foams in literature. This can possibly be attributed to the existence of filaments with fine, dense and high strength microstructures. The SiC and the filaments respond homogeneously to applied loading.

Establishment of Constitutive Model of Silicone Rubber Foams Based on Statistical Theory of Rubber Elasticity

In this study, a constitutive model based on microscopic physical mechanism of silicone rubber foams was established. A theoretical statistical model of rubber elasticity considering the effect of dangling chains was modified to build this model. When a strain amplification factor （X） was introduced, the theoretical model could fit the tensile stress-strain data of mono- and bi-modal foam matrix well （Adj. R-Square = 0.9989, 0.9983）. Parameters related to the polymer network, namely, average molecular weight （Me） and volume fraction （Ф） of chain segments between adjacent cross-linking points （network strands）, were calculated by probabilistic method from the number-average molecular weight （Mn）, vinyl content （wvi） of the primary polysiloxanes and percent conversion （q） of vinyl groups. The primary and infinite strain amplification factors （X0, X∞） and decay exponent （z）, introduced by X and related to the nanoparticles, were obtained by fitting. Inspired by the fact that the actual strain of matrix was lower than that of the foams＇, we introduced another item, strain hysteresis item （H, related with the foam porosity and cell structure）, into the statistical model as well. With the same above values of Mc, Ф, X0 and X∞, the model could also fit the compressive stress-strain data of mono- and bi-modal foams well （Adj. R-Square = 0.9948, 0.9985）. Interestingly, the strain hysteresis items of the mono- and bi-modal foams almost completely coincided under all experimental strains, which may be attributed to the almost equal porosity and similar cell structure of the two foams. This constitutive model may connect the macroscopic stress-strain behaviour to the parameters of microscopic molecular structures, promisingly providing a basis for the performance improvement and optimization of silicone rubber foams.

Preparation and Properties of Conductive Foamed Silicone Rubber

The conductive foamed silicone rubber was prepared by Polymethylvinylsiloxane(PMVS)mixed with acetylene black,fumed silica,and AC foaming agent(azodicarbonamide).Influences of fillers on the microstructure,electrical conductivity and mechanical property were discussed.The results showed that the pore structure was affected by acetylene black.Acetylene black delayed the vulcanization speed of silicone rubbers,leading to bigger pores.Higher content of acetylene black decreased the mechanical properties and the electrical resistivity of rubbers.Fumed silica increased the mechanical properties and limited the aggregation of gas.Higher content of fumed silica led to small and obturator pores generated.Higher content of fumed silica increase the mechanical properties and the electrical resistivity of rubbers.AC foaming agents generated more gas,leading to bigger and irregular pores which affected the mechanical properties negatively,meanwhile AC foaming agents increased the conductivity of rubbers.

Economic evaluation of soft silicon foam dressings versus sterile gauze for the treatment of pressure ulcers in China

The aim of this study was to evaluate the cost and effectiveness of soft silicone foam dressings （SSFD, Mepilex） on the treatment of pressure ulcers. We searched electronic databases and retrieved articles to make a systematic evaluation, and then make a cost-effectiveness analysis by decision tree model combined with data from clinical treatments. The result shows that compared with the common sterile gauze, SSFD possesses an apparent advantage. The effective ratio is 96.3% versus 77.3%, although the cost of SSFD is much higher than that of sterile gauze, Mepilex appears to be more cost-effectiveness for preventive use.

Hydrochlorination of Acetylene Using SiC Foam Supported Structured C/Au Catalysts

AuCl3 loaded structured catalysts were prepared on SiC foam supported with pre-coated activated carbon layers. The catalytic properties of the structured catalysts towards hydrochlorination of acetylene were tested in a fixed- bed reactor with the AuCl3 loaded on activated carbon pellets as a reference. For isopyknic catalysts, the structured catalyst with only one fifth of the Au amount as that was used on the reference catalyst exhibited even a little higher acetylene conversion and much better stability than the latter no matter what the gas hourly space velocities of acetylene were used. The results indicated that the more homogeneous distribution of AuCl3 particles and better heat transfer along the fixed-bed reactor originated from the low pressure drop and high thermal conductivity of the SiC foam supported structured catalysts might be able to account for their improved efficiency and stability. It is befieved that these novel structured C/Au catalysts can be potentially applied in VCM industrialization in view of their greatly reduced cost and much prolonged life.